U.S. patent application number 16/715457 was filed with the patent office on 2020-06-18 for durable superhydrophobic surfaces.
The applicant listed for this patent is UNIVERSITY OF FLORIDA RESEARCH FOUNDATION, INCORPORATED. Invention is credited to Shu-Hau HSU, Wolfgang M. SIGMUND, Ravi Kumar VASUDEVAN.
Application Number | 20200190276 16/715457 |
Document ID | / |
Family ID | 55747530 |
Filed Date | 2020-06-18 |
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United States Patent
Application |
20200190276 |
Kind Code |
A1 |
SIGMUND; Wolfgang M. ; et
al. |
June 18, 2020 |
DURABLE SUPERHYDROPHOBIC SURFACES
Abstract
A superhydrophobic appliance is an elastomeric material with a
surface having a multiplicity of re-entrant features. The
elastomeric material can be a polydimethylsiloxane network. The
superhydrophobic appliance can be formed by infusing a portion of a
polydimethylsiloxane polymeric precursor partially into the pores
of a porous membrane, curing to the polymeric network, and
separating the membrane from the appliance to expose the
superhydrophobic surface. The superhydrophobic surface can be
subsequently modified to form a fluorinated surface that is
oleophobic or superoleophobic in addition to being
superhydrophobic.
Inventors: |
SIGMUND; Wolfgang M.;
(Gainesville, FL) ; HSU; Shu-Hau; (Gainesville,
FL) ; VASUDEVAN; Ravi Kumar; (Somerville,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UNIVERSITY OF FLORIDA RESEARCH FOUNDATION, INCORPORATED |
GAINESVILLE |
FL |
US |
|
|
Family ID: |
55747530 |
Appl. No.: |
16/715457 |
Filed: |
December 16, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15327508 |
Jan 19, 2017 |
10508182 |
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PCT/US2015/041972 |
Jul 24, 2015 |
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16715457 |
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62029141 |
Jul 25, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08J 5/18 20130101; C08J
7/12 20130101; C08J 7/065 20130101; C08J 2383/04 20130101 |
International
Class: |
C08J 5/18 20060101
C08J005/18; C08J 7/12 20060101 C08J007/12; C08J 7/06 20060101
C08J007/06 |
Claims
1. A superhydrophobic appliance, comprising a polymeric network,
the polymeric network having elastomeric properties and comprising
at least one surface with a multiplicity of re-entrant features,
wherein the multiplicity of re-entrant features render the at least
one surface superhydrophobic, wherein the re-entrant features have
at least one dimension of 100 .mu.m or less, and wherein the
polymeric network comprises a plurality of reinforcing particles
dispersed therein, each of the plurality of reinforcing particles
having a particle size less than about 100 .mu.m.
2. The superhydrophobic appliance according to claim 1, wherein the
re-entrant features comprise non-perpendicular cylinders extending
from a base of the at least one surface.
3. The superhydrophobic appliance according to claim 1, wherein the
polymeric network is a polydimethylsiloxane network.
4. The superhydrophobic appliance according to claim 1, further
comprising a monolayer on the at least one surface, wherein the
monolayer comprises a fluorocarbon, and wherein, in addition to
being superhydrophobic, the at least one surface is oleophobic.
5. A method of preparing a superhydrophobic appliance according to
claim 1, comprising: providing a membrane comprising a multiplicity
of pores; providing a polymeric precursor; contacting the polymeric
precursor and a face of the membrane that accesses the pores;
forcing the polymeric precursor into the pores; curing the
polymeric precursor into a polymeric network; and separating the
membrane from the polymeric network to expose a superhydrophobic
surface of a superhydrophobic appliance.
6. The method according to claim 5, wherein the polymer precursor
comprises a polydimethylsiloxane resin.
7. The method according to claim 6, wherein the
polydimethylsiloxane resin is an addition curable resin.
8. The method according to claim 7, wherein the addition curable
resin is a hydrosilation curable resin.
9. The method according to claim 5, wherein curing is a thermal
curing or a photochemical curing.
