U.S. patent application number 12/311332 was filed with the patent office on 2010-04-01 for electrochemical co-deposition of sol-gel films.
This patent application is currently assigned to YISSUM RESEARCH DEVELOPMENT COMPANY OF THE HEBREW UNIVERSITY OF JERUSALEM. Invention is credited to David Avnir, Daniel Mandler, Ronen Shacham.
Application Number | 20100078328 12/311332 |
Document ID | / |
Family ID | 39135353 |
Filed Date | 2010-04-01 |
United States Patent
Application |
20100078328 |
Kind Code |
A1 |
Mandler; Daniel ; et
al. |
April 1, 2010 |
Electrochemical co-deposition of sol-gel films
Abstract
A method for the co-deposition of sol-gel and one or more
additives selected from a great variety of agents including
monomers, oligomers, polymers, metals and others is provided. The
method affords continuous films of high stability and precision.
Also provided is a surface coated with a film of sol-gel and at
least one additive electrodeposited according to the presently
described methods.
Inventors: |
Mandler; Daniel; (Jerusalem,
IL) ; Avnir; David; (Jerusalem, IL) ; Shacham;
Ronen; (Herzelia, IL) |
Correspondence
Address: |
THE NATH LAW GROUP
112 South West Street
Alexandria
VA
22314
US
|
Assignee: |
YISSUM RESEARCH DEVELOPMENT COMPANY
OF THE HEBREW UNIVERSITY OF JERUSALEM
Jerusalem
IL
|
Family ID: |
39135353 |
Appl. No.: |
12/311332 |
Filed: |
October 7, 2007 |
PCT Filed: |
October 7, 2007 |
PCT NO: |
PCT/IL2007/001216 |
371 Date: |
November 9, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60847378 |
Sep 27, 2006 |
|
|
|
Current U.S.
Class: |
205/50 ; 205/316;
205/333; 205/80 |
Current CPC
Class: |
C25D 9/04 20130101; C25D
9/06 20130101 |
Class at
Publication: |
205/50 ; 205/80;
205/333; 205/316 |
International
Class: |
C25D 7/00 20060101
C25D007/00; C25D 5/00 20060101 C25D005/00; C25D 11/00 20060101
C25D011/00; C25D 7/04 20060101 C25D007/04 |
Claims
1-53. (canceled)
54. A method for co-depositing on a conductive surface a film of
sol-gel and at least one additive, the method comprising inducing
an electrochemical reaction on the conductive surface in the
presence of a composite of at least one sol-gel precursor and at
least one additive, thereby obtaining a conductive surface coated
with a film, the at least one additive being in the film in an
amount greater than 1 ppm.
55. The method according to claim 54, comprising: (i) providing a
conductive surface; (ii) providing a composite of at least one
sol-gel precursor and at least one additive in a solution; (iii)
contacting the surface with the solution comprising the composite;
and (iv) applying a voltage to the surface in contact with the
composite, thereby inducing formation of a sol-gel film on the
surface.
56. The method according to claim 54, comprising: (i) providing a
conductive surface; (ii) providing a composite of at least one
sol-gel precursor and at least one additive in a solution; (iii)
immersing said surface in a solution comprising said composite,
alcohol, water and at least one inert salt; (iv) applying a voltage
to said surface being immersed in the solution, thereby inducing
formation of a sol-gel film on said surface.
57. The method according to claim 54, wherein the at least one
sol-gel precursor is at least one monomer capable of undergoing
electrochemical polymerization.
58. The method according to claim 57, wherein the monomer is
selected from the group consisting of a metal alkoxide monomer, a
transition metal alkoxide monomer, a silicon alkoxide monomer, a
metal ester monomer, a transition metal ester monomer, a silicon
ester monomer, a monomer of the formula (RO).sub.nM(R').sub.4-n, a
partially hydrolyzed and/or partially condensed polymer of each of
said monomers, and mixtures thereof, wherein in the formula
(RO).sub.nM(R').sub.4-n: M is selected from a silicon atom, a
metallic or semimetallic element, R is an organic moiety selected
from C.sub.1-C.sub.3-alkyl, R' is an organic moiety selected from
C.sub.1-C.sub.10-alkyl, C.sub.2-C.sub.8-alkenyl,
C.sub.2-C.sub.8-alkynyl, C.sub.6-C.sub.10-aryl and
C.sub.4-C.sub.10-heteroaryl, optionally substituted by at least one
group selected from C.sub.1-C.sub.8-alkyl, C.sub.2-C.sub.8-alkenyl,
C.sub.2-C.sub.8-alkynyl, C.sub.6-C.sub.10-aryl,
C.sub.4-C.sub.10-heteroaryl, halide, amine (primary, secondary,
tertiary or quaternary), hydroxyl, thiol, and nitro, and n is an
integer from 1 to 4.
59. The method according to claim 58, wherein the monomers are
selected from the group consisting of metal alkoxide monomers and
silicon alkoxide monomers.
60. The method according to claim 59, wherein the silicon alkoxide
monomer is of the formula (RO).sub.nSi(R').sub.4-n, wherein R is an
organic moiety selected from C.sub.1-C.sub.3-alkyl, R' is an
organic moiety selected from C.sub.1-C.sub.10-alkyl or
C.sub.6-C.sub.12-aryl, optionally substituted by at least one amine
or thiol group, and n is an integer from 1 to 4, or a partially
hydrolyzed and a partially condensed polymer thereof, or a mixture
thereof.
61. The method according to claim 58, wherein M is a metal atom or
a transition metal atom selected from the group consisting of
silicon, zirconium, aluminum, titanium, iron, tungsten, vanadium
and mixtures thereof.
62. The method according to claim 54, wherein the at least one
additive is inert to the sol-gel polymerization process.
63. The method according to claim 62, wherein the at least one
additive is capable of undergoing reduction and/or polymerization
under the electrochemical conditions employed.
64. The method according to claim 62, wherein said at least one
additive is selected from the group consisting of reinforcing
elements, metals, metal salts, fillers, polymers, monomers,
prepolymers, nanoparticles, encapsulated materials, and composite
matrix binders.
65. The method according to claim 64, wherein said at least one
additive is in the form of a plurality of micro- or
nanoparticles.
66. The method according to claim 54, comprising: (i) providing a
conductive surface; (ii) immersing said surface in a solution
comprising sol-gel precursors, at least one alcohol, water and at
least one inert salt; (iii) inducing an electrochemical reaction on
the conductive surface by applying voltage to the surface being
immersed the solution; and (iv) treating the solution with at least
one metal salt; thereby inducing the formation of a hybrid film of
sol-gel and metal on the surface.
67. The method according to claim 66, wherein the surface is a
surface of a medical implant selected from the group consisting of
a stent, an artificial heart valve, a cerebrospinal fluid shunt, a
pacemaker electrode, an axius coronary shunt, an endocardial lead,
an orthopedic device, and a vessel occlusion device.
68. A surface coated with a film of sol-gel and at least one
additive electrodeposited according to the method of claim 54.
69. The method according to claim 58, wherein R is an unsubstituted
organic moiety selected from C.sub.1-C.sub.3-alkyl.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a method of electrochemical
co-deposition of sol-gel and different additives to thereby form
films on various surfaces.
BACKGROUND OF THE INVENTION
[0002] Electrochemical deposition, which dates back to the middle
of the 19.sup.th century, is still an extremely powerful process in
particular for depositing metals (electroplating), such as copper,
cobalt, nickel and their alloys on various surfaces. Thin metal
films, deposited on the surface of conducting and non-conducting
materials by electrolysis play an important role in many fields,
such as decorative and anticorrosion coatings. Electrodeposition of
metals, e.g., copper, has become of utmost significance due to its
role in microelectronics.
