• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.6
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• pp.434-440
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• 2013

With polymer properties and ceramic volume fraction as design variables, the optimal structure of 1-3 piezocomposites has been determined to maximize the thickness mode electromechanical coupling factor. When the piezocomposite vibrates in a thickness mode, inter-pillar resonant modes are likely to occur between lattice-structured piezoceramic pillars and polymer matrix, which significantly deteriorates the performance of the piezocomposite. In this work, a new method to design the structure of the 1-3 type piezocomposite is proposed to maximize the thickness mode electromechanical coupling factor while preventing the occurrence of the inter-pillar modes. Genetic algorithm was used for the optimal design, and the finite element analysis method was used for the analysis of the inter-pillar mode.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.11-12
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• 2006

Incorporation of chromophores into multi-chromophore-containing dendrimers is shown to lead to a significant enhancement in electro-optic activity. These results are reasonably well simulated by pseudo-atomistic Monte Carlo calculations that permit dendrimers to interpenetrate (entangle). Calculations also lead to the correct prediction of material densities. An even greater enhancement in electro-optic activity is observed when such dendrimer materials are doped with a second chromophore. This latter effect may reflect an Ising-lattice-type phenomenon where one chromophore impacts the ordering of the other and vice versa.

• Macromolecular Research
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• v.10 no.2
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• pp.91-96
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• 2002

To explore the effects of intramolecular interactions within the copolymer on the phase separation behavior of polymer blends, copolymers having two different types of intramolecular interactions, i.e., intramolecular repulsion and intramolecular attraction were prepared . In this study, poly(styrene-co-methylmethacrylate) (P(S-MMA)) having intramolecular repulsion caused by positive interaction between styrene and MMA and poly(styrene-co-ethyl-methacrylate) (P(S-EMA)) and poly(styrene-co-cyclohexylmethacrylate) (P(S-CHMA)) having intramolecular attraction caused by negative interaction between styrene and methacrylate were blended with tetramethyl poly-carbonate (TMPC). The phase behavior of blends was examined as a function of copolymer composition and blend composition. TMPC formed miscible blends with styrenic copolymers containing less than certain amount of methacrylate. The phase separation temperature of TMPC blends with copolymer such as P(S-MMA) and P(S-EMA), first increases with methacrylate content, goes through a maximum and then decreases just prior to the limiting content of methacrylate for miscibility, while that of TMPC blends with P(S-CHMA) always decreases. The calculated interaction energy for TMPC-P(S-EMA) pair is negative and monotonically increases with EMA content of the copolymer. Such behavior contradicted the general notion that systems with more favorable energetic interactions have higher LCST, The detailed inspection of the lattice-fluid theory related to the phase behavior was performed to explain such behavior.

• Korean Journal of Materials Research
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• v.10 no.12
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• pp.831-837
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• 2000

To improve the catalytic activity of platinum on polymer electrolyte fuel cell(PEFC), platinum was alloyed with cobalt and nickel at various temperature. By XRD, it was observed the crystal structure of alloy catalysts were the ordered face centered cubic(f.c.c) due to the superlattice line at $33^{\circ}$. As heat-treatment temperature was increased, the particle size of alloys also were increased and the crystalline lattice parameters were decreased. According to the results from mass activity, specific activity and Tafel slope measured by cell performance test and cyclic voltammogram, the catalyst activities of alloys are higher than that pure platinum.

• Macromolecular Research
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• v.11 no.5
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• pp.303-310
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• 2003

The phase behavior of binary blends of dimethylpolycarbonate-tetramethyl polycarbonate (DMPCTMPC) copolycarbonates and styrene-acrylonitrile (SAN) copolymers has been examined and then compared with that of DMPC/TMPC/SAN ternary blends having the same chemical components and compositions except that the DMPC and TMPC were present in the form of homopolymers. Both binary and ternary blends were miscible at certain blends compositions, and the miscible blends showed the LCST-type phase behavior or did not phase separated until thermal degradation temperature. The miscible region of binary blends is wider than that of the corresponding ternary blends. Furthermore, the phase-separation temperatures of miscible binary blends are higher than those of miscible ternary blends at the same chemical compositions. To explain the destabilization of polymer mixture with the increase of the number of component, interaction energies of binary pairs involved in these blends were calculated from the phase separation temperatures using lattice-fluid theory and then the phase stability conditions for the polymer mixture was analyzed with volume fluctuation thermodynamics.

