Prof Boris Zaslavsky

Cleveland Diagnostics, Cleveland, OH 44139, USA

Title: Analysis of mechanism of phase separation in aqueous two-phase systems with ATR-FTIR spectroscopy

---

Biography

Abstract

The mechanism behind liquid-liquid phase separation emergence in aqueous mixtures of two polymers remains poorly understood. We reported recently that analysis of the OH-stretch band by Attenuated Total Reflection-Fourier Transfer Infrared (ATR-FTIR) spectroscopy shows that the arrangements of H-bonds in coexisting phases of aqueous two-phase systems (ATPSs) formed by various pairs of polymers are different [1]. In our previous study of the interfacial tensions of various ATPSs, we suggested that aqueous mixture of two polymers at concentrations close to that of the phase separation threshold may be considered as a microheterogenous system [2]. We proposed that these systems form microdomains which differ in regard to the solvent features of water within them. Here, we examine the arrangement of H-bonds in different ATPSs formed by various polymers at a given composition (above binodal line) and of non-phase forming mixtures below the binodal line. We used ATR-FTIR spectroscopy to analyze the OH-stretch band and the model describing water as composed of four subpopulations characterized by Gaussian fractions representing subpopulations of water molecules with various H-bond strengths, geometry, and molecular arrangements. We now show experimentally that the phase transition in terms of H-bond rearrangement in aqueous mixtures of two polymers occur below the binodal line. These data strongly support our previous hypothesis that dissimilar microdomains appear prior to observed phase separation with their dissimilarity increasing with the concentration of the two polymers [2]. Similar effects are observed in a single polymer-salt aqueous mixtures. We conclude that the formation of these microdomains, specifically their increase in size and dissimilarity, initiate phase separation in ATPS.