U.S. patent application number 12/223625 was filed with the patent office on 2009-01-22 for electrografting method for forming and regulating a strong adherent nanostructured polymer coating.
Invention is credited to Christine Jerome, Robert Jerome, Harry Serwas, Samuel Voccia.
Application Number | 20090020431 12/223625 |
Document ID | / |
Family ID | 36346917 |
Filed Date | 2009-01-22 |
United States Patent
Application |
20090020431 |
Kind Code |
A1 |
Voccia; Samuel ; et
al. |
January 22, 2009 |
Electrografting Method for Forming and Regulating a Strong Adherent
Nanostructured Polymer Coating
Abstract
Electrografting method for forming and regulating a strongly
adherent nanostructured polymer coating onto an electro-conductive
surface profile characterized in that the surface profile is
regulated by electrodeposition of nanometre- and/or
micrometre-scale nuclei onto the surface profile prior to or
simultaneously to the formation of the polymer coating.
Inventors: |
Voccia; Samuel; (Liege,
BE) ; Serwas; Harry; (La Calamine, BE) ;
Jerome; Christine; (Ougree, BE) ; Jerome; Robert;
(Sart-Jalhay, BE) |
Correspondence
Address: |
JACOBSON HOLMAN PLLC
400 SEVENTH STREET N.W., SUITE 600
WASHINGTON
DC
20004
US
|
Family ID: |
36346917 |
Appl. No.: |
12/223625 |
Filed: |
January 31, 2007 |
PCT Filed: |
January 31, 2007 |
PCT NO: |
PCT/EP2007/050956 |
371 Date: |
August 5, 2008 |
Current U.S.
Class: |
205/77 |
Current CPC
Class: |
B81C 1/00206 20130101;
C09D 5/4476 20130101; B01L 3/5027 20130101; C25D 15/00 20130101;
B81C 2201/0197 20130101 |
Class at
Publication: |
205/77 |
International
Class: |
C25D 5/00 20060101
C25D005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 10, 2006 |
EP |
06101558.2 |
Claims
1. An electrografting method for forming and regulating a strongly
adherent nanostructured polymer coating onto an electro-conductive
surface profile characterized in that the surface profile is
regulated by electrodeposition of nanometre- and/or
micrometre-scale nuclei onto the surface profile prior to or
simultaneously to the formation of the polymer coating.
2. The electrografting method according to claim 1 wherein the
electro-conductive surface is made of conductive and
semi-conductive material.
3. The electrografting method according to claim 1 characterised in
that the nuclei are inorganic nuclei provided by electrodeposition
of a precursor salt.
4. The electrografting method according to claim 1 comprising the
steps of: a) regulating the surface profile by inorganic,
preferably metallic, nuclei deposition onto the conductive surface
upon application of a potential x to said surface immersed in a
solution comprising a monomer and a precursor salt prior to or
alternate with b) forming a nanostructured polymer by application
of a potential y onto the resulting surface profile.
5. The electrografting method according to claim 4 characterised in
that the potential y equals the potential x.
6. The electrografting method according to claim 4 characterised in
that the potential x is applied repeatedly during the formation of
the nanostructured polymer onto the resulting surface profile.
7. The electrografting method according to claim 4 characterised in
that the potentials x and y are applied repeatedly with different
values.
8. The electrografting method according to claim 1 characterised in
that the nuclei are made of metallic nuclei selected from the group
consisting of a transition metal or a combination of transition
metals.
9. The electrografting method according to claim 1 characterised in
that the nuclei are made of an organic material provided by
electrodeposition from a monomer droplet.
10. The electrografting method according to claim 9 characterised
in that the nuclei further comprise a polymer provided by
polymerisation of the monomer droplet at the conductive surface
upon application of a potential z.
11. The electrografting method according to claim 9 characterised
in that the monomer droplet is provided by an emulsion comprising
the monomer in a protic solvent.
12. The electrografting method according to claim 11 characterised
in that the emulsion further comprises a surfactant.
13. The electrografting method according to claim 11 characterised
in that the protic solvent is water.
14. The electrografting method according to claim 10 characterised
in that the potential z is applied repeatedly with different
values.
15. The electrografting method according to claim 1 comprising a
nucleation step at the electroconductive surface inducing
nanostructuration of the coating.
16. The nanostructured polymer coating obtained by the
electrografting method according to claim 1.
17. Use of the nanostructured polymer coating according to claim 16
for a medical device application.
18. Use of the nanostructured polymer coating according to claim 16
for a biosensor application.
19. Use of the nanostructured polymer coating according to claim 16
for a microfluidic application.
Description
[0001] The present invention relates to a new method for forming
and regulating by electrografting a strongly adherent
nanostructured polymer coating onto an electro-conductive surface
by controlling its surface profile. The present invention also
relates to the strongly adherent nanostructured polymer coating
obtained thereof and its uses.
[0002] Electrografting methods for forming a polymer coating are
known in the art. WO 02/098926 and WO 2005/033378 describe a
polymer film forming at the surface of an electroconductive
surface. Nevertheless, the polymer coatings obtained by such
methods known in the art require aprotic or nearly aprotic
conditions to be formed. Organic solvents are therefore required
which are costly and toxic for the environment.
[0003] WO 2005/033378 describes that protic substances like
Bronsted acids hinder anionic polymerisation during preparation of
a polymer coating by electrografting. Cathodic polarisation induces
an anionic polymerisation which is stopped in the presence of
protic compounds because propagating anions react irreversibly with
the said protic compounds. The formation of a strongly adherent
polymer coating is thus impossible in the presence of such protic
compounds and only very low molecular weight polymer chains may be
formed at the cathode.
[0004] Moreover, if some regulation of such polymer-coated surfaces
is possible in the electrografting methods described in WO
02/098926, it is limited to a rough thickness control of the
polymeric coating onto the surface. No other specific properties of
the conductive surface profile (such as for example, roughness) are
regulated during the electro-coating preparation.
[0005] One interesting characteristic of the surface profile is its
surface roughness which influences many properties of the surface
such as its wetting, adhesion, compatibility and reactivity with
one or more polymeric coating. "Surface roughness" in the context
of the present invention can be defined as small-scale (i.e.,
nanometer- and/or micrometer-scale) variations in the height of a
solid surface as would be caused by a plurality of nodular
formations present on a surface.
[0006] The surface roughness has an influence on many properties of
the said surface and cannot be easily tuned while preparing a
strongly adherent coating. On the other hand, because a
modification of the surface roughness can enhance existing
properties or impart new properties to a surface, the control of
surface roughness is desired for many applications. Varying the
surface roughness may for example modify the wetting, adhesion and
reactivity properties of the surface. It can also enhance or reduce
the contact between two surfaces, the friction at the surface, the
specific area of a surface, the refractive index and so on.
[0007] Beside the good adhesion of the coatings, all these
properties are of the utmost importance if the coating has to be
used for example as self-cleaning surfaces, as anti-adhesive
surfaces, in anti-corrosion, for the design of biosensors, as a
primer to promote adhesion of a second coating or as molecular
Velcro to form composites of different materials. For example,
biosensors may be more sensitive if the surface area of the
functional coating used to detect an analyte is increased.
Furthermore, it can be desirable to optimize the wetting properties
of these functional coatings used in biosensors and this can also
be easily done by tuning the surface profile, particularly the
surface roughness.
[0008] We have now found a new electrografting method comprising a
step of nuclei deposition at a conductive surface regulating its
surface profile and the polymeric coating properties before, during
or resulting from electrografting. The surface profile is therefore
controlled by a controlled nucleation step at the conductive
surface inducing nanostructuration of the coating.
[0009] Accordingly, the present invention provides an
electrografting method for forming and regulating a strongly
adherent nanostructured polymer coating onto an electro-conductive
surface profile characterized in that the surface profile is
regulated by electrodeposition of nanometre- and/or
micrometre-scale nuclei onto the surface profile prior to or
simultaneously to the formation of the polymer coating.
[0010] In the context of the present invention, the term "nuclei"
refers to a nodule of an electrodeposited material with a
nanometre- and/or micrometer-scale diameter, wherein the diameter
is considered to be the greatest diameter of the nodule.
[0011] The electrografting method according to the present
invention may be carried out with conventional electrochemical
techniques, as for example, a three-electrode cell connected to a
potentiostat. A working electrode, i.e., the electroconductive
surface to be electrocoated, is a conductive or semi-conductive
surface made for example from noble metals such as gold or
platinum, transition metals such as chromium, titanium, iron,
copper or nickel, or semi-conductors, such as doped silicon or
carbon.
