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We report an investigation of the influence of block copolymer architectures on formation of nanophases in epoxy thermosets via reaction-induced microphase separation approach. Toward this end, three binary block copolymers composed of polystyrene (PS) and poly(ε-caprolactone) (PCL) were synthesized via the combination of ring-opening polymerization (ROP) and atomic transfer radical polymerization (ATRP). These block copolymers possess PS-b-PCL diblock, PS-b-PCL-b-PS triblock, and PCL-b-PS-b-PCL triblock architectures; they were carefully controlled to have the identical composition and overall molecular weights. It was found that the block copolymers with different architectures in epoxy thermosets displayed quite different reaction-induced microphase separation behavior as evidenced with the results of atomic force microscopy (AFM), small-angle X-ray scattering (SAXS), and dynamic mechanical thermal analysis (DMTA). The morphological transition from spherical to cylindrical to lamellar nanophases occurred with increasing the content of the block copolymer in the thermosets containing PS-b-PCL diblock copolymer. In the thermosets containing PS-b-PCL-b-PS triblock copolymer, unilamellar and multilamellar nanophases were formed depending on the content of the triblock copolymer. In contrast, the macroscopic phase separation occurred in the thermosets containing PCL-b-PS-b-PCL triblock copolymer. The behavior of nanophases in these thermosetting blends have been accounted for the demixing behavior of the miscible blocks (viz. PCL) during the reaction-induced microphase separation and the influence of copolymer architectures on the morphologies of PS microdomains.

Pore interconnectivity of nanoclustering silica porous films as studied by positronium time-of-flight spectroscopy J. Appl. Phys. 98, 094307 (2005); 10.1063/1.2125121 Interfacial analysis using time-of-flight medium energy backscattering

This paper discusses the architecture and provides performance studies of a silicon photonic chip-scale optical switch for scalable interconnect network in high performance computing systems. The proposed switch exploits optical wavelength parallelism and wavelength routing characteristics of an Arrayed Waveguide Grating Router (AWGR) to allow contention resolution in the wavelength domain. Simulation results from a cycle-accurate network simulator indicate that, even with only two transmitter/receiver pairs per node, the switch exhibits lower end-to-end latency and higher throughput at high (>90%) input loads compared with electronic switches. On the device integration level, we propose to integrate all the components (ring modulators, photodetectors and AWGR) on a CMOS-compatible silicon photonic platform to ensure a compact, energy efficient and cost-effective device. We successfully demonstrate proof-of-concept routing functions on an 8 × 8 prototype fabricated using foundry services provided by OpSIS-IME.

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In this work, the synthesis of 3-methacryloxypropylheptaphenyl POSS, a new POSS macromer (denoted MA-POSS) is reported. The POSS macromer is used to synthesize PEO-b -P(MA-POSS)-b -PNIPAAm triblock copolymers via sequential atom transfer radical polymerization (ATRP). The organic-inorganic, amphiphilic and thermoresponsive ABC triblock copolymers are characterized by means of nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC). Differential scanning calorimetry (DSC) and atomic force microscopy (AFM) show that the hybrid ABC triblock copolymers are microphase-separated in bulk. Cloud point measurements show that the effect of the hydrophiphilic block (i.e., PEO) on the LCSTs is more pronounced than the hydrophobic block (i.e, P(MA-POSS)). Both transmission electron microscopy (TEM) and dynamic light scattering (DLS) show that all the triblock copolymers can be self-organized into micellar aggregates in aqueous solutions. The sizes of the micellar aggregates can be modulated by changing the temperature. The temperature-tunable self-assembly behavior is interpreted using a combination of the highly hydrophobicity of P(MA-POSS), the water-solubility of PEO and the thermoresponsive property of PNIPAAm in the triblock copolymers.

Fabrication of micropatterned mesoporous silica film on a flexible polymer substrate through pattern transfer and subsequent photocalcination