SELF-CLEANSING SUPER-HYDROPHOBIC POLYMERIC MATERIALS FOR ANTI-SOILING

Abstract

Disclosed are optically transparent super-hydrophobic materials, and methods for making and using the same, that can include an optically transparent polymeric layer having a first surface and an opposing second surface. At least a portion of the first surface has been plasma-treated with oxygen and a fluorine containing compound. The treated surface includes nano- or micro-structures that are etched into the first surface and that are chemically modified with the fluorine containing compound. The nano- or micro-structures have a height to width aspect ratio of greater than 1, and a water contact angle of at least 150. The optically transparent polymeric layer retains its optical transparency after said plasma-treatment. Due to their optical transparency, chemical and thermal robustness, weatherability, and self-cleaning performance, the super-hydrophobic materials disclosed are useful in high performing solar cell units in harsh semi-arid environments.

Claims

1. An optically transparent super-hydrophobic material comprising an optically transparent polymeric layer having a first surface and an opposing second surface, wherein at least a portion of the first surface has been plasma-treated with oxygen and a fluorine containing compound, wherein the treated surface includes: (i) nano- or micro-structures that are etched into the first surface and that are chemically modified with the fluorine containing compound, wherein the nano- or micro-structures have a height to width aspect ratio of greater than 1; and (ii) a water contact angle of at least 150, wherein the optically transparent polymeric layer retains its optical transparency after said plasma-treatment.

2. The optically transparent material of claim 1, wherein the polymeric layer comprises a polycarbonate or a blend thereof.

3. The optically transparent material of claim 1, wherein the at least a portion of the first surface comprises a functional coating, and wherein the functional coating retains its functional properties after said plasma-treatment.

4. The optically transparent material of claim 3, wherein the functional coating is a silicone hard-coat.

5. The optically transparent material of claim 3, wherein the functional coating is capable of absorbing ultra-violet (UV) light, and wherein the functional coating retains its ability to absorb UV light after said plasma-treatment.

6. The optically transparent material of claim 1, wherein the fluorine containing compound is an organofluorine.

7. The optically transparent material of claim 6, wherein the organofluorine is a fluorocarbon.

8. The optically transparent material of claim 7, wherein the fluorocarbon is CF.sub.4, C.sub.2F.sub.4, C.sub.2F.sub.6, C.sub.3F.sub.6, C.sub.4F.sub.8, or any combination thereof.

9. (canceled)

10. The optically transparent material of claim 1, wherein the at least a portion of the first surface has been plasma treated with a first plasma comprising oxygen followed by a second plasma comprising the fluorine containing compound.

11. (canceled)

12. (canceled)

13. The optically transparent material of claim 1, wherein the polymeric layer comprises a polyethylene terephthalate, a polyolefin, a polystyrene, a poly(methyl)methacrylate, a polyacrylonitrile, a poly(vinylacetate), a poly(vinyl alcohol), a chlorine-containing polymer, a polyoxymethylene, a polyamide, a polyimide, a polyurethane, an amino-epoxy resin, or a polyester, or combinations or blends thereof.

14. (canceled)

15. The optically transparent material of claim 1, wherein the material is disposed on an article of manufacture.

16. The optically transparent material of claim 15, wherein the article of manufacture is a photovoltaic cell or a solar panel.

17-23. (canceled)

24. The optically transparent material of claim 1, wherein the polymeric layer does not include an inorganic compound.

25. (canceled)

26. A method of preparing the optically transparent super-hydrophobic material of claim 1, the method comprising: (a) obtaining an optically transparent polymeric layer having a first surface and an opposing second surface, wherein the first surface has a water contact angle of less than 150; (b) subjecting at least a portion of the first surface of the polymeric layer to a first plasma comprising oxygen under reaction conditions sufficient to obtain nano- or micro-structures that are etched into the polymeric layer, wherein the nano- or micro-structures have a height to width aspect ratio of greater than 1; and (c) subjecting the treated surface from (b) to a second plasma comprising a fluorine containing compound under reaction conditions sufficient to chemically modify the nano- or micro-structures with the fluorine containing compound, wherein the treated surface from step (c) has a water contact angle of at least 150, and wherein the optically transparent polymeric layer from (a) retains its optical transparency after steps (b) and (c).

27. The method of claim 26, wherein steps (b) and (c) are performed in a continuous process such that the oxygen from step (b) is switched to the fluorine containing compound from step (c) without stopping the process.

28. The method of claim 26, wherein the polymeric layer comprises a polycarbonate or a blend thereof.

29. The method of claim 26, wherein the at least a portion of the first surface in step (b) comprises a functional coating, and wherein the functional coating retains its abrasion resistant properties after steps (b) and (c).

30. The method of claim 29, wherein the functional coating is a silicone hard-coat.

31-43. (canceled)

44. A method of protecting a substrate or article of manufacture from soiling, the method comprising disposing the optically transparent super-hydrophobic material of claim 1 onto a substrate or article of manufacture, wherein the super-hydrophobic material protects the substrate or article of manufacture from soiling.

45. (canceled)

46. (canceled)

47. (canceled)

48. (canceled)

49. A method of maintaining or increasing the efficiency of a photovoltaic cell or protecting the outermost surface of a photovoltaic cell from soiling, the method comprising disposing the optically transparent super-hydrophobic material of claim 1 onto the outermost surface of the photovoltaic cell, wherein the efficiency of the photovoltaic cell is maintained or increased by protecting the outermost surface of the photovoltaic cell from soiling.

50. (canceled)

51. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1: Illustration of a super-hydrophobic material of the present invention being used as a protective cover for a solar panel.

