论文部分内容阅读
采用分子动力学模拟方法研究了多个温度下氧气、氮气及甲烷在无定型顺式1,4-聚异戊二烯中的扩散系数。在模拟过程中,使用COMPASS力场作为分子力场。应用COMPASS力场的势能函数,聚合物的密度及玻璃化转变温度的计算结果与实验值有较好吻合。在278-378K的温度范围内,通过3或1.5 ns时长的正则系综动力学模拟,计算了不同温度下氧气、氮气及甲烷的扩散系数。结果表明,根据爱因斯坦关系式计算得到的扩散系数与实验结果比较接近。对气体扩散系数与温度的关系进一步研究,发现在278-378K温度范围内,甲烷的扩散系数随温度变化的半对数曲线图是非线性的,而氧气和氮气的扩散系数随温度变化的半对数曲线图是线性的。本文研究结果有助于理解温度对气体扩散的影响机制,并为高温下气体在天然橡胶中扩散系数的测定及天然橡胶热氧老化建模分析提供依据。
The diffusion coefficients of oxygen, nitrogen and methane in amorphous cis 1,4-polyisoprene were investigated by molecular dynamics simulation. During the simulation, the COMPASS force field was used as the molecular force field. The potential energy function of COMPASS force field, the calculation of polymer density and glass transition temperature are in good agreement with the experimental ones. The diffusion coefficients of oxygen, nitrogen and methane at different temperatures were calculated by regular ensemble dynamics simulations of 3 or 1.5 ns at a temperature range of 278-378K. The results show that the diffusion coefficient calculated according to Einstein’s formula is close to the experimental result. The relationship between gas diffusion coefficient and temperature was further studied. It was found that in the temperature range of 278-378K, the semi-logarithmic curve of methane diffusion coefficient with temperature was nonlinear. However, the half-logarithm of the diffusion coefficient of oxygen and nitrogen with temperature The number of graphs is linear. The results of this paper are helpful to understand the influence mechanism of temperature on gas diffusion and provide the basis for the determination of diffusion coefficient of gas in natural rubber and modeling of thermo-oxidative aging of natural rubber at high temperature.