From Molecular Dehydration to Excess Volumes of Phase-Separating PNIPAM Solutions

Citations Over TimeTop 11% of 2014 papers

Abstract

For aqueous poly(N-isopropyl acrylamide) (PNIPAM) solutions, a structural instability leads to the collapse and aggregation of the macromolecules at the temperature-induced demixing transition. The accompanying cooperative dehydration of the PNIPAM chains is known to play a crucial role in this phase separation. We elucidate the impact of partial dehydration of PNIPAM on the volume changes related to the phase separation of dilute to concentrated PNIPAM solutions. Quasi-elastic neutron scattering enables us to directly follow the isotropic jump diffusion behavior of the hydration water and the almost freely diffusing water. As the hydration number decreases from 8 to 2 for the demixing 25 mass % PNIPAM solution, only a partial dehydration of the PNIPAM chains occurs. Dilatation studies reveal that the transition-induced volume changes depend in a remarkable manner on the PNIPAM concentration of the solutions. The excess volume per mole of H2O molecules expelled from the solvation layers of PNIPAM during phase separation probably strongly increases from dilute to concentrated PNIPAM solutions. This finding is qualitatively related to the immense strain-softening previously observed for demixing PNIPAM solutions.

Related Papers

• → Ionic Solvation in Aqueous and Nonaqueous Solutions(2001)136 cited
• → Effect of leaf dehydration duration and dehydration degree on PSII photochemical activity of papaya leaves(2014)13 cited
• → Extended solvent-contact model for protein solvation: Test cases for dipeptides(2013)5 cited
• → Internal solvation effects on the conformation of acyclics(1971)9 cited
• SOLVATION FREE ENERY OF THIENO [3, 2 - b] PYRIMIDINE ANALOGS COMPRISING INTERMOLECULAR SOLVATION AND INTRAMOLECULAR SELF-SOLVATION(2014)