Hot from the Mussel Lab: Model captures a transient swelling-deswelling behavior in gels exposed to large concentrations of strong salts

A mathematical model is presented that describes the time evolution of volume transition induced by the competition of ions in charged polymer gels.  Gels are a common form of soft matter, capable to respond to changes in the environmental conditions in a reversible manner.  This makes them useful functional materials in diverse applications. For example, gels that swell or shrink in response to external stimuli are widely used for controlled drug delivery. Ion-induced volume transition is a common situation harnessed by many applicative systems.  It also plays essential role in various biological processes. These include DNA condensation, mucus secretion, and control of water flow in vascular plants. Understanding the intricate molecular interactions between the components – charged polymers, ions, and water – is challenging and computationally expansive. The present work has adopted a coarse-grained multicomponent model whose roots date back to the 20^th century.  In particular, Katchalsky made pioneering contributions to this field.  Semi-quantitative agreement with experimental observations demonstrates that gels exposed to strong salts (such as calcium chloride) do not deswell immediately. Rather, the gel absorbs a large amount of salt solution before expelling water and retaining ions. Recognizing universal elements in the coupled dynamics between polymers, salts, and water could provide a powerful framework to understand, control, and manipulate biological and man-made functions. More information may be found here.