Luettmer-Strathmann Jutta
Department of Physics, The University of Akron, Akron, Ohio 44325-4001, USA.
J Chem Phys. 2005 Jul 1;123(1):014910. doi: 10.1063/1.1931548.
Processes on different length scales affect the dynamics of chain molecules. The friction experienced by a short chain segment depends on both small-scale chain properties and on the local environment of the segment. As a consequence, the (monomeric) friction coefficients of the two components of a binary polymer blend will, in general, differ from each other and from the friction coefficients of the corresponding melts. In this work, we investigate local friction in polyolefin blends with the aid of a small-scale simulation approach. The polymer chains, in united atom representation, are assumed to occupy the sites of a partially filled simple cubic lattice. The simulation focuses on short chain sections with straight backbones and enumerates all possible binary contacts and relative movements of such sections. By evaluating the exact enumeration results in conjunction with equations of state for the blends, we are able to make predictions about the variation of the friction coefficients with local chain architecture and thermodynamic state (temperature, pressure, and composition). We calculate relative values of friction coefficients at temperatures well above the glass transition for blends of PEP, an alternating copolymer of polyethylene and polypropylene, with polyethylene and polyisobutylene and for blends of polyethylene and atactic polypropylene. We also investigate a blend of PEP with head-to-head polypropylene and compare our results with experimental data.
不同长度尺度上的过程会影响链分子的动力学。短链段所经历的摩擦既取决于小规模的链特性，也取决于该链段的局部环境。因此，二元聚合物共混物中两种组分的（单体）摩擦系数通常会彼此不同，也与相应熔体的摩擦系数不同。在这项工作中，我们借助小规模模拟方法研究聚烯烃共混物中的局部摩擦。聚合物链采用联合原子表示法，假定占据部分填充的简单立方晶格的位点。模拟聚焦于具有直链主链的短链段，并列举此类链段所有可能的二元接触和相对运动。通过结合共混物的状态方程评估精确的列举结果，我们能够预测摩擦系数随局部链结构和热力学状态（温度、压力和组成）的变化。我们计算了在远高于玻璃化转变温度下，聚乙烯和聚丙烯的交替共聚物PEP与聚乙烯和聚异丁烯的共混物，以及聚乙烯和无规立构聚丙烯的共混物的摩擦系数相对值。我们还研究了PEP与头对头聚丙烯的共混物，并将我们的结果与实验数据进行比较。
