Cho Hyun Woo, Kim Haein, Sung Bong June, Kim Jun Soo
Department of Chemistry, Sogang University, Seoul 04107, Korea.
Department of Chemistry and Nanoscience, Ewha Womans University, Seoul 03760, Korea.
Polymers (Basel). 2020 Sep 11;12(9):2067. doi: 10.3390/polym12092067.
We report Brownian dynamics simulations of tracer diffusion in regularly crosslinked polymer networks in order to elucidate the transport of a tracer particle in polymer networks. The average mesh size of homogeneous polymer networks is varied by assuming different degrees of crosslinking or swelling, and the size of a tracer particle is comparable to the average mesh size. Simulation results show subdiffusion of a tracer particle at intermediate time scales and normal diffusion at long times. In particular, the duration of subdiffusion is significantly prolonged as the average mesh size decreases with increasing degree of crosslinking, for which long-time diffusion occurs via the hopping processes of a tracer particle after undergoing rattling motions within a cage of the network mesh for an extended period of time. On the other hand, the cage dynamics and hopping process are less pronounced as the mesh size decreases with increasing polymer volume fractions. The interpretation is provided in terms of fluctuations in network mesh size: at higher polymer volume fractions, the network fluctuations are large enough to allow for collective, structural changes of network meshes, so that a tracer particle can escape from the cage, whereas, at lower volume fractions, the fluctuations are so small that a tracer particle remains trapped within the cage for a significant period of time before making infrequent jumps out of the cage. This work suggests that fluctuation in mesh size, as well as average mesh size itself, plays an important role in determining the dynamics of molecules and nanoparticles that are embedded in tightly meshed polymer networks.
我们报告了示踪剂在规则交联聚合物网络中扩散的布朗动力学模拟，以阐明示踪剂粒子在聚合物网络中的传输情况。通过假设不同的交联度或溶胀度来改变均匀聚合物网络的平均网眼尺寸，且示踪剂粒子的尺寸与平均网眼尺寸相当。模拟结果表明，示踪剂粒子在中间时间尺度下呈现亚扩散，在长时间下呈现正常扩散。特别地，随着交联度增加平均网眼尺寸减小，亚扩散的持续时间显著延长，在这种情况下，长时间扩散是通过示踪剂粒子在网络网眼的笼子内长时间进行晃动运动后发生跳跃过程来实现的。另一方面，随着网眼尺寸随着聚合物体积分数增加而减小，笼子动力学和跳跃过程不太明显。这可以根据网络网眼尺寸的波动来解释：在较高的聚合物体积分数下，网络波动足够大，允许网络网眼发生集体的结构变化，从而示踪剂粒子可以从笼子中逸出，而在较低的体积分数下，波动非常小，以至于示踪剂粒子在笼子内被困很长一段时间后才偶尔跳出笼子。这项工作表明，网眼尺寸的波动以及平均网眼尺寸本身，在确定嵌入紧密网眼聚合物网络中的分子和纳米颗粒的动力学方面起着重要作用。
