Gu Yuanqing, Ma Yubing, Vogt Bryan D, Zacharia Nicole S
Department of Polymer Engineering, University of Akron, Akron, OH 44325, USA.
Soft Matter. 2016 Feb 14;12(6):1859-67. doi: 10.1039/c5sm02313k. Epub 2015 Dec 24.
Weak polyelectrolyte multilayers (PEMs) prepared by the layer-by-layer assembly technique have recently been found to demonstrate a unique contraction upon exposure to organic solvents. This response is dependent upon which organic solvent is employed, and fundamental questions have not been clarified regarding the correlation of the magnitude of the film contraction with solvent type. In this work, we used solubility parameters to analyze the response of branched poly(ethylene imine)/poly(acrylic acid) (BPEI/PAA) multilayers when exposed to a variety of solvents. BPEI/PAA multilayers were immersed in a series of 16 different organic solvents and solvent mixtures. Immersion in organic solvent caused film dehydration and therefore contraction and also induced changes in the mechanical properties of PEMs. The film thickness was the best predictor of how a film swelled in water or contracted in organic solvent when using different batches of commercially available polyelectrolytes, rather than polyelectrolyte assembly pH conditions. The degree of film contraction was correlated with Hansen and Kamlet-Taft solubility parameters as well as solvent dielectric constant. In most cases, the hydrogen bonding ability of solvents is the primary factor to determine the magnitude of film contraction. For these solvents, increasing the temperature which corresponds to decreasing the strength of hydrogen bonding, also decreases the ability to dehydrate the films. For solvents that do not follow these trends with the strength of hydrogen bonding, a stronger correlation was found between contraction and dielectric constant, indicating that both traditional solvent quality arguments and electrostatics are important to understanding the contraction of PEMs in organic solvents.
最近发现，通过层层组装技术制备的弱聚电解质多层膜（PEMs）在暴露于有机溶剂时会表现出独特的收缩现象。这种响应取决于所使用的有机溶剂，并且关于膜收缩幅度与溶剂类型之间的相关性等基本问题尚未得到阐明。在这项工作中，我们使用溶解度参数来分析支化聚乙烯亚胺/聚丙烯酸（BPEI/PAA）多层膜在暴露于各种溶剂时的响应。将BPEI/PAA多层膜浸入一系列16种不同的有机溶剂和溶剂混合物中。浸入有机溶剂会导致膜脱水，从而引起收缩，还会引起PEMs力学性能的变化。当使用不同批次的市售聚电解质时，膜厚度是预测膜在水中膨胀或在有机溶剂中收缩情况的最佳指标，而不是聚电解质组装的pH条件。膜收缩程度与汉森和卡姆莱特 - 塔夫特溶解度参数以及溶剂介电常数相关。在大多数情况下，溶剂的氢键能力是决定膜收缩幅度的主要因素。对于这些溶剂，升高温度（对应于氢键强度降低）也会降低使膜脱水的能力。对于那些在氢键强度方面不遵循这些趋势的溶剂，在收缩与介电常数之间发现了更强的相关性，这表明传统的溶剂质量观点和静电作用对于理解PEMs在有机溶剂中的收缩都很重要。
