Molecular Dynamics Simulation Of Bubble Nucleation Of Microcellular Plastics

Microcellular foam plastics have steady nucleation and the microcell size is less than 100μm. The typical microcell size is between 5 to 50 microns and the number of microcell is ranging from 109 to 1012 per cubic centimeter. Microcellular foam plastics has the advantages of traditional foam plastics (such as light weight, low cost, heat insulation and sound insulation properties, high specific strength, absorbing shock loads, etc.), and microcell passivates the crack tip in the materials and is beneficial to prevent crack expanding, thereby it improves the mechanical properties of products. Therefore, products of microcellular plastics are used in the automotive, construction, instrumentation and other industries widely.Molecular dynamics is a new experimental method which has grown up rapidly in recent years, and it is widely used in materials, physics, chemistry, biology and other fields. Not only molecular dynamics has set up a bridge from the micro to the macro, but also it can simulate in the conditions which the traditional experimental methods can not study. The principle of molecular dynamics is:calculating the potential energy between or atoms in the systems and the Newton equation of the molecules or atoms, recording site and speed of all molecules in the different moment, and then statistic to obtain thermodynamics, kinetics and energy information, that is, deriving the macroscopic properties based on microstructure of particles in the system.This paper is aimed at study the bubble nucleation of microcellular plastics using molecular dynamics simulations. This paper mainly includes following works:1. Summarized the process and characteristics of microcellular foam plastics, and elaborated the bubble nucleation mechanism of microcellular foam plastics in detail.2. Summarized the molecular dynamics simulation techniques, introduced theoretical basis of the molecular dynamics simulations.3. Studied the mixed system of hexadecane and carbon dioxide to simulate the bubble nucleation of microcellular plastics. Established a molecular dynamics model of system, and used the corresponding force field to describe the interaction between atoms. Selected NPT ensemble in the simulation, used Velocity-Verlet integration algorithm to calculate Newton's equations, and obtained the particle trajectories of bubble nucleation process.4. Given methods of discriminating and tracking of bubble, then analyzed the bubble nucleation process based on the result of molecular dynamics simulation, it indicated:forming low-density bubble in the liquid phase firstly during pressure reduction of carbon dioxide and hexadecane saturated solution, then, carbon dioxide molecules go into the gas phase continuously until forming the bubbles of many gas molecules in the polymer. This is consistent with the classical nucleation theory.