Distinct Cation–Anion Interactions in the UCST and LCST Behavior of Polyelectrolyte Complex Aqueous Solutions,ACS Macro Letters

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Distinct Cation–Anion Interactions in the UCST and LCST Behavior of Polyelectrolyte Complex Aqueous Solutions
ACS Macro Letters ( IF 5.1 ) Pub Date : 2020-06-17 , DOI: 10.1021/acsmacrolett.0c00303
Zhangxin Ye ₁ , Shengtong Sun ₂ , Peiyi Wu _{1,

2}

Affiliation

Polyelectrolyte complexes (PECs) are recently observed to possess diversified thermoresponsive phase transition behaviors in aqueous solutions. Herein, by adjusting the initial polymer concentrations (C_pi) of poly(styrenesulfonate) (PSS)/poly(diallyldimethylammonium) (PDADMA) PEC in the same saline solution, in addition to previously reported lower critical solution temperature (LCST), we experimentally observed the upper critical solution temperature (UCST)-type phase transition behavior of PSS/PDADMA PECs at a lower polymer concentration. As elucidated by temperature-dependent Raman spectroscopy and two-dimensional correlation analysis, at temperatures lower than UCST, more hydrophobic polyelectrolyte chains lead to a high proportion of contact ion pairs (CIPs), contributing to UCST-type solid–liquid phase transition; however, at higher concentrations of PEC, the less hydrophobic polyelectrolyte chains correspond to a higher proportion of solvent-separated ion pairs (SIPs), which enables the occurrence of LCST-type liquid–liquid phase transition. With the spectroscopic indicator of CIPs/SIPs peak ratio and monitoring the hydration state of polymer chains, the complex interplays of PSS/PDADMA PECs are hereby interpreted at the molecular level, which lays the mechanistic foundation for designing other thermoresponsive PEC assemblies.

中文翻译：

聚电解质复合水溶液的 UCST 和 LCST 行为中不同的阳离子-阴离子相互作用

最近观察到聚电解质复合物 (PEC) 在水溶液中具有多样化的热响应相变行为。在此，通过调整初始聚合物浓度（C _pi）聚（苯乙烯磺酸盐）（PSS）/聚（二烯丙基二甲基铵）（PDADMA）PEC在相同的盐水溶液中，除了先前报道的较低临界溶解温度（LCST）外，我们还通过实验观察了上临界溶解温度（UCST）型PSS/PDADMA PECs 在较低聚合物浓度下的相变行为。正如温度相关拉曼光谱和二维相关分析所阐明的那样，在低于 UCST 的温度下，更疏水的聚电解质链导致接触离子对 (CIP) 的比例较高，从而导致 UCST 型固液相变；然而，在较高浓度的 PEC 下，疏水性较低的聚电解质链对应于较高比例的溶剂分离离子对 (SIP)，这使得发生 LCST 型液-液相转变成为可能。

更新日期：2020-07-21

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