摘要
聚二甲基硅氧烷(PDMS)因其优异的黏弹性能被广泛地应用~([1])。尽管一些经典的聚二甲基硅氧烷全原子力场和联合原子力场能较好地描述其气液性质,但长时间、大尺度的粗粒化力场仍研究较少~([2])。本文依据第一性原理计算的PDMS低聚体分子结构和能量数据以及密度和蒸发焓的实验测量值,开发了TEAM函数形式的PDMS全原子力场,并进一步构建了具有温度可迁移性的粗粒化模型。我们应用该粗粒化模型计算了PDMS的密度、表面张力、溶解度参数、回旋半径、玻璃化转变温度等物理性质。结果表明:新构建的粗粒化模型很好地再现了密度、表面张力以及回旋半径的实验值;准确地预测出聚二甲基硅氧烷的玻璃化转变温度;但高分子量的溶解度参数计算值比实验值低,这一结果是合理的因为溶解度参数是自由能参数,由高分子链伸展和缠绕状态引起的分子内构象熵无法通过小分子量的模拟得到。
Polydimethylsiloxane(PDMS),due to its excellent viscoelastic properties,is widely used for both scientific and industrial applications.Although the gaseous and liquid properties of PDMS are well described using all-atom and united-atom force fields for molecular dynamics simulations,not much attention has been given to the development of coarse-grained force fields.In this work,parameters of the TEAM all-atom force field for PDMS have been derived by optimization against quantum chemical and experimental data on PDMS oligomers.Additionally,a coarse-grained(CG) model,with built on temperature corrections,is constructed.Several properties such as density,surface tension,solubility parameters,radius of gyration and glass transition temperature are calculated to verify the validity of CG force field.The results show that the density,surface tension,and radius of gyration are well reproduced by the force field.The glass transition temperature of PDMS is accurately predicted as well.However,the computed solubility parameter values are lower than those of experiments,due to the fact that the solubility parameter is a free-energy dependent parameter and can't be modelled correctly by fitting the force field to the chemical properties of oligomers.
引文
[1]Frischknecht,Amalie L.;John,G Curro.Macromolecules.2003,36(6):2122-2129.
[2]Johnson,J Casey.;LaShanda,T J Korley.;Mesfm,Tsige.JPCB.2014,118(47):13718-13728.
