Co-Solutes Induced Changes in the Properties of Polymeric Solution and Water Dynamics

In this paper we are addressing the co-solute-induced changes in the properties of an aqueous solution of a block copolymer. Due to the preferential interaction of different co-solute with different regions of the block copolymer, the changes were observed in both the physical properties and water dynamics. The modulation of both the physical properties and water dynamics was monitored using different spectroscopic techniques. Different co-solutes affect micellar properties of copolymer to a different extent signifying their interactions with different regions within the copolymer. The solvent relaxation dynamics were also modulated with the additions of different co-solutes. The change in free-energy (ΔG_bf) and rate constant for bound to free water interconversion (k_bf) in a copolymeric micelle was calculated which gets affected by the addition of co-solutes. The calculated k_bf suggests that betaine, sarcosine, TMAO, and GnHCl favor the ordering of water molecules around the micelle and are excluded from the micellar surface whereas, urea favors the formation of free-water molecules rather than the structurally ordered bound water molecules around the micelle by accumulating at the micellar surface. Among the added methylamines trimethylamine N-oxide affected the water dynamics and its kinetics most profoundly. The protective property of GnHCl was revealed.