VDF-CTFE共聚物在TATB表面吸附链构象的分子动力学模拟

采用COMPASS力场和NVT正则系综的动力学计算模拟了偏氟乙烯(PVDF)与三氟氯乙烯(PCTFE)及其共聚物在1,3,5-三氨基-2,4,6-三硝基苯(TATB)表面吸附能和吸附链的构象. 结果表明, 氟聚合物链与TATB表面距离小于0.8 nm时, 产生吸附放热效应. 在TATB表面, PVDF有强吸附作用, 而PCTFE的吸附能力差. 对VDF与CTFE单体摩尔比为1∶1, 1∶2, 1∶3和1∶4的共聚物吸附模拟结果表明, 共聚物的组成和链的序列结构对其在TATB表面的吸附行为和吸附链构象影响很大. 单体摩尔比为1∶2的交替共聚物链的吸附效果最佳. 随着共聚物链段中PCTFE链节的增加, 聚合物链的刚性增大, 在TATB表面吸附能力逐渐下降、吸附能亦降低, 尾型(tail)或环型(loop)构象数逐渐增多.

Molecular Dynamics Simulation of Adsorbed Chain's Conformations of Copoly(vinylidene fluoride-chlorotrifluoroethylene) at 1,3,5-Triamino-2,4,6-trinitrobenzene Surface

The surface absorption energy and the absorbed chains’ conformation were investigated by molecular dynamics(MD) simulations using compass force field and NVT ensemble model, in the case of poly(vinylidene fluoride)(PVDF), polychlorotrifluoroethylene(PCTFE) and their copolymers being absorbed on the crystal surface of 1,3,5-triamino-2,4,6-trinitrobenzene(TATB). The results show that the absorption exothermic effect appeared as the distance between polymer chains and the TATB crystal surface shorten to less than 0.8 nm. The absorption effect of PVDF was strong on the TATB crystal surface and it was reverse of PCTFE. MD simulations of alternative copolymers and random copolymers, with VDF and CTFE monomer ratio varying with 1∶1, 1∶2, 1∶3 and 1∶4 respectively, were carried out. The results indicte that the composition and serial structure of polymer chain influenced significantly the chain’s spatial conformations and its absorption behavior on TATB crystal surface. Especially, the alternative copolymer with the monomer ratio of 1∶2 showed the best absorption effect, attaching TATB crystal surface with train-conformations. As CTFE fraction increased, the stiffness of the copolymer was also increased, while the absorption ability and absorption energy decreased gradually with more tail and loop conformations formed.