Syed Vaqar M S, Srivastava Samanvaya
Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, California 90095, United States.
ACS Macro Lett. 2020 Jul 21;9(7):1067-1073. doi: 10.1021/acsmacrolett.0c00252. Epub 2020 Jul 10.
Addition of salt speeds up chain relaxation dynamics in polyelectrolyte complexes (PECs), and time-salt superposition (TSS) approaches to describe the linear viscoelastic response of PECs are well-established. However, TSS is carried out at fixed initial polyelectrolyte concentrations, and varying the initial polyelectrolyte concentration results in distinct TSS master curves. In this contribution, we show that accounting for the small ions that accompany the oppositely charged polyelectrolyte chains (designated as accompanying counterions) enables assimilation of these distinct TSS master curves into a single universal master curve. This approach, that we christen as time-ionic strength superposition (TISS), enables a unified description of the PEC viscoelastic response in terms of the solution ionic strength, that accounts for both the accompanying counterions and the added ions, and underlines the dynamic similarities between PECs and semidilute polymer solutions. The sticky electrostatic associations among the oppositely charged chains, however, contribute additional relaxation modes in the PECs. We demonstrate that the time scales of these additional relaxation modes are described quantitatively by a modified sticky Rouse model that accounts for the influence of solution ionic strength on electrostatic screening and chain friction.
添加盐会加速聚电解质复合物（PEC）中的链松弛动力学，并且用于描述PEC线性粘弹性响应的时间-盐叠加（TSS）方法已经成熟。然而，TSS是在固定的初始聚电解质浓度下进行的，改变初始聚电解质浓度会导致不同的TSS主曲线。在本论文中，我们表明，考虑与带相反电荷的聚电解质链相伴的小离子（称为伴随抗衡离子）能够将这些不同的TSS主曲线合并为一条通用主曲线。我们将这种方法命名为时间-离子强度叠加（TISS），它能够根据溶液离子强度对PEC的粘弹性响应进行统一描述，该离子强度既包括伴随抗衡离子也包括添加的离子，并突出了PEC与半稀聚合物溶液之间的动力学相似性。然而，带相反电荷的链之间的粘性静电缔合在PEC中贡献了额外的松弛模式。我们证明，这些额外松弛模式的时间尺度可以通过一个修正的粘性Rouse模型进行定量描述，该模型考虑了溶液离子强度对静电屏蔽和链摩擦的影响。
