Minnikanti Venkatachala S, Qian Zhenyu, Archer Lynden A
School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, USA.
J Chem Phys. 2007 Apr 14;126(14):144905. doi: 10.1063/1.2721542.
The effect of polydispersity on surface segregation of a lower molecular weight polymer component in a higher molecular weight linear polymer melt host is investigated theoretically. We show that the integrated surface excess zM of a polymer component of molecular weight M satisfies a simple relation zM=2Ue(M/Mw-1)phiM, where Mw is the weight averaged molecular weight, phiM is the polymer volume fraction, and Ue is the attraction of polymer chain ends to the surface. Ue is principally of entropic origin, but also reflects any energetic preference of chain ends to the surface. We further show that the surface tension gammaM of a polydisperse melt of high molar mass components depends on the number average degree of polymerization Mn as, gammaM=gammainfinity+2UerhobRT/Mn. The parameter gammainfinity is the asymptotic surface tension of an infinitely long polymer of the same chemistry, rhob is the bulk density of the polymer, R is the universal gas constant, and T is the temperature. The predicted gammaM compare favorably with surface tension values obtained from self-consistent field theory simulations that include equation of state effects, which account for changes in polymer density with molecular weight. We also compare the predicted surface tension with available experimental data.
从理论上研究了多分散性对较高分子量线性聚合物熔体基质中较低分子量聚合物组分表面偏析的影响。我们表明，分子量为M的聚合物组分的积分表面超额zM满足简单关系zM = 2Ue(M/Mw - 1)phiM，其中Mw是重均分子量，phiM是聚合物体积分数，Ue是聚合物链端对表面的吸引力。Ue主要源于熵，但也反映了链端对表面的任何能量偏好。我们进一步表明，高摩尔质量组分的多分散熔体的表面张力gammaM取决于数均聚合度Mn，即gammaM = gammainfinity + 2UerhobRT/Mn。参数gammainfinity是相同化学组成的无限长聚合物的渐近表面张力，rhob是聚合物的本体密度，R是通用气体常数，T是温度。预测的gammaM与从包含状态方程效应的自洽场理论模拟获得的表面张力值吻合良好，该效应考虑了聚合物密度随分子量的变化。我们还将预测的表面张力与现有实验数据进行了比较。