[0025] FIGS. 2A-D: An illustration of the self-cleaning ability illustration of the plasma treated silicone hard-coated polycarbonate (SHC-PC) of the present invention.

[0026] FIG. 3: SEM image of SHC-PC prior to plasma treated (insert: water contact angle (WCA) 820).

[0027] FIG. 4: SEM image of O.sub.2 plasma treated SHC-PC (insert: water contact angle (WCA)<10).

[0028] FIG. 5: SEM image of O.sub.2/C.sub.4F.sub.8 plasma treated SHC-PC (insert: water contact angle (WCA) 1680).

[0029] FIG. 6: Transmission UV-Vis profiles of pre-treated and post-treated of O.sub.2/C.sub.4F.sub.K plasma treated SHC-PC of the present invention.

[0030] FIG. 7A: 3D AFM images of O.sub.2 plasma treated SHC-PC of the present invention.

[0031] FIG. 7B: 3D AFM images of O.sub.2 plasma O.sub.2/C.sub.4F.sub.8 plasma treated SHC-PC of the present invention showing needle like structures of variable mean surface roughness.

[0032] FIG. 8A: Optical profilometry images of O.sub.2 plasma treated SHC-PC of the present invention

[0033] FIG. 8B: Optical profilometry images of O.sub.2/C.sub.4F.sub.8 plasma treated SHC-PC of the present invention showing different surface topology and roughness.

[0034] FIG. 9: Graphical representation of variation of water contact angle of O2/C.sub.4F.sub.8 plasma treated SHC-PC of the present invention versus treatment time.

[0035] FIG. 10: An image of the plasma treated SHC-PC after 10 min of DRIE plasma processing showing the optical clarity of the SHC-PC.

[0036] FIG. 11A: An image of the plasma treated SHC-PC after immersion in organic solvents.

[0037] FIG. 11B: An image of a comparative sample of polycarbonate after immersion in acetone.

[0038] FIG. 12A: An image of DRIE plasma treated SHC-PC of the present invention at 60 C. (on hot heating plate surface) showing no conformal shrinkage or expansion of the SHC-PC.

[0039] FIG. 12B: An image of DRIE plasma treated comparative sample of polycarbonate at 60 C. showing structural deformation.

[0040] FIG. 13A: An image of water beads on plasma treated SHC-PC material of the present invention.

[0041] FIG. 13B: An image of water beads on comparative sample of an untreated SHC-PC material.

[0042] FIG. 14A: An image of self-cleaning of dust from the surface of a plasma treated SHC-PC material of the present invention.

[0043] FIG. 14B: An image of self-cleaning of dust from the surface of a comparative sample of an untreated SHC-PC material.

DETAILED DESCRIPTION OF THE INVENTION

[0044] The present invention relates generally to plasma treatment processes that can create polymeric materials having sufficient durability, optical transparency, and self-cleansing properties. The plasma processes can be performed without the use of solvents (e.g., deep reactive ion etching), thereby reducing the risk of cross-contamination with the polymeric material that is to be treated. Materials produced by the processes of the present invention can have a polymeric layer having nano- or micro-structures and a water contact angle of at least 150. As illustrated in a non-limiting aspect in the Examples, the materials of the present invention can exhibit any one of or all of the following properties post-plasma treatment: [0045] 1. Maintain high transmission (e.g., at least 70%) in the visible spectrum. [0046] 2. Maintain low transmission in the ultra-violet light spectrum (e.g., less than 2% at 330 nm. [0047] 3. Have a water contact angle of at least 150, a low hysteresis angle (e.g., <10), and a low water rolling angle (e.g., <10). [0048] 4. Have chemical resistance to a variety of solvents and cleansing materials (e.g., alcohols (e.g., methanol and ethanol), ketones, DMF, chlorinated solvents (e.g., chlorobenzene and toluene), etc.). [0049] 5. Have sufficient thermal stability characteristics (e.g., no evidence of softening when exposed to 60 C. for ten minutes). [0050] 6. Retain conformal dimensional stability with no evidence of size reduction or expansion at 80 C. [0051] 7. Provide self-cleansing polymeric material that can be integrated into a variety of products (e.g., solar panels). [0052] 8. Provide opportunities to develop water-repelling transparent coatings for various applications relating to the automotive industry, anti-fogging products, and anti-fouling products.

[0053] These and other non-limiting aspects of the present invention are discussed in detail in the following sections.

A. Polymeric Materials Having Optical Transparency and Sufficient Impact Strength

[0054] Polymers and matrices having optical clarity and sufficient impact strength include those that can be used to form films and layers in products that require such featurese.g., photovoltaic cells or solar panels, automotive headlamp lenses, lighting lenses, sunglass lenses, eyeglass lenses, swimming goggles and SCUBA masks, safety glasses/goggles/visors including visors in sporting helmets/masks, windscreens in motorized vehicles (e.g., motorcycles, ATVs, golf carts), electronic display screens (e.g., e-ink, LCD, CRT, plasma screens), etc. Non-limiting examples of polymers that can be used to form the materials and layers of the present invention include polycarbonate polymers or copolymers thereof, polyethylene terephthalates or co-polymers thereof, polysulphone polymers or co-polymers thereof, cyclo olefin polymers or co-polymers thereof, thermoplastic polyurethane polymers or co-polymers thereof, thermoplastic polyolefin polymers or co-polymers thereof, polystyrene polymers or co-polymers thereof, poly(methyl)methacrylate polymers or co-polymers thereof, and any other optically transparent polymers or co-polymers thereof. Blends of the aforementioned polymers and co-polymers can also be used.