10. The method according to claim 5, wherein separating is peeling
the membrane from the polymeric network.
11. The method according to claim 5, wherein separating comprises
dissolving of the membrane in a solvent and removing the solvent
residual on and/or absorbed within the superhydrophobic
appliance.
12. The method according to claim 5, further comprising modifying
the superhydrophobic surface to have a perfluorinated hydrocarbon
coating on the polymeric network, wherein the superhydrophobic
surface is a superhydrophobic and oleophobic or superoleophobic
surface.
13. The method according to claim 12, wherein the polymeric network
is a polydimethylsiloxane network and modifying comprises oxidizing
the superhydrophobic surface to an oxidized surface and reacting
the oxidized surface with a perfluorinated hydrocarbon silane
coupling agent.
14. The method according to claim 13, wherein oxidizing comprises
treating with a mixture of H.sub.2O, HCl, and H.sub.2O.sub.2 and
wherein the perfluorinated hydrocarbon silane coupling agent is
heptadecafluoro-1,1,2,2-tetrahydrodecyltrichlorosilane.
15. The superhydrophobic appliance according to claim 4, wherein,
in addition to being superhydrophobic, the at least one surface is
superoleophobic.
16. The superhydrophobic appliance according to claim 1, wherein
each of the multiplicity of re-entrant features has a homogeneous
composition through any cross-section thereof, and wherein the
homogeneous composition is the same as that of the polymeric
network.
17. The superhydrophobic appliance according to claim 1, wherein
the polymeric network is produced by a process comprising:
providing a membrane comprising a multiplicity of pores; providing
a polymeric precursor; contacting the polymeric precursor and a
face of the membrane that accesses the pores; forcing the polymeric
precursor into the pores; curing the polymeric precursor into a
polymeric network; and separating the membrane from the polymeric
network to expose the at least one surface with the multiplicity of
re-entrant features.
18. The superhydrophobic appliance according to claim 1, wherein
the plurality of reinforcing particles comprises a metal oxide.
Description
CROSS-REFERENCE TO A RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/327,508, filed Jan. 19, 2017, titled
"Durable Superhydrophobic Surfaces," which was a National Stage
Entry of PCT/US2015/041972, filed on Jul. 24, 2015, which claims
the benefit of U.S. Provisional Application Ser. No. 62/029,141,
filed Jul. 25, 2014, the disclosures of which are hereby
incorporated by reference in their entireties, including all
figures, tables and drawings.
BACKGROUND OF INVENTION
[0002] Surface cleaning and repair of the surface of, for example,
buildings, vehicles, and energy collection devices, are
time-consuming and costly, and a surface with an inherent
repellency of water, oil, and dirt can be a significant advantage.
Surface wetting is governed by surface-energy parameters between
the surface and the contacting liquid or solid surface. Where the
sum of the free surface energies of the contacting materials
components is very low, adhesion between these materials is weak.
Hence, it is generally beneficial to lower the free surface energy
of an edifice if one hopes to ignore its cleaning and repair.
Non-stick materials, such as perfluorinated hydrocarbons have very
low surface energies, and few materials adhere to Teflon.RTM.. The
wetting of these low surface energy materials is reflected in the
contact area that is observed between the surface of the low
surface energy solid and a wetting material. The interactions
between these materials generally result from van der Waals
forces.
[0003] Nature diminishes the interaction of a surface of a solid
and water without resorting to materials with surface energies as
low as Teflon.RTM.. This is achieved by reducing the amount of the
surface that contacts the water. For example, lotus leaves, cabbage
leaves, and various fruits are covered by small wax bumps that
reduce the van der Waals contact area presented to a water droplet,
which forms due to its high surface tension, and significantly
reduces the adhesion of the droplets to the surface. A
superhydrophobic textured surface displays a water contact angle
that exceeds 150.degree. and displays a low sliding angle, which is
the critical angle from horizontal of the inclined surface where a
water droplet of a defined mass rolls off the inclined surface.
