Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637, USA.
Soft Matter. 2018 Mar 28;14(13):2454-2464. doi: 10.1039/c7sm02041d.
Scattering investigations of the structure and chain conformations, and the rheological properties of polyelectrolyte complexes (PECs) comprising model polyelectrolytes are presented. The use of charged polypeptides - (poly)-lysine and (poly)-glutamic acid with identical backbones allowed for facile tuning of the system parameters, including chain length, side-chain functionality, and chirality. Systematic studies using small-angle X-ray scattering (SAXS) of liquid PEC coacervates revealed a physical description of these materials as strongly screened semidilute polyelectrolyte solutions comprising oppositely charged chains. At the same time, solid PECs were found to be composed of hydrogen-bonding driven stiff ladder-like structures. While the coacervates behaved akin to semidilute polyelectrolyte solutions upon addition of salt, the solids were largely unaffected by it. Rheology measurements of PEC coacervates revealed a terminal relaxation regime, with an unusual plateauing of the storage modulus at low oscillation frequencies. The plateau may be ascribed to a combination of instrumental limitations and the long-range electrostatic interactions contributing to weak energy storage modes. Excellent superposition of the dynamic moduli was achieved by a time-salt superposition. The shift factors, however, varied more strongly than previously reported with added salt concentration.
介绍了包含模型聚电解质的聚电解质复合物（PEC）的结构和链构象以及流变性质的散射研究。使用带相同主链的带电多肽 - （聚）赖氨酸和（聚）谷氨酸，可轻松调整系统参数，包括链长、侧链功能和手性。使用小角 X 射线散射（SAXS）对液体 PEC 共凝聚物的系统研究揭示了这些材料的物理描述，它们是由带相反电荷的链组成的强屏蔽半浓聚电解质溶液。同时，发现固体 PEC 由氢键驱动的刚性梯形结构组成。虽然共凝聚物在添加盐后表现为类似于半浓聚电解质溶液，但固体受其影响很小。PEC 共凝聚物的流变测量揭示了末端松弛状态，在低振荡频率下存储模量出现异常平台化。该平台可归因于仪器限制和长程静电相互作用的组合，这些相互作用有助于形成较弱的储能模式。通过时间-盐叠加实现了动态模量的出色叠加。然而，与以前报道的相比，随着添加盐浓度的增加，移位因子的变化更为强烈。