[0055] In a preferred embodiment of the present invention, polycarbonates (PCs) are used. PCs include a particular class of thermoplastic polymers that are commercially available from a wide variety of sources (e.g., Sabic Innovative Plastics (Lexan)). In a particularly preferred embodiment, Lexan can be used in the context of the present invention. PCs typically have high impact-resistance and are highly transparent to visible light, with light transmission properties that exceed many types of glass products. Preferred examples of PCs include dimethyl cyclohexyl bisphenol or high-flow ductile (HFD) polycarbonates (e.g., bisphenol-A polycarbonate, sebacic acid copolymer).

[0056] PCs are polymers that include repeating carbonate groups (O(CO)O). A well-known PC is bisphenol-A polymer, which has the following structure:

##STR00001##

However, all types of polycarbonates, co-polymers, and blends thereof are contemplated in the context of the present invention. By way of example, and in addition to the dimethyl cyclohexyl bisphenol and high-flow ductile (HFD) polycarbonates (e.g., bisphenol-A polycarbonate, sebacic acid copolymer) mentioned above, WO 2013/152292 (the contents of which are incorporated into the present specification by reference) provides a wide range of PCs that can be used. In particular, polycarbonates can include polymers having repeating structural carbonate units of formula (1):

##STR00002##

in which at least 60/o of the total number of R.sup.1 groups contain aromatic moieties and the balance thereof are aliphatic, alicyclic, or aromatic. In an embodiment, each R.sup.1 is a C.sub.6-30 aromatic group, that contains at least one aromatic moiety. R.sup.1 can be derived from a dihydroxy compound of the formula HOR.sup.2OH, in particular of formula (2):

OH-A.sup.1-Y.sup.1-A.sup.2OH(2)

in which each of A.sup.1 and A.sup.2 is a monocyclic divalent aromatic group and Y 1 is a single bond or a bridging group having one or more atoms that separate A 1 from A 2. In an embodiment, one atom separates A.sup.1 and A.sup.2. Specifically, each R.sup.1 can be derived from a dihydroxy aromatic compound of formula (3):

##STR00003##

wherein R.sup.a and R.sup.b are each independently a halogen or C.sub.1-12 alkyl group; and p and q are each independently integers of 0 to 4. It will be understood that R is hydrogen when p is 0, and likewise R.sup.b is hydrogen when q is 0. Also in formula (3), X.sup.a is a bridging group connecting the two hydroxy-substituted aromatic groups, where the bridging group and the hydroxy substituent of each C.sub.6 arylene group are disposed ortho, meta, or para (specifically para) to each other on the C.sub.6 arylene group. In an embodiment, the bridging group X.sup.a is single bond, O, S, S(O), S(O).sub.2, C(O), or a C.sub.1-18 organic group. The C.sub.1-18 organic bridging group can be cyclic or acyclic, aromatic or non-aromatic, and can further comprise heteroatoms such as halogens, oxygen, nitrogen, sulfur, silicon, or phosphorous. The C.sub.1-18 organic group can be disposed such that the C.sub.6 arylene groups connected thereto are each connected to a common alkylidene carbon or to different carbons of the C.sub.1-18 organic bridging group. In an embodiment, p and q is each 1, and R.sup.a and R.sup.b are each a C.sub.1-3 alkyl group, specifically methyl, disposed meta to the hydroxy group on each arylene group.

[0057] In an embodiment, X.sup.a can be a substituted or unsubstituted C.sub.1-8 cycloalkylidene, a C.sub.1-25 alkylidene of formula C(R.sup.c)(R.sup.d)wherein R.sup.c and R.sup.d are each independently hydrogen, C.sub.1-12 alkyl, C.sub.1-12 cycloalkyl. C.sub.7-12 arylalkyl, C.sub.1-12 heteroalkyl, or cyclic C.sub.7-12 heteroarylalkyl, or a group of the formula C(R.sup.e)wherein R.sup.e is a divalent C.sub.1-12 hydrocarbon group. Groups of this type include methylene, cyclohexylmethylene, ethylidene, neopentylidene, and isopropylidene, as well as 2-[2.2.1]-bicycloheptylidene, cyclohexylidene, cyclopentylidene, cyclododecylidene, and adamantylidene. A specific example wherein X.sup.a is a substituted cycloalkylidene is the cyclohexylidene-bridged, alkyl-substituted bisphenol of formula (4)

##STR00004##

wherein R.sup.a and R.sup.b, are each independently C.sub.1-12 alkyl, R is C.sub.1-12 alkyl or halogen, r and s are each independently 1 to 4, and t is 0 to 10. In a specific embodiment, at least one of each of R.sup.a and R.sup.b are disposed meta to the cyclohexylidene bridging group. The substituents R.sup.a, R.sup.b, and R.sup.g can, when comprising an appropriate number of carbon atoms, be straight chain, cyclic, bicyclic, branched, saturated, or unsaturated. In an embodiment, R.sup.a and R.sup.b are each independently C.sub.1-4 alkyl, R.sup.g is C.sub.1-4 alkyl, r and s are each 1, and t is 0 to 5. In another specific embodiment, R.sup.a, R.sup.b and R.sup.g are each methyl, r and s are each 1, and t is 0 or 3. The cyclohexylidene-bridged bisphenol can be the reaction product of two moles (mol) of o-cresol with one mole of cyclohexanone. In another embodiment, the cyclohexylidene-bridged bisphenol is the reaction product of two moles of a cresol with one mole of a hydrogenated isophorone (e.g., 1,1,3-trimethyl-3-cyclohexane-5-one). Such cyclohexane-containing bisphenols, for example the reaction product of two moles of a phenol with one mole of a hydrogenated isophorone, are useful for making polycarbonate polymers with high glass transition temperatures and high heat distortion temperatures.