[0012] In a first embodiment, the present invention provides an
electrografting method wherein the nuclei are made of an inorganic
material provided by electrodeposition from a precursor salt.
[0013] The inorganic material is preferably a transition metal such
as iron, copper, cobalt, nickel, titanium, silver or an alloy
thereof.
[0014] The precursor salt according to the invention is generally
an inorganic salt such as for example chloride, chlorate, triflate,
perchlorate of iron, cupper, cobalt, nickel, titanium, silver, and
the like or a mixture thereof.
[0015] Preferably, the electrografting method comprises a step of
regulating the surface profile by inorganic (metallic) nuclei
deposition onto the conductive surface upon application of a
potential x to said surface immersed in a solution comprising a
monomer and the inorganic (metallic) precursor-salt, prior to or in
alternation with the electropolymerization step of the monomer
resulting in a nanostructured surface profile.
[0016] In such embodiment, one selected potential x may be applied
constantly or repeatedly to the electrically conductive or
semi-conductive surface (also called hereafter (semi)-conductive
surface), so that an inorganic salt is electrolyzed forming
inorganic nuclei on the surface consequently modifying the surface
profile. At another selected potential y, a strongly adherent
polymer coating can be formed from a selected monomer. The strongly
adherent polymer coating totally or partly covers the surface
profile depending on the nature, size and shape of the inorganic
nuclei deposited on the surface.
[0017] As illustrated in scheme 1, the surface profile is therefore
regulated by the consecutive (step A to D) or simultaneous
formation (step C) of such inorganic nuclei electrodeposited on the
(semi)-conductive surface and electrografting of the monomer. The
resulting nanostructured polymer coating is therefore also
regulated by such nucleation step. Size and shape of the nuclei
deposited on the surface are regulated by the selected potentials
and the surrounding polymer formation at the surface (particularly
in step B and C of scheme 1).
[0018] The strongly adherent polymer coating according to the
present invention may be at least partially covalently bonded to
the surface and/or to the metal nuclei formed on the surface upon
electrolysis of the salt, so that even if the polymer is not
cross-linked, it cannot be completely removed by a continuous
washing with a good solvent of the polymer or by a so-called peel
test.
[0019] The selected potential x applied to the electrically
conductive surface may be, for example, in the potential range
between 10 V and -10 V, being especially preferred between 0 V and
-4.5 V. In some preferred embodiments of the present invention, the
potential applied to the electrically-conductive or semi-conductive
surface may be constant or vary during electrolysis, for example,
at a speed between 0.1 mV/s and 5 V/s, preferably between 1 mV/s
and 250 mV/s. Furthermore, a constant potential (or current) may be
applied to the electrically conductive or semi-conductive surface,
for example, during between 0.001 seconds and 15 minutes,
preferably between 0.1 seconds and 1 minute. Two or more different
selected potentials may also be applied to the surface. A sequence
of different potentials can be applied one time or repeated several
times (up to 100 times for example) to the electrically conductive
or semi-conductive surface.
[0020] It is also preferred in the first embodiment to select two
(or more) different potentials to form the nanostructured coating
on the electrically (semi)-conductive surface. For example,
nucleation and electrografting may be not simultaneous but may also
occur at different polarisation conditions. By polarization is
meant application of a selected potential or current to an
electrode.
[0021] It is preferred in the first embodiment to repeat the steps
of the selected potential x applied to the electro-conductive
surface in order to tailor the nanostructuration of the surface
profile and reach efficient electrografting of polymer chains.
[0022] The profile and particularly the surface roughness of the
nanostructured coating may be modified by applying the same
selected potential x a second time or even several times. For
example, the surface roughness may be controlled by repeating in
alternation, the electro-nucleation and the electrografting steps
as illustrated in step 1 to 3 of scheme 2A. The dimension of the
nuclei formed during the first electro-nucleation step 1 increases
with an increasing number of cycles. The alternating polymer
electrografting step regulates the growth of these nuclei. Above a
maximum of cycles, the size of the nuclei may decrease again (step
3). The control of the size of the nuclei thus allows the precise
tailoring of the surface roughness.
[0023] By tuning the applied potential during these cycles,
different levels of nanostructuration of the surface may be
achieved for example by creating raspberry-shaped nuclei (as
illustrated in scheme 2B).
[0024] Surfaces with a two-scale roughness, for example a roughness
at the micrometer scale provided by the nuclei and a roughness at
the nanometer scale provided by the nanostructuration of these
nuclei may be created also by variation of the polarisation time as
illustrated in scheme 2B.
[0025] The monomer according to the first embodiment are acrylic or
methacrylic derivatives, such as alkyl(meth)acrylate, fluorinated
(meth)acrylate, succinimidyl (meth)acrylate, (meth)acrylonitrile,
pyrrole (meth)acrylate, thiophene (meth)acrylate, and the like, and
polymers bearing one or more acrylic or methacrylic functions, such
as poly(ethylene oxide), polysiloxanes, polyesters, polyurethanes,
poly(methylvinyl ether), polystyrene, and the monomers and polymers
described in WO 02/098926, which are incorporated herein by
reference.
[0026] The solution according to the first embodiment of the
invention comprising a monomer and an inorganic precursor salt may
further comprise an organic solvent.
[0027] The organic solvent may be selected, for example, from ethyl
acetate, dichloromethane, chloroform, dimethylformamide,
acetonitrile, diethylcarbonate, dimethylsulfoxide,
hexamethylenephosphoramide, ionic liquids (for example,
immidazolium salts), supercritical solvents (for example,
supercritical CO.sub.2) and a combination of these solvents.
[0028] In such embodiments, the electrografting method has to take
place in a mainly oxygen-free atmosphere which may, for example, be
a nitrogen or argon atmosphere. A mainly oxygen-free atmosphere
according to the invention means an atmosphere which contains
between 0 ppm and 499000 ppm of oxygen, most preferrably between 0
ppm and 300 ppm of oxygen.
[0029] A preferred method allows formation of a composite
metal-polymer coating by a combination of electrodeposition of a
metallic salt and electrografting of at least one (macro)monomer.
The strongly adherent polymer coating is nanostructured by the
metal nuclei that are electrodeposited before and during the
electropolymerization as illustrated in schemes 1 and 2.
[0030] Moreover, the electrografting method according to the
present invention may be successfully applied to a surface of any
size and shape. For example, surfaces of medical devices, such as
coronary stents, dentistry tools or surfaces of analytical devices,
such as atomic force microscopy (AFM) tips, microelectronic
circuitry, microfluidic devices and also conducting (metallic)
surfaces used in packaging, householding, the automobile sector, or
design goods.
[0031] The advantages of such embodiments for the nanostructured
strongly adhering polymer coatings are a precise tailoring of both
chemistry and topography of the (semi)-conducting surface. When
controlling both parameters, new properties can be afford to the
coated material, such as superhydrophobicity, superhydrophilicity
and anti-fouling properties. Other surface properties can also be
deeply enhanced such as anti-bacterial activity, reactivity,
catalytic reaction selectivity, friction, and reflectivity.
[0032] Applications of such nanostructured and strong adhering
polymer coatings are found when corrosion-resistant coatings and
self-cleaning coatings are required for biocompatibilization or the
building-up of bioactive medical implants, for the elaboration of
(bio)sensors particularly electrochemical biocaptors, for
functionalization of channels of microfluidic devices, for tuning
the visual aspect of goods (for example, decorative handles and
watches), for imparting anti-bacterial properties to surfaces (such
as air filters and medical tools).
[0033] In a second embodiment, the present invention provides an
electrografting method wherein the nuclei are made of an organic
material provided by electrodeposition from monomer droplets.
[0034] By monomer droplet is meant a droplet comprising a monomer
(M). A monomer droplet is for example an emulsion droplet as
illustrated in scheme 3A and comprising a monomer (M), a surfactant
(Su) and a protic solvent (PSo) or a droplet as illustrated in
scheme 3B comprising a reactive amphiphile (R) in a selective
(protic) solvent (SSo).
[0035] Reactive amphiphile is defined as a molecule comprising a
hydrophilic part and a hydrophobic part, and bearing at least one
polymerizable moiety such as a (meth)acrylic function as
illustrated in scheme 4.
[0036] The protic solvent according to the present embodiment means
a solvent having one dissociable proton such as water, but also
methanol, ethanol, formamide and the like and combinations
thereof.
[0037] The surfactant according to the present embodiment may be
any molecule comprising a hydrophilic part and a hydrophobic part.
The surfactant may be an anionic (such as sodium dodecyl sulfate),
a cationic (such as alkyl quaternary ammonium), a zwiterionic (such
as betaines), or a neutral (non-ionic) (such as pluronics)
surfactant.
