Electrolyte and pH responsive surfactant association in ionic semi-interpenetrating networks containing cellulose or chitin synthesized in lithium chloride N,N-dimethylacetamide

Semi-interpenetrating networks (SIPNs) of N,N-dimethylacrylamide (DMAm)-N,N -dimethylamino-ethylacrylamide (DMAEAm), or N,N-dimethylacrylamide (DMAm)-2 -acrylamido-2-methyl-1-propanesulfonic acid (AMPS) containing cellulose or chitin were synthesized in 9% LiCl-N,N-dimethylacetamide (DMAc). The SIPNs were formulated to contain (1, 2, or 5% w/w) cellulose or 0.8% w/w chitin. Control systems (without polysaccharide) were also synthesized in 9% LiCl-D MAc. An acrylamide (Am)AMPS hydrogel was synthesized for comparison with th e SIPN composites. The swelling behavior of these materials was investigate d as a function of pH (DMAEAm-containing networks) or electrolyte concentra tion (AMPS-containing networks). The DMAm-AMPS materials were found to have higher equilibrium water content (EWC) values in deionized water than the DMAm-DMAEAm materials. The EWC of the DMAm-DMAEAm materials was largest bet ween pH 4 and 5 due to the protonation of the tertiary amine, with the chit in-containing material exhibiting the largest EWC. The DMAm-AMPS materials exhibited a decrease in EWC values with an increase in electrolyte concentr ation. Polymer-surfactant interactions were shown to exist for surfactants of opposite charge of the ionic mer units incorporated into the polymeric n etwork. Surfactant sequestration by the polysaccharide-containing materials was greater than that of the control gels; however, the rates of surfactan t binding were lower. Release of the bound surfactant was achieved by the d isruption of the charge-charge interactions by changing the pH of the mediu m (DMAEAm-containing networks) or by the addition of electrolyte (AMPS-cont aining networks). The DMAm-DMAEAm SIPNs released only 4% of the surfactant originally sequestered. By contrast, the DMAm-AMPS SIPNs released approxima tely 80%. The control Am-AMPS hydrogel-surfactant complex collapsed in the presence of electrolyte, and no surfactant was released from the complex. ( C) 1999 John Wiley & Sons, Inc.