Hydrophobic Modification of Layered Clays and Compatibility for Epoxy Nanocomposites

Recent studies on the intercalation and exfoliation of layered clays with polymeric intercalating agents involving poly(oxypropylene)-amines and the particular uses for epoxy nanocomposites are reviewed. For intercalation, counter-ionic exchange reactions of clays including cationic layered silicates and anionic Al-Mg layered double hydroxide (LDH) with polymeric organic ions afforded organoclays led to spatial interlayer expansion from 12 to 92 angstrom (X-ray diffraction) as well as hydrophobic property. The inorganic clays of layered structure could be modified by the poly(oxypropylene) amine-salts as the intercalating agents with molecular weights ranging from 230 to 5,000 g/mol. Furthermore, natural montmorillonite (MMT) clay could be exfoliated into thin layer silicate platelets (ca. 1 nm thickness) in one step by using polymeric types of exfoliating agents. Different lateral dimensions of MMT, synthetic fluorinated Mica and LDH clays had been cured into epoxy nanocomposites. The hydrophobic amine-salt modification resulting in high spacing of layered or exfoliation of individual clay platelets is the most important factor for gaining significant improvements of properties. In particular, these modified clays were reported to gain significant improvements such as reduced coefficient of thermal expansion (CTE), enhanced thermal stability, and hardness. The utilization of these layered clays for initiating the epoxy self-polymerization was also reported to have a unique compatibility between clay and organic resin matrix. However, the matrix domain lacks of covalently bonded crosslink and leads to the isolation of powder material. It is generally concluded that the hydrophobic expansion of the clay inter-gallery spacing is the crucial step for enhancing the compatibility and the ultimate preparation of the advanced epoxy materials

The Pharmacogenetics Research Network: From SNP Discovery to Clinical Drug Response

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109975/1/cpt6100087.pd

Poly(N-isopropylacrylamide)-Tethered Silicate Platelets for Colloidal Dispersion of Conjugated Polymers with Thermoresponsive and Photoluminescence Properties

Poly(N-isopropylacrylamide)-tethered nanosilicate platelets (NSP-PNiPAAm) have been synthesized by covalently bonding the polymer onto the surfaces of silicate platelets of nanometer dimension, and this class of nanohybrids has proved to be effective for dispersing water-insoluble conjugated polymers (CPs). Simple pulverization of poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) with NSP-PNiPAAm rendered the powder material dispersible in water, whereupon it displayed thermoresponsive properties at 37.5 degrees C and CP particle size variation between ea, 50 and 100 nm by SEM observation. The same dispersion had a maximum UV-vis absorption at 524 mu and PL emission at 605 nm. The PL emission was significantly higher at 4 degrees C than at 45 degrees C. Being coated as a film, it showed an orange emission under an ultraviolet lamp, consistent with the PL measurement. The water-borne process of dispersing the CP in aqueous media by the presence of NSP-PNiPAAm and followed by film formation to demonstrate a unique method of manipulating hydrophobic conjugated polymers in a facile manner

Hierarchical synthesis of silver nanoparticles and wires by copolymer templates and visible light

Self-assembled silver wires in micro-meter scale were obtained from aqueous silver nitrate solution in the presence of a comb-like copolymer as the sole organic component. The requisite copolymer was easily prepared by the grafting poly(oxyethylene)-monoamine (POE-amine) onto poly(styrene-co-maleic anhydride) (SMA). Upon storage at ambient temperature with exposure to daylight, the aqueous AgNO(3)/SMA-POE solution gradually underwent a color changed from transparent pale-yellow to dark-violet over a period of hours, and after several months a solid precipitate was deposited. The formation process was monitored by ultraviolet-visible spectrometer, particle size analysis, scanning electron microscope, and transmission electron microscope. Silver wires were hierarchically formed by progressive transformation from the initial appearance of silver nanoparticles (ca. 10 nm in diameter), followed by the intermediate rectangles (0.6-1.0 mu m in width and 0.4 mu m in length) in solution and ultimately the precipitates in micro-scale of silver wires at 1.6-6.4 mu m in diameter and 100-370 mu m in length. The progressive formation of the precipitated silver wires was accelerated by the exposure of visible light as a photo-reducing energy source. The micron-scale wires have a silver content over 97.4 wt.% and a sheet resistance of 5.5 x 10(1) Omega/square. (C) 2010 Elsevier Inc. All rights reserved