Dabin Park

Characterization of the interaction energies for polystyrene blends with various methacrylate polymers

The binary interaction energies between styrene and various methacrylates were determined from newly examined phase boundaries with lattice–fluid theory. Because the blends of polystyrene (PS) and poly(cyclohexylmethacrylate) (PCHMA) were only miscible at high molecular weights when the blends were prepared by solution casting from tetrahydrofuran, we examined the miscibility of other blends by changing the molecular weights of PS or methacrylate polymers. On the basis of the phase-separation temperature caused by the lower critical solution temperature, the miscibility of PS with the various methacrylates appeared to be in the order PCHMA > poly(n-propyl-methacrylate) (PnPMA) > poly(ethyl methacrylate) (PEMA) > poly(n-butyl-methacrylate) (PnBMA) > poly(iso-butyl-methacrylate) > poly(methyl methacrylate) (PMMA) > poly(tert-butyl methacrylate), and the branching of butylmethacrylate appeared to decrease the miscibility with PS. The interaction energies between PS with various methacrylates obtained from phase boundaries with lattice–fluid theory reached minimum value corresponding to the styrene/n-propylmethacrylate interaction. They were in the order PnPMA < PEMA < PCHMA < PnBMA < PMMA. The difference in the order of miscibility and interaction energies might be attributed to the terms related to the compressibility. The phase-separation temperatures calculated with the interaction energies obtained here indicated that the PS/PEMA and PS/PnPMA blends at high molecular weights were miscible, whereas the PS/PnBMA blends were immiscible at high molecular weights.

Solution-processable flexible thermoelectric composite films based on conductive polymer/SnSe0.8S0.2 nanosheets/carbon nanotubes for wearable electronic applications

Flexible thermoelectric composite films consisting of conductive polyaniline (PANI)-coated SnSe0.8S0.2 nanosheets (NSs) and polyvinylidene fluoride (PVDF) are fabricated via a solution processing procedure. The SnSe0.8S0.2 NSs are chemically exfoliated from a bulk ingot, and camphorsulfonic acid-doped PANI (CSA-PANI) is coated on the surface of the SnSe0.8S0.2 NSs. The thermoelectric properties of the composite film can be further enhanced by introducing a small amount of carbon nanotubes (CNTs) into the composite. The maximum thermoelectric power factor of the CSA-PANI-coated SnSe0.8S0.2 NS/PVDF/CNT composite film is 297 μW m−1 K−2 at 400 K, which is significantly higher than that of the CSA-PANI-coated SnSe0.8S0.2 NS/PVDF composite film without CNTs. The incorporation of SnSe0.8S0.2 NSs and conductive PANI mixed with CNTs is a promising strategy to realize high-performance flexible thermoelectric applications.

A p-type multi-wall carbon nanotube/Te nanorod composite with enhanced thermoelectric performance

In this study, multi-walled carbon nanotube (MWCNT)/tellurium (Te) nanorod composites with various MWCNT contents are prepared and their thermoelectric properties are investigated. The composite samples are prepared by mixing Te nanorods with surface-treated MWCNTs. Te nanorods are synthesized by solution phase mixing using polyvinylpyrrolidone (PVP). The MWCNTs used in this study are surface-treated with a solution consisting of H2SO4 and HNO3. With increasing MWCNT content, the composite samples exhibit a reduction in the Seebeck coefficient and enhanced electrical conductivity. The maximum power factor of 5.53 μW m K−2 is observed at 2% MWCNT at room temperature. The thermal conductivity of the composite reduced after the introduction of MWCNTs into the Te nanorod matrix; this is attributed to the generation of heterostructured interfaces between MWCNTs and the Te nanorods. At room temperature, the composites containing 2% MWCNTs exhibited the maximum thermoelectric figure of merit (ZT), which is ∼3.91 times larger than that of pure Te nanorods.

Fabrication of Polyaniline-Coated SnSeS Nanosheet/Polyvinylidene Difluoride Composites by a Solution-Based Process and Optimization for Flexible Thermoelectrics

The fabrication of dodecylbenzenesulfonic acid-doped polyaniline (PANI)-coated SnSe0.8S0.2 (PANI-SnSeS) nanosheets and their application to flexible thermoelectric composite films are demonstrated. The thermoelectric power factor of PANI-SnSeS nanosheets was optimized by manipulating the number of PANI coating cycles, and changes in their electrical conductivity and Seebeck coefficients were investigated and analyzed by considering carrier transport properties. An optimized, solution-based procedure for introducing inorganic nanoparticles comprising PANI-SnSeS nanosheets into a polyvinylidene fluoride (PVDF) matrix maximized the power factor. A composite film with a PANI-SnSeS nanosheet-to-PVDF weight ratio of 2:1 showed outstanding durability and thermoelectric performance, exhibiting a maximum power factor of ∼134 μW/m·K2 at 400 K. These results demonstrate that the incorporation of conductive PANI into SnSeS nanosheets can facilitate high-performance flexible thermoelectric applications.

Hydrothermal transformation of SnSe crystal to Se nanorods in oxalic acid solution and the outstanding thermoelectric power factor of Se/SnSe composite

The present work demonstrates the synthesis of one-dimensional (1D) Se nanorods with ~50u2009nm diameter by hydrothermal transformation of SnSe crystals in oxalic acid solution and suggests the reaction mechanism for this chemical transformation. SnSe particles react with oxalic acid to generate numerous Se nuclei, which crystallize into Se nanorods due to the intrinsic character of the 1D growth of Se. The resulting Se/SnSe composite exhibits outstanding thermoelectric power factor without the aid of any rare dopants, which is higher than both undoped polycrystalline SnSe and SnSe doped with Pb and Cu.