應用分子動力學模擬探討不同分子量對奈米尺寸液滴碰撞之影響

Abstract

本文使用平行化分子動力學程式(Parallelized cellular molecular dynamics. PCMD)來模擬兩顆在奈米尺度下(~10 nm)由氦(Helium)或氙(Xenon)原子所構成的液滴，並採用L-J (12-6)的勢能模型來探討兩顆液滴於真空環境時相互撞擊的行為及影響。在模擬中影響液滴碰撞時的行為參數主要分為液滴間的相對速度、碰撞參數(Impact Parameter)及材質。本文模擬氦原子的相對速度範圍為250 m/s~750 m/s，氙原子的相對速度範圍為250 m/s~2250 m/s，碰撞參數則皆為0~8.75 nm。利用可視化程式模擬觀察到的行為有：液滴結合(Direct Coalescence)、液滴變形結合(Stretching Coalescence)、液滴拉伸破裂 (Stretching Separation)以及液滴碎裂(Shattering)。當相對速度和碰撞参數越高時，碰撞後的液滴其破裂和旋轉的現象會較為明顯，而材質的不同則會影響液滴碰撞時碎裂的程度，並與之前的文獻做比較來判斷不同分子量下，奈米尺寸的液滴相互撞擊後的行為及能量變化。

In this thesis, Parallelized cellular molecular dynamics (PCMD) to simulate two droplets consist of Helium or Xenon in nanoscale and adopt the L-J (12-6) potential to discuss the behavior and effects when two droplets collide in vacuum. In the simulation, parameters which influence the behavior of collision primarily involve the relative velocity between droplets, the impact parameter and the material we use. The simulation in this context sets the relative velocity of helium atom range from 250 m/s to 750 m/s, the relative velocity of xenon atom range from 250 m/s to 2250 m/s, and the impact parameters all range from 0 to 8.75 nm. By the way of visualization program “pvwin” we can observe several behavior of simulation as follow: Direct Coalescence, Stretching Coalescence, Stretching Separation, and Shattering. The greater the relative velocity and impact parameters are, the more obvious separation and rotation the droplets display after collision. Furthermore differences in material will affect the degree of shattering after collision. And we can compare the results with literature before to study the behavior and the change of energy in different molecular weights after the collision of droplets in the collision of droplets in nanoscale.