Zong Jing, Wang Qiang
Department of Chemical and Biological Engineering, Colorado State University, Fort Collins, Colorado 80523-1370, USA.
J Chem Phys. 2015 Nov 14;143(18):184903. doi: 10.1063/1.4934992.
We performed both the fast off-lattice Monte Carlo simulations of symmetric diblock copolymers (DBC) in an isothermal-isobaric ensemble and the self-consistent field calculations of asymmetric DBC to properly determine the order-disorder transition (ODT) of a model system of compressible DBC melts used in the literature when it is a first-order phase transition, and studied for the first time the co-existence of the two phases at ODT. We found that the co-existing region is quite small and decreases as the system becomes less compressible, which justifies the previous ODT results obtained by equating the Helmholtz free energy per chain of the two phases. We also found that for the most compressible system where there is no repulsion between the same type of segments, the self-consistent field theory predicts that ODT is a second-order phase transition even for asymmetric DBC melts due to its mean-field approximation.
我们对等温等压系综中的对称二嵌段共聚物（DBC）进行了快速非格点蒙特卡罗模拟，并对非对称DBC进行了自洽场计算，以恰当地确定文献中所使用的可压缩DBC熔体模型系统在发生一级相变时的有序-无序转变（ODT），并首次研究了在ODT时两相的共存情况。我们发现共存区域相当小，并且随着系统可压缩性降低而减小，这证明了通过使两相中每条链的亥姆霍兹自由能相等而获得的先前ODT结果是合理的。我们还发现，对于同一类型链段之间不存在排斥作用的最可压缩系统，由于其平均场近似，自洽场理论预测即使对于非对称DBC熔体，ODT也是二级相变。