[0003] Electrodeposition of ceramic films employing electrochemical
methods is a fast evolving field. The methods for electrodeposition
may be divided into two: electrophoretic and electrolytic
deposition. Electrolytic deposition can be driven using cathodic
currents by either reducing the metal ions, which causes their
deposition, e.g., Cu.sub.2O, or by driving a proton-dependent
reducing process, leading to an increase of the pH on the electrode
surface and the subsequent metal hydroxide deposition.
Alternatively, the deposition of metal oxides and hydroxides can be
driven by anodic currents as a result of oxidizing the metal ions,
thus increasing their oxidation state, which usually results in
lower solubility of their hydroxide salts, such as in Fe(OH).sub.3
deposition.
[0004] Ormocers (ORganically MOdified CERamics) are metal oxides
that are formed at room temperature and comprise organic moieties.
They are formed as a result of the hydrolysis and condensation of
functionalized trialkoxymetals, e.g., alkyl-trimethoxysilanes, as
shown in Equations 1 and 2.
R-M(OR').sub.3+3H.sub.2O.fwdarw.R-M(OH).sub.3+3R'OH (Eq. 1)
R-M(OH).sub.3+R-M(OR').sub.3.fwdarw.R-M(OH).sub.2--O-M(OR').sub.2+R'OH
(Eq. 2)
[0005] There are enormous advantages to using sol-gel technologies
for preparing thin films as the non-hydrolizable group, R, can be
used to tune the chemical and physical properties of the
coating.
[0006] Recently, porous solids made of well-ordered silica walls
were developed. These porous solids are spatially arranged by
micelle-templating to form channels of regular size in the
mesoporous range. They are called micelle-templated silica, MTS.
Their surface reactivity is rather close to that of silica gel so
that grafting organic functionalities to the inner walls of these
silicates with uniform channel structures can be readily achieved.
Incorporation of organic groups in MTS can also be performed by
co-condensation under surfactant control. Due to the fluid
character of the sol, the sol-gel synthesis of ordered mesoporous
films on solid substrates is possible, but their use in connection
to electrochemistry is scarce.
[0007] The electro-assisted deposition of ormocers has recently
been reported by the inventors of the invention disclosed herein
(Refs [1]-[3]). This approach takes the advantage of enhancing the
hydrolysis and condensation (both processes are acid and base
catalyzed) of the sol-gel process by altering the pH at the surface
as a result of applying a potential.
[0008] The electrodeposition of metal-ceramic composite coatings
has been reported (Refs [4]-[8]) to involve performing the
electrolysis in a suspension of ceramic particles. Many various
classes of inert particles have been used; however, best results
were obtained with carbides or oxides. On the other hand, the
formation of ceramic-metal composite materials has been
accomplished (Refs [9]-[10]) by the incorporation of metallic
particles in the course of sol-gel formation or the entrapment of
metal cations followed by their reduction. Most of these
conventional methods are limited by the metals and ceramics that
can be deposited and do not allow precise controlling of the
deposit structure. For these reasons as well as due to the
importance of these materials in plating, catalysis, solar cells,
etc., there is an enormous interest in developing better-controlled
and efficient preparation methods for metal-ceramic and
ceramic-metal composite materials.
[0009] Recently, the inventors of the present invention have
developed a method for coating a conducting material by
electrodeposition of a sol-gel film of silicon oxide originating
from methyltrimethoxysilane (Refs [1] and [11]). The mechanism of
the electrochemical sol-gel coating described, involves the
alteration of the local pH next to the conducting surface,
resulting in an enhancement of the deposition specifically on the
desired surface. This technique was suitable for sol-gel coating of
flat surfaces utilizing a basic pH above 8.2.
LIST OF REFERENCES
[0010] [1] R. Shacham, et al., Electrodeposition of
Methylated-Sol-Gel Films on Conducting Surfaces. Adv. Mater. 1999,
11, 384-388; [0011] [2] R. Shacham, et al., Chem. Eur. J., 2004,
10, 1936-1943; [0012] [3] R. Shacham, et al., J. Sol-Gel Sci.
Technol., 2004, 31, 329-334; [0013] [4] Low, C. T. J., et al.,
Surface & Coatings Technology 2006, 201, 371-83; [0014] [5]
Kerr, C., et al., Transactions of the Institute of Metal Finishing
2000, 78, 171-78; [0015] [6] Benea, L. Materials and Manufacturing
Processes 1999, 14, 231-42; [0016] [7] Helle, K., et al.,
Transactions of the Institute of Metal Finishing 1997, 75, 53-58;
[0017] [8] Hovestad, A., et al., Journal of Applied
Electrochemistry 1995, 25, 519-27; [0018] [9] Daniel B. S. S., et
al., J. Mater. Proc. Tech., 1997, 68, 132; [0019] [10] Howe J. M.,
Inter. Mater. Rev., 1993, 38, 233; [0020] [11] WO 05/100642.
SUMMARY OF THE INVENTION
[0021] The electrochemical co-deposition approach described herein
is based on an entirely new concept of electrodeposition of organic
sol-gel materials by electrochemistry. The two basic processes that
lead to the formation of organo-sol-gel materials, i.e., hydrolysis
and condensation, comprise acid/base processes and therefore it is
not trivial that they can be driven by electrochemistry, which, as
a person skilled in the art would realize, is mostly used for
driving oxidation/reduction reactions. The invention does not lie
only in the approach, but also in its wide-range potential
applications. That is, the process of electrochemical co-deposition
of additives and organo-ceramics as films adds a unique control,
i.e., by the applied potential, as a means of controlling the film
composition as well as the deposition rate. Since this approach is
generic, its applicability covers a wide range of ceramic materials
and additives. Possible impact spans from reinforcing metal
coatings to forming functionally graded materials.
[0022] The uniqueness of the approach disclosed herein lies in the
ability to co-deposit an inorganic or organic insulating matrix
together with an additive material, e.g., metallic particles, and
conductive polymers and more so in the ability to form a film on a
substrate by controlling the kinetics of both processes which
allows tailoring of film morphology.
[0023] This co-deposition process affords a film which may in some
instances have at least two distinct phases.
[0024] Additionally, the inventors have shown that such an
electrochemical co-deposition method of sol-gel and at least one
additional additive is reproducible and highly versatile. Some
additional advantages of employing the method of the invention as
compared with other known methods for coating surfaces are:
[0025] 1. Since electron transfer occurs very close to the surface,
i.e., within less than 100 .ANG., the coating follows very closely
the intimate structure of the surface, allowing the coating of
complex geometries, such as screws, stents, sprints, etc;
[0026] 2. The thickness of the coating and the nature thereof is
highly controllable and depends primarily on the ratio between the
sol-gel monomer and the additional substance and the potential
applied and duration of application;
[0027] 3. The method may be used with reproducible results,
affording coatings of a great variety, on a great variety of
surfaces, including those with complex geometries;
[0028] 4. A great variety of additives may be used;
[0029] 5. The inclusion of the additive in the reaction mixture
does not interfere with the sol-gel polymerization; and
[0030] 6. The electrochemical sol-gel polymerization process allows
for secondary processes such as reductions of metal or organic
compounds to take place at the same time without affecting or
interfering with the sol-gel polymerization process.
[0031] Accordingly, in one aspect of the present invention, there
is provided a method for electrochemical co-depositing on a
conductive surface a film of sol-gel and at least one additive,
said method comprising inducing an electrochemical reaction on said
conductive surface in the presence of a composite of at least one
sol-gel precursor and at least one additive, thereby obtaining a
film of said composite on the surface.
