Abstract
Cosolvent effects on the coil-globule transitions in aqueous polymer solutions are not well understood, especially in the case of amphiphilic cosolvents that preferentially adsorb on the polymer and lead to both polymer swelling and collapse. Although a predominant focus in the literature has been placed on the role of polymer-cosolvent attractive interactions, our recent work has shown that excluded-volume interactions (repulsive interactions) can drive both preferential adsorption of the cosolvent and polymer collapse via a surfactant-like mechanism. Here, we further study the role of polymer-(co)solvent attractive interactions in two kinds of polymer solutions, namely, good solvent (water)-good cosolvent (alcohol) (GSGC) and poor solvent-good cosolvent (PSGC) solutions, both of which exhibit preferential adsorption of the cosolvent and a non-monotonic change in the polymer radius of gyration with the addition of the cosolvent. Interestingly, at low concentrations, the polymer-(co)solvent energetic interactions oppose polymer collapse in the GSGC solutions and contrarily support polymer collapse in the PSGC solutions, indicating the importance of the underlying polymer chemistry. Even though the alcohol molecules are preferentially adsorbed on the polymer, the trends of the energetic interactions at low cosolvent concentrations are dominated by the polymer-water energetic interactions in both the cases. Therefore, polymer-(co)solvent energetic interactions can either reinforce or compensate the surfactant-like mechanism, and it is this interplay that drives coil-to-globule transitions in polymer solutions. These results have implications for rationalizing the cononsolvency transitions in real systems such as polyacrylamides in aqueous alcohol solutions where the understanding of microscopic driving forces is still debatable.
Highlights
Cosolvent induced coil-to-globule transitions are ubiquitous and range from modulating the stability of proteins1,2 to governing the aqueous solubility of thermoresponsive polymers.3–11 The microscopic forces driving these transitions still remain poorly understood
We study the interplay between excluded-volume interactions and polymer–(co)solvent attractive interactions and their impact on preferential adsorption of the cosolvent and on coil–globule–coil transitions
A stronger surfactant-like behavior of the cosolvent enhances the cononsolvency phenomenon and increases the preferential adsorption of scitation.org/journal/jcp the cosolvent, which is in agreement with the behavior in aqueous alcohol mixtures of PNIPAM and PDEAM.5,6,10,11,26–29,80
Summary
Cosolvent induced coil-to-globule transitions are ubiquitous and range from modulating the stability of proteins to governing the aqueous solubility of thermoresponsive polymers. The microscopic forces driving these transitions still remain poorly understood. Poly(N-isopropylacrylamide) (PNIPAM), poly(N, N-diethylacrylamide) (PDEAM), and elastin-like scitation.org/journal/jcp polypeptides (ELPs) are well known thermoresponsive polymers that exhibit cononsolvency in a wide variety of cosolvents These systems exhibit a lower critical solution temperature (LCST) type phase transition in aqueous solutions, which is experimentally observed to be of first order (two state).. Over the last 30 years, there have been several experimental, theoretical, and simulation efforts to understand the cononsolvency phenomenon the mechanism still remains unresolved For amphiphilic cosolvents such as alcohols, which preferentially adsorb on the polymer surface, a predominant emphasis has been placed on the role of polymer–cosolvent attractive interactions, whereas a limited focus has been placed on the role of excluded-volume (repulsive) interactions.. Note that the surfactant-like behavior is generic and would be applicable to a wide variety of soft matter systems These observations from our previous study show that the excluded-volume interactions are as important as the polymer–(co)solvent attractive interactions. We expand on our recent work and study the role of polymer–(co)solvent energetic interactions and their competition with the excluded-volume interactions
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