This "Lotus effect" provides a self-cleaning surface, as contact
water droplets adhere to dust particles and, to a much lesser
degree, to some oils that are poorly adhered to the surface, to
allow the "dirt" to be carried away as the water droplet rolls from
the surface. Most oils are not readily removed from hydrophobic
surfaces as the enlarged surface area increases the effective van
der Waals interface and the Lotus-effect surface does not repel
oils that interact less favorably with water than with the
superhydrophobic surface.
[0004] Oil repellent surfaces are an engineering challenge because
the surface tensions of oily liquids are usually in the range of
20-30 mN/m. The essential criterion for having a surface with
superoleophobicity is to maintain oil drops in a Cassie-Baxter (CB)
state, one where vapor pockets are trapped underneath the liquid.
The CB state is dependent on the surface's structure and the
surface energy of the material. If the structure and surface area
are insufficient, the meta-stable energetic state is transformed
into a Wenzel state, which displays wetting of the structure. The
geometric structures that allow a CB state have re-entrant
features, such as mushroom heads, micro-hoodoos, or horizontally
aligned cylindrical rods. A re-entrant structure implies that a
line drawn vertically, from the base solid surface through the
geometric feature, must proceed through more than one solid gas
interface of that feature.
[0005] One problem with these superhydrophobic or superoleophobic
structures is a lack of durability. To this end, a material that
has a long life when exposed to the environment without loss of the
shape and surface functionality is desired, because durability is
critical for successful implementation of a superhydrophobic or
superoleophobic application.
BRIEF SUMMARY
[0006] Embodiments of the invention are directed to
superhydrophobic appliances that are an elastomeric polymeric
network with at least one surface with re-entrant features that
render the surface superhydrophobic. The re-entrant features have
at least one dimension of 100 .mu.m or less, for example the
diameter, and extend from a base of the surface at a plurality of
angles from about 0.degree. to about 180.degree.. In an embodiment
of the invention, the polymeric network is a polydimethylsiloxane
network. The silicone appliance can have a fluorocarbon comprising
monolayer on the surface of at least the re-entrant features to
render the superhydrophobic surface oleophobic or superoleophobic
in addition to being superhydrophobic.
[0007] Other embodiments of the invention are directed to a method
of preparing superhydrophobic appliances. A mold, for example, a
membrane comprising a multiplicity of pores of the desired
re-entrant feature's cross-section is contacted with a polymeric
precursor with the polymeric precursor being forced into the pores
and cured into a polymeric network, deriving the shape of cured
re-entrant structures from the shape of the pores. The infusion
into the mold can be promoted by the application of a sufficient
pressure differential at the interface of the mold and the resin.
The membrane is separated from the polymeric network to expose the
superhydrophobic surface of the appliance with re-entrant
structures extend from the surface. Cure can be chemically or
photochemically initiated. The membrane can be separated by
delaminate the membrane from the appliances surface or by
dissolving the membrane, such that the re-entrant features are
exposed. The appliance can be rendered oleophobic or
superoleophobic by the deposition of a perfluorinated hydrocarbon
coating.
BRIEF DESCRIPTION OF DRAWINGS
[0008] FIG. 1 shows a scanning electron microscope (SEM) image of a
polydimethylsiloxane hydrophobic surface formed using a 1.2 .mu.m
membrane and peeling the membrane from the surface, according to an
embodiment of the invention.
[0009] FIG. 2 shows a SEM image of a polydimethylsiloxane
superhydrophobic surface, according to an embodiment of the
invention, formed using a 3 .mu.m membrane and peeling the membrane
from the surface, according to an embodiment of the invention.
[0010] FIGS. 3A-C show SEM images of a polydimethylsiloxane
superhydrophobic surface, according to an embodiment of the
invention, at increasing magnification, displaying size bars of
FIG. 3A 100, FIG. 3B 50, and FIG. 3C 20 .mu.m, where the surface
was formed using a 3 .mu.m membrane and isolated by dissolving the
membrane, extracting the solvent for dissolving, and drying,
according to an embodiment of the invention.
[0011] FIGS. 4A-B shows SEM images of FIG. 4A, a water droplet and
FIG. 4B, an olive oil droplet, on a surface fluorinated
polydimethylsiloxane superhydrophobic and oleophobic appliance,
according to an embodiment of the invention.