[0032] In some embodiments, the at least one additive is selected
so as to be capable of undergoing reduction or oxidation during the
electrodeposition process.
[0033] The composite as used in the context of the present
invention is a combination of at least one sol-gel precursor and at
least one additive, each having different properties than that of
the composite as a whole, and have different chemical and physical
characteristics such that they do not dissolve or merge completely
in one another. Complete dissolution of both in a liquid medium
(e.g., a solution) is nevertheless required for the formation of
the composite. In the composite, the sol-gel precursors and the
additives have strong interactions therebetween, such interactions
being one or more of covalent, electrostatic, complex-forming
interactions, hydrophobic-hydrophilic and hydrogen bonding. In the
absence of such strong interactions, only doping is achieved,
namely, only minute quantities of the at least one additive, as
defined herein, will be deposited along with the sol-gel.
[0034] The composite is typically prepared as a solution of at
least one sol-gel precursor and at least one additive. The solution
may be prepared by adding the components simultaneously and mixing
until complete dissolution of both components is achieved or by
adding one component after the other as demonstrated herein below.
In one embodiment, said solution is an aqueous solution. In another
embodiment, the solution is an alcoholic solution containing water.
In another embodiment, the composite is a nanocomposite.
[0035] As stated above, the method allows the electro co-deposition
of sol-gel and an additive(s). It should be noted that herein, for
the sake of clarity, the term "electro co-deposition" is used
interchangeably with the "electrodeposition of the composite", as
defined. The term "co-deposition" or any lingual variation thereof,
refers to the "depositing together", namely to a single-step
simultaneous deposition of the two components, namely sol-gel and
additive(s) and the formation of a film or a coat on a substrate
according to the invention, wherein the film which is formed is a
hybrid (in some cases two-phase) film of the sol-gel and additive
(the phases can be of the order of a few nanometers resulting in
nanocomposite materials). In some embodiments, in the process of
co-deposition, a sol-gel polymerization reaction takes place
simultaneously with the reduction of a metal or an oxidation of an
organic compound, such as pyrrole.
[0036] The sol-gel precursors are typically monomers, which can
undergo polymerization under the electrochemical conditions
employed. The precursors are selected from metal alkoxide monomers,
transition metal alkoxide monomers, silicon alkoxide monomers,
metal ester monomers, transition metal ester monomers, silicon
ester monomers, monomers of the formula (RO).sub.nM(R').sub.4-n,
partially hydrolyzed and/or partially condensed polymers of said
monomers and mixtures thereof, wherein in the formula
(RO).sub.nM(R').sub.4-n, M is selected from a silicon atom, a
metallic or semimetallic element such as Si, Zr, Ti and others, R
is an organic moiety selected from C.sub.1-C.sub.3-alkyl, being
preferably unsubstituted, R' is an organic moiety selected from
C.sub.1-C.sub.10-alkyl, C.sub.2-C.sub.8-alkenyl,
C.sub.2-C.sub.g-alkynyl, C.sub.6-C.sub.10-aryl,
C.sub.4-C.sub.10-heteroaryl, each being optionally substituted by
at least one group selected from C.sub.1-C.sub.8-alkyl,
C.sub.2-C.sub.8-alkenyl, C.sub.2-C.sub.8-alkynyl,
C.sub.6-C.sub.10-aryl, C.sub.4-C.sub.10-heteroaryl, halide, amine
(primary, secondary, tertiary or quaternary), hydroxyl, thiol,
nitro, repeating methylenedioxy (--O--CH.sub.2--O--) or
ethylenedioxy (--O--(CH.sub.2).sub.2--O--) groups, and n is an
integer from 1 to 4.
[0037] In one embodiment, the at least one sol-gel precursor is a
mixture of such precursors. In another embodiment, the mixture of
precursors is chosen so as to improve one or more of the following
properties of the coating: adhesion, charge and charge
distribution, hydrophobicity, hydrophilicity, thickness,
reactivity, resistivity, resistance to oxidation, etc.
[0038] In another embodiment, the precursors are monomers being
selected amongst metal alkoxide monomers and silicon alkoxide
monomers.
[0039] In still another embodiment, the silicon alkoxide monomer is
of the formula (RO).sub.nSi(R').sub.4-n, wherein R is an organic
moiety selected from C.sub.1-C.sub.3-alkyl, R' is an organic moiety
selected from C.sub.1-C.sub.10-alkyl or C.sub.6-C.sub.12-aryl,
optionally substituted by at least one amine or thiol group, and n
is an integer from 1 to 4, or partially hydrolyzed and partially
condensed polymer thereof, or a mixture thereof.
[0040] Within the context of the present invention, the term
"alkyl" refers to an aliphatic moiety having at least 1 carbon atom
and being optionally substituted by at least one group selected
from C.sub.2-C.sub.8-alkenyl, C.sub.2-C.sub.8-alkynyl,
C.sub.6-C.sub.10-aryl and C.sub.4-C.sub.10-heteroaryl, optionally
substituted by at least one group selected from
C.sub.1-C.sub.g-alkyl, C.sub.2-C.sub.8-alkenyl,
C.sub.2-C.sub.8-alkynyl, C.sub.6-C.sub.10-aryl,
C.sub.4-C.sub.10-heteroaryl, halide, amine (primary, secondary,
tertiary or quaternary), hydroxyl, thiol, nitro and repeating
methylenedioxy (--O--CH.sub.2--O--) or ethylenedioxy
(--O--(CH.sub.2).sub.2--O--) groups. For example, the specific
designation "C.sub.1-C.sub.3-alkyl" refer to an alkyl group having
between 1 and 3 carbon atoms and unless specifically defined may be
substituted. Unless specifically stated, the alkyl group may be
linear or branched. Non-limiting examples of alkyl groups are a
methyl, ethyl, propyl, isopropyl, butyl, 2-butyl, pentyl, hexyl,
heptyl, octyl, nonyl and dodecyl.
[0041] The term "alkenyl" refers to a carbon chain having at least
2 carbon atoms and at least one double bond, which may be at one of
the terminal positions of the chain or be an inner-chain double
bond. The term "alkynyl" refers similarly to a carbon chain having
at least two carbon atoms and at least one triple bond which may be
a terminus bond or an inner-chain triple bond.
[0042] The term "aryl" refers to an aromatic moiety, preferably a
benzene ring (i.e., a phenyl ring), which may optionally be
substituted by at least one or more functional group, provided that
such does not interfere with the hydrolysis and condensation of the
sol-gel, said group being selected from C.sub.1-C.sub.8-alkyl,
C.sub.2-C.sub.8-alkenyl, C.sub.2-C.sub.8-alkynyl,
C.sub.6-C.sub.10-aryl, C.sub.4-C.sub.10-heteroaryl, halide, amine
(primary, secondary, tertiary or quaternary), hydroxyl, thiol,
nitro and repeating methylenedioxy (--O--CH.sub.2--O--) or
ethylenedioxy (--O--(CH.sub.2).sub.2--O--) groups. The aryl group
may also be a biaryl such as a biphenyl. The specific designation
"C.sub.6-C.sub.12-aryl" refers to an aromatic moiety having between
6 carbon atoms and 12 carbon atoms. Non-limiting examples of aryls
are a phenyl, biphenyl, and naphthyl.
[0043] Within the scope of the present invention, the term "aryl"
also encompasses heteroaryls having between 5 and 10 atoms, at
least one of which being a heteroatom selected from N, O and S. The
heteroaryls may be similarly substituted.
[0044] In another embodiment, M is a metal atom or a transition
metal atom selected from Si, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni,
Cu(I) Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, La, Hf, Ta, W, Re,
Os, Ir, Pt, Au, Hg and Ac and mixtures thereof.