[0058] In another embodiment, X.sup.a can be a C.sub.1-8 alkylene group, a C.sub.3-8 cycloalkylene group, a fused C.sub.6-18 cycloalkylene group, or a group of the formula B.sup.1WB.sup.2wherein B.sup.1 and B.sup.2 are the same or different C.sub.1-6 alkylene group and W is a C.sub.3-12 cycloalkylidene group or a C.sub.6-16 arylene group.

[0059] X.sup.a can also be a substituted C.sub.3-18 cycloalkylidene of formula (5)

##STR00005##

wherein R.sup.r, R.sup.p, R.sup.q, and R.sup.t are each independently hydrogen, halogen, oxygen, or C.sub.1-12 organic groups; I is a direct bond, a carbon, or a divalent oxygen, sulfur, or N(Z) where Z is hydrogen, halogen, hydroxy, C.sub.1-12 alkyl, C.sub.1-12 alkoxy, or C.sub.1-12 acyl; h is 0 to 2, j is 1 or 2, i is an integer of 0 or 1, and k is an integer of 0 to 3, with the proviso that at least two of R.sup.r, R.sup.p, R.sup.q, and R.sup.t taken together are a fused cycloaliphatic, aromatic, or heteroaromatic ring. It will be understood that where the fused ring is aromatic, the ring as shown in formula (5) will have an unsaturated carbon-carbon linkage where the ring is fused. When k is one and i is 0, the ring as shown in formula (5) contains 4 carbon atoms, when k is 2, the ring as shown in formula (5) contains 5 carbon atoms, and when k is 3, the ring contains 6 carbon atoms. In an embodiment, two adjacent groups (e.g., R.sup.q and R.sup.t taken together) form an aromatic group, and in another embodiment, R.sup.q and R.sup.t taken together form one aromatic group and R.sup.r and R.sup.p taken together form a second aromatic group. When R.sup.q and R.sup.t taken together form an aromatic group, R.sup.p can be a double-bonded oxygen atom, i.e., a ketone.

[0060] Other useful aromatic dihydroxy compounds of the formula HO-ROH include compounds of formula (6)

##STR00006##

wherein each R.sup.b is independently a halogen atom, a C.sub.1-10 hydrocarbyl such as a C.sub.1-10 alkyl group, a halogen-substituted C.sub.1-10 alkyl group, a C.sub.6-10 aryl group, or a halogen-substituted C.sub.6-10 aryl group, and n is 0 to 4. A preferred halogen is bromine.

[0061] Some illustrative examples of specific aromatic dihydroxy compounds include the following: 4,4-dihydroxybiphenyl, 1,6-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, bis(4-hydroxyphenyl)methane, bis(4-hydroxyphenyl)diphenylmethane, bis(4-hydroxyphenyl)-1-naphthylmethane, 1,2-bis(4-hydroxyphenyl)ethane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, 2-(4-hydroxyphenyl)-2-(3-hydroxyphenyl)propane, bis(4-hydroxyphenyl)phenylmethane, 2,2-bis(4-hydroxy-3-bromophenyl)propane, 1,1-bis(hydroxyphenyl)cyclopentane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 1,1-bis(4-hydroxyphenyl)isobutene, 1,1-bis(4-hydroxyphenyl)cyclododecane, trans-2,3-bis(4-hydroxyphenyl)-2-butene, 2,2-bis(4-hydroxyphenyl)adamantane, alpha, alpha-bis(4-hydroxyphenyl)toluene, bis(4-hydroxyphenyl)acetonitrile, 2,2-bis(3-methyl-4-hydroxyphenyl)propane, 2,2-bis(3-ethyl-4-hydroxyphenyl)propane, 2,2-bis(3-n-propyl-4-hydroxyphenyl)propane, 2,2-bis(3-isopropyl-4-hydroxyphenyl)propane, 2,2-bis(3-sec-butyl-4-hydroxyphenyl)propane, 2,2-bis(3-t-butyl-4-hydroxyphenyl)propane, 2,2-bis(3-cyclohexyl-4-hydroxyphenyl)propane, 2,2-bis(3-allyl-4-hydroxyphenyl)propane, 2,2-bis(3-methoxy-4-hydroxyphenyl)propane, 2,2-bis(4-hydroxyphenyl)hexafluoropropane, 1,1-dichloro-2,2-bis(4-hydroxyphenyl)ethylene, 1,1-dibromo-2,2-bis(4-hydroxyphenyl)ethylene, 1,1-dichloro-2,2-bis(5-phenoxy-4-hydroxyphenyl)ethylene, 4,4-dihydroxybenzophenone, 3,3-bis(4-hydroxyphenyl)-2-butanone, 1,6-bis(4-hydroxyphenyl)-1,6-hexanedione, ethylene glycol bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl) sulfoxide, bis(4-hydroxyphenyl)sulfone, 9,9-bis(4-hydroxyphenyl)fluorine, 2,7-dihydroxypyrene, 6,6-dihydroxy-3,3,3,3-tetramethylspiro(bis)indane (spirobiindane bisphenol), 3,3-bis(4-hydroxyphenyl)phthalimide, 2,6-dihydroxydibenzo-p-dioxin, 2,6-dihydroxythianthrene, 2,7-dihydroxyphenoxathin, 2,7-dihydroxy-9, 10-dimethylphenazine, 3,6-dihydroxydibenzofuran, 3,6-dihydroxydibenzothiophene, and 2,7-dihydroxycarbazole, resorcinol, substituted resorcinol compounds such as 5-methyl resorcinol, 5-ethyl resorcinol, 5-propyl resorcinol, 5-butyl resorcinol, 5-t-butyl resorcinol, 5-phenyl resorcinol, 5-cumyl resorcinol, 2,4,5,6-tetrafluoro resorcinol, 2,4,5,6-tetrabromo resorcinol, or the like; catechol; hydroquinone; substituted hydroquinones such as 2-methyl hydroquinone, 2-ethyl hydroquinone, 2-propyl hydroquinone, 2-butyl hydroquinone, 2-t-butyl hydroquinone, 2-phenyl hydroquinone, 2-cumyl hydroquinone, 2,3,5,6-tetramethyl hydroquinone, 2,3,5,6-tetra-t-butyl hydroquinone, 2,3,5,6-tetrafluoro hydroquinone, 2,3,5, 6-tetrabromo hydroquinone, or the like, or combinations comprising at least one of the foregoing dihydroxy compounds.

