Zheng Zijian, Liu Hongji, Shen Jianxiang, Liu Jun, Wu Youping, Zhang Liqun
Key Laboratory of Beijing City on Preparation and Processing of Novel Polymer Materials, Beijing University of Chemical Technology, 100029 Beijing, China.
Beijing Engineering Research Center of Advanced Elastomers, Beijing University of Chemical Technology, 100029 Beijing, China.
Polymers (Basel). 2016 Sep 19;8(9):335. doi: 10.3390/polym8090335.
Although the research of the self-assembly of tri-block copolymers has been carried out widely, little attention has been paid to study the mechanical properties and to establish its structure-property relation, which is of utmost significance for its practical applications. Here, we adopt molecular dynamics simulation to study the static and dynamic mechanical properties of the ABA tri-block copolymer, by systematically varying the morphology, the interaction strength between A-A blocks, the temperature, the dynamic shear amplitude and frequency. In our simulation, we set the self-assembled structure formed by A-blocks to be in the glassy state, with the B-blocks in the rubbery state. With the increase of the content of A-blocks, the spherical, cylindrical and lamellar domains are formed, respectively, exhibiting a gradual increase of the stress-strain behavior. During the self-assembly process, the stress-strain curve is as well enhanced. The increase of the interaction strength between A-A blocks improves the stress-strain behavior and reduces the dynamic hysteresis loss. Since the cylindrical domains are randomly dispersed, the stress-strain behavior exhibits the isotropic mechanical property; while for the lamellar domains, the mechanical property seems to be better along the direction perpendicular to than parallel to the lamellar direction. In addition, we observe that with the increase of the dynamic shear amplitude and frequency, the self-assembled domains become broken up, resulting in the decrease of the storage modulus and the increase of the hysteresis loss, which holds the same conclusion for the increase of the temperature. Our work provides some valuable guidance to tune the static and dynamic mechanical properties of ABA tri-block copolymer in the field of various applications.
尽管三嵌段共聚物自组装的研究已广泛开展，但对于其力学性能的研究以及结构-性能关系的建立却鲜有关注，而这对于其实际应用至关重要。在此，我们采用分子动力学模拟来研究ABA三嵌段共聚物的静态和动态力学性能，系统地改变形态、A-A链段间的相互作用强度、温度、动态剪切振幅和频率。在我们的模拟中，设定由A链段形成的自组装结构处于玻璃态，B链段处于橡胶态。随着A链段含量的增加，分别形成了球形、圆柱形和层状微区，应力-应变行为逐渐增强。在自组装过程中，应力-应变曲线也得到增强。A-A链段间相互作用强度的增加改善了应力-应变行为并降低了动态滞后损耗。由于圆柱形微区随机分散，应力-应变行为表现出各向同性的力学性能；而对于层状微区，沿垂直于层状方向的力学性能似乎优于平行于层状方向的性能。此外，我们观察到随着动态剪切振幅和频率的增加，自组装微区会破碎，导致储能模量降低和滞后损耗增加，温度升高时也得出相同结论。我们的工作为在各种应用领域中调节ABA三嵌段共聚物 的静态和动态力学性能提供了一些有价值的指导。