[0045] In a further embodiment, said metal is Si, Zr, Al, Ti, Fe,
V, and W.
[0046] In some embodiments, the sol-gel precursor is a metal oxide
selected from (i) aluminum oxides such as, but not limiting to,
aluminum triethoxide, aluminum isopropoxide, aluminum sec-butoxide,
and aluminum tri-t-butoxide; (ii) titanium oxides such as, but not
limiting to, titanium methoxide, titanium ethoxide, titanium
isopropoxide, titanium propoxide, titanium butoxide, titanium
ethylhexoxide, titanium (triethanolaminato)isopropoxide, titanium
bis(ethyl acetoacetato)diisopropoxide, and titanium
bis(2,4-pentanedionate)diisopropoxide; (iii) zirconium oxides such
as, but not limiting to, zirconium ethoxide, zirconium
isopropoxide, zirconium propoxide, zirconium sec-butoxide, and
zirconium t-butoxide; (iv) aluminum oxides such as, but not
limiting to, and aluminum di-s-butoxide ethylacetonate; (v) copper
(I) oxides such as, but not limiting to, copper ethoxide, and
copper methoxyethoxyethoxide; (vi) titanium oxides such as, but not
limiting to, titanium dioxide and titanium n-nonyloxide; (vii)
vanadium oxides such as, but not limiting to, vanadium
tri-n-propoxide oxide, and vanadium triisobutoxide oxide; (viii)
silicon oxides such as silicon dioxide; and combinations of two or
more of the above compounds.
[0047] Metal salts such as metal carboxylates, metal halides, and
metal nitrates may also be added as the metal oxide compound to
make the sol-gel precursors. Metal carboxylates include metal
acetates, metal ethylhexanoates, metal gluconates, metal oxalates,
metal propionates, metal pantothenates, metal cyclohexanebutyrates,
metal bis(ammonium lacto)dihydroxides, metal citrates, and metal
methacrylates. The metals are the same metals as the metal
alkoxides. Specific examples of metal carboxylates include aluminum
lactate, acetate, ethylhexanoate, gluconate, oxalate, propionate,
pantothenate, cyclohexanebutyrate, and methoxyethoxide, iron
alkoxide, iron isopropoxide, tin acetate, tin oxalate, titanium
bis(ammonium lacto)dihydroxide, zinc acetate, zinc methacrylate,
zinc stearate, zinc cyclohexanebutyrate, zirconium acetate, and
zirconium citrate.
[0048] In some cases, the at least one sol-gel precursor is an
organosilane such as phenyltrimethoxysilane; phenyltriethoxysilane;
diphenyldimethoxysilane; diphenyl diethoxysilane;
3-aminopropyltrimethoxysilane; 3-aminopropyltriethoxysilane;
N-(3-trimethoxysilylpropyl)pyrrole;
N[3-(triethoxysily)propyl]-4,5-dihydroimidazole;
beta-trimethoxysilylethyl-2-pyridine;
N-phenylaminopropyltrimethoxysilane; 3-(N-styryl
methyl-2-aminoethylamino)propyltrimethoxysilane;
methacryloxy-propenyltrimethoxy silane;
3-methacryloxypropyltrimethoxysilane; 3-methacryloxypropyltris
(methoxyethoxy)silane; 3-cyclopentadienylpropyltriethoxysilane;
7-oct-1-enyl trimethoxysilane, 3-glycidoxypropyl-trimethoxysilane;
gamma-glycidoxypropyl methyldimethoxysilane;
gamma-glycidoxypropylpylpentamethyldisiloxane;
gamma-glycidoxypropylmethyldiethoxysilane;
gamma-glycidoxypropyldimethylethoxysilane;
(gamma-glycidoxypropyl)-bis-(trimethylsiloxy)methylsilane;
vinylmethyldiethoxy silane; vinylmethyldimethoxysilane;
methylaminopropyltrimethoxysilane; n-octyl triethoxysilane;
n-octyltrimethoxysilane; hexyltriethoxysilane; isobutyltrimethoxy
silane; 3-ureidopropyltriethoxysilane;
3-isocyanatepropyltriethoxysilane;
N-phenyl-3-aminopropyltrimethoxysilane;
3-triethoxysilyl-N-(1,3-dimethyl-butyliden) propylamine;
N-2(aminoethyl)-3-aminopropyltriethoxysilane; triethoxysilane;
N-2(aminoethyl)-3-aminopropyltrimethoxysilane;
N-2(aminoethyl)-3-aminopropylmethyldimethoxysilane;
3-acryloxypropyltrimethoxysilane;
methacryloxypropylmethyldiethoxysilane;
meth-acryloxypropylmethyldimethoxysilane;
glycidoxypropylmethyldiethoxysilane;
2-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane;
vinyltriethoxysilane; amonophenyl trimethoxysilane;
p-chloromethyl)phenyltri-n-propoxysilane; diphenylsilanediol;
vinyltrimethoxysilane;
2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; epoxyhexyl
triethoxysilane; tris(3-trimethoxysilylpropyl)isocyanurate;
dococentyl trimethoxysilane; 3-mercaptopropyltriethoxysilane;
1,4-bis(trimethoxysilylethyl)benzene; phenylsilane;
trimethoxysilyl-1,3-dithiane;
n-trimethoxysilylpropylcarbamoylcaprolactam;
2-(diphenylphosphine)ethyltriethoxysilane,
3-cyanopropyltrimethoxysilane, and
diethylphosphatoethyltriethoxysilane.
[0049] In some embodiments, the sol-gel precursor is one or more of
TiO.sub.2, SiO.sub.2, titanium tetra-n-propoxide (Ti(OPr).sub.4),
phenyltrimethoxy silane (PhTMOS), aminopropyltriethoxy silane
(APTEOS), tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), and
silicon oxide.
[0050] The at least one additive of the composite may be any
substance which is inert to the sol-gel process, does not interfere
therewith, does not take part in the sol-gel polymerization
(namely, it is not an essential component of the sol-gel
polymerization process which can proceed even in its absence) and
which is distributed in the sol-gel film in a homogenous or
heterogeneous fashion.
[0051] The at least one additive may be a mixture of different
additives, in different quantities or in different forms.
Non-limiting examples of the at least one additive are reinforcing
elements, metals, metal salts, fillers, polymers, monomers,
nanoparticles, encapsulated materials, and composite matrix
binders.
[0052] In one embodiment, the at least one additive is a mixture of
additives, such as two or more different polymers or two or more
different monomers thereof.
[0053] In another embodiment, the at least one additive is a
plurality of micro- or nanoparticles or nano- or microcapsules
constructed from and/or containing different materials.
[0054] In a further embodiment, the at least one additive is a
substance which is capable of undergoing a reduction or an
oxidation under the conditions employed, without interfering with
the sol-gel deposition. Non-limiting examples of such are monomers,
oligomers, metals, and metal salts.
[0055] In a still further embodiment, the at least one additive is
an additive or a plurality thereof, such as monomers or oligomers,
capable of polymerizing during the electrochemical co-deposition
process without affecting the sol-gel process.
[0056] Typically, the ratio between the sol-gel and the additive
may range from 1:1, 10:1, 100:1, 100:1, 1000:1, respectively, or
any ratio therebetween. As such, a person skilled in the art should
realize that the at least one additive is not a doping agent or a
dopant existing in the film in minute concentrations (ppm or lower)
so as to alter a specific property or a colloquium of properties of
the substance in which it is present. In contrast to dopants added
in so-called "doping quantities", the at least one additive of the
composite constitutes a substantial part of the composite, as
demonstrated in the examples below.
