New Type of Swelling Behavior upon Gel Ionization: Theory vs Experiment

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• 作者：Olga E. Philippova ; Artem M. Rumyantsev ; Elena Yu. Kramarenko ; Alexei R. Khokhlov
• 刊名：Macromolecules
• 出版年：2013
• 出版时间：December 10, 2013
• 年：2013
• 卷：46
• 期：23
• 页码：9359-9367
• 全文大小：360K
• 年卷期：v.46,no.23(December 10, 2013)
• ISSN：1520-5835

文摘

We report a combined experimental and theoretical study on the swelling behavior of polyelectrolyte gels with various types of counterions. Experimental research was focused on poly(methacrylic acid) and poly(acrylic acid) gels in methanol neutralized with different bases providing sodium, cesium, tetramethyl-, tetraethyl- or tetrabutylammonium counterions. The novelty of the theoretical treatment is that the counterion size is explicitly taken into account as well as the dependence of the ion association constant on the volume fraction of polymer within the gel. We demonstrate that, depending on the counterion size, three different regimes of the gel behavior are realized. In case of bulky tetrabutylammonium counterions the gel swells upon ionization. For small counterions (Na⁺, Cs⁺) the gel swelling at low ionization degrees is succeeded by its collapse. New type of behavior was observed and theoretically described for the gels with counterions of intermediate sizes (tetramethyl- and tetraethylammonium). In this case, the gel ionization causes first swelling, then collapse and finally reswelling of the gel. This distinction in gel behavior with counterions of different types is explained by decreasing tendency for ion pair and multiplet formation with growing counterion dimensions. Our finding of the counterion-controlled collapse/decollapse transition is significant for fundamental understanding of the role of ion association processes in polyelectrolyte gel behavior as well as for design of sensors and environmentally responsive containers for controlled delivery applications.