[0038] The amount of surfactant which is added in the emulsion,
preferably exceeds the critical micellar concentration (CMC) of the
surfactant in the protic solvent. It is, for example, 10.sup.-7 M
to 10 M, preferably between 10.sup.-5 M to 10.sup.-1 M.
[0039] The electrografting method using such monomer containing
droplets allows regulating both topography and chemistry of the
(semi)-conducting surface by electrochemical formation of organic
(polymer) nuclei onto the conductive surface upon application of a
potential z to said surface.
[0040] In such second embodiment the electro conductive surface is
preferably immersed in a monomer droplets suspension comprising a
protic solvent
[0041] By the application of at least one selected potential z to
the electricallyconductive or semiconductive surface of electrode
(E), the droplets of the monomer which are formed in a protic
solvent such as water may form a nanostructured strongly adherent
polymer coating (C) on the electrically conductive or
semiconductive surface as illustrated in scheme 5.
[0042] The monomer droplets upon applying a potential to the
electrically conductive surface may be attracted to the
electrically conductive surface (scheme 5 step 1). The droplets of
the monomer which are formed in the protic solvent may be projected
onto the electrically conductive surface, forming nuclei at the
surface, and therefore modifying the profile of the conductive
surface. While upon reaching said surface, the formation of a
strongly adherent polymer coating begins at the edge of the
droplets which first contacts with the electrically conductive
surface. Each said droplet may therefore form a strongly adherent
polymer protuberance, especially a hemispheric or ellipsoidal
polymer protuberance, on the electrically conductive surface
(scheme 5). Depending on the potential which is used to project the
droplets against the electrode, the crash of the droplets may be
strong enough to spread the monomer on the electrode so that a
smoother coating may be obtained.
[0043] The diameter of the polymer protuberances of the strongly
adherent polymer coating which are formed on the electrically
(semi)conductive surface may depend on the diameter of the droplets
which are formed in the protic solvent.
[0044] It is therefore possible to tune the conductive surface
profile particularly the surface roughness of the at least
partially polymer coated surface by modifying the diameter of the
droplets of the monomer which may be formed in the protic solvent
and/or by tuning the selected potential(s) which may be applied to
the electrically conductive or semiconductive surface, going
progressively from a nearly smooth polymer coated surface, which
can for example be obtained using small droplets, especially, for
example, droplets with a mean diameter <100 nm, and/or high
potential(s), to a rough polymer coated surface, which can for
example be obtained using large droplets, especially, for example,
droplets and/or aggregates with a diameter >100 nm, and/or low
potential(s).
[0045] The selected potential y applied to the electrically
conductive surface may be, for example, in the potential range
between 10 V and -10 V, preferably between 0 V and -4.5 V. In some
preferred embodiments of the present invention, the potential
applied to the electrically conductive or semiconductive surface
may vary during application, for example, at a speed between 0.1
mV/s and 5 V/s, preferred between 1 mV/s and 250 mV/s. Furthermore,
a constant potential may be applied to the electrically conductive
or semiconductive surface, for example, during between 0.001
seconds and 15 minutes, preferably 0.1 seconds and 1 minute.
[0046] The monomer involved in the monomer droplets in the second
embodiment of the invention is any kind of acrylic or methacrylic
derivatives, such as alkyl(meth)acrylate, fluorinated
(meth)acrylate, succinimidyl (meth)acrylate, pyrrole
(meth)acrylate, thiophene (meth)acrylate, and so on, and polymers
bearing one or more acrylic or methacrylic functions, such as
polysiloxanes, polyesters, polyurethanes, poly(methylvinyl ether),
polystyrene, polyethers, and the monomers and polymers described in
WO 02/098926 incorporated herein by reference.
[0047] In the second embodiment of the invention, the
electroconductive surface is also preferably immersed in a micellar
composition comprising a reactive amphiphile in a selective
(protic)solvent (Sso).
[0048] The reactive amphiphile (also called a reactive surfactant)
involved in the monomer droplets in case of micelles are
amphiphilic monomers that self-assemble in a selective solvent (eg,
water). For example, alkyl quaternary ammonium bearing a
(meth)acrylate, amphiphilic block copolymers bearing one or several
(meth)acrylic functions on one block, or a combination thereof.
[0049] Emulsions in water require hydrophobic monomers and
consequently lead to polymer coatings with a hydrophobic character
(if prepared in one step). Whenever hydrophilic coatings have to be
prepared in one step in water, the emulsion has to be replaced by a
micellar composition as illustrated in scheme 3B. For that purpose,
reactive surfactants have to be prepared that meet several
requirements. Such reactive surfactants have to be able to form
micelles in water, to repulse water from the electrical double
layer upon polarization and to electrochemically react to form the
strongly adhering nanostructured coating. Examples of suitable
monomers for this strategy are described in scheme 4. Indeed in
schemes 4A and 4B, there is illustrated amphiphilic and reactive
(acrylic derivative) molecules that are able to self-associate in
water to form micelles thanks to their hydrophilic (charged) and
hydrophobic (long alkyl chain) character, whereas because of the
(meth)acrylic group they can also electropolymerize. In such
systems, the polymer coating is built by the polymerized surfactant
and thus includes some charged groups that increases the
hydrophilicity of the coating.
[0050] In scheme 4C, a similar use of a polymeric reactive
surfactant is illustrated.
[0051] In such cases, the hydrophilic part and the hydrophobic part
are constituted by two polymer sequences, one made of a hydrophilic
polymer, such as poly(ethylene oxide) or quaternized
poly(vinylpyridine), and one made of a hydrophobic chain bearing at
least one (meth)acrylic group, for example a copolymer of
.epsilon.-caprolactone and
.gamma.-acryloyl-.epsilon.-caprolactone.
[0052] Advantages of the second embodiment of the invention with
monomer droplets are that nuclei formation for the nanostructured
polymer coating is in general similar to that described for the
first embodiment of the invention. Furthermore, the applications
for a nanostructured polymer coating obtained from the method of
the second embodiment are also in the same fields as those cited in
respect of the first embodiment.
[0053] Most advantageous of the second embodiment of the invention
compared to the first embodiment is the use of protic solvents, and
particularly the cheap, non-toxic solvent water, a solvent being
particularly opportune for the industrial development of the method
of the invention.
[0054] The present invention also refers to a strong adherent
nanostructured polymer coating obtained by the electrografting
method according to the invention. The nanostructuration is made of
nuclei that can be provided by inorganic material such as metal or
by organic (monomer) droplet that may be further polymerized to
form a polymer aggregate and formation of a nanostructured polymer
coating.
[0055] The invention is now illustrated with reference to the
following Schemes and Figures of the accompanying drawings:
Scheme 1:
[0056] Schematic representation of the first embodiment of the
electrografting method according to the present invention as
performed in the example 1 in which upon applying an increasing
cathodic potential (from left to right on the scheme) to the
electrically (semi)conductive surface immersed in a solution
comprising Ag(I) ions and ethyl acrylate (EA) (represented under
A), Ag(0) metal nuclei may be formed in a first step (represented
under B), before a strongly adherent polymer coating is formed on
the Ag nuclei (represented under C). Finally, if the selected
potential further increases the strongly adherent polymer coating
is removed from the Ag(0) nuclei and a strongly adherent coating
surrounding the metal nuclei is formed on the electrically
(semi)conductive surface (represented under D).
Scheme 2:
[0057] Schematic representation of the first embodiment of the
electrografting method according to the present invention as
performed in example 2 comprising the application of three
different selected potential in three steps. A) Repeating 15 times,
the cycling of the three steps below. B) Repeating the cycling of
the steps more than 15 times.
[0058] In a first step, a selected potential is applied to the
electrically conductive surface to form Cu(0) nuclei which are
coated by a strongly adherent polymer coating from a Cu(I) and
ethyl acrylate (EA) solution (step 1 part A). In a second step,
another selected potential is applied one or more than one time to
further reduce the Cu(I) ions and to remove the strongly adherent
polymer coating from the Cu(0) nuclei while forming an adherent
polymer coating on the electrically conductive surface. By further
reducing the Cu(I) ions the diameter of the Cu(0) nuclei increases
(step 2 part A). Finally, a third selected potential is applied in
a third step to form a strongly adherent polymer coating on the
Cu(0) nuclei (step 3 part A). By repeating the second step it may
be possible to get metal nuclei which are at least partially
covered by smaller metal nuclei (not shown).
