LCST-Driven Stimuli Responsive Polymers: Analytical Models

Stimuli responsive polymers are of great interest in a variety of fields ranging from biomedical engineering to robotics. The key property of these ‘smart' materials is their ability to respond to small changes in environmental conditions such as temperature, pressure, pH and ionic strength. One physical mechanism commonly driving this behavior is the lower critical solution temperature (LCST) transition. In polymer-solvent solutions above the overlap concentration, this transition takes the form of a phase separation into polymer-rich and polymer-depleted phases. In highly dilute solution, on the other hand, the corresponding transition is the collapse of isolated chains from an expanded coil state to a collapsed globule state. Several theoretical models are offered for these transitions. Systems addressed include uncharged aqueous and non-aqueous polymer systems, aqueous polymers in the presence of free salt, and lightly charged polyelectrolyte systems.