注射保压过程中O2/N2分子在PMMA熔体内部的扩散行为

研究了注射成型保压过程中，不同工艺条件下O2/N2混合气体在聚甲基丙烯酸甲酯（PMMA）聚合物内部的扩散行为。针对注射成型工艺特点，将注射保压阶段的低分子扩散简化为不同温度条件下的准静态扩散行为；建立了包含O2/N2气体和10条聚合度为10的全同立构PMMA链团的扩散映射模型。经能量最小化及退火算法实现了扩散模型的能量初始化；基于COMPASS力场，实现了O2/N2混合气体在PMMA熔体内部扩散的分子动力学模拟实验。结果表明，O2和N2的扩散系数均随温度的升高而增大，且同一温度下，O2比N2更容易扩散；不同温度下O2和N2的均方位移函数（MSD）对数lg(MSD)与时间对数lg(t)关系曲线的斜率（n）都接近于1，符合Einstein扩散机制。

Diffusion of O2/N2 in PMMA Melts During Packing Stage of Injection Molding

The diffusion behavior of the mixture of O2/N2 in PMMA melts during the packing stage of injection molding was studied. According to the characteristics of injection molding, the diffusion of the gas in the packing stage was simplified asaquasi static diffusion. Establishing a kind of a diffusion mapping model was formulated made up of O2/N2 gas and ten isotactic PMMA chains whose degree of polymerization was 10.By energy minimization and annealing algorithm, this diffusion model achieved an energy initialization.Based on the COMPASS force field,the diffusion of the mixture gas of O2/N2 in PMMA melts was simulated successfully. The result was that the diffusion coefficients of O2 and N2 increased with increasing temperature, and at the same temperature, the diffusion of O2 was easier than N2. Plotting lg(MSD) against lg(t) for O2 and N2, both the slopes of the curves were close to 1 at different temperatures, which conformed to the diffusion mechanism of Einstein. In addition, the activation energy of diffusion of N2 was higher than that of O2.