[0059] By repeating the sequence of the first and second steps up
to 40 times (steps 1 and 2 part B) before performing the third
step, the roughness of the polymer coated nanostructured surface
may be increased. Beyond 40 cycles, the metal nuclei merge together
and the surface roughness decreases again. For a number of cycles
comprised between 15 and 40 metal nuclei at least partially covered
by smaller metal nuclei may be formed so that the at least
partially polymer-coated nanostructured surfaces may comprise a
roughness on two different scales (step 3 part B) (for example, a
roughness at the micrometre scale and a roughness at the nanometre
scale).
Scheme 3
[0060] Schematic description of the monomer droplets of the second
embodiment of the invention showing an emulsion system (diagram A)
and a micellar system (diagram B), wherein M represents a
hydrophobic monomer, Su a surfactant, RSu a reactive surfactant,
PSo a protic solvent, and SSo a selective solvent.
Scheme 4:
[0061] Possible structures for the reactive surfactants able to
give micelles as monomer droplets. Diagram C shows a polymeric
surfactant with one hydrophilic (left-side part) and one
hydrophobic and reactive (right-side part) segments.
[0062] Scheme 5: Schematic description of the nanostructuration of
the surface by using the monomer droplets systems. Firstly, the
monomer droplets (M) are in suspension in the solvent (e.g. water)
(left-side image). Then, upon polarization (middle image), some
droplets go to the electrode (E) surface forming there nuclei from
which the electropolymerization starts. The polymer grown from
these droplets nuclei forms a nanostructured coating (C)
(right-side image), the nanostructuration originating from the
original monomer compartmentation within the droplets.
[0063] FIG. 1: Typical voltammogram recorded on a stainless steel
surface for the electrografting method according to the present
invention as performed in example 1 using a 8-quinolinyl acrylate
(0.5 M) as monomer in dimethylformamide (DMF) solution saturated by
silver acetate and added with 0.05 M tetraethylammonium perchlorate
(TEAP) (selected potential variation speed=20 mV/s). The first
increase of the measured current intensity (I), is due to the
formation of silver nuclei, the second increase of the measured
current intensity (II), is due to the formation of a strongly
adherent poly(8-quinolinyl acrylate) coating on the silver nuclei,
the third increase of the measured current intensity (III), due to
the electrografting of 8-quinolinyl acrylate onto the steel
surface. First, second and third scans are represented by traces
(a), (b) and (c), respectively. The measured current intensity
decreases with each potential scanning because of the formation of
the insulating properties of the strongly adherent polymer
coating.
[0064] FIG. 2: Voltammogram recorded on stainless steel surface in
a DMF solution of (A) Cu(II) ions, (B) Cu(II) ions with added ethyl
acrylate (EA), and (C) for ethyl acrylate (EA) without Cu(II) ions
as in example 2. ESEM micrographs of the accordingly obtained
surfaces (5 .mu.m.times.5 .mu.m) after the electrograftingmethod in
case of A and B, respectively. The left-side insert is a zoom of
the voltammogram.
[0065] FIG. 3: Atomic force microscopy (AFM) height micrographs for
the samples of nanostructured surfaces of example 2 corresponding
to (A) sample entry 1 in Table 1 and (B) for the "raspberry-shaped"
surface of the sample entry 3 in Table 2. These AFM height
micrographs clearly evidence the possibility of a double-level of
structuration of the surface with a raspberry-shaped surface
comprising a roughness at the micrometer scale and a roughness at
the nanometre scale.
[0066] FIG. 4: Voltammogram illustrating the second embodiment of
the invention for the reduction of an emulsion of
heptadecafluorodecyl acrylate (2M) with cetyltrimethylammonium
bromide as surfactant recorded on carbon surface (A), with two
reduction cycles (1 and 2) on the same electrode, and (B) different
substrates (i.e., SS: stainless steel, SiHC: highly-doped silicon,
SiLC: slightly-doped silicon, C: carbon) as performed in example
3.
[0067] FIG. 5: AFM micrographs showing the nanostructuration of
steel (micrograph A) and carbon (micrograph B) surfaces after
electrografting step as described in example 3 for the second
embodiment of the invention.
[0068] FIG. 6: Voltammogram illustrating the second embodiment for
the reduction of a micellar solution of reactive monomer on carbon
surface as performed in example 4.
[0069] The invention will now be illustrated with reference to the
following examples which are not intended to limit the scope of the
claimed invention.
EXAMPLES OF THE FIRST EMBODIMENT ACCORDING TO THE INVENTION
Example 1
[0070] Preparation of Nanostructured Polymer Coated Surfaces with
Antibacterial Properties
General Conditions.
[0071] Cyclic voltammetry and chronoamperometry were carried out in
a one-compartment cell with a platinum counter electrode and a
platinum pseudo-reference in a glove box under an inert and dry
nitrogen atmosphere (5 ppm of oxygen and <10 ppm of water) at
room temperature using an EG&G potentiostat/galvanostat (M273).
The working electrode (2 cm.sup.2 square-like plate of stainless
steel) was washed with heptane and acetone, and dried overnight at
150.degree. C. under vacuum. For the preparation of the polymer
coatings, dry DMF solutions of the monomer (ethyl acrylate (EA),
8-quinolinyl acrylate (8QA) or an acrylate with nitroxide-mediated
polymerization (NMP) initiator (i.e.
2-phenyl-2-(2,2,6,6-tetramethyl-piperidin-1-yloxy)-ethylacrylate
(PTEA) are used) [for the structure of the last monomer see Chem.
Mater., 2003, 15, 923] in the concentration range 0.3 to 1 M
saturated with AgOOCCH.sub.3 and added with tetraethyl ammonium
perchlorate (TEAP) (5.times.10.sup.-2 M) as an additional
conducting salt were used. The potential of the conductive
substrate was varied at 20 mV/s during voltammetry (FIG. 1). After
polarization, the nanostructured polymer surfaces were extensively
rinsed with dried DMF and acetonitrile before characterization.
Different nanostructured coatings made of metal nuclei and
different polyacrylate have been obtained and are illustrated
below.
Coatings Comprising Silver and Polyethyl Acrylate (PEA)
[0072] When a reduction ramp is applied to ethyl acrylate
(concentration 1 M) and Ag acetate mixture in dimethylformamide
(DMF), with deposition of Ag(0) nuclei at -0.7 V, then a strongly
adherent poly(ethylacrylate) film is formed at a lower cathodic
potential (.about.-1.5 V). At a more cathodic potential (.about.-2
V), the formation of a strongly adherent polyacrylate coating can
occur on the stainless steel surface in between the silver nuclei.
At the same time, the increased potential on the metal nuclei
removes the PEA coating which was formed at -1.5 V because of the
local overpotential occurring at the top of the nuclei that induces
local polymer degrafting. This was confirmed by the AFM analysis of
samples prepared by scanning a solution containing ethyl acrylate,
silver (I) acetate and a conducting salt (TEAP) until -1.5 V and
-2.1 V, respectively. This potential dependence of the polyacrylate
grafting/degrafting process permits the underlying silver to be
apparent again for the external medium, which is of prime
importance for controlling the growth of these Ag nuclei. The
samples were prepared by increasing the selected potential from 0 V
up to -2.1V and applying a selected potential of -2.1 V for 30
seconds, so that the silver nuclei are not coated, but surrounded
by the electrografted polyacrylate. The coatings were characterized
by Attenuated Total Reflectance Fourier Transform Infrared
Spectroscopy (ATR-FTIR) and Energy Dispersive X-ray spectroscopy
(EDX) surface analysis which confirmed the presence of both of PEA
and Ag on the surface. By ATR-FTIR absorptions characteristic of
PEA are observed at 2960 cm.sup.-1-2860 cm.sup.-1 (alkyl C--H),
1735 cm.sup.-1 (ester C.dbd.O) and 1180 cm.sup.-1 (ester C--O). The
contact angle is reported in Table 1.
Coatings Comprising Silver and poly(8-quinolinyl)acrylate
(P8QA)
[0073] The procedure is repeated with 8-quinolinyl acrylate (8QA)
as the monomer rather than EA. The 8QA bears a complexing function
that can act as a ligand for the Ag(I), the resulting coatings will
thus contain both Ag(I) ions and Ag (0) nuclei that are expected to
exhibit powerful antibacterial properties. As for the EA/Ag(I)
system, three reduction reactions are observed by a raise in the
measured current intensity when the potential varies between 0 V
and -2.5 V using 8QA instead of EA. By analogy with the EA/Ag(I)
model, Ag(I) is reduced to Ag(0) at between -1 V and -1.5 V and a
strongly adherent polymer coating of P8QA chains is formed on the
Ag(0) nuclei. At -2 V the P8QA chains are released from the surface
and new ones are formed on stainless steel.
