Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2000-11-07
2002-11-12
Le, Hoa T. (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C106S409000, C428S404000, C428S407000
Reexamination Certificate
active
06479146
ABSTRACT:
SPECIFICATION
The invention refers to a new process for preparing coated capsules and hollow shells by coating colloidal particles with alternating layers of oppositely charged nanoparticles and polyelectrolytes.
The area of thin film fabrication, in which ordered, functional supramolecular structures are the chief goal, has been greatly impacted by the recent introduction of the layer-by-layer (LbL) self-assembly technique (Decher, Science 1997, 277, 1232). The LbL method permits the fabrication of multilayer thin film assemblies on solid supports by the spontaneous sequential adsorption of oppositely charged species from dilute aqueous solutions onto charged substrates. The driving force for the multilayer film build-up is primarily due to the electrostatic attraction and complex formation between the charged species deposited. The LbL approach was initially employed to construct multilayer films of polyelectrolytes (Decher, Science 1997, 277, 1232), and subsequently extended to include proteins (Lvov et al, J. Am. Chem. Soc. 1995, 117, 6117; Onda et al, T. Biotech. Bioeng. 1996, 51, 163; Caruso et al, Langmuir 1997, 13, 3427), nucleic acids (Decher et al, J. Biosens. Bioelectron. 1994, 9, 677; Sukhorukov et al, Thin Solid Films 1996, 284/285, 220; Caruso et al, Anal. Chem. 1997, 69, 2043), dyes (Araki et al, Langmuir 1996, 12, 5393; Yoo et al, Synthetic Metals 1997, 85, 1425; Ariga et al, J. Am. Chem. Soc. 1997, 119, 2224), dendrimers (Tsukruk et al, Langmuir 1997,13, 2171), and various inorganic nanoparticles (Kleinfeld et al, Science 1994, 265, 370; Keller et al, J. Am. Chem. Soc. 1994, 116, 8817; Kotov et al, J. Am. Chem. Soc. 1997, 119, 6821; Kotov et al, J. Phys. Chem. 1995, 99, 13065; Feldheim et al, J. Am. Chem. Soc. 1996, 118, 7640; Schmitt et al, Adv. Mater 1997, 9, 61; Lvov et al, Langmuir 1997, 13, 6195) in polyelectrolyte multilayer assemblies by replacing one of the polyions by a similarly charged species.
The vast majority of studies concerning the LbL technique have employed macroscopically flat charged surfaces as substrates for multilayer film formation. For example, U.S. Pat. No. 5,716,709 describes multilayered nanostructures comprising alternating organic and inorganic ionic layers on a flat substrate, such as a silicon wafer. Recently, Keller et al reported the preparation of alternating composite multilayers of exfoliated zirconium phosphate sheets and charged redox polymers on (3-aminopropyl)-triethoxysilane-modified silica particles (Keller et al, J. Am. Chem. Soc. 1995, 117, 12879).
In more recent studies (Caruso et al, J. Phys. Chem. B. 1998, 102, 2011; Sukhorukov et al., Colloids Surf. A: Physicochem.Eng.Aspects 1998, 137, 253), the LbL approach was successfully applied to utilise submicron- and micron-sized charged colloidal particles as the adsorbing substrates to produce colloid-supported polyelectrolyte multilayer films: regular step-wise polyelectrolyte multilayer growth was observed on the colloids.
