硅酮密封胶体系中增塑剂扩散性能的分子动力学模拟

Molecular dynamics simulation of diffusion properties of plasticizers in silicone sealant systems

采用分子动力学模拟方法在COMPASS II力场下分析了3种增塑剂(白油、甲基硅油和双端乙烯基硅油)在脱酮肟硅酮密封胶中的扩散性能。研究结果表明:(1)在相同温度(298 K)下,增塑剂的扩散系数大小顺序为:白油>甲基硅油>双端乙烯基硅油。随着温度升高,3种增塑剂的扩散系数均随之升高。当温度超过318 K后,白油扩散系数急剧增加,双端乙烯基硅油增加最缓慢。随着增塑剂含量的升高,3种增塑剂在硅酮密封胶体系中的扩散系数均随之升高,增塑剂的扩散能力随着其含量的增加而增加。(2)在3种混合体系中,脱酮肟密封胶/白油体系的相容性最差,体系分子间的自由体积和自由体积分数最大,增塑剂分子的占有体积及尺寸最大,这些因素综合作用均导致白油具有较强的扩散能力,而双端乙烯基硅油具有较好的抗迁移能力。(3)温度升高使脱酮肟密封胶与增塑剂分子间作用减弱,同时体系的自由体积和自由体积分数增大,增加了增塑剂分子的运动空间,提高了增塑剂分子的扩散能力。(4)增塑剂含量越高,与脱酮肟密封胶分子间形成的相互作用能及范德华作用力能也越大,但同时体系的自由体积和自由体积分数也随着增塑剂含量的增加而增加。增塑剂分子扩散能力是分子间相互作用的力学效应及空间效应共同作用的结果。

The diffusion properties of three kinds of plasticizers(white oil,methyl silicone oil,and vinyl-terminated silicone oil)in de-ketoxime silicone sealant were analyzed by using molecular dynamics simulation method under the COMPASS II force field.The research results showed that,(1)At the same temperature(298 K),the order of diffusion coefficients of plasticizers was:white oil>methyl silicone oil>vinyl-terminated silicone oil.As the temperature increased,the diffusion coefficients of three kinds of plasticizers also increased.When the temperature exceeded 318 K,the diffusion coefficient of white oil increased sharply,and the increase in vinyl-terminated silicone oil was the slowest.As the content of plasticizers increased,the diffusion coefficients of three kinds of plasticizers in the silicone sealant system also increased,and the diffusion ability of plasticizers increased with the increase of their content.(2)Among three kinds of blending systems,the compatibility of de-ketoxime sealant/white oil system was the worst,the intermolecular free volume and free volume fraction of the system were the highest,and the occupied volume and size of plasticizer molecules were the largest.The combined effect of these factors led to strong diffusion ability of white oil,while vinyl-terminated silicone oil had good anti-migration ability.(3)The increase in temperature weakened the intermolecular interaction between de-ketoxime sealant and plasticizer,while increasing the free volume and free volume fraction of the system,increasing the movement space of plasticizer molecules and improving their diffusion ability.(4)The higher the plasticizer content,the greater the interaction energy and van der Waals force interaction energy formed between the molecules of de-ketoxime sealant.However,at the same time,the free volume and free volume fraction of the system also increased with the increase of plasticizer content.The molecular diffusion ability of plasticizers was the result of the mechanical effect and spatial effect of intermolecular interactions.