[0062] Specific examples of bisphenol compounds of formula (3) include 1,1-bis(4-hydroxyphenyl) methane, 1,1-bis(4-hydroxyphenyl) ethane, 2,2-bis(4-hydroxyphenyl) propane (hereinafter bisphenol A or BPA), 2,2-bis(4-hydroxyphenyl) butane, 2,2-bis(4-hydroxyphenyl) octane, 1,1-bis(4-hydroxyphenyl) propane, 1,1-bis(4-hydroxyphenyl) n-butane, 2,2-bis(4-hydroxy-2-methylphenyl) propane, 1,1-bis(4-hydroxy-t-butylphenyl) propane, 3,3-bis(4-hydroxyphenyl) phthalimidine, 2-phenyl-3,3-bis(4-hydroxyphenyl) phthalimidine (PPPBP), and 1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane (DMBPC). Combinations comprising at least one of the foregoing dihydroxy compounds can also be used. In one specific embodiment, the polycarbonate is a linear homopolymer derived from bisphenol A, in which each of A.sup.1 and A.sup.2 is p-phenylene and Y.sup.1 is isopropylidene in formula (3).

[0063] Methods for the preparation of polycarbonates by interfacial polymerization are well known. Although the reaction conditions of the preparative processes may vary, several of the useful processes typically involve dissolving or dispersing the dihydric phenol reactant in aqueous caustic soda or potash, adding the resulting mixture with the siloxane to a suitable water immiscible solvent medium and contacting the reactants with the carbonate precursor, such as phosgene, in the presence of a suitable catalyst such as triethylamine or a phase transfer catalyst, and under controlled pH conditions, e.g., 8 to 10. The most commonly used water immiscible solvents include, but are not limited to, methylene chloride, 1,2-dichloroethane, chlorobenzene, toluene, and the like.

[0064] Among the useful phase transfer catalysts that can be used are catalysts of the formula (R.sup.3).sub.4Q.sup.+X, wherein each R.sup.3 is the same or different, and is a C.sub.1-10alkyl group; Q is a nitrogen or phosphorus atom; and X is a halogen atom or a C.sub.1-8 alkoxy group or C.sub.6-188 aryloxy group. Suitable phase transfer catalysts include, for example, [CH.sub.3(CH.sub.2).sub.3].sub.4NX, [CH.sub.3(CH.sub.2).sub.3].sub.4PX, [CH.sub.3(CH.sub.2).sub.5].sub.4NX, [CH.sub.3(CH.sub.2).sub.6].sub.4NX, [CH.sub.3(CH.sub.2).sub.3].sub.4NX, CH.sub.3[CH.sub.3(CH.sub.2).sub.3].sub.3NX, CH.sub.3[CH.sub.3(CH.sub.2).sub.2].sub.3NX wherein X is Cl.sup., Br.sup. ora C.sub.1-8 alkoxy group or C.sub.6-188 aryloxy group. An effective amount of a phase transfer catalyst may be from 0.1 to 10 wt. %, and, in another embodiment, from 0.5 to 2 wt. % based on the weight of bisphenol in the phosgenation mixture.

[0065] In alternative embodiments, melt processes are used. A catalyst may be used to accelerate the rate of polymerization of the dihydroxy reactant(s) with the carbonate precursor. Representative catalysts include, but are not limited to, tertiary amines such as triethylamine, quaternary phosphonium compounds, quaternary ammonium compounds, and the like.

[0066] Alternatively, polycarbonates may be prepared by co-reacting, in a molten state, the dihydroxy reactant(s) and a diaryl carbonate ester, such as diphenyl carbonate, in the presence of a transesterification catalyst in a Banbury mixer, twin screw extruder, or other melt extrusion process equipment to form a uniform dispersion. Volatile monohydric phenol is removed from the molten reactants by distillation and the polymer is isolated as a molten residue.

[0067] The polycarbonates can be made in a wide variety of batch, semi-batch or continuous reactors. Such reactors are, for example, stirred tank, agitated column, tube, and recirculating loop reactors. Recovery of the polycarbonate can be achieved by any means known in the art such as through the use of an anti-solvent, steam precipitation or a combination of anti-solvent and steam precipitation.

[0068] Polycarbonates include homopolycarbonates (wherein each R.sup.1 in the polymer is the same), copolymers comprising different R.sup.1 moieties in the carbonate (copolycarbonates), copolymers comprising carbonate units and other types of polymer units, such as ester units, and combinations comprising at least one of homopolycarbonates and/or copolycarbonates.

B. Functional Coatings

[0069] While many polymers that can be used in the context of the present invention have good optical transparency and impact resistance characteristics, many of such polymers lack good abrasion resistance and are also susceptible to degradation from exposure to ultra-violet light. In instances where it is desirable to increase the abrasion resistance and/or reduce exposure to ultra-violet light, of a given polymeric layer or material of the present invention, functional coatings can be applied to the polymeric layer prior to the plasma treatment steps.