DETAILED DISCLOSURE
[0012] Embodiments of the invention are directed toward appliances
having at least one superhydrophobic surface and a method to
prepare the article. The surface possesses a topography that
includes re-entrant features that range from 10 nm through 100
.mu.m in size. The method involves placement of a polymeric
precursor to a physical or chemical polymeric network on a membrane
having pores that proceed from one large face of the membrane to
the other large face of the membrane, where the pores have
dimensions that are desired for the re-entrant features and forcing
polymer network precursor into the pores. Subsequently, the polymer
precursor is cured into a polymeric network. After curing, the
membrane is removed by peeling the polymeric network from the
membrane or dissolving the membrane to expose reentrant features on
the surface resulting from the removal of the membrane. The
superhydrophobic surface made in this manner can be converted to
superhydrophobic and oleophobic surface by rendering the surface
amenable to modification, for example, by oxidation of the surface,
and treating the modified surface with a functional fluorinated
hydrocarbon.
[0013] In an exemplary embodiment of the invention, the polymeric
network of the superhydrophobic article is a polydimethylsiloxane
network formed by an addition cure. In an embodiment of the
invention, the method of forming the polymeric network is by an
addition crosslinking of a polymer precursor. The polymer precursor
must be of a sufficient viscosity such that it does not readily
flow into and through a membrane when a pressure differential is
applied to the interface of the membrane and resin, yet permit
filling of at least a portion of the pores of a membrane when
forced into the pores. Although the minimum viscosity of the
polymeric precursor depends inversely on the size of the pores and
the mode used to force the polymer precursor into the pores of the
membrane, the minimum viscosity can be, for example, 1000 cps for a
pore size of 1.2 .mu.m when the polymer precursor is drawn into the
pores by imposing a vacuum to draw the polymeric precursor upward,
against gravity, into the pores. For any mode of infusion into the
pores, the viscosity can be identified by blending a very high
viscosity polymer of the type desired with a very low molecular
weight polymer of the same structure and testing the infusion with
differing proportions until an ideal viscosity is identified at a
desired temperature for infusion. The temperature is limited by the
melting temperature or glass transition temperature of a membrane
employed to form the re-entrant structures and by the curing rate
of the resin.
[0014] Curing of the polymeric precursor can be thermal or
photochemical curing. For example, the polydimethylsiloxane
polymeric precursor can be cured by a hydrosilation reaction
between vinyl units and silicon-hydrogen units within the polymeric
precursor. The polydimethylsiloxane can be filled with a
reinforcing material, for example, silica fillers, for example,
fumed silica, colloidal silica, or other metal oxide, for example,
alumina or titania. The particle size of the filler is matched to
the pore size of the membrane used to impart the re-entrant
structure to the surface of the polymeric network, where the
particle size is less than the pore size. The pore size of the
membrane can be about 100 .mu.m or less, for example, less than
about 50 .mu.m, less than about 40 .mu.m, less than about 30 .mu.m,
less than about 20 .mu.m, or less than about 10 .mu.m. For purposes
of the invention, "about" implies a variance of up to 10%. To form
the superhydrophobic surface, the polydimethylsiloxane polymer
precursor is placed in contact with the porous membrane, which is
constructed of a material that can be dissolved in a solvent, for
example, but not limited to, a polycarbonate membrane or a
cellulose ester membrane, or where the polymeric network can be
peeled from the membrane, where the peel-able membrane can be a
soluble polymer, insoluble polymer, polymer network, or a ceramic.
Generally, but not necessarily, the re-entrant structures exposed
upon peeling require larger dimensions than do re-entrant
structures exposed by dissolution of a membrane. The polymer
precursor is forced into the pores of the membrane by either
placing a pressure on the polymer precursor side of the interface
or reducing the pressure on the membrane face distal to the polymer
precursor. The pressure can be imposed on the polymer precursor as
a positive gas pressure or mechanically by a press where the
contacting surface of the press does not adhere to the polymer
precursor, and/or the cured polymeric network. After curing of the
polymeric network the membrane can be separated from the
superhydrophobic article or a pre-superhydrophobic article that can
be functionalized to impart superhydrophobicity.
