瞬逝凝胶：贴纸动力学与单链弛豫之间的竞争
Evanescent Gels: Competition Between Sticker Dynamics and Single Chain Relaxation
AI总结：
该研究通过非平衡布朗动力学模拟缔合聚合物凝胶，揭示网络结构与流变响应的差异，并由贴纸解离和单链弛豫的时间尺度竞争界定瞬逝凝胶机制。
摘要：
本文采用非平衡布朗动力学模拟对聚合物链溶液进行建模，其中物理缔合珠粒可形成可逆交联，从而建立贯穿整个体系的物理凝胶网络。研究系统考察了零剪切速率黏度和弛豫模量等流变性质随聚合物浓度以及缔合位点间结合能的变化。结果表明，在足够高的浓度下，无论结合能如何，体系都能形成贯穿网络。然而，该物理网络所承受应力的贡献可能比其他弛豫过程衰减得更快，甚至快于单链弛豫。如果聚合物弛豫时间尺度与短寿命缔合发生重叠，凝胶的力学响应就会变得“瞬逝”，即在能够被流变学观测到之前便已衰减，尽管该网络在瞬时仍具有力学刚性。在我们的模拟中，弹性活性链浓度和动态模量是分别独立计算的。这使得结合结构信息与流变信息成为可能，从而确定随结合能变化的溶胶—凝胶转变浓度。此外，研究还表明，贴纸解离时间与单根聚合物弛豫时间之间的尺度竞争决定了凝胶是否处于瞬逝区间。
英文摘要：
Solutions of polymer chains are modelled using non-equilibrium Brownian dynamics simulations, with physically associative beads which form reversible crosslinks to establish a system-spanning physical gel network. Rheological properties such as the zero-shear-rate viscosity and relaxation modulus are investigated systematically as functions of polymer concentration and the binding energy between associative sites. It is shown that a system-spanning network can form regardless of binding energy at sufficiently high concentration. However, the contribution to the stress sustained by this physical network can decay faster than other relaxation processes, even single chain relaxations. If the polymer relaxation time scales overlap with short-lived associations, the mechanical response of a gel becomes ``evanescent'', decaying before it can be rheologically observed, even though the network is instantaneously mechanically rigid. In our simulations, the concentration of elastically active chains and the dynamic modulii are computed independently. This makes it possible to combine structural and rheological information to identify the concentration at which the sol-gel transition occurs as a function of binding energy. Further, it is shown that the competition of scales between the sticker dissociation time and the single-polymer relaxation time determines if the gel is in the evanescent regime.
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