[0057] In one embodiment, the at least one additive is at least one
monomer of a conducting polymer which polymerizes independently of
the polymerization of the sol-gel, without disrupting it, and the
method affords a surface coated with a film of sol-gel embedded
with a conductive polymer.
[0058] In another embodiment, the at least one additive is a
polymer. In still another embodiment, said polymer is
conductive.
[0059] In another embodiment, the at least one additive is a
prepolymer, i.e., an oligomer made of several monomers capable of
further polymerization.
[0060] The conductive polymers or monomers thereof which are
suitable for use in the present invention include, in a
non-limiting fashion, polymers having a polymeric component of one
or more olefin, such as polyethylene; polyacetylenes, polypyyroles,
polythiophenes, and polyanilines, copolymers thereof and blends of
two or more such polymers. Each of said conductive polymer may or
may not be substituted.
[0061] The polypyrroles may be selected from, in a non-limiting
fashion, unsubstituted polypyrrole, alkylated polypyrrole,
copolymers of polypyrrole, polypyrrole/poly (styrene sulfonic
acid), 3,4-dialkoxy substituted polypyrrole styrene sulfonate, and
3,4-dialkoxy substituted polythiophene styrene sulfonate.
[0062] As stated above, the at least one additive may be the
polymer it self or a precursor thereof in the form of monomers,
oligomers or shorter polymers capable of undergoing polymerization
into the desired polymer.
[0063] In another embodiment, the polymer is pluronic, preferably
F127, polyethylene glycol of various molecular weights, and oligo
or polypyrrole or other conducting polymers of various molecular
weights.
[0064] In yet another embodiment, the at least one additive is a
plurality of nanoparticles. In some embodiments, the nanoparticles
contain at least one substance or mixture of substances. In other
embodiments, the nanoparticles are hollow (empty, or contain a gas
or a non-particular solvent).
[0065] The nanoparticles which may be added as additives may be
made of a variety of materials such as silica, carbon, metals of
different types, such as gold, platinum or metal oxides thereof. In
some embodiments, the nanoparticles are silica hollow particles. In
other embodiments, the nanoparticles are particles encapsulating at
least one substance or a mixture of substances.
[0066] The substance or mixture of substances which may be
encapsulated in the particles may be selected from drugs, fillers,
metals, metal oxides, metal salts, metal particulates, reinforcing
materials, colorants, fluorescent materials, magnetic materials,
and semiconductive materials.
[0067] In another embodiment, the at least one additive is a metal.
In some embodiments, the metal is added to the reaction solution in
the form of a metal salt. Non-limiting examples of such metals are
copper (II), cobalt, nickel, silver, palladium and gold.
[0068] The at least one metal salt may be added as a solid (as
powder or semi-solid) to the solution containing the sol-gel
precursors and thereafter allow to dissolve therein, as a
concentrate (a high concentration solution of the metal salt), or
as a solution of any other concentration. The solution may be a
water solution containing only the metal salt and water, or an
aqueous solution containing also inert metal forms (being different
from the additive metal salts), alcohol, acids, bases or other
additives.
[0069] In one embodiment, the at least one metal salt is one metal
salt.
[0070] In other embodiments, the at least one metal salt is a
mixture of salts of the same metal but of at least two different
counter ions.
[0071] In further embodiments, the at least one metal salt is a
mixture of salts of different metals.
[0072] The at least one metal salt is not a dopant.
[0073] As stated above, in order for the electrodeposition of the
composite to succeed, the surface to be coated (be it the whole
surface or a portion thereof which coating is desired) must be
conductive. In cases where the surface is conductive only in
specific regions thereof, the electrodeposition will be affected at
the conductive regions only. Surfaces which are non-conductive may
be coated with a conductive layer, for example by electroless
processes, before sol-gel electrodeposition. As a person skilled in
the art would recognize, the term "conductive" refers generally to
the ability of the surface to conduct electric current. The
conductivity of surfaces may be measured according to methods known
in the art.
[0074] The conductive surface to be coated according to the
invention may be a surface of any device, structure, article, or
element. The surface may be flat, smooth, coarse, round, a
three-dimensional surface, inner and/or outer surfaces, a surface
having regions of restricted access and cavities, multilayered
surfaces and a surface of any thickness, constitution and size.
[0075] The conductive surfaces may be for example of metallic
materials or alloys such as, but not limited to, stainless steel
(316L), MP35N (an alloy of 35% cobalt, 35% nickel, 20% chromium,
and 10% molybdenum), MP20N (an alloy of 50% cobalt, 20% nickel, 20%
chromium, and 10% molybdenum), ELASTINITE (Nitinol),
cobalt-chromium alloys (e.g., ELGILOY), tantalum, tantalum-based
alloys, nickel-titanium alloy, platinum, platinum-based alloys such
as platinum-iridium alloy, iridium, gold, magnesium, titanium,
titanium-based alloys, zirconium-based alloys, copper, graphite, or
combinations thereof. Semiconductive or superconductive compounds
may also serve as conductive surfaces suitable for the
electrodeposition of the invention. Devices made from bioabsorbable
or biostable polymers can also be used with the embodiments of the
present invention, provided that at least a portion thereof to be
coated is conductive.
[0076] In one embodiment, said surface is made of stainless steel.
In a preferred embodiment, the stainless steel is stainless steel
316L.
[0077] In another embodiment, said surface is a metallic
surface.
[0078] In yet another embodiment, said surface is made of
indium-tin oxide (ITO).
[0079] Non-limiting examples of devices, structures, articles, and
elements having such surfaces are metals wires, metal sheets,
metallic surfaces of electronic devices, patterned surfaces,
electric elements, medical devices, medical implants, household
appliances, refractive elements, structures requiring insulation,
and containers.
[0080] In one embodiment, said surface is the surface of a medical
device or an implant. As a person skilled in the art would
recognize, a medical implant is a structure which may be implanted
into the body of an animal, e.g., non-human or human. The structure
may be implanted in the body of the subject during a medical
procedure which purpose may be the treatment or prevention of a
disease or disorder or the diagnosis of a condition. The implant
may also be one which is used as a vehicle for providing therapy.
The implant may act as scaffoldings, functioning to physically hold
open and, if desired, to expand the wall of a passageway, inserted
through small vessels, such as via catheters, and then expanded to
a larger diameter once it is at the desired location. Non-limiting
examples of such medical implants are a stent, an artificial heart
valve, a cerebrospinal fluid shunt, a pacemaker electrode, an axius
coronary shunt, an endocardial lead, an orthopedic device, and a
vessel occlusion device.
[0081] In one embodiment, the surface to be coated by the composite
according to the invention is the surface of a medical implant,
said composite comprising apart from the sol-gel precursors a
plurality of nanoparticles containing at least one drug. The at
least one drug may be selected, in a non-limiting fashion amongst
analgesics/antipyretics, antiasthamatics, antibiotics,
antidepressants, antidiabetics, antifungal agents, antihypertensive
agents, anti-inflammatories, antineoplastics, antianxiety agents,
immunosuppressive agents, antimigraine agents, sedatives/hypnotics,
antipsychotic agents, antimanic agents, antiarrhythmics,
antiarthritic agents, antigout agents, anticoagulants, thrombolytic
agents, antifibrinolytic agents, antiplatelet agents and
antibacterial agents, antiviral agents, antimicrobials,
anti-infectives, and combination thereof.
[0082] In another embodiment, said medical implant is a stent or an
orthopedic device such as a screw or nail.
