Reserch On The Molecular Dynamics Of Gas Diffusion Behavior In Melts During Packing Stage Of Injection Molding

The aggregation structure and diffusion behavior of impurities gas in the air coated within the material melts will have an impact on the mechanical and optical properties after the molded product, many researchers from different angles to study the link between the two, respectively. With the rapid development of computers science and technology and molecular simulation technology, and its highly organic combination, in this paper, by means of molecular dynamics simulation, from the microscopic point of focus on research on the packing stage of gas molecules of the low molecular weight coated within the polymeric material diffusion behavior in melts, it contribute to deeper understanding the mechanism of form internal defects such as micro pores after the molded product, thus providing an important scientific basis and theoretical for the best product quality performance to achieve process control and new technology development.This paper applied optical material poly(methyl methacrylate) [PMMA] as experimental materials, according to the characteristics of packing stage, in order to establishing a king of a mapping physical model that the diffusion of the mixture of O2/N2 in PMMA melts, the diffusion of the gas in the packing stage is simplified as the quasi-static diffusion behavior at different conditions; By energy minimization and annealing algorithm, the diffusion model achieved the structural optimization and system balance; After the model was validated, shows the build molecules physics model si set up. Then, by NVT and NPT molecular dynamics simulations at different conditions,it acquired this physical parameters have been able to characterize the diffusion behavior.The experimental results show: Any conditions, the diffusion of the mixture of O2/N2 in PMMA melts belong to the diffusion modes of Einstein, which conformed to the Einstein's equations. The diffusion coefficients?free volume and fractional free volume increased with increasing temperature, its decreased with increasing the degree of polymerization, which conformed to the free volume theory that The larger the free volume, the greater the diffusion coefficient; For the influence of pressure, the free volume and fractional free volume decreased with increasing pressure, but the diffusion coefficients to be maximized when a certain pressure. Due to the small van der Waals radius of an oxygen atom, the lower interaction energy with the matrix and the smaller diffusion activation energy required, consequently in each of these conditions, the diffusion coefficient of O2 was larger than that of N2, the wider of the diffusion region, the farther of the transition distance, the consumption of a shorter time of the transitions between holes.