基于黏弹模型的聚合物溶液相分离的三维数值模拟

利用GPU加速技术实现黏弹模型的三维数值模拟,系统研究了中等浓度聚合物溶液的分相形貌和相分离动力学.模拟结果表明本体应力的不对称是体系出现相反转的重要原因.与实验观察的聚合物溶液相反转的演化过程一致,首先聚合物富集相形成网络结构,然后聚合物网络收缩断网,最后变为离散的液滴相.本体松弛模量的增加,一方面会抑制相分离初期的浓度涨落,导致相反转发生时间延迟;另一方面在相分离后期有助于形成大的聚合物富集液滴相,加速相区增长.剪切松弛模量的增加只有助于聚合物富集相保持网络结构,并在剪切松弛模量较大的情况下,不规则相结构的缓慢松弛导致了剪切应力在相分离后期长期存在.     

最大熵原理推导自由结合链末端距的径向分布函数

将自由结合链看成一个微观系统,应用最大熵原理推导出自由结合链末端距的径向分布函数,进而证明自由结合链的末端距符合高斯分布。     

Three-dimensional numerical simulation of viscoelastic phase separation under shear: the roles of bulk and shear relaxation moduli

The morphological, dynamic and rheological characteristics in the viscoelastic phase separation(VPS) of sheared polymer solutions are investigated by three-dimensional(3D) numerical simulations of viscoelastic model. The simulations are accelerated by graphic process unit(GPU) to break through the limitation of computation power. Firstly, the morphological and dynamic characteristics of VPS under shear are presented by comparing with those in classic phase separation(CPS). The results show that the phase inversion and phase shrink take place in VPS under shear. Then, the roles of bulk and shear relaxation moduli in VPS are investigated in details. The bulk relaxation modulus slows down the phase separation process under shear, but not affects the dynamic path of VPS. The dynamic path can be divided into three stages: freezing stage, growth stage and stable stage. The second overshoot phenomenon in the shear stress is observed, and explained by the breakdown and reform of string structures. The shear modulus affects morphology evolution in the late stage of VPS under shear.