[0074] The samples were prepared by decreasing the selected
potential from 0 V down to -2.1 V and applying a selected potential
of -2.1 V for 30 seconds. At this potential the silver nuclei are
not coated, but surrounded by the polyacrylate (P8QA) as evidenced
by AFM phase contrast measurements. The water contact angle
measurements (Table 1) show that the coatings so obtained are quiet
hydrophilic, which is expected as compared to PEA coatings.
ATR-FTIR and EDX surface analysis confirmed the presence of both
P8QA and Ag on the electrically conducting or semiconducting
surface. By ATR-FTIR absorptions characteristic of P8QA are
observed at 2960 cm.sup.-1-2860 cm.sup.-1 (alkyl C--H), 1735
cm.sup.-1 (ester C.dbd.O) and 1180 cm.sup.-1 (ester C--O).
Coatings Comprising Silver and
poly(2-Phenyl-2-(2,2,6,6-tetramethyl-piperidin-1-yloxy)-ethylacrylate)
(PPTEA)
[0075] As for the other two acrylic monomers/Ag(I) systems cited
here before, three reduction reactions are observed when the PPTEA
is used instead of other acrylates. By analogy with the EA/Ag(I)
model, Ag(I) is reduced to Ag(0) at between -1V and -1.5V, and a
strongly adherent polymer coating of PPTEA chains is formed on the
Ag(0) nuclei. At -2 V these chains are released from the surface
and new ones are formed on stainless steel.
[0076] The samples were prepared increasing the selected potential
from 0 V up to -2.1 V and applying a selected potential of -2.1 V
for 30 seconds. Again, the coatings were characterized by contact
angle (Table 1), showing that the coatings are hydrophobic,
ATR-FTIR and EDX surface analysis confirmed the presence of both
PTEA and Ag on the surface. By ATR-FTIR absorptions characteristic
of PPTEA are observed at 2960 cm.sup.-1-2860 cm.sup.-1 (alkyl
C--H), 1735 cm.sup.-1 (ester C.dbd.O) and 1180 cm.sup.-1 (ester
C--O).
Nitroxide-Mediated Random Copolymerization of butyl acrylate (BuA)
and 2-(dimethylamino ethyl)acrylate (DAEA) from Coatings Comprising
Silver and PPTEA
[0077] Advantages of the PPTEA-based coatings are the possible
chemical initiation of a second and controlled polymerization from
the surface. Random copolymers of BuA and DAEA were prepared from
the PPTEA/silver coating. These random copolymers have already been
prepared from PPTEA electrografted on stainless steel. It was shown
that making polyBuA more hydrophilic by copolymerization with DAEA
increases the anti-adhesive properties towards proteins
(fibrinogen). On the other hand, the presence of silver in the
coating imparts antibacterial properties to the coating, as it will
be shown in the following.
[0078] To a reaction tube containing a stainless steel surface
modified by PTEA containing Ag, was added a mixture of BuA (2.3 ml,
15.8 mmol), DAEA (2.4 ml, 15.8 mmol),
2,2,5-trimethyl-3-(1-phenylethoxy)-4-phenyl-3-azahexane (0.086 g,
0.263 mmol), 2,2,5-trimethyl-4-phenyl-3-azahexane-3-nitroxide
(0.0033 g, 0.0132 mmol) and 0.6 ml dry toluene. The reaction
mixture was degassed by three freeze/throw cycles, closed by a
three-way stopcock under nitrogen, and heated at 125.degree. C. for
24 h. After extensive washing with dry toluene, the coated plates
were dried in vacuum, and analyzed by ATR-FTIR, AFM and
Environmental Scanning Electron Microspcope (ESEM).
[0079] The coatings were characterized by contact angle (Table 1),
showing that they are hydrophilic. The presence of the copolymer
was assessed by ATR-FTIR. Absorptions characteristic of the
copolymer are observed at 2952 cm.sup.-1 and 2923 cm.sup.-1
(aliphatic C--H stretching vibration), 1727 cm.sup.-1 (C.dbd.O
stretching vibration), 1444 cm.sup.-1, 1383 cm.sup.-1 (aliphatic
C--H bending vibration) and 1157 cm.sup.-1 (C--O stretching
vibration).
Antibacterial Activity of Coated Stainless Steel Surfaces
[0080] The antibacterial activity of modified stainless steel with
nanostructured silver/polymer coatings against the Gram-negative
bacteria Escherichia coli and Gram-positive Staphyloccocus aureus
were measured by classical analytical techniques clearly described
in Langmuir, 2003, 19, 8971, 2004, 20, 10718, and 2006, 22,
255.
Adhesion of E. coli to Nanostructured Silver/Polymer Coated
Stainless Steel.
[0081] Uncoated stainless steel surfaces do not inhibit the growth
of E. coli. In all cases, the coated plates containing silver
particles are active against E. coli. The highest inhibition zone
of 30 mm is observed in the case of stainless steel containing
silver particles modified with P8QA. This effect was probably due
to remarkable antibacterial properties of silver particles and
8-hydroxyquinoline derivatives. An inhibition zone of 20 mm is
observed in the case of plates modified with PEA containing silver
particles and 5 mm for the modified PPTEA/Ag plates. The
differences in the hydrophobicity of these two polymer films that
surround the silver particles probably influence antibacterial
activity of these coatings.
Adhesion of S. aureus to Nanostructured Silver/Polymer Coated
Stainless Steel
[0082] Clinical studies show that among the species that dominate
biomaterial-centred infections, S. aureus is one of the most common
pathogens which causes implant-associated infection. That is why we
also evaluated the adhesion of Gram-positive bacteria S. aureus
onto modified stainless steel plates containing silver particles by
using a test that determined the number of viable bacteria that
adhered to the support.
[0083] The test showed that most effective in preventing bacterial
adhesion were the nanostructured surfaces comprising P8QA and Ag,
the nanostructured surface comprising PEA and Ag, the
nanostructured surface comprising P(BuA-co-DAEA) and PPTEA and Ag
which reduce completely (100%) the adhesion of S. aureus. A
reduction of two orders of magnitude over uncoated stainless steel
is observed for Ag and PPTEA coatings in agreement with the
antibacterial activity observed against the Gram-negative bacteria
E. coli. In comparison, the number of bacteria adhered for 1 h
contact onto uncoated stainless steel surfaces is
.about.6.4.times.10.sup.4 colony-forming units (cfu)/ml. The lower
effect of bacteria reduction observed for coatings comprising PPTEA
and Ag compared to the other silver nanostructured coatings was
probably due to higher hydrophobicity of the coating.
[0084] The incorporation of groups with intrinsic antibacterial
properties 8QA or hydrophilic groups, which are biocompatible
(copolymer brushes of BuA and DAEA or PEA) in combination with the
silver nuclei leads to particularly efficient, i.e. complete,
reduction of the number of adhered bacteria compared to uncoated
stainless steel plates.
Example 2
[0085] Preparation of Nanostructured Surfaces with Hydrophobic or
Superhydrophobic Properties
[0086] For this example, acetonitrile (Aldrich), ethyl acrylate
(EA, Aldrich) and heptadecafluorodecyl acrylate (HDFDA) (from ABCR)
were dried over calcium hydride and distilled under reduced
pressure. Dimethylformamide (DMF, Aldrich) was dried over
P.sub.2O.sub.5 and distilled under reduced pressure.
Tetraethylammonium perchlorate (TEAP, Fluka) and copper (II)
acetate (Aldrich) were heated in vacuum at 80.degree. C. for 12 h
prior to use.
[0087] Cyclic voltammetry and chronoamperometry were carried out in
a one-compartment cell equipped with a platinum counter-electrode
and a platinum pseudo-reference by using an EG&G
potentiostat/galvanostat (M273) in a glove box, under an inert and
dry atmosphere nitrogen atmosphere (.+-.5 ppm of oxygen and <10
ppm of water) at room temperature. The working electrode (2
cm.sup.2-stainless steel plates) was washed with heptane and
acetone, and dried overnight at 150.degree. C. in vacuum. The
electrode was immersed in dry DMF containing the acrylate (EA (1M)
or HDFDA (2.5 M)), the conducting salt (TEAP, 5.times.10.sup.-2 M)
and Cu(OOCCH.sub.3).sub.2 (at saturation) and at least one selected
potential was applied. The potential scanning rate was 20 mV/s
during voltammetry. The nanostructured surfaces were washed
extensively with dry DMF followed by acetonitrile in case of
electrografting of polyEA and by trifluorotoluene when fluorinated
polyacrylate was used. It was dried in vacuum before
characterization.
