Collapse of polyelectrolyte networks induced by their interaction with an oppositely charged surfactant. Theory

Abstract

SUMMARYA very simple theory of swelling and collapse of weakly charged polyelectrolyte networks in the solution of an oppositely charged surfactant has been developed. The following contributions to the free energy were taken into account: free energy of volume interaction and of elastic deformation of the network chains, free energy connected with micelle formation and free energy of translational motion of all mobile ions in the system (translational entropy). Both the cases of a solution of charged surfactant and that of a mixed solution of charged and neutral surfactant components have been taken into account. It has been shown that the behaviour of the network depends on the total surfactant concentration in the system and corresponds to one of the three following regimes: At low concentration, micelles inside the network are not formed and the behaviour of the polymer network is similar to that of a network swelling in the solution of a lowmolecular-weight salt (regime 1). In the second regime, surfactant concentration inside the network exceeds the critical micelle concentration and micelles are formed; in this regime the network collapses because surfactant molecules, aggregated in micelles, cease to create "exerting" osmotic pressure in the network sample. In the third regime, at very high surfactant concentration, formation of additional micelles inside the network ceases, and the network dimensions coincide with those of the corresponding neutral network.

Synthesis, characterization, and swelling studies of pH‐ and thermosensitive hydrogels for specialty applications

“…11 Apart from the effect of the copolymeric composition and also of the external environmental factors; surfactant-polymer interactions, especially, at the critical micelle concentration (CMC) of the surfactant affects swelling behavior of the hydrogels in a significant manner. [12][13][14][15][16] The presence of surfactants affects swelling behavior of hydrogels by micelle formation. 17 The local mobility of the surfactant molecules those enter association with the hydrogel is considerably higher than in the complex with a compact conformation, and this mobility grows with the increasing number of micelles involved in the associates.…”

High resolution interferometry as a tool for characterization of swelling of weakly charged hydrogels subjected to amphiphile and cyclodextrin exposure

“…The hydrogels only slightly swelled at the CTAB concentrations lower than 10 M. The pronounced hydrogel deswelling is suggested to arise from self-assembling of the adsorbed surfactant molecules inside the hydrogel network. Due to this aggregation the concentration of mobile counterions inside the gel decreases thus reducing the internal osmotic pressure of the gel [58]. Surfactant micelles interconnecting different elastically active chains may additionally contribute to hydrogel deswelling by increasing the crosslinking density [58].…”

“…Due to this aggregation the concentration of mobile counterions inside the gel decreases thus reducing the internal osmotic pressure of the gel [58]. Surfactant micelles interconnecting different elastically active chains may additionally contribute to hydrogel deswelling by increasing the crosslinking density [58]. The finding that these surfactant dependent hydrogel swelling are larger for the more anionic hydrogels and less for the more highly crosslinked hydrogels ( is likely due to adsorption of excessive charged surfactant molecules [59] and is dominated by increasing osmotic pressure.…”

The cooperative binding behavior of sodium dodecyl sulfate to crosslinked chitosan films

“…5 Chitosan, which is a copolyInvestigations of surfactant binding in polyemer mostly of 2-amino-2-deoxy-b-D-glucopyralectrolyte networks have only more recently been nose (GLcN) and 2-acetamido-2-deoxy-b-D-glucoreported and theoretically described. [10][11][12][13] Along with the expected cooperative binding behavior, crosslinked polyelectrolyte gels generally show a 15 The degree of N-deacetylation was then 93-42). The advantages of a surfactant selective electrode in binding studies include excellent sendetermined by acid-base titration 16,17 and molecular weights were obtained by viscometry, using sitivity and reproducibility, small required sample volume, and an electrode tolerance of large the method of Wang et al 18 The chitosan polymer characteristics are reported in Table I To characterize the chitosan-SDS complex, infrared spectra were measured on a Nicolet 510P FT-IR spectrophotometer.…”