Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state
Reexamination Certificate
1999-11-24
2001-07-24
Utech, Benjamin L. (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
C117S068000, C117S070000
Reexamination Certificate
active
06264741
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for producing a nanocomposite self-assembly and the structured materials thereby produced and, more particularly, to an evaporation-induced self-assembly method for producing nanocomposite structures and the materials thereby produced.
The exceptional strength, hardness, and toughness of biological nanocomposite systems, composed of seemingly mundane materials, has fueled considerable attention from scientists of many disciplines. Natural nanocomposites, such as shell, are formed by biomineralization, a templated, self-assembly process in which pre-organized organic surfaces regulate the nucleation, growth, morphology and orientation of inorganic crystals. Efficient synthesis and processing of layered organic/inorganic nanocomposites that mimic bone and shell structures has been a goal of the materials chemist. The most highly studied material is that of abalone shell nacre which has an oriented coating composed of alternating layers of aragonite (CaCO
3
) and biopolymer (~1 vol %). The organism fabricates the layers with precise microstructure to minimize pores and other defects. As a result, the bioceramic has esthetic qualities, smooth surface finishes and is 2-times harder and 1000-times tougher than its constituent phases.
In an attempt to mimic these examples from nature, a synthetic process termed “biomimetics” has gained momentum within the scientific community. Such approaches include crystallization beneath Langmuir monolayers, crystallization on self-assembled monolayers, supramolecular self-assembly (SSA), and sequential deposition (SD). Of these only SSA and SD offer the ability to introduce the periodic microstructural and compositional changes necessary for layered nanocomposite formation. Processes utilizing SSA have provided lamellar films but these structures collapse upon surfactant removal (Ogawa, M., J. Am. Chem. Soc., 1994, 116, 7941-7942). Stable inorganic/organic nanocomposites have been prepared with SD (see, Keinfeld, E. and Ferguson, G., Science, 1994, 265, 370-373) but this process has some experimental disadvantages as it requires many repeated deposition steps to build-up a practical coating thickness.
In forming structured materials, methods have been attempted which rely on evaporation-induced self-assembly by evaporating a component of the reaction system. For example, Bruinsma et al. (U.S. Pat. No. 5,922,299, issued on Jul. 13, 1999) describes an evaporative method of making films, fibers, and powders using an alkoxide silica precursor in a few minutes or less. Bruinsma et al. evaporate an aqueous solvent to form a structured mesoporous material but it is intentionally not a dense, non-porous film. Roth (U.S. Pat. No. 5,925,330, issued on Jul. 20, 1999) describes a method of producing a structured molecular sieve material by removing a templating surfactant, again a porous material. Brinker et al. (U.S. Pat. No. 5,858,457 issued on Jan. 12, 1999; incorporated herein by reference) describe a method for preparing mesostructured films by a solvent evaporation method using only a metal oxide, aqueous solvent and surfactant with an acidic or basic catalyst where controlled mesophase structures are prepared. Lu et al. (Lu, Y., Fan, H., Stump, A., Ward, T., Rieker, T. and Brinker, C., Nature, 1999, 398, 223-226; incorporated herein by reference) show that porous, mesostructured spherical nanoparticles can be formed within several seconds by an evaporation-induced interfacial self-assembly method.
Useful would be an efficient and simple method wherein organized inorganic/organic nanocomposite materials with little porosity can be formed within a few minutes or less. Such nanocomposite materials would have organized, polymerized phases which would lead to enhanced structural stability. Sellinger et al. (Sellinger, A., Weiss, P., Nguyen, A., Lu, Y., Assink, R., Gong, W., and Brinker, C., Nature, 1998, 394, 256-260; incorporated herein by reference) describe a method of producing such nanocomposite materials by an efficient evaporation-induced, self assembly process that results in simultaneous organization of both organic and inorganic phases to form many layers of the nanocomposite material.
SUMMARY OF THE INVENTION
According to the present invention, a method of making a nanocomposite self-assembly is provided where at least one hydrophilic compound, at least one hydrophobic compound, and at least one amphiphilic surfactant are mixed in a solvent consisting essentially of a polar organic compound and water, and where the amphiphilic surfactant has an initial concentration below the critical micelle concentration, to form a homogeneous solution. A portion of the solvent is evaporated to organize the hydrophilic compound and the hydrophobic compounds to form a self-assembled liquid crystalline mesophase material which can then be polymerized to form a nanostructure self-assembly assembly. A coupling agent can be added to enhance coupling between the hydrophilic and hydrophobic compounds. An initiator can be added to facilitate the polymerization step. Various polymerization methods can be utilized, including the use of ultra-violet radiation, thermal treatment, catalytic treatment, and aging. The polymerized material can be washed to remove surfactant and any residual unpolymerizated material.
In one embodiment, a method of making a nanocomposite self-assembly is provided comprising mixing a silica sol with a coupling agent, a surfactant, a monomer and an initiator in an aqueous, polar organic solvent with an initial surfactant concentration below the critical micelle concentration, evaporating the polar organic solvent and water to induce micelle formation and subsequent nanocomposite self assembly; and means for inducing polymerization to form the nanocomposite self assembly.
REFERENCES:
patent: 5538710 (1996-07-01), Guo et al.
patent: 5607686 (1997-03-01), Totakura et al.
patent: 5858457 (1999-01-01), Brinker et al.
patent: 5922299 (1999-07-01), Bruinsma et al.
patent: 5925330 (1999-07-01), Roth
Merriam Webster Collegiate Dictionary, 10th ed. (Springfield MA: Merriam-Webster), 1997.*
Lu, Y., Fan, H., Stump, A., Ward, T., Rieker, T., and Brinker, C., “Aerosol-assisted self-assembly of mesostructured spherical nanoparticles,” Nature, 1999, 398, 223-226.
Sellinger, A., Weiss, P., Nguyen, A., Lu, Y., Assink, R., Gong, W., and Brinker, C., “Continuous self-assembly of organic-inorganic nanocomposite coatings that mimic nacre,” Nature, 1998, 394,256-260.
Ogawa, M., “Formation of novel oriented transparent films of layered silica-surfactant nanocomposites”, J. Am. Chem. Soc., 1994, 116, 7941-7942.
Kleinfeld, E., and Ferguson, G., “Stepwise formation of multilayered nanostructural films from macromolecular precursors”, Science, 1994, 265, 370-373.
Brinker C. Jeffrey
Lu Yunfeng
Sellinger Alan
Chen Kin-Chan
Klavetter Elmer A.
Sandia Corporation
Utech Benjamin L.
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