Specific ion effects determine the structure and function of the hierarchically lower structures that support life. Tremendous effort has been devoted to understanding the mechanisms of ion-specific effects on polymer solubility in single salt solutions, as ranked by the Hofmeister series. By contrast, the behavior of mixed electrolyte solutions remains relatively unexplored. In this work, we systematically investigate the lower critical solution temperature (LCST) of a thermoresponsive polymer in various salt mixtures. We demonstrate that the combined effects of the mixtures containing a weakly hydrated and a strongly hydrated anion are non-additive. Using molecular dynamics simulations and vibrational sum frequency spectroscopy, we show that the driving forces for the complex polymer phase transition involve competing roles for ion hydration and ion-polymer interaction. We expect that this newly discovered insight into Hofmeister ion chemistry will shed light on understanding the behaviors of complex solutions, such as the dense cellular environments and the brine solutions of ocean waters.

Investigating nonadditive ion effects in salt mixtures

2019 Fall National Meeting

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