Coatings Comprising Copper and poly(ethylacrylate)
[0088] A nanostructured surface comprising Cu(0) nuclei and
strongly adherent poly(ethylacrylate) (PEA) was formed using a
stainless steel surface and a 1 M EA solution of DMF containing
TEAP (5.times.10.sup.-2M). The reduction peak of very low intensity
observed at -2.1V is the signature of the cathode passivation as a
consequence of the formation of an insulating PEA coating. Indeed,
even after extensive washing of the surface with a good solvent for
PEA, a polyacrylate coating is detected on the surface by ATR-FTIR
spectroscopy. At -2.3 V, the PEA coating is removed from the
electrically conductive or semiconductive surface and the
polymerization of EA may continue in solution.
[0089] Before investigating the behavior of a EA/Cu salt mixture in
a TEAP/DMF solution, the electrodeposition of Cu has been first
studied, in a saturated solution of Cu acetate in DMF added with
TEAP (0.05 M). Under these conditions, Cu starts to be
electrodeposited on stainless steel by voltammetry (FIG. 2, curve
A) at -0.8 V and the intensity reaches a maximum at -1.6 V, as a
result of the limited diffusion of Cu(II) to the cathode. When
ethyl acrylate is added to the solution of Cu acetate
(concentration 1 M), FIG. 2, curve B shows that the current
intensity decreases dramatically because of the formation of an
insulating polyethylacrylate coating on the electrically conductive
surface and/or on the metal nuclei. Formation of Cu(0) nuclei on
stainless steel has been attested by EDX analysis and directly
observed by ESEM (FIG. 2 insert). The nuclei which are formed are
smaller in the presence of ethylacrylate when all other conditions
are identical. The presence of both EA and Cu(0) has been confirmed
by the surface analysis by ATR-FTIR (detection of PEA) and EDX
(detection of Cu). A typical ATR-FTIR spectrum for the coating
formed by varying the selected potential from 0 V to -1.6 V is in
agreement with the spectrum for PEA which is formed in absence of
Cu(II). The absorptions characteristic of PEA are observed at 2960
cm.sup.-1-2860 cm.sup.-1 (alkyl C--H), 1735 cm.sup.-1 (ester
C.dbd.O) and 1180 cm.sup.-1 (ester C--O). Moreover, if the selected
potential varies scanned until higher values (i.e., -2.1 V), the
ATR-FTIR and EDX spectra confirmed the persistence of polyethyl
acrylate and Cu on the electrode. From these experiments, it may be
concluded that the acrylic monomer (EA) forms a strongly adherent
polymer coating while the Cu(II) is simultaneously reduced at -1.5
V. Although the use of a pseudo-reference does not allow the
experimental potential to be directly compared, the potential at
which the formation of a strongly adherent polymer coating of EA is
observed to change from -2.1 V to -1.5 V upon the addition of Cu
acetate to the solution, all the other conditions being the same.
This qualitative shift is important enough to assign it, at least
partly, to the modification of the cathode surface by the
deposition of Cu(0). The growing Cu(0) nuclei contribute to the
roughness of the surface and to the local increase of the potential
at the Cu(0) nuclei as compared to the selected potential which is
applied to the underlying nearly planar stainless steel surface
because of the "tip effect" or "rod effect". The formation of the
PEA coating occurs on the Cu(0) nuclei. The formation of a strongly
adherent PEA coating occurs therefore on the Cu(0) nuclei at a
lower cathodic potential (-1.5 V). At a more cathodic potential
(-2.1 V), the formation of a PEA coating can occur on the stainless
steel surface in between the Cu(0) nuclei. At the same time, the
increase of the potential at the Cu(0) nuclei removes the PEA
chains of the polymer coating which were formed at -1.5 V from the
Cu(0) nuclei. This is confirmed by the AFM analysis of the samples
prepared by varying the selected potential from 0 V to -1.6 V and
from 0 V to -2.1 V, respectively. AFM shows that the surface is
homogeneously covered by Cu(0) nuclei with a diameter of 30-80 nm
for the at least partially polymer-coated nanostructured surface by
varying the selected potential from 0 V to -1.6 V, and the phase
contrast measurement while scanning the surface shows only a little
differences of the phase delay. When the selected potential is
varied from 0 V to -2.1 V, the surface is smoother, because of the
insertion of the PEA polymer coating in between the Cu(0) nuclei
and exhibits by AFM phase contrast measurements different phase
delays for the neat metallic Cu(0) nuclei and the surrounding
strongly adherent polymer coating which is partially covalently
bonded to the stainless steel surface.
[0090] The potential dependence of the formation and the removing
of the strongly adherent PEA coating is thus important to regulate
the growth of Cu(0) nuclei and thus to tune the surface roughness
and the surface coverage of the polymer coating.
Superhydrophobic Surfaces: Nanostructured Coatings Comprising
Copper and poly(heptadecafluorodecyl acrylate)
[0091] The formation of nanostructured coating comprising Cu(0)
nuclei and a strongly adherent poly(heptadecafluorodecyl acrylate)
has been shown to be effective at a concentration of 2.5 M in DMF
solution containing TEAP (5.times.10.sup.-2 M). Cu(OAc).sub.2
remains soluble in this medium. As for the EA/Cu(II) system, two
reduction reactions are observed when the fluorinated acrylate is
used instead of EA. By analogy with what we have observed using a
solution comprising EA and Cu(II), Cu(II) is reduced to Cu(0) at
-1.2 V, while the poly(heptadecafluorodecyl acrylate) forms a
strongly adherent polymer coating on the Cu(0) nuclei
simultaneously. At -2 V this coating is removed from the Cu(0)
nuclei and strongly adherent polymer coating is formed on stainless
steel surface. According to analysis of the surface by ATR-FTIR and
EDX, the fluorinated polyacrylate and Cu(0) coexist on
nanostructured surface even when the selected potentials varies
only from 0 V to -1.6 V.
[0092] When a selected potential of -1.6 V is applied to the
electrically conducting stainless steel surface for 20 seconds, the
contact angle of water is approximately 118.degree., which is
nearly the same value, as the one measured in case of
electrografting of fluorinated polyacrylate on polished stainless
steel in the absence of Cu salt (contact angle of water of
approximately 120.degree.). A similar result is reported whenever a
selected potential of -2 V is applied for 20 seconds (contact angle
of water of approximately 117.degree.). The surface coating is thus
hydrophobic in these cases mainly because of the presence of the
fluorinated polymer. The AFM analysis of the two samples shows
respectively a nanostructured surface that comprises of a limited
number of protuberances with a diameter comprised between 80-150 nm
when a selected potential of -1.6 V is applied for 20 seconds or
many smaller protuberances when a potential of -2 V is applied for
20 seconds. However, in these two cases the surface is essentially
smooth.
[0093] The size of the Cu(0) nuclei can then be increased at the
benefit of the surface area of the coating and the expense of the
intimate contact of water droplets with the underlying surface via
a mechanism of air occlusion.
[0094] For this purpose, the electrografting conditions have been
changed as follows. A first selected potential of -1.2 V has been
applied to the stainless steel surface to form Cu(0) nuclei coated
by fluorinated polyacrylate. In a second step, a second selected
potential of -2.2 V has been applied to the stainless steel
surface, so that the stainless steel left available in between the
Cu(0) nuclei is coated by a strongly adherent fluorinated
polyacrylate, while the fluorinated polyacrylate is removed from
the Cu(0) nuclei, allowing the Cu(0) nuclei to grow further. In a
third step, a selected potential which varies from 0 V to -1.6 V is
applied to the stainless steel surface to form a strongly adherent
fluorinated polyacrylate coating on the copper nuclei, so that the
whole nanostructured surface (Cu(0) nuclei and stainless steel) may
be coated by the fluorinated polyacrylate.
[0095] The first two steps have been conducted by chronoamperometry
(CA), that means that a selected potential is applied during a
certain time, recording the measured current intensity as a
function of the application time of the selected potential, and the
third one by cyclic voltammetry (CV), that means that the selected
potential which may be applied varies in a selected potential range
with a selected variation speed during a selected application
time.
[0096] In addition, the selected potential of -2.2 V has been
applied for increasing period of time to increase the size of the
Cu(0) nuclei. Each time in the third step, after the third selected
potential which varies from 0 V to -1.6 V, a selected potential of
-1.6 V has been applied until the current intensity dropped, due to
the formation of a strongly adherent insulating fluorinated
polyacrylate coating even on the copper nuclei. The experimental
observations are reported in Table 1, together with the
experimental contact angle of water. The roughness of
nanostructured surface and the surface coverage by the polymer
coating may be estimated by AFM. In all the cases, coexistence of
Cu(0) and fluorinated polymer has been confirmed by ATR-FTIR and
EDX.