• Elastomers and Composites
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• v.35 no.1
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• pp.29-37
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• 2000

In this study as a basic research of the elastomer, we show the results of the behavior of the two different chain length polymers in the melt confined between two impenetrable planes. The cubic lattice simulations are conducted in the canonical ensemble with a method that is a combination of reptation and crackshaft bond flip motions. A total of 680 chains which are 544 short chains comprising 10 beads and 136 long chains comprising 160 beads were placed in 20 lattice layers. It was assumed that there is no energetic interactions between covalently connected beads. while all other neighbors will interact with a truncated 6-12 Lennard-Jones potential. From the analysis of the simulation results, it was shown that purely entropic effects caused the shorter chains to partition preferentially to the surface. We also showed that the center of mass density of the shorter chains shows maximum near the surface. This is the opposite phenomena when compared to that of the longer chains. However, the segments of the shorter and the longer chains did not display any significant changes in bond order.

• Elastomers and Composites
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• v.43 no.4
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• pp.259-263
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• 2008

An effect of low-temperature long-term thermal degradation on a degree of crystallinity of a low density polyethylene (LDPE) was investigated by using $^1H$ solid state nuclear magnetic resonance (SSNMR). Firstly, the long-term thermal treatment makes a color of LDPE from white to pale yellow which is indicative of thermal oxidation. Secondly, it makes the $^{1}H$ NMR spin-spin and spin-lattice relaxation times ($T_1$) to be long. Lastly, the degree of crystallinity of the semicrystalline aged-LDPE also decreases with thermal treatment. Above all, the $T_1$ increase is envisaged to be due to either a decrease of the amorphous regions governing overall spin-lattice relaxation mechanism in LDPEs or a dynamically restricted motion of specific molecular motions by intermolecular hydrogen bonding or crosslinking. However, since the decrease of crystallinity implies an increase of amorphous regions by the thermal treatment, the former case is contrast to our results. Accordingly, we concluded that the latter effect is responsible for the $T_1$ increase.

• Macromolecular Research
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• v.9 no.4
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• pp.210-219
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• 2001

Quenched and slow cooled as well as isothermally crystallized poly(tetramethylene succinate)(PTMS) films at two different temperatures were prepared. In the process of hydrolysis of the four specimens, structural changes such as the crystallinity, crystal size distribution, lattice parameter, lamellar thickness, long period and surface morphology were investigated by using wide and small angle X-ray scattering (WAXS and SAXS), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The hydrolytic degradation of quenched film was faster than that of slow cooled and isothermally crystallized films. The film crystallized at 100$\^{C}$ exhibited extensive micro voids and thus showed faster degradation than that crystallized at 75$\^{C}$, demonstrating surface morphology is another important factor to govern degradation rate. The crystallinity of the specimen increased by 5-10% and long period decreased after hydrolysis for 20 days. At the initial stage of degradation, the lamellar thickness of quenched film rather increased, while that of slow cooled and isothermally crystallized films decreased. The hydrolytic degradation preferentially occurred in the amorphous region. The hydrolytic degradation in crystal lamellae are mainly at the crystal surfaces.

• Polymer(Korea)
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• v.32 no.2
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• pp.150-156
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• 2008

Two different polyacrylonitrile samples (PANs, triad tacticity fraction is 0.25 and 0.64) were synthesized and used to study the kinetics of cyclization. Polymers were treated at different temperatures between 250 to $300^{\circ}C$ under air atmosphere, and analyzed by X-ray diffractometer. The sharp and strong peak at $2{\theta}=16.5^{\circ}$ corresponds to a lateral repeat distance that is the (100) diffraction in hexagonal lattice, while the peak at $2{\theta}=25.5^{\circ}$ reflects the (101) diffraction. In comparing their areas of different heat treated samples, the cyclization of both PANs was identified as a first-order reaction. The rate constants of cyclization reaction at different temperatures and the active energy parameter were obtained. This results might provide an important effect on pre-oxidation of polyacrylonitrile fiber.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.11
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• pp.790-800
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• 2013

The optimal structure of 1-3 piezocomposites has been determined by controlling polymer properties, ceramic volume fraction, thickness of composite and aspect ratio of the composite to maximize the TVR (transmitting voltage response), RVS (receiving voltage sensitivity) and FBW (fractional bandwidth) of underwater acoustic transducers. Influence of the design variables on the transducer performance was analyzed with equivalent circuits and the finite element method. When the piezocomposite is vibrating in a pure thickness mode, inter-pillar resonant modes are likely to occur between lattice-structured piezoceramic pillars and polymer matrix, which significantly deteriorate the performance of the piezocomposite. In this work, a new method to design the structure of the 1~3 type piezocomposite was proposed to maximize the TVR, RVS and FBW while preventing the occurrence of the inter-pillar modes. Genetic algorithm was used in the optimal design.