[0070] The functional coating can be a weathering or protective coating. It can include silicones (e.g., a silicone hard-coat), polyurethanes (e.g., polyurethane acrylate), acrylics, polyacrylate (e.g., polymethacrylate, polymethyl methacrylate), polyvinylidene fluoride, polyesters, epoxies, and combinations comprising at least one of the foregoing. The functional coating can include ultraviolet absorbing molecules (e.g., such as hydroxyphenylthazine, hydroxybenzophenones, hydroxylphenylbenzothazoles, hydroxyphenyltriazines, polyaroylresorcinols, and cyanoacrylate, as well as combinations comprising at least one of the foregoing). In one preferred aspect of the present invention, the functional coatings are silicone hard-coats comprising condensed silanols, colloidal silica, and ultraviolet (UV) absorbers. Examples include AS4000, AS4010, and AS4700, all of which are available commercially from Momentive Performance Materials. Such coatings can be applied by dipping the plastic substrate layer in a coating solution at room temperature and atmospheric pressure (i.e., dip coating). Alternative methods such as flow coating, curtain coating, and spray coating can also be used.

[0071] The functional coating can comprise a primer layer and/or a coating (e.g., a top coat). A primer layer can aid in adhesion of the functional coating to the polymeric layer. The primer layer can include, but is not limited to, acrylics, polyesters, epoxies, and combinations comprising at least one of the foregoing. The primer layer can also include ultraviolet absorbers in addition to or in place of those in the functional coating. For example, the primer layer can comprise an acrylic primer (SHP401 or SHP470, commercially available from Momentive Performance Materials).

[0072] Another non-limiting example of a functional coating that can be used is an abrasion resistant coating to improve abrasion resistance. Generally, the abrasion resistant coating can comprise an organic coating and/or an inorganic coating such as, but not limited to, aluminum oxide, barium fluoride, boron nitride, hafnium oxide, lanthanum fluoride, magnesium fluoride, magnesium oxide, scandium oxide, silicon monoxide, silicon dioxide, silicon nitride, silicon oxy-nitride, silicon carbide, silicon oxy carbide, hydrogenated silicon oxy-carbide, tantalum oxide, titanium oxide, tin oxide, indium tin oxide, yttrium oxide, zinc oxide, zinc selenide, zinc sulfide, zirconium oxide, zirconium titanate, glass, and combinations comprising at least one of the foregoing. Such abrasion resistant coatings can be applied by various deposition techniques such as vacuum assisted deposition processes and atmospheric coating processes.

C. Plasma Processing and Surface Treatment

[0073] Polymeric layers, whether coated with a functional coating or not, can be used in the context of the present invention. The surfaces of such layers can be treated with plasma techniques to impart super-hydrophobic self-cleansing properties to said surfaces. While both wet and drying etching plasma treatment techniques can be used, in preferred aspects dry etching is used. An advantage of dry etching is that solvents do not have to be used, and cross contamination of the solvents with the polymeric layers can be avoided.

[0074] Various dry etching techniques can be used in the context of the present invention, non-limiting examples of which include reactive ion etching (RIE), deep reactive ion etching (DRIE), ion beam etching (IBE), etc. In preferred aspects, the DRIE process is used. An objective is to reach a high ionization rate in the gases to enhance the RIE effect. Notably, the plasma treatment process can be a continuous process in which the polymeric layer is first subjected to plasma generated via oxygen to create a surface having the nano- and micro-structures. Subsequently, the oxygen plasma is replaced with fluorine containing compounds (e.g., C.sub.4F.sub.8) to functionalize the nano- or micro-structures, thereby imparting super-hydrophobic properties to the treated surface. In a preferred non-limiting embodiment, the following processing steps can be used in the context of the present invention: [0075] 1. A polymeric layer can be placed into an appropriate plasma chamber device such that one of its surfaces is faced towards the plasma flow (first surface) and the opposite surface is faced away from the plasma flow (second surface). [0076] 2. Pure oxygen gas can be introduced into the chamber at a flow rate of about 50 to 100 sccm at a base pressure of about 25 to 500 mTorr or 25 to 100 mTorr. [0077] 3. Plasma can be created via a radio frequency (RF) power source at about 50 to 950 W. [0078] 4. The first surface of the polymeric layer can be subjected to the O.sub.2 generated plasma for about 1 minute to 25 minutes to create nano- and micro-structures. [0079] 5. Without shutting down the power source, the O.sub.2 feed can be replaced with C.sub.4F.sub.8 at a similar flow rate to O.sub.2 and under similar pressure and power conditions. The first surface of the polymeric layer can then be subjected to the C.sub.4F.sub.8 generated plasma for 1 minute to 25 minutes to functionalize the nano- and micro-structures, thereby imparting super-hydrophobicity to the treated surface.