[0015] The polymeric network can be friable to a degree where
re-entrant features remain, although the features may be of
differing dimensions and/or quantity, yet the surface remains
superhydrophobic. The failure strain rates for the cured polymer
can range from about 5% to 700%. For purposes of the invention,
"about" implies a variance of up to 10%. The polymeric precursor
can be a commercially available system or can be synthesized to
have specific desired functionality for specific curing behavior,
for specific bulk properties, or specific surface properties of the
superhydrophobic article or pre-superhydrophobic surface. The
polymeric network is an elastomer. The elastomer can be a
chemically crosslinked elastomer or a thermoplastic-elastomer where
the effective crosslinking is due to minority thermoplastic
aggregates in an elastomer continuum. In this manner, the surface
can be distorted within the elastic limits of the material used as
the polymeric network when an impinging force is applied, whereas
the feature extends from and returns to at least an approximation
of its original shape. In this manner, the durability is much
greater than that of inherently plastic materials, which will
either distort irreversibly in shape or fracture upon deformation.
In addition to polydimethylsiloxanes, other elastomers that can be
formed as the superhydrophobic article include, for example,
fluorinated polybutadienes, fluorinated poly(isoprenes),
fluorinated butyl rubber, fluorinated EPM rubber, fluorinated
elastomers (Viton.RTM.), other fluorinated elastomers, or other
elastomers that can be fluorinated after curing. For example, a
polybutadiene polymeric precursor can be infused into the pores of
a membrane, cured, separated as a pre-superhydrophobic article, and
fluorinated using a CF.sub.4 plasma to yield a superhydrophobic
article.
[0016] Once a superhydrophobic article is formed, reaction
chemistry can be carried out on the superhydrophobic surface in a
manner where the surface properties can be modified independently
of the bulk material. For example, with a polydimethylsiloxane
network, the surface can be oxidized to produce a plurality of
surface hydroxyl groups from a portion of the surface methyl groups
and treating with a silane coupling agent, for example, a
perfluorinated hydrocarbon comprising silane coupling agent, such
that the modified surface becomes superhydrophobic and oleophobic
or superoleophobic. The perfluorinated hydrocarbon silane coupling
agent can be any perfluoroalkane comprising silane coupling agent
where a perfluorinated C.sub.3 to C.sub.18 alkane is coupled
through a C.sub.2-C.sub.3 alkylene bridge to a silicon atom that is
substituted with 0-2 methyl groups and 3-1 halo, alkoxy, alkyl or
dialkylamino, or alkylcarboxy groups, for example,
R.sub.(3-y)X.sub.ySiCH.sub.2CH.sub.2C.sub.nF.sub.(2n+1) where n is
1 to 16, y is 1 to 3 and R is C.sub.1-C.sub.3 alkyl and X is Cl,
Br, I, methoxy, C.sub.2 to C.sub.5-alkoxy, methylamino, C.sub.2 to
C.sub.5-alkylamino, dimetylamino, di-(C.sub.2 to
C.sub.5-alkyl)amino, acetoxy, or C.sub.3-C.sub.5-alkycarboxy can be
used as the coupling agent. Specific perfuorinated hydrocarbon
silane coupling agents that can be used include:
heptafluoro-1,1,2,2-tetrahydropentyltrimethoxysilane,
undecafluoro-1,1,2,2-tetrahydroheptylacetoxydimethylsilane,
pentadecafluoro-1,1,2,2-tetrahydrononyl-bis-(dimethylamino)methylsilane,
and heptadecafluoro-1,1,2,2-tetrahydrodecyltrichlorosilane.
