Chih-Yuan Hsu

Preparation and thermal properties of epoxy-silica nanocomposites from nanoscale colloidal silica

Epoxy-silica nanocomposites were obtained from directly blending diglycidylether of bisphenol-A and nanoscale colloidal silica and then curing with 4,4-diaminodiphenylmethane. The epoxy-silica nanocompoites showed good transparency and miscibility observed with AFM, SEM, and TEM. The thermal stability of the epoxy resins was improved with the incorporation of the colloidal silica. However, a depression on the glass transition temperature of the resins was observed, owing to the plasticizing effect of the colloidal silica. Moreover, the nanoscale colloidal silica did not show effectively synergistic effect on char formation and flame retardance with phosphorus.

A novel approach of chemical functionalization on nano-scaled silica particles

Chemical functionalization on nano-scaled silica particles was performed through the reaction between the silanol group of silica and the oxirane ring of epoxy compounds. The occurrence of the surface functionalization and the chemical structures of the resulting products were characterized with FTIR and 1H NMR. Energy dispersive x-ray spectrometry and transmission electronic micrography observation on the silica particles also confirmed the surface functionalization. This approach provides another method to organically functionalize nano-scaled silica particles and can be applied to the preparation of organic–inorganic nanocomposites.

Rhodamine B-anchored silica nanoparticles displaying white-light photoluminescence and their uses in preparations of photoluminescent polymeric films and nanofibers.

This work reports white-light photoluminescent (PL) silica nanoparticles and their applications of preparation of PL polymer films and nanofibers. Rhodamine B (RhB) physically adsorbs or chemically bonds to silica nanoparticle (SNP) surfaces, resulting in PL SNPs. The RhB-modified SNPs exhibit white-light PL emissions under an excitation at 365nm, which is different from the inherent yellow light emission of RhB. The SNPs with physically-adsorbed RhB show stimuli-responsive properties. In solutions, the RhB molecules which physically adsorb to SNPs release from SNPs, consequently turning the PL emission from white-light to yellow. On the other hand, the SNPs having covalently-bonded-RhB molecules are effective additives for preparation of white-light PL polymer composites. Both PL poly(methylmethacrylate) (PMMA) films (from casting process) and nanofibers (from electrospinning process) showing white-light PL emission have been prepared.

Direct white light photoluminescent nanoparticles with one fluorophore.

Aggregation of Rhodamine B (RhB) fluorophore in confined nanoscale domains changes the photoluminescence behavior of RhB in core-shell silica/PGMA-RhB nanoparticles. Under an excitation at 365 nm, silica/PGMA-RhB nanoparticles exhibit a two-band emission of yellow and blue in a tetrahydrofuran (THF) solution, compared to the yellow emission of RhB in a THF solution. The yellow and blue emissions of silica/PGMA-RhB nanoparticles are of approximately equal intensity, and mix together to show white light emission from the core-shell nanoparticles. Removal of the silica core from the core-shell nanoparticles does not alter its photoluminescence behavior. Therefore, the white light emission of RhB in the nanoparticles originates from the aggregation of RhB molecules in a nanoscale domain. This finding provides a new and convenient approach to the preparation of white light photoluminescent materials.

Multi-functional branched polysiloxanes polymers for high refractive index and flame retardant LED encapsulants

Polymers with integrated functions might have greater possibility to meet the various requirements for a specific application. This work demonstrates a molecule-design based development of multi-functional polymers with a branched polysiloxane polymer which exhibits integrated functions including good thermal stability, high thermal resistance, high flame retardancy and self-extinguishing properties, high transparency in the ultraviolet to blue light region, and relatively high RI value (1.59). This multi-functional polymer is potentially applicable in high performance LED encapsulants.

Enhancement of light emission in GaAs epilayers with graphene quantum dots

A green and one-step synthesis of graphene quantum dots (GQDs) has been implemented using pulsed laser ablation from aqueous graphene. The synthesized GQDs are able to enhance the photoluminescence (PL) of GaAs epilayers after depositing them on the GaAs surface. An enhancement of PL intensity of a factor of 2.8 has been reached at a GQD concentration of 1.12 mg ml−1. On the basis of the PL dynamics, the PL enhancement in GaAs is interpreted by the carrier transfer from GQDs to GaAs due to the work function difference between them.

Photoluminescent toroids formed by temperature-driven self-assembly of rhodamine B end-capped poly(N-isopropylacrylamide).

In this paper, self-assembled polymeric toroids formed by a temperature-driven process are reported. Rhodamine B (RhB) end-capped poly(N-isopropylacrylamide) (PNIPAAm) demonstrating a lower critical solution temperature (LCST) is prepared. In a two-phase system, the polymer in the aqueous phase could move to the chloroform phase on raising the temperature above its LCST. This temperature-driven process results in the formation of polymeric toroids in the chloroform phase, and the strategy affords a new pathway to toroidal self-assembly of polymers. Moreover, the photoluminescent behavior of the RhB end-capped PNIPAAm species formed by the process is also studied and discussed.