[0080] Additives can also be included in the polymeric layer prior to plasma-treatment. The amounts of such additives can range from 0.001 to 40 wt. %. Non-limiting examples of such additives include plasticizers, ultraviolet absorbing compounds, optical brighteners, ultraviolet stabilizing agents, heat stabilizers, diffusers, mold releasing agents, antioxidants, antifogging agents, clarifiers, nucleating agents, phosphites or phosphonites or both, light stabilizers, singlet oxygen quenchers, processing aids, antistatic agents, fillers or reinforcing materials, or any combination thereof. Non-limiting examples of ultraviolet light absorbing compounds include those capable of absorbing ultraviolet A light comprising a wavelength of 315 to 400 nm (e.g., avobenzone (Parsol 1789), Bisdisulizole disodium (Neo Heliopan AP), Diethylamino hydroxybenzoyl hexyl benzoate (Uvinul A Plus), Ecamsule (Mexoryl SX), or Methyl anthranilate, or any combination thereof. Non-limiting examples of ultraviolet light absorbing compounds capable of absorbing ultraviolet B light comprising a wavelength of 280 to 315 nm include 4-Aminobenzoic acid (PABA), Cinoxate, Ethylhexyl triazone (Uvinul T 150). Homosalate, 4-Methylbenzylidene camphor (Parsol 5000), Octyl methoxycinnamate (Octinoxate), Octyl salicylate (Octisalate), Padimate O (Escalol 507), Phenylbenzimidazole sulfonic acid (Ensulizole). Polysilicone-15 (Parsol SLX), Trolamine salicylate. Non-limiting examples of ultraviolet light absorbing compounds capable of absorbing ultraviolet A and B light comprising a wavelength of 280 to 400 nm include Bemotrizinol (Tinosorb S), Benzophenones 1 through 12, Dioxybenzone, Drometrizole trisiloxane (Mexoryl XL). Iscotrizinol (Uvasorb HEB), Octocrylene, Oxybenzone (Eusolex 4360), Sulisobenzone, or polybenzoylresorcinol. Such additives can be compounded into a masterbatch with the desired polymeric resin.

D. Applications for the Super-Hydrophobic Material

[0081] The super-hydrophobic materials of the present invention can be used in a wide variety of applications. For instance, and as illustrated in the Examples, the materials have sufficient optical and self-cleansing properties, strength, and structural integrity at elevated temperatures. Thus, the materials can be used to protect surfaces from soiling while also allowing visible light to pass-through. FIG. 1 provides a non-limiting example of the super-hydrophobic material of the present invention incorporated into a solar panel (20). The Solar panel (20) includes a super-hydrophobic material of the present invention (21) that includes a plasma treated surface having nano- or micro-structures and a water contact angle of at least 150 (22). The plasma treated surface (22) faces away from the solar panel (20), towards the sun, so as to provide its antifouling or self-cleansing effect while also protecting the internal parts of the solar panel (20). The internal parts can include a first electrode (23), a first active layer (24), a second active layer (25), and a second electrode (26).

[0082] FIG. 2 provides a non-limiting illustration of the mechanism of the self-cleaning ability of the super-hydrophobic of the material of the present invention. In FIG. 2A, the plasma treated surface (22) has dirt particles (27) on the surface. Water is applied to the surface in FIG. 2B and the water forms droplet (28) due to the hydrophobic nature of the plasma treated surface. The dust particles (27) are attached to the droplet (28) as shown in FIGS. 2C and 2D.

[0083] Additional non-limiting examples of uses for the materials of the present invention include optical elements, displays, windows (or transparencies), mirrors, and liquid crystal cells. As used herein the term optical means pertaining to or associated with light and/or vision. The optical elements according to the present invention may include, without limitation, ophthalmic elements, display elements, windows, mirrors, and liquid crystal cell elements. As used herein the term ophthalmic means pertaining to or associated with the eye and vision. Non-limiting examples of ophthalmic elements include corrective and non-corrective lenses, including single vision or multi-vision lenses, which may be either segmented or non-segmented multi-vision lenses (such as, but not limited to, bifocal lenses, trifocal lenses and progressive lenses), as well as other elements used to correct, protect, or enhance (cosmetically or otherwise) vision, including without limitation, magnifying lenses, protective lenses, visors, goggles, as well as, lenses for optical instruments (for example, cameras and telescopes). As used herein the term display means the visible or machine-readable representation of information in words, numbers, symbols, designs or drawings. Non-limiting examples of display elements include screens, monitors, and security elements, such as security marks. As used herein the term window means an aperture adapted to permit the transmission of radiation there-through. Non-limiting examples of windows include automotive and aircraft transparencies, windshields, filters, shutters, and optical switches. As used herein the term mirror means a surface that specularly reflects a large fraction of incident light. As used herein the term liquid crystal cell refers to a structure containing a liquid crystal material that is capable of being ordered. One non-limiting example of a liquid crystal cell element is a liquid crystal display.

EXAMPLES

[0084] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results.

Example 1

Super-Hydrophobic Material

[0085] Silicone hard-coated polycarbonate (SHC-PC) substrates were prepared from a silicone hard-coat obtained from Momentive Performance Materials, Inc. (AS4010) and a polycarbonate resin obtained from SABIC Innovative Plastics (LEXAN). In particular, these substrates were prepared by injection molding a PC panel, flow-coating and curing the primer coating and flow-coating and curing the topcoat.

[0086] 11 cm.sup.2 samples were cleaned with isopropanol (IPA) and water, and then oven-dried at 50 C. for 15 minutes (See, FIG. 3). The polymer surfaces were then treated with plasma. The plasma treatment included etching and chemically modifying the samples using a deep reactive ion etching (DRIE) in a two-step continuous plasma process (pure oxygen for texturing and C.sub.4F.sub.8 for hydrophobization), which resulted in functional material that combine fluorinated chemistry with surface morphology. Surfaces were subjected to the O.sub.2 and C.sub.4F treatments for about 1 to 25 minutes to create the desired nano- and micro-structures. Gases were introduced into the chamber at a flow rate of 100 sccm, and the base pressure was kept at 85 mTorr while the RF power was maintained at 100 W in each experiment (See, FIGS. 4 and 5).

