Department of Physics, National Taiwan University, Taipei 106, Taiwan.
J Chem Phys. 2013 May 21;138(19):194901. doi: 10.1063/1.4802963.
A density functional theory is developed for the diblock copolymer melt, where one block contains the segment orientation dependent chiral interaction. In addition to the standard (scalar) pair interaction between the two types of monomers, the chiral block has the additional pairwise interaction, which is linear in the tangent vectors of the segments. We construct a density functional, which contains both the scalar density field and the vector chain alignment field. The quadratic part of the density functional comes from the mean field theory of the microscopic model, whereas the fourth order terms are introduced phenomenologically in the spatially local form. From the stability analysis of this model, we find that the additional chiral interaction shifts the order-disorder transition, which is consistent with the behavior of experimental system. Further numerical calculation reveals a new metastable chiral helical cylinder structure, which is similar to the one found experimentally. Another similar metastable structure but with zigzag modulation is also observed. As the helical and zigzag structures disappear when the chiral interaction is switched off, we understand that the chiral effect is the driving force for the formation of these exotic metastable structures.
我们为嵌段共聚物熔体开发了一种密度泛函理论，其中一个嵌段包含了与链段取向相关的手性相互作用。除了两种类型单体之间的标准（标量）对相互作用外，手性嵌段还有额外的成对相互作用，它在线性的链段切向量上。我们构造了一个密度泛函，它包含标量密度场和向量链排列场。密度泛函的二次部分来自微观模型的平均场理论，而四阶项则以空间局部形式引入。从这个模型的稳定性分析中，我们发现额外的手性相互作用会转移有序-无序转变，这与实验系统的行为一致。进一步的数值计算揭示了一种新的亚稳态手性螺旋圆柱结构，它与实验中发现的结构相似。还观察到另一种类似的亚稳态结构，但带有锯齿调制。由于当手性相互作用关闭时，螺旋和锯齿结构消失，我们理解手性效应是形成这些奇异亚稳态结构的驱动力。
