Entropy-Driven Phase Separation of a Nominally Athermal Model Polymer/Solvent Solution

本文是以蒙地卡羅法研究幾近無熱效 應高分子溶液的相平衡行為。我們發現當 溫度提高時，高分子粒子與溶劑粒子間的 自由體積差異隨之加大。在到達所謂的下 臨界溫度時，因為商的效應，使得溶劑粒 子排斥高分子，而造成相分離的現象。我 們也發現較長的高分子因為它們與溶劑粒 子的自由體積差異較大，所以相分離的起 始溫度亦較低。對於等長的高分子且溫度 相同的情況下，壓力的增加會減少高分子 與溶劑粒子間自由體積的差異，故相分離 現象會較不明顯。我們亦將模擬結果與 SAFT 理論比較，發現SAFT 理論在對於高 分子溶液定性的描繪上，有很好的預測性，但在定量上尚無法有精確的結果。The Phase equilibrium behaviors of a nearly athermal polymer/solvent solution are studied by using the Monte Carlo method. It is found that as temperature increases, the free volume differences between solvent molecules and polymer chains become larger. To a certain temperature, which is the so called Lower Critical Solution Temperature (LCST) the entropic effect dominates over the enthalpic effect, thus phase separation occurs. We have also found that phase separation takes place at lower temperature for longer chain polymer solution. By comparing the phase envelope of polymer of the same chain length but at different pressure, LCST increases as pressure increases. We have also applied the SAFT theory to study the phase behavior and it is found to be able to give qualitatively good predictions