[0097] Atomic force microscopy shows that large protuberances with
a micrometric size coexist with nanosized entities, the roughness
being determined using 100 .mu.m.times.100 .mu.m AFM pictures
(Table 2). However, the contact angle of water is close to
140.degree., independently of the duration of the second step,
which ranges from 30 seconds to 120 seconds. A possible explanation
is that the fluorinated polyacrylate chains that are released at
-2.2 V from the copper surface are poorly soluble in DMF and
remains accumulated in the close vicinity of this surface, which
dramatically slows down the growth of the Cu(0) nuclei.
[0098] The three steps previously used have therefore been
implemented differently. Indeed, the duration of the two first
steps has been fixed at 3 seconds and 15 seconds, respectively. The
first step was followed by the second step and then the first step
followed by the second step again. This was repeated several times
to repeat the first step followed by the second step sequence from
10 to 40 times (Table 3). At the end of each first step followed by
the second step sequence the solution has been stirred vigorously
in order to prevent the fluorinated polyacrylate removed from the
Cu(0) from accumulating at the Cu(0) nuclei surface. The third step
has been carried out as before, i.e. varying a selected potential
by CV from 0 V to -1.6 V and applying a selected potential of -1.6
V until the measured current intensity dropped.
[0099] Entries 1 to 3 in Table 3 shows that the surface roughness
related to the average diameter of the Cu(0) nuclei, increase with
the number of times the first step followed by the second step
sequence is repeated. In parallel, the contact angle of water
increases from 120.degree. to 157, which is the desired transition
from a hydrophobic and superhydrophobic surface. There is however
an ideal number of cycles because too many cycles (40 cycles, Entry
4 Table 3) results in the merging of the Cu(0) nuclei and thus in a
decreased roughness and hydrophobicity.
[0100] It is worth nothing that the superhydrophobic surfaces
reported in entries 2 and 3 of Table 3 exhibit a hierarchical
roughness which comprises both a roughness at the micrometer and
the nanometer scale, due to Cu(0) nuclei with a diameter between
.about.5-10 .mu.m that comprise other small Cu(0) nuclei with a
diameter between .about.500-999 nm. The large Cu(0) nuclei which
are at least partially covered by small Cu(0) nuclei confer a
raspberry-shaped structure to the surface as shown in FIG. 3. In
contrast, none of the surface prepared in Table 1 shows a two-scale
roughness. As a rule, the number of nuclei is determined by the
first step of the process. These nuclei are allowed to grow during
the second step. Provided that the sequence of the two first steps
is not repeated too many time (for example 10 to 15 times),
formation of additional nuclei is not observed, being hampered by
the passivation of the stainless steel by the fluorinated chains.
However, when the Cu(0) nuclei are large enough (thus for example
beyond 10-15 cycles), Cu nucleation at the surface of the Cu(0)
nuclei providing them with a raspberry-shaped aspect as seen in
FIG. 5B. A contact angle of water of 157.degree. confirms the
superhydrophobicity.
[0101] The contact angle values and the roughness measured for the
samples of the coating comprising copper and poly(HDFDA) prepared
in example 2 by varying the surface and the polarization method
show that both the surface, this underlying roughness and the
polarization method have an influence on the contact angle values
and the roughness measured for the strongly adherent polymer
coatings.
EXAMPLES OF THE SECOND EMBODIMENT ACCORDING TO THE INVENTION
Example 3
[0102] Preparation of Nanostructured Surfaces from Monomer Droplets
Consisting of an Emulsion in Protic Solvents
[0103] Emulsions are used to create droplets of an organic
hydrophobic compound, the monomer, in protic hydrophilic medium,
e.g. water. The emulsion of hydrophobic acrylates in water has been
performed in the presence of a cationic surfactant (long alkyl
chain bearing quaternary ammonium groups). Moreover the
conductivity of the solution is thus ensured by the cationic
surfactant, so there is no need to add other salt to the
medium.
[0104] Acetonitrile (Aldrich), tert-butyl methacrylate (TBMA,
Aldrich), isooctyl acrylate (iOA, Aldrich) and heptadecafluorodecyl
acrylate (HDFDA, ABCR) were dried over calcium hydride and
distilled under reduced pressure. Dimethylformamide (DMF, Aldrich)
was dried over P.sub.2O.sub.5 and distilled under reduced pressure.
Tetraethylammonium perchlorate (TEAP, Fluka) and copper(II) acetate
(Aldrich) were heated in vacuum at 80.degree. C. for 12 h prior to
use.
[0105] Voltammetry and chronoamperometry were carried out in a
one-compartment cell equipped with a platinum counter-electrode and
a platinum pseudo-reference by using an EG&G
potentiostat/galvanostat (M273) under the ambient atmosphere. The
working electrode (2 cm.sup.2 stainless steel, silicon or carbon
plates) was washed with heptane and acetone (the silicon plates
were washed with HF), and dried overnight at 150.degree. C. in a
vacuum. The working electrode was immersed in dry DMF containing
the acrylate (tBMA) (1.5 M) or HDFDA (2 M), the surfactant
cetyltrimethylammonium bromide (12.5 mg) and a selected potential
was applied. The potential varies at 20 mV/s during voltammetry.
The nanostructured surfaces were washed extensively with dry DMF
followed by acetonitrile in the case of PtBMA and by
trifluorotoluene when fluorinated polyacrylate was used. The
nanostructured surface was dried in vacuum before
characterization.
Preparation of Nanostructured Poly(Heptadecafluorodecyl)Acrylate
Coatings in Water: Formation of Superhydrophobic Surfaces
[0106] If a surfactant, cetyltrimethylammonium bromide, is added to
water until saturation, the surfactant self-associates and may be
characterized by dynamic light scattering (DLS). The diameter of
the observed aggregates is large, about 3 to 10 .mu.m, with a mean
diameter of about 5 .mu.m these aggregates are formed of micellar
rods.
[0107] After addition of the acrylate (HDFDA) and a subsequent
sonication, an emulsion comprising droplets of HDFDA at least
partially surrounded by the surfactant molecules is formed in the
protic solvent. The diameter of the droplets of HDFDA of the
emulsion may also be measured by DLS. The diameter of the droplets
is about 600 nm to 800 nm, with a mean diameter of about 700
nm.
[0108] The formation of the strongly adherent polymer coating is
performed in an electrochemical cell containing 5 ml of a 2M HDFDA
solution comprising 12.5 mg of cetyltrimethylammonium bromide in
water at about -2 V on doped-silicon, steel and carbon. The
cationic surfactant insures the conductivity of the aqueous
solution. After each application of a selected potential the
electrically conductive or semiconductive surface is washed with
water and trifluorotoluene.
[0109] Cetyltrimethylammonium bromide surfactant comprises an alkyl
chain containing 16 carbon atoms and is only poorly soluble in the
aqueous solution (saturation for about 30 mg of surfactant added to
10 ml water 2M in HDFDA).
[0110] However, a decrease of the current intensity is measured
after each scan (FIG. 4). The current intensity corresponding to
the hydrolysis of H.sub.2O decreases after each potential scanning,
because hydrophocicity of the electrically conductive or
semiconductive surface increases due to the formation of a strongly
adherent hydrophobic polymer coating which reduces the access of
water to the working electrode.
[0111] The formation of a strongly adherent fluorinated
polyacrylate coating on steel, stainless steel, carbon and silicon
(of different resistivity values from 0.001 .OMEGA.*cm heavily p-
and n-doped Si, to 50 .OMEGA.*cm lightly n-doped Si: LC=low
conductivity and HC=high conductivity) surfaces evidenced by
voltammetry (FIG. 4) is confirmed by ATR-FTIR. Absorptions
characteristic of the polymer are observed at 1727 cm.sup.-1
(C.dbd.O stretching vibration) and 1157 cm.sup.-1 (C--O stretching
vibration). The contact angle values measured for the different
nanostructured surfaces confirm the presence of a strongly adherent
hydrophobic poly(HDFDA) on the different electrically conductive or
semiconductive surfaces. Depending on the method which is used,
chronoamperometry or voltammetry, the contact angle of water may
vary. However all the contact angles measured for nanostructured
coatings prepared using a surfactant and a protic solvent are
higher then the contact angle which can be measured for a strongly
adherent poly(HDFDA) coating prepared using a 2 M HDFDA DMF based
solution on the same surfaces (average contact angle
118.degree..+-.4.degree.). Moreover, nanostructured coatings, which
may be called superhydrophobic because they exhibit a contact angle
of more then 130.degree., may be obtained for all the different
electrically conductive or semiconductive surfaces, due to the
roughness of the strongly adherent polymer coating (FIG. 5).
