Substrates used in various applications are coated to provide desired surface properties. There is a continued need for methods that apply such coating that provide strongly bonded coatings and the ability to tailor the reactivity or non-reactivity of the surface. A problem that can occur in existing coatings, such as those used in chromatography, is that the bond between the coating and the substrate fails. Many of these coating systems use strong covalent and ionic bonds, but under conditions of use, even if a small number the bonds may fail, leading to gaps in the coating that expose the substrate surface. This can be aggravated if the unbonded coating chemical has any solubility in the system. This uncovered substrate gaps may introduce reactivity to the system that potentially compromises or interferes with the function of the coating.
An aspect of the invention is a coating upon a substrate that is useful in chromatography and other applications. The coating is attached to the substrate with strong ionic or covalent bonds. However, the coating system is also highly cross-linked. Accordingly should a bond fail, the coating is maintained since adjacent bonds hold it in place. Even in the event, several bonds should fail, the coating, which is essentially a very large cross-linked molecule, is very insoluble because of its size. The result is a coating that is very resistant to failure under a wide range of operating conditions.
Another aspect the ability to tailor the thickness of the coating, either by applying multiple layers, or by choosing the particular coating chemicals. The final or active layer can be easily determined by a final application with a finishing layer having the desired activity.
An aspect is a process for making homogeneous multilayers on substrates that either have active chemical sites or can be modified to contain active chemical sites. A gas phase deposition is used as the main tool to deposit multilayers onto a variety of different substrates. In an aspect, the process is as follows:
(1) Chemical A is gas-phase deposited onto a substrate.
(2) Another chemical, chemical B, that can react with chemical A is deposited to add another layer.
(3) Chemicals C is deposited to provide a finishing layer, or to form the final surface with the desired activity, by reacting with reaction sites on deposited Chemical B. Depending upon the chosen chemistry, Chemical C may be used to form an intermediate layer, which is then used for deposition by reacting with Chemical D, which forms the finishing layer.
Steps (1) and (2) can be conducted once or repeated if a thicker layer is dersire before deposition of C. The chemicals A, B, C, and D are evaporable, in the gas phase at the conditions of the reaction. Deposition conditions and the chemical are chosen to provide the suitable deposition reactions in the gas-phase.
For step (1), the substrate may be silicon, glass, metals, ceramics, silica, aluminum, titanium, zirconia, or any other materials that can be activated to bond with chemical A. Chemical A can comprise one or a mixture from any suitable chemical can be chosen from silanes with active groups (e.g., amine, succinic anhydride, gluteric anhydride, epoxy, isocyanate, alcohol, thioisocynates, and the like), or other bifunctional, trifunctional, or tetrafunctional molecules with multiple amines or multiple isocyanates, or combinations of other reactive groups as discussed above. Chemical A can also comprise a monofunctional or bifunctional isocynate or an amine containing molecule. A suitable Chemical A is a amine, epoxide, or isocyanate with at least two functional groups. This allows for cross-linking in the deposited layer, while also providing unreacted groups for bonding the Chemical B.
For step (2), Chemical B can be any evaporable chemical that contains a functional group that can react with molecule A thus tethering the two molecules together by means of a covalent or electrostatic bond. Chemical B should be a molecule that under reasonable temperature can react with A.
For step (3) C and/or D must contain a reactive heteroatom or moiety that can either react with A or B. Either can be a mono- or di-functional molecule that can react with available functional groups from either/or A and/or B. Chemical C may be the same or different from Chemical A, and may provide the finished surface or function as an intermediate bonding layer of deposition of a Chemical D.
As the layers are applied, the gas-phase chemical will react with the previously applied layers. For example, B will reactive with A, and C will react with B, but may also react with any remaining active sites of A. In addition, the gas-deposited chemicals in Chemical A, B, C will react with each other during deposition, thus creating a cross-linked system. Available active sites will remain unreacted to provide active sites for reaction with layers applied subsequently. In the final product a reaction product of the substrate and the applied chemicals, in the form of a multilayers that are with covalently or ionically bonded, and that are highly cross-linked within layers and between layers.
The method for applying Chemicals A, B, C, and D is by a gas-phase chemical deposition or chemical vapor deposition. Such methods are well known. The exact operating conditions and the chemicals chosen are selected where the chemical in the vapor phase and stable, and can be reliably contacted with the substrate for reaction on deposition with the substrate.
Multilayer growth can be important for semiconductor fabrication, biological adsorption, and chromatography and for new materials development.
Types and Examples of Molecules:
Exemplary molecules that can function as A, B, or C, include.
Where R can represent: isocynate, alcohol, amine, thioisocynate, acid chloride, ketone, aldehyde, hydrogen, a charged specie, e.g., sulfonate (—SO3), phosphate (—PO4), carbonate (—CO2).