Considerable scientific effort has focussed on the fabrication of composite micro- and nanoparticles that consist of either organic or inorganic cores coated with shells of different chemical composition (Kawahashi and Matijevic, J. Colloid Interface Sci. 1991, 143, 103; Garg and Matijevic, J. Colloid Interface Sci. 1988, 126; Kawahashi and Matijevic, J. Colloid Interface Sci. 1990, 138, 534; Ohmori and Matijevic, J. Colloid Interface Sci. 1992, 150, 594; Giersig et al., Adv. Mater. 1997, 9, 570; Liz-Marzan et al., Langmuir 1996, 12, 4329; Liz-Marzan et al., J. Chem.Soc.Chem.Commun. 1996, 731; Giersig et al., Ber.Bunsenges.Phys.Chem. 1997, 101, 1617; Correa-Duarte et al., Chem.Phys.Lett. 1998, 286, 497; Bamnolker et al., J.Mater.Sci.Lett. 1997, 16, 1412; Margel and Weisel, J.Polym.Sci.Chem.Ed. 1984, 22, 145; Philipse et al., Langmuir 1994, 10, 92). These core-shell particles often exhibit properties which are significantly different to those of the templated core (e.g. different surface chemical composition, increased stability, higher surface area, as well as different magnetic and optical properties), thus making them attractive both from a scientific and technological viewpoint. Applications for such particles are diverse, ranging from capsule agents for drug delivery, catalysis, coatings, composite materials, as well as for protecting sensitive agents such as enzymes and proteins. Previous investigations have demonstrated that polymeric microparticles and inorganic cores can be coated with uniform layers of various materials, including silica, yttrium basic carbonate, zirconium hydrous oxide, either by controlled surface precipitation reactions on the core particles, or by direct surface reactions.
U.S. Pat. No. 5,705,222 discloses a process for preparing composite particle dispersions wherein a plurality of core particles is dispersed in a first solution wherein the core particles do not irreversibly self-flocculate, an amount of polymer is added to the dispersion of core particles, wherein the polymer has an affinity for the dispersed core particles and the excess polymer is removed by a solid/liquid separation process, i.e. centrifugation or decanting.
An important extension of core-shell particles is the subsequent removal of the core, resulting in hollow particles or shells. Removal of the templated core has previously been achieved by calcining the coated particles at elevated temperatures or by chemical reactions causing dissolution of the core material. Hollow, submicron sized shells of yttrium compounds have been produced (Kawahashi and Matijevic, 1991, supra) by coating cationic polystyrene latex with yttrium basic carbonate and subsequently calcining. More recently, silica shells were generated by seeded polymerization of tetraethoxysilane on the surface of polystyrene particles, followed by calcination (Bamnolker et al., 1997, supra). Using a similar method, monodisperse, hollow silica nanoparticles have been produced by silicacoating gold nanoparticles, and by chemically dissolving the cores (Giersig et al., Ber.Bunsenges.Phys.Chem., 1997, supra). Hollow particles represent a special class of materials: their lower density and optical properties make them of interest in the fields of medicine, pharmaceutics, materials science and the paint industry.
Conventional methods for the preparation of coated nanoparticles or hollow nanoshells, however, have several disadvantages, since in many cases the formation of uniform and smooth layer structures having sufficient particle coverage as well as control of thickness is very difficult to achieve.
Further, it was suggested (DE 198 12 083.4) that the use of soluble colloidal cores as templates for the sequential deposition of polyelectrolytes can be used to fabricate novel three-dimensional hollow polymer shells.
Herein we report the construction of composite multilayers of nanoparticles and an oppositely charged polyelectrolyte on submicron-sized colloidal particles via the sequential electrostatic adsorption of nanoparticles and polyelectrolyte from dilute solution. Alternating nanoparticle-polyelectrolyte multilayers with various thicknesses have been fabricated. Further, a novel and yet simple method for the fabrication of submicron-sized, hollow, inorganic or composite organic-inorganic particles via colloid templated electrostatic LBL self-assembly of nanoparticle-polymer multilayers, followed by removal of the templated core and optionally the polymer used in the assembly process is presented.
Thus, a first aspect of the present invention is a process for preparing coated particles comprising the steps:
(a) providing template particles and
(b) coating said template particles with a multilayer comprising (i) alternating layers of oppositely charged nanoparticles and polyelectrolytes and/or (ii) alternating layers of oppositely charged nanoparticles.
Preferably, the template particles have an average diameter of up to 10 &mgr;m, more preferably≦5 &mgr;m, and most preferably≦2 &mgr;m. The minimum diameter of the template particles is preferably 10 nm, more preferably 100 nm, and
Caruso Frank
Caruso Rachel Anne
Donath Edwin
Möhwald Helmuth
Sukhorukov Gleb
Fulbright & Jaworski L.L.P.
Le Hoa T.
Max-Planck-Gesellschaft zur Forderung der Wissenschaften E.V.
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