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The Molecular Simulations and a Percolation Study of the Effects of Chain Stiffness and Polymer Segmental Dynamics on the Tracer Diffusion

2009년 8월 14일 11시 56분 20초
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목 17시 : 10분
고분자화학 - General Topics on Polymer Science I (대학원생 발표)
저자 및
정현태, 성봉준
서강대학교 화학과, Korea
The diffusion of tracer molecules in polymeric materials has been an issue of great importance because the tracer diffusion has been an important factor to improve the performance of fuel cells and separation membranes. The tracer diffusion is determined not only by the intermolecular interaction between a tracer and a polymer, but also by the polymer structure. Recently, it was reported that as one changed the polymer structure by stiffening polymers, the diffusion of tracers was significantly changed. (J. Phys. Chem. B 113, 2247 (2009)) However, the effects of the chain stiffness and the polymer structure have not been understood clearly yet. For example, it is still not clear whether the pore space in polymeric materials, which is considered a dominant factor to determine the tracer diffusion, should be changed upon stiffening chains. Therefore, we investigate the effect of the chain stiffness on the diffusion of tracer molecules using molecular simulations and a percolation theory. Using the equilibrated configuration of polymers, which is quenched in space, the diffusion coefficients of tracers are calculated via molecular simulations. And we locate a pore percolation threshold by carrying out Voronoi tessellation and calculating the mean cluster sizes of pores. We found that the diffusion coefficients of tracer molecules are decreased significantly, as polymers become stiffer and extended. However, the pore percolation threshold concentrations do not vary much with an increase in chain stiffness. We found by comparing to a previous simulation study (Polymer 45, 3923 (2004)) that the decrease in the tracer diffusion is attributed mainly not to a change in pore structure but to the segmental dynamics of polymers that slows down as one stiffens the polymer chains.