Mei Baicheng, Grest Gary S, Liu Songyue, O'Connor Thomas C, Schweizer Kenneth S
Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801.
Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801.
Proc Natl Acad Sci U S A. 2024 Jul 30;121(31):e2403964121. doi: 10.1073/pnas.2403964121. Epub 2024 Jul 23.
Conformationally fluctuating, globally compact macromolecules such as polymeric rings, single-chain nanoparticles, microgels, and many-arm stars display complex dynamic behaviors due to their rich topological structure and intermolecular organization. Synthetic rings are hybrid objects with conformations that display both ideal random walk and compact globular features, which can serve as models of genomic DNA. To date, emphasis has been placed on the effect of ring molecular weight on their unusual behaviors. Here, we combine simulations and a microscopic force-level theory to build a unified understanding for how key aspects of ring dynamics depend on different tunable molecular properties including backbone rigidity, monomer concentration, degree of traditional entanglement, and molecular weight. Our large-scale molecular dynamics simulations of ring melts with very different backbone stiffnesses reveal unanticipated behaviors which agree well with our generalized theory. This includes a universal master curve for center-of-mass diffusion constants as a function of molecular weight scaled by a chemistry and thermodynamic state-dependent critical molecular weight that generalizes the concept of an entanglement cross-over for linear chains. The key physics is how backbone rigidity and monomer concentration induced changes of the entanglement length, interring packing, degree of interpenetration, and liquid compressibility slow down space-time dynamic-force correlations on macromolecular scales. A power law decay of the center-of-mass diffusion constant with inverse molecular weight squared is the first consequence, followed by an ultraslow activated hopping transport regime. Our results set the stage to address slow dynamics and kinetic arrest in different families of compact synthetic and biological polymeric systems.
构象波动的全局紧凑大分子，如聚合物环、单链纳米颗粒、微凝胶和多臂星型聚合物，由于其丰富的拓扑结构和分子间组织而表现出复杂的动力学行为。合成环是具有同时展现理想随机游走和紧凑球状特征构象的混合体，可作为基因组DNA的模型。迄今为止，重点一直放在环分子量对其异常行为的影响上。在此，我们结合模拟和微观力水平理论，以建立对环动力学的关键方面如何依赖于不同可调分子性质（包括主链刚性、单体浓度、传统缠结程度和分子量）的统一理解。我们对具有非常不同主链刚度的环熔体进行的大规模分子动力学模拟揭示了与我们的广义理论非常吻合的意外行为。这包括一个通用主曲线，用于描述质心扩散常数作为分子量的函数，该分子量通过化学和热力学状态相关的临界分子量进行缩放，这推广了线性链缠结转变的概念。关键物理在于主链刚性和单体浓度如何引起缠结长度、环间堆积、互穿程度和液体可压缩性的变化，从而减缓大分子尺度上的时空动态力相关性。质心扩散常数随分子量平方的倒数呈幂律衰减是第一个结果，随后是超慢活化跳跃传输 regime。我们的结果为解决不同类型的紧凑合成和生物聚合物系统中的慢动力学和动力学停滞奠定了基础。
