| Summary: | 碩士 === 國立清華大學 === 化學工程學系 === 91 === In this study, the orientation behavior of polymer chains in weld-line region, which usually occurs in polymer processing when two melt fronts combine together, is simulated by molecular dynamics. Simulation is carried out at different temperature to show polymer chains arrangement and their inter-diffusion in the weld interface.
The first part of this work is to simulate thin films of hexadecane (C16H34) fluid under Couette shear flow. The analysis results about slip boundary phenomena according to different wall properties and shear rates are demonstrated to be in good agreement with references. As the wall roughness or εw increase, the degree of slip will be reduced.On the other hand, larger shear rates cause more slip between fluids and wall. We also show that the fluid velocity profile is not affected by different lattice arrangement.
As to simulation of weld-line, the fluid molecule used is C25H52. Based on the results, the orientation in z-direction, which is perpendiculato the flow direction, is observed to concentrate in the weld-line region formed by two melt fronts. As temperature increases, polymer chains diffuse more into each other, and the z-direction orientation is eliminated.
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