聚丙烯表面的计算机模拟

用计算机模拟的方法详细研究了聚丙烯薄膜表面分子级别的结构 .采用无定形本体聚丙烯产生初始的随机父链 ,将一条随机父链在二维边界条件下进行塌陷 ,研究薄膜在真空中的构型 .用 10 0个重复单元的父链生成厚度为 3 5nm的薄膜 .发现薄膜内部密度等于聚丙烯的本体密度 ,而离自由表面 0 8nm处薄膜的密度开始跌落 .主链键在内部随机取向 ,在自由表面附近则明显沿薄膜表面平面取向 ,键开始有序取向的程度大致与质量密度相对于本体密度的减小一致 .与聚丙烯本体相比 ,薄膜表面中CH2 CH 的反式结构和旁式结构是增加的 ,这是因为分子链能更好的沿薄膜平面舒展 .同时通过聚丙烯无定形本体 (3D周期性 )和薄膜 (2D周期性 )中的链的能量的差异计算了薄膜内部能量对表面能量的贡献 .

COMPUTER SIMULATION OF POLYPROPYLENE SURFACES

Computer simulation is employed to study the structure of a thin PP film in vacuum.A initial random parent chain is obtained from the simulation of bulk amorphous polypropylene and collapsed under two-dimension boundary conditions.Films with a thickness of ～3\^5?nm are obtained for parent chain with 100 repetitive units.In the interior of PP films bulk density is obtained,while density drops off sigmoidally over a distance of ～0\^8 nm near the free surfaces.The backbone bonds are randomly oriented in the interior and markedly oriented along the film plane near the free surfaces:the onset of order corresponds roughly with the drop in the mass density from its bulk value.Because of the thin film more effectively relaxing along with the plane of the thin film,the trans state and the gauche state of the (CH_2)(CH) are also enriched compared to the bulk.The difference in the energy of a chain in the amorphous bulk (3D periodic) and in the film (2D periodic) allows us to calculate the internal energy contribution to the surface energy.