[0083] As stated hereinbefore, the coating of the conductive
surface by a film of the composite is achieved by the induction of
electrochemical reaction on the surface to be coated. The induction
of the electrochemical reaction is typically achieved by applying a
voltage to said surface while in contact with the composite. In a
typical experiment, DC power supply has the negative output lead
electrically connected to the surface to be coated through one or
more contacts. The positive output lead of the power supply is
electrically connected to an anode located in the plating solution
comprising the additives, sol-gel precursors and other agents as
detailed before. During electrodeposition, power supply biases the
surface to provide a negative potential relative to the anode
causing electrical current to flow from the anode to the surface.
This causes an electrochemical reaction on the surface to be coated
which results in deposition of the composite of a sol-gel and an
additive on the surface.
[0084] The term "contacting" or any lingual variation thereof,
refers within the context of the present invention to having the
surface and the composite in intimate proximity to allow the above
detailed electro-co-deposition, i.e., the formation of a film on
the surface. Preferably, the contacting is achieved by immersion of
the surface in a composite solution containing the sol-gel
precursors and the at least one additive, as disclosed.
[0085] Thus, in another embodiment, the method comprises: [0086]
(i) providing a conductive surface, as defined; [0087] (ii)
providing a composite of at least one sol-gel precursor and at
least one additive, said composite being in a solution; [0088]
(iii) contacting said surface with a solution comprising the
composite; [0089] (iv) applying a voltage to said surface in
contact with the composite, thereby inducing formation of a sol-gel
film on the surface.
[0090] Preferably, the at least one additive is selected so as to
have the capability of undergoing reduction or oxidation during the
electrodeposition process.
[0091] In one embodiment, the contacting is achieved by immersion
of the surface in a solution containing the composite prior to and
throughout the electrodeposition process.
[0092] The term "solution" refers to the liquid media in which the
sol-gel precursors and at least one additive are contained. In some
embodiments, the solution further contains at least one electrolyte
that can reduce the solution resistance. In some other embodiments,
the solution is a transparent solution. In other embodiments, the
solution is an emulsion. In other embodiments, the solution is a
microemulsion. In further embodiments, the solution comprises
micelles.
[0093] The solution may a pre-made solution of all required
components or may be a solution which is assembled by adding each
of the components at a different point in the process. However, as
the solution has to contain a mixture of the sol-gel precursors and
additives, the addition of each should take place sufficient time
prior to contacting with the substrate so as to allow formation of
the composite.
[0094] The applied voltage is typically a low voltage which
application creates a positive or negative potential for a
determined period of time. The potential is selected to allow the
deposition of the composite on the surface.
[0095] In one embodiment, the potential is selected to allow
sol-gel polymerization reaction and reduction or oxidation of at
least one additive on the surface. A person skilled in the art
would be able to ascertain from available data or previous
experiments the potential or potential range which would be
necessary to achieve both the primary sol-gel polymerization and
the secondary reduction/oxidation of e.g., the metal or the organic
monomer or oligomer. For data concerning reduction/oxidation
potentials of a great variety of organic and inorganic materials,
one may refer to "CRC Handbook of Chemistry and Physics", David R.
Lide, Ed, 86.sup.th Edition, 2005.
[0096] Generally, the applied voltage is a low voltage not
exceeding a few volts in its absolute value.
[0097] In one embodiment, said voltage not exceeding a few volts in
its absolute value is a voltage between (-1.7) V to (+2.6) V versus
Ag/AgBr. In another embodiment, the voltage is between (-1.4) V to
(+1.4) V. In another embodiment, the voltage is between (-1.0) V to
(+1.4) V.
[0098] In another embodiment, the metal to be reduced and
co-deposited is copper and the potential is between .+-.1.0 V and
.+-.1.4 V.
[0099] In another embodiment, the sol-gel to be deposited along
with a metal salt is SiO.sub.2 or TiO.sub.2 and the potential is
between .+-.1.0 V and .+-.1.4 V.
[0100] In a further embodiment, the additive is polypyrrole (PPY)
and the voltage is between 0.7 V and 1V.
[0101] In still another embodiment, the additive is pyrrole
(monomers) and the voltage required for its polymerization and
electrochemical co-deposition is between 0.5 V and 1V.
[0102] In a still further embodiment, the voltage is applied for a
period of from about 5 minutes to about 60 minutes.
[0103] In another embodiment, said negative or positive potential
induces electrochemical formation of solvated H.sup.+ or
OH.sup.-.
[0104] In yet another embodiment, said solution comprising the
sol-gel precursors further comprises at least one alcohol, water
and at least one inert salt. The alcohol is a
C.sub.1-C.sub.4-alcohol selected from methanol, ethanol, propanol,
iso-propanol, 1- or 2-butanol, tert-butanol and 2-methylpropanol.
The at least one inert salt, being different from said at least one
metal salt, is a water-soluble salt which can dissociates into ions
to reduce the solution resistance. In some embodiments, the at
least one inert salt is a salt of an alkali metal such as Na, K,
and Li. In other embodiments, the at least one inert salt is a
tetralkylammonium salt.
[0105] Non-limiting examples of such inert salts are NaCl, NaBr,
KCl, KBr, LiClO.sub.4, KNO.sub.3, KBF.sub.4 and ammonium
NH.sub.4.sup.+ containing salt.
[0106] In another embodiment, the method comprises: [0107] (i)
providing a conductive surface; [0108] (ii) providing a composite
of at least one sol-gel precursor and at least one additive, said
composite being in a solution; [0109] (iii) immersing said surface
in a solution comprising a composite according to the invention, at
least one alcohol, water and at least one inert salt; [0110] (iv)
applying a voltage to said conductive surface being immersed in
said solution comprising the composite, thereby inducing formation
of a sol-gel film on said surface.
[0111] In another embodiment, said at least one additive is a
monomer of a conductive polymer and the method comprises: [0112]
(i) providing a conductive surface; [0113] (ii) providing a
composite of at least one sol-gel precursor and a plurality of
monomers of at least one conductive polymer, said composite being
in a solution; [0114] (iii) immersing said surface in a solution
comprising a composite according to the invention, at least one
alcohol, water and at least one inert salt; [0115] (iv) applying a
voltage to said conductive surface being immersed in said solution
comprising the composite, thereby inducing the polymerization of
sol-gel and oxidation of said plurality of monomers of at least one
conductive polymer, whereby a hybrid sol-gel/conductive polymer
film is deposited on said surface.
[0116] In another embodiment, the at least one additive is a metal
and the method comprises: [0117] (i) providing a conductive
surface; [0118] (ii) immersing said surface in a solution
comprising sol-gel precursors, at least one alcohol, water and at
least one inert salt; [0119] (iii) inducing an electrochemical
reaction on said conductive surface by applying voltage to said
surface being immersed said solution; and [0120] (iv) treating said
solution with at least one metal salt; thereby inducing the
polymerization of said sol-gel and reduction of said metal salt,
whereby a hybrid sol-gel/metal film is deposited on said
surface.
[0121] In some embodiments, the step of treating the solution with
said at least one metal salt is carried out before induction of the
electrochemical reaction.
[0122] In some other embodiments, the solution of step (ii) is
admixed with at least one metal salt prior to the immersion of the
surface therein.
[0123] In another aspect of the present invention, there is
provided a surface coated with a film of a composite of at least
one sol-gel precursor and at least one additive, deposited as
defined above, said film being a hybrid film.
[0124] In yet another aspect of the present invention there is
provided a surface coated with a hybrid film according to the
methods of the invention.
[0125] The film produced according to the methods of the invention
is referred to as a hybrid film. The homogeneity or heterogeneity
of the two-phase film, namely the visual appearance of micro- or
nanostructures in the sol-gel matrix may be determined visually by
the naked eye, under an optical or electronic microscopes. Without
wishing to be bound by theory, the presence of such micro- or
nanostructures in the film depends on the grain size of the
embedded additive material(s), which may be in the micrometer scale
and/or in the nanometer scale. Typically, a film is said of being a
hybrid homogenous film when a single phase is observed by the naked
eye or under an optical or electronic microscope, under the
specific resolution. In some cases, a homogenous film may be
observed even at a high resolution. In such cases, the film may be
a classic continuous and homogenous film or may have small enough
nanostructures which are not observed even under the high
resolution employed.