Suitable chemicals also include any suitable selected from a triamine, a diamine, a tetraamine, a diisocyanate, a triisocyanate, a diepoxide, a triepoxide, a diacid chloride, a triacid chloride. Particular compounds are diethylenetriamine and tris (2-amino ethyl) amine. To promote cross-linking in the layer, at least a portion of Chemical A or Chemical B is a compound with more than two functional groups that can participate in cross-linking reactions, as well as A to B reactions.
The final layer is a finishing layer, Chemical C or D is reactive with the underlying layers and also contains groups that provides the desired reactivity of the final layer, and can be any suitable such group. The finishing layer chemical may also be selected to provide no reactivity. Examples include mono amines, epoxides, or isocyantes (for reaction with the underlying layers) with alkyl chains, and may include reactive thiol groups, For chromatography it may contain an alkyl chain. For ion chromatography or other type of chromatography it may an amine group, sulfonate group, or nitro group.
The present invention provides the following advantages over previous layered systems;
Semiconductor
Surface functionalization can be used in the semiconductor industry. The system presented here can be used to allow for precise placement of certain types of metals or metal ions that can react with heteroatoms present on the surface, e.g., a difunctional molecule used in the finishing layer can have a chemical moiety that can react or interact with a metal or metal ion. The chemical for the finishing layer contains at one end a reactive group, i.e., amino or isocynate to react with the underlaying layer formed by Chemical A or B. The other functional group being, for example, a thiol to provide activity for reaction of the metal or metal ion.
The reactive amino or isocyante can react with either the surface layer silanols (chemical A) or a heteroatom (on an underlying layer from Chemical C or Chemical) on the already functionalized surface. The free thiol groups then can further reacted with gold, silver, copper, or other types of noble metals nanodots; thus, allowing for the placement of nanodot materials.
Chromatography
The multilayer system can be applied to chromatography to provide a functionalized surface that will offer different chemical selectivity. This process will provide a highly crossed-link stationary phase. Typical substrates for chromatography are; silica, alumina, zirconia, and titania. The mentioned substrates contain surface moieties (usually OH groups) that can react either with amines or isocynates as shown in Examples 1 and 2.
An example of the application of Chemical A to start application of a multilayer system is shown in
R can be a carbon chain where n is from 1 to 30, and R is a charged specie for cantionic/anionic chromatograpy, or an isocyanate or thioisocyante.
Another example of the application of chemical A for formation of is multilayer system is shown in
An amino-terminated monolayer as in Example 2 can react with a chemical B, an isocyanate, to create a crossed linked material that will be stable under acidic conditions. The monolayer is applied and reacted as shown in
This multilayer system can be characterized as ABCD where C=A, where A=triamine, B=diisocyanate, D=a monoisocyanate or mono epoxide with an alkyl chain of length 2-30 carbon units. This method produces a stationary phase that is highly cross-linked which can be attributed to either the di-isocyanate or triamine. Further A and B layers can similarly be applied to form AB)nCD or (AB)nC multilayer systems, where n is 2 greater.
An amino-terminated monolayer as in Example 2 can react with a chemical B, an di-epoxide, to create a crossed linked material that will be stable under acidic conditions as shown in
The resulting multilayer system can be characterized as ABCD where A=triamine, B=diepoxide, C=A; D=a mono epoxide with an alkyl chain of length 2-30 carbon units. This method produces a stationary phase that is highly cross-linked which can be attributed to either the di-epoxide or triamine.
The isocyanate-terminated monolayer as in Example 1 can react with a chemical B, an amine to create a crossed linked material that will be stable under acidic conditions as shown in
The isocyanate-terminated monlayer is reacted with, chemical B, an amine to form a cross-linked amine terminated layer, which is in turn reacted, as shown in
This multilayer system can be characterized as ABCD, where A=di-isocyanate, B=triamine, C=A, D=mono amine with an alkyl chain of length 2-30 carbon units. This method produces a stationary phase that is highly cross-linked which can be attributed to either the di-isocyanate or triamine.
This example shows, how application of layers A and B can be repeated to form a multilayer of desired thickness. A multilayer coating was applied is a silicon substrate. With reference to
A first cycle was conducted by reacting the —OH radicals with a Chemical A, a diisocyante(1,6-diisocyanatohexane). The diioscyate surface was then treated with a Chemical B, a triamine (diethylenetriamine). Both coatings were accomplished using conventional gas phase coating techniques
After the first cycle, and second cycle was conducted using essentially the same reactants and conditions as in the first cycle, using the same Chemical A and Chemical B.
Further cycles were conducted in the same way. After selected cycles thickness was measured using spectroscopic ellipsometry.
Chemical B can be the final layer if it provides the desired reactivity. But, as above, the final layer may be a Chemical D to provide the desired reactivity.
A multilayer system was made, essentially as in Example 6, except Chemical A was the triamine, and Chemical B was the diiosocycante. The cycle was repeated.
Priority is claimed from U.S. Provisional Patent Application 61/280,866, filed Nov. 10, 2009, which is hereby incorporated by reference
Number | Date | Country | |
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61280866 | Nov 2009 | US |