Although the roughness seems to be correlated to the diameter of
the droplets which are formed in the emulsion, the formation of
hydrogen bubbles at the working electrode during the formation of
the strongly adherent polymer coating, may induce an additional
porosity of the polymer coating because hydrogen bubbles may be
trapped in the strongly adherent polymer coatings, so that this
porosity may also contribute to increase the overall roughness of
the obtained strongly adherent polymer coatings.
[0112] Furthermore, the roughness depends on how the selected
potential(s) is/are applied to the electrically conductive or
semiconductive surfaces. When using chronoamperometry, i.e.
applying a constant potential with time, rather than cyclic
voltammetry, the coatings are more hydrophobic (Table 4) because
the number of strongly adherent protuberances which are formed and
subsequently the roughness of the strongly adherent polymer coating
is higher. AFM measurements have confirmed that roughness of the
nanostructured coating is increased when the coating is prepared by
chronoamperometry whatever the used surface (carbon, steel or
stainless steel). This explains the increase of the contact angle
of water for these nanostructured surfaces prepared by
chronoamperometry.
Preparation of Nanostructured Coatings Comprising Poly(Tert-Butyl
methacrylate) or poly(isooctyl acrylate) using a Protic Solvent
[0113] After addition of tert-butyl methacrylate (tBMA) or isooctyl
acrylate (iOA) to water, an emulsion is formed upon sonication. The
diameter of the droplets of tBMA and iOA of the emulsion may be
measured by DLS. The diameter of the droplets is about 1 .mu.m to 3
.mu.m for tBMA and about 0.8 to 2 .mu.m for iOA. The emulsion
prepared using 1.5 ml of tBMA is not stable and 600 .mu.l of
decaline (decahydronaphtalene) have been added to the emulsion to
decrease the diameter of the tBMA droplets and to increase the
stability of the emulsion.
[0114] The formation of the strongly adherent polymer coating is
performed in a electrochemical cell containing 5 ml of a 1.5 M tBMA
or iOA solution comprising 15 mg of cetyltrimethylammonium bromide
in water at about -2.2 V for both monomers on carbon and stainless
steel. The cationic surfactant also increases the conductivity of
the aqueous solution. After each application of a selected
potential the electrically conductive surface is washed with water
and good solvents for the polymer (toluene or THF).
[0115] The nanostructured coatings prepared using tBMA or iOA, a
surfactant and water are smoother as compared to coatings obtained
with HDFDA. However, the presence of the strongly adherent polymer
coating was assessed by ATR-FTIR. Absorptions characteristic of the
polymer are observed at 1727 cm.sup.-1 (C.dbd.O stretching
vibration) and 1157 cm.sup.-1 (C--O stretching vibration).
Preparation of Strongly Adherent Nanostructured Coatings of
ZONYL.TM. Fluoromonomer Using a Protic Solvent
[0116] After addition of ZONYL.TM. fluoromonomer
(2-(perfluoroalkyl)ethyl methacrylate) to the surfactant/water
mixture, an emulsion is formed upon sonication. The size of the
droplets measured by DLS is about 0.5 .mu.m to 2 .mu.m.
[0117] The formation of the strongly adherent polymer coating is
performed in a electrochemical cell containing 5 ml of 0.05 M to 1
M ZONYL.TM. fluoromonomer (average Mn.about.534) solutions
comprising 15 mg of cetyltrimethylammonium bromide in water at
potentials between -0.8 V and -2 V depending on the concentration
on stainless steel. After each application of a selected potential
the electrically conductive or semiconductive surface is washed
with water and trifluorotoluene.
[0118] The presence of the strongly adherent polymer coating was
assessed by ATR-FTIR. Absorptions characteristic of the polymer are
observed at 1727 cm.sup.-1 (C.dbd.O stretching vibration) and 1157
cm.sup.-1 (C--O stretching vibration). Comparable contact angle as
with poly(HDFDA) were reached on these surfaces.
Example 4
[0119] Preparation of Nanostructured Surfaces from Monomer Droplets
Consisting of Micelles of a Reactive Surfactant in a Selective
Solvent
[0120] The monomer dimethyldecylaminoethylacrylate quaternary
ammonium bromide (DMDAEABr) (scheme 4 structure A with n=10) has
been synthesized by quaternization of dimethylamino-ethylacrylate
(DMAEA) with decylbromide following a general synthesis pathway
described in Polymer Preprints, 2003, 44(2), 264-265 and references
therein.
[0121] The formation of the nanostructured and strongly adherent
polymer coating is performed in an electrochemical cell containing
5 ml of a 0.1 M of DMDAEABr solution in water at about -2.2 V on
carbon. The ionic reactive surfactant ensures the conductivity of
the aqueous solution. Voltammetry (FIG. 6) shows four successive
scans of the potential on the same carbon electrode and clearly
evidence the at least partial passivation of the surface due to the
formation of the strongly adherent polymer coating. In such
coating, quaternary ammonium salt is part of the nanostructured
coating so that the contact angle decreases drastically below
40.degree.. Nanostructuration of the coating is still present due
to the micellar monomer droplets spontaneously formed when the
monomer is put in water. Interestingly, it must be noted that
surfaces coated with quaternary ammonium of this type have
efficiency in bacterial lyses. In a one step and in an aqueous
micellar medium, such coatings have thus been achieved.
TABLE-US-00001 TABLE 1 Contact angle values measured for the
samples prepared in example 1. Contact Angle Sample type of water
(.degree.) Coatings comprising silver and PEA 90.degree. .+-.
2.degree. Coatings comprising silver and P8QA 66.degree. .+-.
3.degree. Coatings comprising silver and PPTEA 109.degree. .+-.
3.degree. Coatings comprising silver and PPTEA + 32.degree. .+-.
5.degree. random copolymer of BuA and DAEA
TABLE-US-00002 TABLE 2 Contact angle values measured for the
samples of the coating comprising copper and poly(HDFDA) prepared
in example 2 by varying the duration of the second step. Contact
Roughness (nm) angle of 100 .mu.m .times. Entry Polarization
procedure water (.degree.) 100 .mu.m surface 1 CA: -1.2 V 60 s, 140
.+-. 4 260 CA -2.2 V 30 s, CV with hold at -1.6 V 2 CA: -1.2 V 60
s, 135 .+-. 2 270 CA -2.2 V 60 s, CV with hold at -1.6 V 3 CA: -1.2
V 60 s, 144 .+-. 2 300 CA -2.2 V 120 s, CV with hold at -1.6 V
TABLE-US-00003 TABLE 3 Contact angle values measured for the
samples of the coating comprising copper and poly(HDFDA) prepared
in example 2 by varying the number of times the cycle formed by the
sequence step one followed by step two is repeated. Contact
Roughness (nm) angle of 100 .mu.m .times. Entry Polarization
procedure water (.degree.) 100 .mu.m surface 1 10 cycles: 120 .+-.
2 130 CA: -1.2 V 3 s + CA -2.2 V 15 s, CV with hold at 1.6 V 2 20
cycles: 141 .+-. 1 190 CA: -1.2 V 3 s + CA -2.2 V 15 s, CV with
hold at 1.6 V 3 30 cycles: 157 .+-. 2 290 CA: -1.2 V 3 s + CA -2.2
V 15 s, CV with hold at 1.6 V 4 40 cycles: 148 .+-. 2 210 CA: -1.2
V 3 s + CA -2.2 V 15 s, CV .fwdarw. -1.6 V
TABLE-US-00004 TABLE 4 Contact angle values measured and roughness
for the samples of the coating comprising copper and poly(HDFDA)
prepared in example 2 by varying the surface and the polarization
method. Contact angle of Roughness Surface Polarization method
water (.degree.) (AFM) Carbon chronoamperometry 152.degree. .+-.
2.degree. 208 nm Carbon cyclic voltammetry 135.degree. .+-.
2.degree. 33 nm Steel chronoamperometry 157.degree. .+-. 2.degree.
91 nm Steel cyclic voltammetry 128.degree. .+-. 3.degree. 25 nm
Stainless steel chronoamperometry 140.degree. .+-. 3.degree. 52 nm
Stainless steel cyclic voltammetry 125.degree. .+-. 4.degree. 12
nm
* * * * *