Luettmer-Strathmann Jutta, Mantina Manjeera
Department of Physics and Department of Chemistry, The University of Akron, Akron, Ohio 44325-4001, USA.
J Chem Phys. 2006 May 7;124(17):174907. doi: 10.1063/1.2189244.
Local chain structure and local environment play an important role in the dynamics of polymer chains in miscible blends. In general, the friction coefficients that describe the segmental dynamics of the two components in a blend differ from each other and from those of the pure melts. In this work, we investigate polymer blend dynamics with Monte Carlo simulations of a generalized bond fluctuation model, where differences in the interaction energies between nonbonded nearest neighbors distinguish the two components of a blend. Simulations employing only local moves and respecting a no bond crossing condition were carried out for blends with a range of compositions, densities, and chain lengths. The blends investigated here have long time dynamics in the crossover region between Rouse and entangled behavior. In order to investigate the scaling of the self-diffusion coefficients, characteristic chain lengths N(c) are calculated from the packing length of the chains. These are combined with a local mobility mu determined from the acceptance rate and the effective bond length to yield characteristic self-diffusion coefficients D(c)=muN(c). We find that the data for both melts and blends collapse onto a common line in a graph of reduced diffusion coefficients DD(c) as a function of reduced chain length NN(c). The composition dependence of dynamic properties is investigated in detail for melts and blends with chains of length N=20 at three different densities. For these blends, we calculate friction coefficients from the local mobilities and consider their composition and pressure dependence. The friction coefficients determined in this way show many of the characteristics observed in experiments on miscible blends.
局部链结构和局部环境在互溶共混物中聚合物链的动力学中起着重要作用。一般来说，描述共混物中两种组分链段动力学的摩擦系数彼此不同，且与纯熔体的摩擦系数也不同。在这项工作中，我们用广义键涨落模型的蒙特卡罗模拟研究聚合物共混物动力学，其中非键合最近邻之间相互作用能的差异区分了共混物的两种组分。对一系列组成、密度和链长的共混物进行了仅采用局部移动并遵守无键交叉条件的模拟。这里研究的共混物在Rouse行为和缠结行为之间的交叉区域具有长时间动力学。为了研究自扩散系数的标度关系，从链的堆积长度计算特征链长N(c)。将这些与根据接受率和有效键长确定的局部迁移率μ相结合，得到特征自扩散系数D(c)=μN(c)。我们发现，在约化扩散系数DD(c)作为约化链长NN(c)的函数的图中，熔体和共混物的数据都落在一条共同的线上。详细研究了长度N = 20的链在三种不同密度下的熔体和共混物动力学性质的组成依赖性。对于这些共混物，我们从局部迁移率计算摩擦系数，并考虑其组成和压力依赖性。以这种方式确定的摩擦系数表现出在互溶共混物实验中观察到的许多特征。
