Swelling equilibria for heterogeneous polyacrylamide gels

Abstract

SYNOPSIST o correlate swelling equilibria for heterogeneous polyacrylamide gels in water to the monomer concentration a t preparation, it is necessary to modify the classic Flory-Rehner theory. The necessary modification concerns the relation which links the number of segments between junction points to the monomer concentration at preparation; that relation is here adjusted empirically. Modified theory is compared to experimental swelling equilibria for polyacrylamide gels synthesized in water by free-radical copolymerization of acrylamide (AAm) and N,N-methylenebis(acry1amide) (BIS) at various monomer concentrations. Synthesis conditions studied are (1) different AAm-to-BIS ratios with fixed total monomer concentrations, (2) different total monomer concentrations with fixed AAm-to-BIS ratios, and (3) different AAm-to-BIS ratios with a fixed number of BIS molecules. The modified theory and experiment show good agreement.

Accounting for Cooperativity in the Thermotropic Volume Phase Transition of Smart Microgels

“…The hydrodynamic radius of the particle is a free variable, which can be found by solving Equation ( 2 ). In 1996, Hino and Prausnitz suggested a modified version of Equation ( 2 ) which is more suitable for heterogeneous gels [ 49 ]. However, due to the considerations mentioned in the Introduction, we will not use their approach in the present work.…”

Characterizing charge and crosslinker distributions in polyelectrolyte microgels

“…However, in larger (N100 nm) poly(NIPAM)-based microgels crosslinked with N, N-methylenebisacrylamide, swelling predictions become more complicated. Fernandez-Nieves et al required a concentration-dependent polymer-solvent interaction parameter to predict poly(NIPAM) microgel swelling [58] while Wu et al could fit poly(NIPAM) microgel swelling profiles to a modified form of the Flory-Huggins theory developed by Hiro and Prausnitz permitting adjustment of the average number of free segments between crosslinking points as a function of monomer concentration [81]. However, in both cases, significantly lower swelling prediction accuracy was achieved than with the smaller, more homogeneous microgels [82].…”