Black Jana E, Silva Gonçalo M C, Klein Christoph, Iacovella Christopher R, Morgado Pedro, Martins Luís F G, Filipe Eduardo J M, McCabe Clare
Department of Chemical and Biomolecular Engineering, Vanderbilt University , Nashville, Tennessee 37235, United States.
Multiscale Modeling and Simulation (MuMS), Vanderbilt University , Nashville, Tennessee 37235, United States.
J Phys Chem B. 2017 Jul 13;121(27):6588-6600. doi: 10.1021/acs.jpcb.7b00891. Epub 2017 Jun 27.
A force field for perfluoropolyethers (PFPEs) based on the general optimized potentials for liquid simulations all-atom (OPLS-AA) force field has been derived in conjunction with experiments and ab initio quantum mechanical calculations. Vapor pressures and densities of two liquid PFPEs, perfluorodiglyme (CF-O-(CF-CF-O)-CF) and perfluorotriglyme (CF-O-(CF-CF-O)-CF), have been measured experimentally to validate the force field and increase our understanding of the physical properties of PFPEs. Force field parameters build upon those for related molecules (e.g., ethers and perfluoroalkanes) in the OPLS-AA force field, with new parameters introduced for interactions specific to PFPEs. Molecular dynamics simulations using the new force field demonstrate excellent agreement with ab initio calculations at the RHF/6-31G* level for gas-phase torsional energies (<0.5 kcal mol error) and molecular structures for several PFPEs, and also accurately reproduce experimentally determined densities (<0.02 g cm error) and enthalpies of vaporization derived from experimental vapor pressures (<0.3 kcal mol). Additional comparisons between experiment and simulation show that polyethers demonstrate a significant decrease in enthalpy of vaporization upon fluorination unlike related molecules (e.g., alkanes and alcohols). Simulation suggests this phenomenon is a result of reduced cohesion in liquid PFPEs due to a reduction in localized associations between backbone oxygen atoms and neighboring molecules.
基于通用液体模拟全原子优化势（OPLS - AA）力场，结合实验和从头算量子力学计算，推导出了全氟聚醚（PFPEs）的力场。实验测量了两种液态PFPEs，全氟二甘醇二甲醚（CF - O - (CF - CF - O) - CF）和全氟三甘醇二甲醚（CF - O - (CF - CF - O) - CF）的蒸气压和密度，以验证该力场并增进我们对PFPEs物理性质的理解。力场参数基于OPLS - AA力场中相关分子（如醚和全氟烷烃）的参数构建，并引入了针对PFPEs特定相互作用的新参数。使用新力场进行的分子动力学模拟表明，对于几种PFPEs的气相扭转能（误差<0.5 kcal/mol）和分子结构，与RHF/6 - 3G*水平的从头算计算结果具有极好的一致性，并且还能准确再现实验测定的密度（误差<0.02 g/cm³）和由实验蒸气压得出的汽化焓（误差<0.3 kcal/mol）。实验与模拟之间的其他比较表明，与相关分子（如烷烃和醇类）不同，聚醚在氟化后汽化焓显著降低。模拟表明，这种现象是由于主链氧原子与相邻分子之间的局部缔合减少，导致液态PFPEs内聚力降低的结果。
