• Macromolecular Research
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• v.14 no.6
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• pp.596-602
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• 2006

The effect of high-temperature spinning and poly(vinyl pyrrolidone) (PVP) additive on poly(vinylidene fluoride) (PVDF) hollow fiber membranes was investigated using differential scanning calorimetry, X-ray diffraction measurement, and scanning electron microscopy, together with the corresponding microfiltration performances such as water flux, rejection rate, and elongational strength. Using high-temperature spinning, porous hollow fiber membranes with particulate morphology were prepared through PVDF crystallization. The particulate structure of the membranes was further modified by the addition of miscible PVP with PVDF. Due to these effects, the rejection rate and strength of the fibers were increased at the expense of reduced water flux and mean pore size, which indicates that high-temperature spinning and PVP addition are vary effective to control the morphology of PVDF hollow fiber membranes for microfiltration.

• Korean Journal of Materials Research
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• v.18 no.9
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• pp.507-510
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• 2008

Electrical properties of multi-channel metal-induced unilaterally precrystallized polycrystalline silicon thin-film transistor (MIUP poly-Si TFT) devices and circuits were investigated. Although their structure was integrated into small area, reducing annealing process time for fuller crystallization than that of conventional crystal filtered MIUP poly-Si TFTs, the multi-channel MIUP poly-Si TFTs showed the effect of crystal filtering. The multi-channel MIUP poly-Si TFTs showed a higher carrier mobility of more than 1.5 times that of the conventional MIUP poly-Si TFTs. Moreover, PMOS inverters consisting of the multi-channel MIUP poly-Si TFTs showed high dynamic performance compared with inverters consisting of the conventional MIUP poly-Si TFTs.

• Polymer(Korea)
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• v.36 no.6
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• pp.745-755
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• 2012

Two types of polymers were tested in this study; poly(ethylene terephthalate) (PET) as a synthetic example and poly(lactic acid) (PLA) as a natural polymer. DSC analyses showed that the use of nanofiller increased the degree of crystallinity ($X_c$) of both PET and PLA polymers, but the effect was more noticeable on PET nanocomposites. The crystallization of PLA and PET nanocomposites occurred at higher temperatures in comparison to neat polymers. According to dynamic mechanical-thermal analysis (DMTA), the damping factor of PET/$TiO_2$ nanoparticles decreased compared to the neat matrix, but for PLA nanocomposites the opposite trend was observed. Results of the mechanical test showed that for both PET and PLA nanocomposites, the most successful toughening effect was observed at 3 wt% loading of $TiO_2$ nanoparticles. SEM micrographs revealed uniform distribution of $TiO_2$ nanoparticles at 1 and 3 wt% loading levels. The results of WAXD spectra explained that the polymorphs of PLA and PET was not affected by $TiO_2$ nanoparticles. UV-visible spectra showed that $TiO_2$ nanocomposite films had high ultraviolet shielding compared to neat polymer, but there was significant reduction in transparency.

• Applied Chemistry for Engineering
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• v.10 no.8
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• pp.1216-1220
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• 1999

Different amounts of zinc stearate were incorporated as a plasticizer into poly(styrene-co-sodium methacrylate) ionomers prepared by bulk-suspension plymerization and neutralization with sodium hydroxide and effects of the zinc stearate on the thermal and rheological properties were investigated. It was obseved that the crystallization of zinc stearate in the ionomers were partially suppressed depending on the content of ionic moieties. It is postulated that the ionic moieties dissolved zinc stearate and suppressed crystallization of the zinc stearates. We speculated that 0.4~0.6 mole of zinc stearate was dissolved by one mole of the ionic moiety. Poly(styrene-co-sodium methacrylate) containing only the dissolved zinc stearates showed typical rheological properties of homogeneous systems in Cox-Mertz plots. However, poly(styrene-co-sodium methacrylate) containing crystallizable zinc stearates as well as dissolved ones showed typical rheological properties of heterogeneous systems.

• Polymer(Korea)
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• v.38 no.5
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• pp.602-612
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• 2014

Polyurethanes containing poly(dimethyl siloxane) (PDMS) unit, PU-Si, were synthesized and their thermal and shape memory properties were investigated. Various amounts of PDMS units were incorporated via a solution polymerization method using mixed diols of poly(tetramethylene ether glycol) (PTMEG) and PDMS-diol as the soft segment (SS) and methylene diphenyl diisocyanate and 1,4-butanediol as the hard segment (HS). Two series of PU-Si samples with an HS content of 23% or 32% were prepared and analyzed. For PU-Si with an HS content of 23%, both the cold crystallization temperature ($T_{cc}$) and melt crystallization temperature of the SS domain moved higher temperature with increasing PDMS content, while the melting temperature ($T_m$) of the SS domain remained unaffected. The increase in HS content from 23% to 32% resulted in the increased $T_m$ and disappearance of $T_{cc}$. The shape recovery of PU-Si flim with an HS content of 32% increased while its shape retention decreased as PDMS content increased.

• Polymer(Korea)
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• v.38 no.3
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• pp.307-313
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• 2014

The physical properties of functionalized graphene sheet (FGS)/poly(ethylene-co-vinyl acetate) (EVA) was examined with various kinds of EVA, having vinyl acetate (VA) contents in the range of 0 to 40 wt%. The compatibility between FGS and EVA was enhanced as the polar VA content of EVA increased. Thus, the dispersion of FGS in EVA became finer, and the decrease of surface resistivity and the increase of tensile modulus by the added FGS became more effective when the VA content of EVA was high. When the VA content was low, the elongation at break was reduced drastically by added FGS due to the poor adhesion of FGS/EVA interface. The crystallization of EVA was generally retarded by the interaction with dispersed FGS. However, when both the VA content of EVA and the added amount of FGS were low, the crystallization of EVA was enhanced, probably due to the predominant nucleating effect by FGS.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.2
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• pp.269-277
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• 1998

The crystallization method determines the material quality and consequent device performance. This paper investigates the crystallization of a-Si:H films on various substrate materials and analyzes the crystallization effect with and without using eutectic forming metals. From the examinations of the various substrate materials, a metal Mo was selected for the a-Si:H films growth and subsequent crystallization of it. For a sample without any eutectic metal layer, we observed grain size of $0.8{\mu}m$ after $1100^{\circ}C$ anneal treatment. To reduce crystallization temperature, we used some of the eutectic forming metals such as Au, Al and Ag. Poly-Si films with grain size over $10{\mu}m$ and (111) preferential plains were achieved using a premetal layer of Au at an anneal temperature of $700^{\circ}C$. The various crystallization effects of eutectic metal thickness and type were investigated for photovoltaic (PV) device applications.

• Polymer(Korea)
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• v.24 no.5
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• pp.656-663
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• 2000

The Effects of thermal history during the melt spinning process on the mechanical properties and crystallinity of polylactic acid (PLLA) fibers have been studied. Thermal history applied on PLLA during the melt process caused the decrease of number-average molecular weights and this resulted in the lowering of orientation and crystallinity in PLLA fibers. As a result, the longer applied thermal history, the less tensile strength and modulus, and the higher elongation at break. It was also found that primary factor for controlling crystallinity of PLLA fiber was the stress induced crystallization while the thermal induced crystallization had a little effect on the crystallinity of PLLA fibers. However, the thermal induced crystallization turn out to be important in the crystallinity developed by annealing of PLLA fibers.

• Proceedings of the Korean Fiber Society Conference
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• 1999.10a
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• pp.385-390
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• 1999

• Proceedings of the Materials Research Society of Korea Conference
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• 1996.11a
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• pp.114-114
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• 1996