Muthukumar M
Department of Polymer Science and Engineering, University of Massachusetts, Amherst, MA 01003, USA.
Philos Trans A Math Phys Eng Sci. 2003 Mar 15;361(1804):539-56. doi: 10.1098/rsta.2002.1149.
We have investigated the molecular mechanisms of primordial stages of polymer crystallization from solutions using Langevin dynamics simulations and theoretical models. The key feature that distinguishes polymers from small molecules at early stages of nucleation is that, in the case of polymers, a single chain can participate in several nuclei. This results in entropic frustration, leading to spontaneously selected temporary finite structures during nucleation. The experimental observation of finite lamellar thickness (much smaller than extended chain dimension) has been historically attributed to kinetic origins. Our simulations and an exactly solvable model to account for chain entropy show that the finite lamellar thickness is actually the equilibrium result. The growth at the lamellar growth front is found in our simulations to be dominated by chain adsorption and highly cooperative dynamics of all chains. Our results contradict the conventional assumptions and theories of polymer crystallization.
我们使用朗之万动力学模拟和理论模型研究了聚合物从溶液中结晶初始阶段的分子机制。在成核早期，聚合物与小分子的关键区别在于，对于聚合物而言，单条链可参与多个晶核的形成。这导致了熵的受挫，从而在成核过程中产生自发选择的临时有限结构。有限片晶厚度（远小于伸展链尺寸）的实验观测结果在历史上一直被归因于动力学起源。我们的模拟以及一个考虑链熵的精确可解模型表明，有限片晶厚度实际上是平衡的结果。我们的模拟发现，片晶生长前沿的生长主要由链吸附和所有链的高度协同动力学主导。我们的结果与聚合物结晶的传统假设和理论相矛盾。
