Effects of cononsolvency on preferential adsorption phenomenon in poly(N-isopropylacrylamide) ternary solutions
Journal
Journal of Applied Polymer Science
Journal Volume
107
Journal Issue
4
Pages
2732-2742
Date Issued
2008
Author(s)
Abstract
In this work, the effect of cononsolvency on the phase transition and preferential adsorption phenomenon behaviors of poly(N-isopropylacrylamide)/ methanol/ water ternary solutions was studied. In this cononsolvent system, the ΔV̄E , ΔḠm , and χ12 values show a nonlinear behavior and the minimum values of ΔV̄ E and ΔḠm , while the maximum value of χ12 at φ2 is around 0.7. These facts indicated that one water molecule could directly bond with one methanol molecule to form the H2P-MeOH complex. The H2P-MeOH complex structure was found to remarkably affect the phase transition of poly(N-isopropylacrylamide) (PNIPAM) in ternary solution. However, at the composition of mixed cononsolvent, φ2 < 0.2, the PNIPAM molecules may preferentially adsorbed pure water molecules; therefore, the LCST decreases slightly with composition of mixed cosolvent and this may be because of the small amount of H 2P-MeOH complexes in the mixed cononsolvent. While, at φ2 > 0.7, the PNIPAM molecules may preferentially adsorbed pure methanol molecules. PNIPAM ternary solutions were transparent and no transition occurred in this region. This indicates that the PNIPAM coils exhibited a much-extended conformation in solutions. In contrast, at 0.2 < φ2 < 0.4 and 0.4 < φ2 < 0.7, PNIPAM molecules preferentially adsorbed water and methanol molecules, respectively, and also adsorbed large amount of H2P-MeOH complexes. In these regions, the clathrate-like structure around the side chain of PNIPAM molecule became more defected with adsorbing H2P-MeOH complex. Therefore, we considered that the various thermodynamic behaviors between PNIPAM and mixture solvents must be related different preferential adsorption phenomena, which were mainly related to different degrees of polymer-solvent interaction and structures of solvent used. © 2007 Wiley Periodicals, Inc.
SDGs
Type
journal article