Yen-Chi Hsu

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. 10nm in diameter), followed by the intermediate rectangles (0.6-1.0μm in width and 0.4μm in length) in solution and ultimately the precipitates in micro-scale of silver wires at 1.6-6.4μm in diameter and 100-370μm 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 97.4wt.% and a sheet resistance of 5.5×10(1)Ω/square.

Temperature and pH-responsive properties of poly(styrene-co-maleic anhydride)-grafting poly(oxypropylene)-amines.

A series of temperature- and pH-responsive copolymers were prepared by grafting poly(oxypropylene)-diamines (POP-amine) onto poly(styrene-co-maleic anhydride) (SMA) copolymers. Owing to the presence of poly(oxypropylene)-segments in the pendants and their expressive hydrogen bonding properties, the copolymers exhibited lower critical solution temperature (LCST) behavior in water with a range of 11-49 degrees C depending on the POP-segmental weight and the SMA backbone structure. Furthermore, the co-existence of -NH(2) termini in the pendants and amidoacids in the linking sites in the structures rendered the copolymers also responsive to environmental pH changes. Structural variations in the SMA backbones, particularly the ratio of styrene/maleic anhydride monomers, POP lengths, and amine functionalities largely influenced the copolymer aggregation in the medium with different pH or thermal conditions. The responsiveness was correlated to the surface morphologies observed by tapping/phase mode atomic force microscopy (TM-AFM) on Mica film surface and also fluorescent properties in aqueous solution.