Molecular dynamics study of diffusion in bidisperse polymer melts
Molecular dynamics study of diffusion in bidisperse polymer melts
复制标题
双分散聚合物熔体扩散的分子动力学研究
DOI：
10.1063/1.480925
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发表时间：
2000
影响因子：
4.4
通讯作者：
S. Barsky
中科院分区：
文献类型：
--
作者：
S. Barsky
用分子动力学方法模拟了多分散链系统的扩散系数。每个系统由两段化学性质相同的柔性聚合物链组成。每种物质的质心的均方位移被测量为其在共混物中的长度和体积分数的函数。聚合物长度范围从N=10单体/链到N=90，约为缠结长度的三倍。无论构成其余部分的聚合物的长度如何，构成大部分熔体的聚合物物质表现出很小的行为变化。相比之下，当一个物种是少数组分时，它的运动会受到基质链长度的显着影响。当链浸入长链的基质中时，其扩散系数小于其单分散值;相反，当链处于短链的共混物中时，其扩散系数与单分散熔体相比增加。对于短于缠结长度的链，扩散系数与理论预测相比较。最长的聚合物的均方位移的标度指数被发现是次线性的，除非与非常短的聚合物共混。标度指数似乎是长链聚合物所经历的纠缠的度量。
Molecular dynamics simulations of the diffusion coefficient of systems of polydisperse chains are presented. Each system consists of two lengths of chain of chemically identical flexible polymers. The mean square displacement of the center of mass of each species is measured as a function its length and volume fraction in the blend. The polymer lengths range from N=10 monomers per chain to N=90, about three times the entanglement length. The polymer species that comprises the bulk of the melt shows little change in behavior regardless of the length of polymer which makes up the remainder. By contrast, when a species is the minority component, its motion is significantly affected by the length of the matrix chains. When a chain is immersed in a matrix of longer chains, its diffusion coefficient is smaller than its monodisperse value; conversely when a chain is in a blend of shorter chain its diffusion coefficient increases compared to a monodisperse melt. For chains shorter than the entanglement length, the diffusion coefficient compares well to theoretical predictions. The scaling exponent of the mean square displacement of the longest polymer is found to be sublinear, unless blended with very short polymers. The scaling exponent seems to be a measurement of the entanglements that the long polymers experience.