[0126] The films prepared according to the invention may have
different thicknesses based on the reaction time and/or voltage
employed. Typically, the electrodeposited two-phase film is between
about 1 and 100 micrometer thick.
BRIEF DESCRIPTION OF THE DRAWINGS
[0127] In order to understand the invention and to see how it may
be carried out in practice, embodiments will now be described, by
way of non-limiting example only, with reference to the
accompanying drawings, in which:
[0128] FIGS. 1A-C show scanning electron microscope (SEM) images of
Cu/TiO.sub.2-- electrodeposited films (-1.4V), deposited on ITO at
three different concentrations: FIG. 1A 100 mM, FIG. 1B 10 mM. and
FIG. 1C, in accordance with the method of the invention.
[0129] FIGS. 2A-B show SEM images of electrodeposited Cu/TiO.sub.2
upon applying a less negative potential of .+-.1.0 V (FIG. 2A) and
electrodeposited Cu/SiO.sub.2 upon applying a potential of .+-.1.4
V (FIG. 2B).
[0130] FIGS. 3A-B show electrochemically co-deposited Cu/TiO.sub.2
that was peeled off the surface (FIG. 3A) and a cross-section of a
layer deposited on ITO (FIG. 3B).
[0131] FIGS. 4A and 4B show scanning electron micrograph (SEM)
images of a film of PEG 20000 co-deposited with phenylTMOS
(deposition ratio 1:1) on stainless steel plate, according to the
invention (FIG. 4A). An image of a bare stainless plate is shown in
FIG. 4B.
[0132] FIGS. 5A and 5B show SEM images of two two-phase films of
F127 co-deposited with APTEOS (deposition ratio 0.1:1) on stainless
steel plate.
[0133] FIGS. 6A and 6B show SEM images of a film of pure PhTMOS
(FIG. 6A) and of a composite of PhTMOS and pluronic (FIG. 6B).
[0134] FIGS. 7A and 7B are scanning electron micrographs (SEM) of a
stent electrochemically coated with a mixture of sol-gel and
pluronic.
[0135] FIGS. 8A and 8B are electrochemically deposited films made
of silica nanoparticles containing a fluorescent dye and
tetramethoxysilane. Picture A was acquired by SEM. Picture B was
taken by a fluorescence optical microscopy.
[0136] FIGS. 9A-9D show SEM images of PPY/SiO.sub.2
electrodeposited films after applying different positive potential:
FIG. 9A at 0.7 V, FIG. 9B at 0.8 V, FIG. 9C at 0.9 V, and FIG. 9D
at 1V.
[0137] FIGS. 10A and 10B depict in FIG. 10A the optical micrograph
of four different electrochemically deposited sol-gel/pyrrole
samples, which were deposited under different potentials, as shown.
In FIG. 10B is depicted a SEM image of an electrochemically
deposited sol-gel/polypyrrole film.
[0138] FIGS. 11A-11D show EDX analysis plots of the film shown in
FIGS. 6A-6D, at different potentials: FIG. 11A at 0.7 V, FIG. 11B
at 0.8 V, FIG. 11C at 0.9 V, and FIG. 11D at 1V.
[0139] FIG. 12 shows the absorbance measurements of the
electrodeposited films, PPY/SiO.sub.2.
[0140] FIG. 13 shows electrodeposited films obtained at different
deposition times.
[0141] FIGS. 14A-14B show SEM images of PPY and PhTMOS
electrodeposited film at two different resolutions: 2500.times.
(FIG. 14A) and 10,000.times. (FIG. 14B).
DETAILED DESCRIPTION OF EMBODIMENTS
[0142] Sol-gel polymers are usually formed as thin films or
coatings with a thickness that can vary between a few nanometers to
tens of microns. The most common methods for depositing sol-gel
films are dip-coating, spin-coating and spraying.
[0143] The inventors of the present invention have now surprisingly
found that composite materials comprising additives such as metals,
polymers and particulates may be embedded in a sol-gel film
electrodeposited on a surface. Despite what had been suspected at
the onset of experimentation that electrodeposition of a foreign,
non-sol-gel precursor material may result in a disruptive
interaction with the sol-gel precursors and the production of a
defective sol-gel layer, it has now been shown that the additives
recited herein may be embedded in a sol-gel layer provided that the
sol-gel precursors and at least one additive are presented as a
composite material as defined hereinabove.
[0144] When the additive is added not as part of a composite, and
therefore in the absence of a strong interaction with the sol-gel
precursors, the amount of incorporated additive is reduced to nil.
It should be pointed out that thus far deposition of sol-gel
together with additional materials was succeeded only by using
conventional dip-coating, spin-coating or spraying methods.
[0145] Without being limited by theory, it is presumed that the
electrochemical deposition of the present invention may be driven
by the formation of a network that embeds the other substance,
e.g., polymer or metal, and forces it to deposit in the course of
sol-gel deposition.
[0146] The single step electrochemical method for the preparation
of sol-gel-additive, e.g., copper-sol-gel or PPY-sol-gel films
involves the application of either negative or positive potentials
to a conducting substrate which alters the pH at the electrode
surface, and catalyses the polymerisation of sol-gel monomers,
leading to the deposition of the appropriate oxide films. This
method of the invention has been successfully employed for the
coating or codeposition of such metals as copper and titania as
well as copper and silica to form Cu/TiO.sub.2 and Cu/SiO.sub.2
films, respectively, and also for the deposition of conductive
polymers and monomers thereof on such surfaces.
Example 1
Electrodeposition of a Composite Containing Copper Metal and
Sol-Gel
[0147] A standard three-electrode cell was used. A potential of
-1.4 V vs. Ag/AgBr was applied to an electrode such as indium-tin
oxide (ITO, R.ltoreq.10 Ohm/.OMEGA., Delta Technologies) for 0.5-60
min, while stirring the deposition solution (0.2 M titanium
tetra-n-propoxide (Ti(OPr).sub.4), 8.9 mM water and 0.1 M
LiClO.sub.4 in dry 2-propanol). CuCl.sub.2 was dissolved in this
solution (1-100 mM). The ITO samples were pulled out of the
deposition solution (maintaining the stirring and the potential) at
a rate of 50
[0148] FIGS. 1A-C are SEM images of Cu/TiO.sub.2 films deposited at
three different concentrations (100, 10 and 1 mM, respectively) of
CuCl.sub.2 according to the method of the invention. Deposits can
be clearly seen at the two higher concentrations (the titania is
not seen in the SEM images due to its insulating nature). EDX
analysis confirmed that the deposits are made of copper and the
area between the deposits contains titania. Moreover, it is evident
that the concentration of the Cu.sup.2+ strongly affects the
morphology and grain size of the deposited copper. As the
concentration of Cu.sup.2+ in the solution increases, the average
size of the grains increases and their number per area
decreases.
[0149] Since the electrochemical co-deposition is controlled by two
simultaneous processes, i.e., the reduction of Cu.sup.2+ and the
deposition of titania, any parameter that controls the kinetics of
each of these processes, is likely to affect the morphology of the
deposits. Indeed, lowering the applied potential to .+-.1.0 V
decreases the kinetics of titania deposition, while maintaining the
reduction of copper under diffusion-controlled conditions, such
that a denser layer of copper (FIG. 2A, as compared with FIG. 1A)
results. Likewise, when Ti(OPr).sub.4 was replaced by
tetramethoxysilane, significantly larger aggregates of copper were
obtained (FIG. 2B, as compared with FIG. 1A), reflecting the slower
polycondensation of the silicon monomer.