Methods and Materials
[0017] Commercial track etched polycarbonate (PC) membranes
(Isopore, Millipore, Inc.) were used as a mold for casting hairy
plastron surfaces as the re-entrant features. The PC membranes had
pore sizes of 1.2 or 3 .mu.m. A commercial polydimethylsiloxane
elastomer formulation (Sylgard 184, Dow Corning Inc) was used as
the polymeric precursor for the superhydrophobic appliance. A blend
having a weight of ratio 10:1 Sylgard 184 polymer base and Sylgard
184 curing agent was mixed, degassed, cast on a polyethylene
terephthalate sheet and further degassed. A PC membrane was then
placed on the polymeric precursor and a vacuum of 122 Torr until no
bubbles could be observed in the polymer precursor. The polymeric
precursor was cured into the polymeric network at 80.degree. C.
over a period of 15 hours. A hairy superhydrophobic surface was
produced by peeling the PC membrane from the silicone network or by
dissolving the PC membrane. The PC membrane dissolved at room
temperature in dichloromethane and excess dichloromethane was
removed by contacting the membrane with isopropanol. The hairy
plastron PDMS surface was dried at 60.degree. C. overnight.
[0018] The 1.2 .mu.m and 3 .mu.m reentrant feature superhydrophobic
surfaces that were generated by peeling displayed a non-uniform
distribution of features. The 1.2 .mu.m surfaces displayed short
stubs instead of long features, as is shown in FIG. 1. The
re-entrant features were sheared from the surface at varying short
lengths as the force applied during peeling appeared to have
exceeded the fracture strength of the 1.2 .mu.m features. In
contrast, as shown in FIG. 2, the mechanical strength of 3 .mu.m
features peeled from the membrane with 3 .mu.m pores is sufficient
to release the features without catastrophic fracturing, although
some shortened features are observed.
[0019] The superhydrophobic surfaces with the 1.2 .mu.m and 3 .mu.m
re-entrant features were exposed without the imposition of shear by
dissolving the PC membranes at room temperature in dichloromethane,
extracting dichloromethane from the swollen network using
isopropanol, and allowing the article to dry at 60.degree. C.
overnight. As can be seen in FIG. 3 for the 3 .mu.m features, the
re-entrant feature remains intact as evident from the concave tops
on all of the cylindrical features.
[0020] The superhydrophobic surfaces were rendered oleophobic in a
two step process. First the samples were rendered hydrophilic by
exposure to a an oxidizing mixture of H.sub.2O:HCl:H.sub.2O.sub.2
(5:1:1 by volumetric ratio) using the method of Sui et al.,
Analytical Chemistry 2006, 78, 5543-51 and treating the oxidized
surface with heptadecafluoro-1,1,2,2-tetrahydrodecyltrichlorosilane
using the method of Tuteja et al., Science 2007, 318, 1618-22. The
oleophobic surfaces appear to display a very weak metastable
Cassie-Baxter state, (Cassie et al. Transactions of the Faraday
Society 1944, 40, 546-50). The weakness is gauged qualitatively by
the change in refractive index that is apparent by a initially
shimmering interface on deposition of an olive oil droplet and a
transition to the wetted Wenzel state (Wenzel, Industrial and
Engineering Chemistry 1936, 28, 988-94 and Gao et al. Langmuir
2009, 25, 14105-15) where the apparent shimmer disappears. Water
and olive oil droplets pin at the triple phase contact interface
with high contact angles are shown in FIG. 4A and FIG. 4B,
respectively.
[0021] Resistance to wear upon rough manual handling and scraping
with a nylon brush was observed for the superhydrophobic surfaces,
The resistance is attributed to the elastomeric nature of the cured
polymer network, because the re-entrant freatures are able to
undergo physical deformation and return to the original state
through the retractive forces induced by the crosslinked
elastomeric matrix and the initial favourable entropic
configuration. Even though some fracture of the surface features is
observed, the surface shows little decrease in the water contact
angle, and remains superhydrophobic.
[0022] All publications referred to or cited herein are
incorporated by reference in their entirety, including all figures
and tables, to the extent they are not inconsistent with the
explicit teachings of this specification.
[0023] It should be understood that the examples and embodiments
described herein are for illustrative purposes only and that
various modifications or changes in light thereof will be suggested
to persons skilled in the art and are to be included within the
spirit and purview of this application.
* * * * *