[0087] Surface morphologies were investigated by field emission scanning electron microscopy (SEM) using Quanta (200 or 600). The samples were gold-palladium metallized by sputter coating using a BioRad Polaron instrument and observed at 5-10 KV. Water contact angles were measured using a contact angle goniometer (KRUSS, Drop Shape Analyzer-DSA100 by KRUSS GmbH, Hamburg, Germany) at five different points of the samples using 10 L of deionized water. Mean water contact angles were 820 pre-plasma treatment (FIG. 3), approximately 10 or less for oxygen plasma treated samples (FIG. 4) and 168 post-plasma for oxygen/C.sub.4F.sub.8 treatment (FIG. 5).

[0088] FIG. 6 are UV-Vis spectra data of SHC-PC before (data line 62) and 10 minutes after (data line 64) DRIE plasma treatment. These data confirm that the DRIE plasma processing does not negatively affect the ultra-violet (UV) absorbing properties of the SHC-PC substrate, as the UV spectrum is substantially the same. Thus, the UV spectral profile is maintained after DRIE plasma processing.

[0089] Fourteen samples of plasma-treated SHC-PC, along with a non-plasma-treated SHC-PC control sample, were exposed to UV light in an Atlas Ci5000 Xenon Arc Weatherometer according to ASTM G 155-05 Cycle 1 except with an irradiance of 0.75 W/m.sup.2.Math.nm instead 0.35 W/m.sup.2.Math.nm, both at 340 nm. After 6.7 MJ/m.sup.2.Math.nm of exposure, equivalent to approximately 2.4 years of outdoor exposure in Florida, the plasma-treated samples and the control sample exhibited no delamination or micro-cracking. The change in haze, determined in accordance with ASTM D1003-11, procedure A with CIE standard illuminant C (see ISO/CIE 10526), was 2.0% for the control sample, was in the range 1.2 to 2.2% for the fourteen plasma-treated samples.

[0090] FIGS. 7A and B are 3D AFM images of O.sub.2 plasma treated SHC-PC (FIG. 7A) and O.sub.2/C.sub.4F.sub.8 plasma treated SHC-PC (FIG. 7B) showing needle like structures of variable mean surface roughness. Surface morphology examination was carried out using Agilent 5400 SPM Atomic Force Microscopy (AFM) scanner in non-contact mode. The reported root mean square surface roughness is the mean of three measurements on different areas of each sample taken to verify the surface sample homogeneity.

[0091] FIGS. 8A and 8B are optical surface profilometry images of O.sub.2 plasma treated SHC-PC (FIG. 8A) and O.sub.2/C.sub.4F.sub.8 plasma treated SHC-PC (FIG. 8B) showing different surface topology and roughness. Sample Surface roughness was mapped using ZYGO NewView 7300 optical profilometer scanning at 3 different sample spots (5050 microns) in vertical scanning interferometer (VSI).

[0092] FIG. 9 is a bar graph of variation of water contact angle of O.sub.2/C.sub.4F.sub.8 plasma treated SHC-PC material with different treatment time in minutes. This data confirmed the tunability of super-hydrophilicity/super-hydrophobicity nature of sequentially plasma treated samples with low hysteresis angle (100) and sliding angles less than (100), vital for their potential application in anti-soiling.

[0093] FIG. 10 is an image of a SHC-PC material demonstrating that the optical transparency of the SHC-PC is maintained after 10 minutes of DRIE plasma processing. Thus, the optical clarity is maintained after DRIE plasma processing. A before image is not provided, as no noticeable change was observed between before DRIE plasma processing and after DRIE plasma processing.

[0094] FIG. 11A is an image of the plasma treated SHC-PC material showing that no hazing or conformal shrinkage of the plasma treated SHC-PC material is seen after being subjected to immersion in acetone, methanol, and ethanol. Conversely, total structural collapse of non-plasma treated and non-SHC coated PC material was observed when immersed in acetone as shown in the image shown in FIG. 11B.

[0095] FIG. 12A is an image showing that no shrinkage or expansion of the plasma treated SHC-PC material of the present invention at temperatures of 60 C. and 120 C., respectively. Conversely, total structural collapse of non-plasma treated and non-SHC coated PC material was observed at a temperature of 60 C. is depicted in the image shown in FIG. 12B.

[0096] To demonstrate the super-hydrophobic properties of the SHC-PC plasma treated according to the present invention, droplets of water were sprinkled on the top of a sample of the plasma treated SHC-PC material of the present invention (mean water angle 168 degree. See FIG. 5) and a comparative sample of untreated SHC-PC material (mean water angle 82 degree, See FIG. 3). FIG. 13A is an image of the water beading on the surface of the plasma treated SHC-PC material. FIG. 13B is an image of the water beading on the surface of the untreated SHC-PC material. Comparing the beading of the water in the two images, the plasma treated SHC-PC has more rounded and taller beads of water than the untreated SHC-PC material. Thus, the plasma treated SHC-PC material of the present invention has super-hydrophobic properties.

[0097] To demonstrate the self-cleaning properties of the SHC-PC plasma treated according to the present invention, dust and water droplets were sprinkled on the surface of a sample of the plasma treated SHC-PC material of the present invention and a comparative sample of untreated SHC-PC material. FIG. 14A is an image of the dust being removed from the surface of the plasma treated SHC-PC material of the present invention. FIG. 14B is an image of dust and water droplets were sprinkled on the surface of a sample of an untreated SHC-PC material. In FIG. 14A, the water droplets on the plasma treated SHC-PC material are collecting the dust while moving down the surface of the plasma treated SHC-PC material. In contrast, the water droplets on the untreated SHC-PC material in FIG. 14 are not collecting the dust particles. Thus, the plasma treated SHC-PC material of the present invention, as demonstrated by the ability to remove the dust, has self-cleaning properties.