Concentration Fluctuations near Lower Critical Solution Temperature in Ternary Aqueous Solutions
writer：1. Di Jia; Murugappan Muthukumar; He Cheng;* Boualem Hammouda; Charles C. Han*
keywords：small angle neutron scattering, spinodal, fluctuation, random phase approximation
source：期刊
specific source：macromolecules
Issue time：2017年
The effects of osmolytes, such as trimethylamine N-oxide (TMAO), on the phase transition in an aqueous solution of polymer, protein or DNA are very complex and several phase transitions can occur. In order to explore such effects, we take a simple ternary system of poly(N,N-diethyl acrylamide) and a favorable solvent pair TMAO and water to monitor the reduction in the miscibility of the polymer using small-angle neutron scattering (SANS) and dynamic light scattering (DLS). The result shows that the LCST of PDEA solutions is significantly depressed by TMAO. Although DLS data clearly shows that aggregates can form as precursors in the homogenous one-phase region depending on the TMAO concentration, after removing the low-q aggregate region, the three-component system still obeys the mean field theory. Based on the ternary random phase approximation (RPA) theory, three Flory?Huggins interaction parameters, i.e. chi(D2O-TMAO), chi(PDEA-TMAO) and chi(PDEA-D2O） are obtained to reveal the microscopic origin of this shift in LCST, that is the strong TMAO-D2O interaction leads to the decrease of LCST. Our study opens up many directions to explore effects such as the interference between aggregation and micro-phase separation.