以分子動力學模擬聚四氟乙烯在奈米尺度下壓延製程分析

Abstract

本研究的目的就是要將利用分子動力學模擬聚四氟乙烯的玻璃轉移溫度及奈米壓延的加工系統。 首先在模擬聚四氟乙烯的玻璃轉移溫度方面，使用的鏈長分別為100、200及400，並探討在不同鏈長下，對玻璃轉移溫度的影響，發現玻璃轉移溫度會隨著鏈長(分子量)增長而昇高。在奈米壓延加工系統中，我們在固定的轉速下，以聚四氟乙烯高分子為材料，探討在不同加工溫度對奈米薄膜成形結構的影響，並找出較佳的溫度，應用在不同轉速及不同拉伸作用力下，觀察在受壓延擠壓過程中高分子鏈性質隨著時間的變化情形，其中包括了外形結構、密度、壓力、應力分佈、分子鏈排向行為及末端末端距離等。 在模擬系統中發現隨著溫度升高、拉伸作用力不足或轉速過慢，使分子鏈與金屬滾筒的沾黏增加，這會造成分子鏈在出滾筒狹縫後因沾黏而使高分子薄膜結構遭到破壞，薄膜密度及厚度不均勻，甚至有空洞及被撕裂的情形; 不過在過低的溫度卻會使得高分子鏈的收縮過度，造成高分子薄膜變形。且在模擬系統中也發現經加工後之分子鏈的順向性及末端末端距離(z方向)均有增加的趨勢。

The purpose of this research focuses on applying molecular dynamics to simulate glass transition temperature of PTFE and the processing system of nano-calendering. First of all, using the length of chains in 100, 200 and 400 to simulate that glass transition temperature of PTFE and discussing the effects on glass transition temperature in different length of chains. The results indicate that glass transition temperature will be raised with the increase of chain’s length (molecular waight). This research adopts the steady rotation rate and PTFE in the processing system of nano-calendering to discuss the effects of different processing temperature on structure of nano-membrane. Meanwhile, the research tries to find out the most appropriate temperature for observing the changes which are based on the different rotation rate and different stretch force of property of polymer chain on calendaring process. The changes include external structure、density、pressure、stress distribution、polymer chains phenomena of orientation and end-to-end distance etc. The simulating system shows that polymer chain adsorb with gold roller increases by the raise of the temperature, the lack of stretching force or low rotation rate. The result causes nano-membrane is damaged because polymer chains adsorb with roller after leaving narrow of roller. Also, the density and the thickness of membrane are not uniform. Moreover, it causes some cavities and laceration. However, the excessively low temperature causes the over shrink of polymer chains and polymer nano-membrane. In addition, the simulating system shows orientation of polymer chains and end-to-end distance of z-direction are increased after processing.