Structure of polyvinylpyrrolidone in water/ethanol mixture in dilute and semi-dilute regimes: Roles of solvents mixture composition and polymer concentration

Abstract

This study aims to describe the structure of polyvinylpyrrolidone (PVP, Mw = 40.000 g/mol) in water/ethanol solution in dilute and semi dilute regimes at 25 °C by viscosity measurements. Intrinsic viscosity of the polymer is determined for different ethanol molar fractions, XA. The cononsolvency of PVP in water/ethanolis evident and manifested by a contraction in the 0.05–0.4ethanol molar fraction range. The overlapping concentration,CPVP∗(XA), of PVP in water/ethanol increases with increasing XA. The Flory exponent, ν(XA), and the Mark-Houwink-Sakurada(MHS) coefficients,a(XA), are deduced by plotting the double logarithm of the relative viscosity versus polymer concentration in semi-dilute regime. The Flory exponent and the MHS values are shown to be dependent on XA. The blob model theory is extended and used to study the structure of a polymer in its mixed solvents. So, the structure of PVP in water/ethanol mixture is described by determining the structural parameters: density of monomers, monomer size, correlation length and the number of monomer in each blob for the PVP concentration ranged from CPVP∗(XA) to 2CPVP∗(XA). A spectacular reduction of the correlation length is observed in the 0.1–0.3 ethanol molar fraction.