[0150] The morphology of the deposited films can be clearly seen in
FIGS. 3A-B that show part of a Cu/TiO.sub.2 film which was peeled
off the surface. The Cu/TiO.sub.2 film is an electrochemically
co-deposited film according to the invention. From the
cross-section shown in FIG. 3B the thickness of the layer can be
estimated at 160 nm.
[0151] The thickness of the film prepared according to the
invention, independent of the surfaces used, can be varied not only
by varying the deposition time but also by varying the potential.
Typically, films of various thicknesses ranging from 1 nanometer to
100 micrometer have been prepared.
Example 2
Electrodeposition of a Composite Containing Phenyltrimethoxysilane
(PhTMOS) and Polyethylene Glycol (20 kDa)
[0152] The composite was first prepared by adding 2.5 ml of 0.1M
HCl to 1 ml of PhTMOS, and then the mixture was dissolved in 6.5 ml
EtOH. The sol solution was stirred at 40.degree. C. After 1.5 h PEG
20,000 was added to the mixture (in a 1:1 ratio to PhTMOS) and the
stirring was continued until it completely dissolved.
[0153] Without wishing to be bound by theory, it is understood that
the interaction between the sol-gel precursors and, e.g., the PEG
added is one of covalent, electrostatic, hydrophobic-hydrophilic
and hydrogen bonding. This interaction allows successful
co-deposition of the two components onto the surface.
[0154] The electrodeposition was carried out in a standard
three-electrode cell. A potential of between (-1.7) V to (+2.6) V
vs. Ag/AgBr was applied to the surface, e.g., ITO to be coated
which was inserted into the cell containing the solution for 1-10
min. FIG. 4A shows a bare stainless steel surface and FIG. 4B shows
a stainless steel surface coated with a two-phase film of sol-gel
and PEG 20,000. As aggregates of PEG 20,000 are not visual to the
naked eye, the film is considered homogenous.
Example 3
Electrodeposition of a Composite Comprising Aminopropyltriethoxy
Silane (APTEOS) or Phenyltrimethoxysilane (PhTMOS) and F127
Pluronic
[0155] The composite was prepared by adding 2.5 ml of 0.1M HCl to 1
ml of APTEOS, and then the mixture was dissolved in 6.5 ml EtOH.
The sol solution was stirred at 25.degree. C. at least 0.5 h prior
before F127 pluronic (a block copolymer based on ethylene oxide and
propylene oxide) was added to the mixture at a concentration of
5-10% of the silane concentration, and stirring was continued until
complete dissolution.
[0156] The electrodeposition was conducted as detailed above on a
stainless steel surface, and an exemplary films obtained are shown
in FIGS. 5A and 5B. As may be noted from the images, the two films
contain aggregates of pluronic which are of different sizes, shapes
and distribution. Each of the aggregates contains a plurality of
nanosize aggregates of pluronic embedded in the sol-gel polymer.
These aggregates and nano-aggregates are characteristic of
two-phase films of APTEOS and pluronic. Homogenoues films of APTEOS
and pluronic were also obtained.
[0157] Images shown in FIGS. 6A and 6B are of films of PhTMOS (FIG.
6A) and of a composite of PhTMOS and pluonic (FIG. 6B). The images
demonstrate that at even at a much higher resolution of
30,000.times., the film is homogenous with no indication of polymer
aggregates as demonstrated above. Further, one may note that the
presence of the polymer in the film does not impose any
morphological change on the sol-gel coating. Both the sol-gel film
alone (FIG. 6A) and the two-phase film of sol-gel and pluronic
(FIG. 6B) exhibit identical morphology on the micro scale.
[0158] The heterogeneity of some PhTMOS films is exhibited in FIGS.
7A and 7B. These SEM images of a stent coated with a PhTMOS and
pluronic show the visible two phases, so called two-phase structure
of the film.
[0159] It should be noted that the homogeneity or lack thereof of
the film does not influence its short-term or long-term stability.
Both homogenous and heterogeneous films fall within the scope of
the present invention.
[0160] FIG. 8A shows a cross section of a coating formed upon
adding onto a tetramethoxysilane (TMOS) solution nanoparticles made
of silica in which a fluorescent dye was incorporated. From the
cross section shown it is evident that the film is a dense phase
embedded with nanoparticles. FIG. 8B is a fluorescent optical
micrograph indicating that the fluorescence of the dye is kept upon
electrochemical co-deposition.
[0161] Deposition of composites comprising conducting polymers,
such as polypyrrole, has also been accomplished. Typically,
conducting polymers are made by the electropolymerization of
monomers such as and not being limiting to pyrrole, aniline and
thiophene or their derivatives, at positive potentials. Since the
electrodeposition of sol-gel can be driven by either acidic or
basic pH, the polymerization of such monomers independently of the
sol-gel process was also achieved (by electrodeposition of a
sol-gel monomer such as teteramethoxysilane and pyrrole) by
applying positive potentials. The positive potential decreases the
pH at the electrode surface and at the same time oxidizes the
pyrrole to form polypyrrole. The potential affects the ratio
between the electropolymerization of monomers of the conducting
polymer and electrodeposition of the sol-gel as can be seen in
FIGS. 9-11.
[0162] In a typical experiment, a standard three-electrode cell was
used. A positive potential vs. Ag/AgBr was applied to a surface
such as indium-tin oxide (ITO) for 1-10 min, while stirring the
deposition solution which contained 0.1 M pyrrole, 0.1 M sodium
p-toluensulfonate (TsONa), tetraethoxysilane (TEOS), ethanol, HCl
and N,N-dimethylformamide (for crack prevention). The ITO samples
were pulled out of the deposition solution at a rate of 50
.mu.msec.sup.-1. The two reactions shown below occurred
simultaneously in the polypyrrole-silica sol-gel densification
process to result in the polypyrrole-silica composite film.
##STR00001##
[0163] FIGS. 9A-9D show SEM images of films that were
electrodeposited after applying different positive potentials. It
is evident that the applied potential strongly affected the
morphology of the deposited films.
[0164] The effect of the potential may be observed further in FIG.
10A which provides a photograph of indium tin oxide substrates
which were coated with a composite based on sol-gel and pyrrole.
With different potentials being applied, different film thicknesses
were obtained. FIG. 10B shows a SEM image of the film that is
formed at a potential of 2.3V. In this case, the conducting polymer
is the continuous phase and the sol-gel are the embedded particles.
The ratio between the monomer of the conducting polymer and that of
the sol-gel dictates whether the two polymers will form two
distinct phases, such as seen in FIG. 10B, or form a continuous one
phase.
[0165] EDX analysis of the films formed according to the invention
confirmed the presence of silica and polypyrrole. It can be seen
from FIGS. 11A-11D that as the applied potential is more negative,
the atomic percent of nitrogen (from the polypyrrole) increases
while the silicon (from the silica) decreases.
[0166] FIG. 12 demonstrates the absorbance measurements of the
electrodeposited films, polypyrrole/SiO.sub.2 at different applied
potential.
[0167] In order to examine the influence of the deposition time,
positive potential was applied for different times. As FIG. 13
demonstrates, the longer the deposition time was, the thicker the
film was.
[0168] In order to examine the effect of the sol-gel monomer on the
electrodeposited films, different monomers were added to the
deposition solution, while the other parameters were kept same.
FIGS. 14A-14B show SEM images of two-phase films of
phenyltrimethoxysilane (PhTMOS) and pyrrole.
* * * * *