Patent Application
20100078328
This invention relates to a method of electrochemical co-deposition of sol-gel and different additives to thereby form films on various surfaces.
Electrochemical deposition, which dates back to the middle of the 19th 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.
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., Cu2O, 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)3 deposition.
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′)3+3H2O→R-M(OH)3+3R′OH (Eq. 1)
R-M(OH)3+R-M(OR′)3→R-M(OH)2—O-M(OR′)2+R′OH (Eq. 2)
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.
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.
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.
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.
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.
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.
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.
This co-deposition process affords a film which may in some instances have at least two distinct phases.
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:
1. Since electron transfer occurs very close to the surface, i.e., within less than 100 Å, the coating follows very closely the intimate structure of the surface, allowing the coating of complex geometries, such as screws, stents, sprints, etc;
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;
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;
4. A great variety of additives may be used;
5. The inclusion of the additive in the reaction mixture does not interfere with the sol-gel polymerization; and
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.
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.
In some embodiments, the at least one additive is selected so as to be capable of undergoing reduction or oxidation during the electrodeposition process.
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.
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.
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.
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)nM(R′)4-n, partially hydrolyzed and/or partially condensed polymers of said monomers and mixtures thereof, wherein in the formula (RO)nM(R′)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 C1-C3-alkyl, being preferably unsubstituted, R′ is an organic moiety selected from C1-C10-alkyl, C2-C8-alkenyl, C2-Cg-alkynyl, C6-C10-aryl, C4-C10-heteroaryl, each being optionally substituted by at least one group selected from C1-C8-alkyl, C2-C8-alkenyl, C2-C8-alkynyl, C6-C10-aryl, C4-C10-heteroaryl, halide, amine (primary, secondary, tertiary or quaternary), hydroxyl, thiol, nitro, repeating methylenedioxy (—O—CH2—O—) or ethylenedioxy (—O—(CH2)2—O—) groups, and n is an integer from 1 to 4.
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.
In another embodiment, the precursors are monomers being selected amongst metal alkoxide monomers and silicon alkoxide monomers.
In still another embodiment, the silicon alkoxide monomer is of the formula (RO)nSi(R′)4-n, wherein R is an organic moiety selected from C1-C3-alkyl, R′ is an organic moiety selected from C1-C10-alkyl or C6-C12-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.
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 C2-C8-alkenyl, C2-C8-alkynyl, C6-C10-aryl and C4-C10-heteroaryl, optionally substituted by at least one group selected from C1-Cg-alkyl, C2-C8-alkenyl, C2-C8-alkynyl, C6-C10-aryl, C4-C10-heteroaryl, halide, amine (primary, secondary, tertiary or quaternary), hydroxyl, thiol, nitro and repeating methylenedioxy (—O—CH2—O—) or ethylenedioxy (—O—(CH2)2—O—) groups. For example, the specific designation “C1-C3-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.
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.
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 C1-C8-alkyl, C2-C8-alkenyl, C2-C8-alkynyl, C6-C10-aryl, C4-C10-heteroaryl, halide, amine (primary, secondary, tertiary or quaternary), hydroxyl, thiol, nitro and repeating methylenedioxy (—O—CH2—O—) or ethylenedioxy (—O—(CH2)2—O—) groups. The aryl group may also be a biaryl such as a biphenyl. The specific designation “C6-C12-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.
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.
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.
In a further embodiment, said metal is Si, Zr, Al, Ti, Fe, V, and W.
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.
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.
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.
In some embodiments, the sol-gel precursor is one or more of TiO2, SiO2, titanium tetra-n-propoxide (Ti(OPr)4), phenyltrimethoxy silane (PhTMOS), aminopropyltriethoxy silane (APTEOS), tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), and silicon oxide.
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.
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.
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.
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.
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.
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.
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.
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.
In another embodiment, the at least one additive is a polymer. In still another embodiment, said polymer is conductive.
In another embodiment, the at least one additive is a prepolymer, i.e., an oligomer made of several monomers capable of further polymerization.
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.
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.
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.
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.
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).
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.
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.
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.
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.
In one embodiment, the at least one metal salt is one metal salt.
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.
In further embodiments, the at least one metal salt is a mixture of salts of different metals.
The at least one metal salt is not a dopant.
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.
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.
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.
In one embodiment, said surface is made of stainless steel. In a preferred embodiment, the stainless steel is stainless steel 316L.
In another embodiment, said surface is a metallic surface.
In yet another embodiment, said surface is made of indium-tin oxide (ITO).
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.
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.
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.
In another embodiment, said medical implant is a stent or an orthopedic device such as a screw or nail.
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.
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.
Thus, in another embodiment, the method comprises:
Preferably, the at least one additive is selected so as to have the capability of undergoing reduction or oxidation during the electrodeposition process.
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.
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.
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.
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.
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, 86th Edition, 2005.
Generally, the applied voltage is a low voltage not exceeding a few volts in its absolute value.
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.
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.
In another embodiment, the sol-gel to be deposited along with a metal salt is SiO2 or TiO2 and the potential is between ±1.0 V and ±1.4 V.
In a further embodiment, the additive is polypyrrole (PPY) and the voltage is between 0.7 V and 1V.
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.
In a still further embodiment, the voltage is applied for a period of from about 5 minutes to about 60 minutes.
In another embodiment, said negative or positive potential induces electrochemical formation of solvated H+ or OH−.
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 C1-C4-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.
Non-limiting examples of such inert salts are NaCl, NaBr, KCl, KBr, LiClO4, KNO3, KBF4 and ammonium NH4+ containing salt.
In another embodiment, the method comprises:
In another embodiment, said at least one additive is a monomer of a conductive polymer and the method comprises:
In another embodiment, the at least one additive is a metal and the method comprises:
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.
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.
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.
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.
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.
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.
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:
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.
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.
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.
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.
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/TiO2 and Cu/SiO2 films, respectively, and also for the deposition of conductive polymers and monomers thereof on such surfaces.
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≦10 Ohm/Ω, Delta Technologies) for 0.5-60 min, while stirring the deposition solution (0.2 M titanium tetra-n-propoxide (Ti(OPr)4), 8.9 mM water and 0.1 M LiClO4 in dry 2-propanol). CuCl2 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
Since the electrochemical co-deposition is controlled by two simultaneous processes, i.e., the reduction of Cu2+ 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 (
The morphology of the deposited films can be clearly seen in
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.
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° 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.
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.
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.
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° 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.
The electrodeposition was conducted as detailed above on a stainless steel surface, and an exemplary films obtained are shown in
Images shown in
The heterogeneity of some PhTMOS films is exhibited in
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.
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
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 μm·sec−1. The two reactions shown below occurred simultaneously in the polypyrrole-silica sol-gel densification process to result in the polypyrrole-silica composite film.
The effect of the potential may be observed further in
EDX analysis of the films formed according to the invention confirmed the presence of silica and polypyrrole. It can be seen from
In order to examine the influence of the deposition time, positive potential was applied for different times. As
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.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IL2007/001216 | 10/7/2007 | WO | 00 | 11/9/2009 |
| Number | Date | Country | |
|---|---|---|---|
| 60847378 | Sep 2006 | US |
