Absorption of ionic amphiphils by oppositely charged polyelectrolyte gels

Abstract

Slightly cross‐linked polyelectrolytes absorb oppositely charged surfactants in aqueous media. Transfer of amphiphilic ions from solution into the swollen network proceeds as a frontal heterogeneous cooperative reaction causing a collapse of the original polyelectrolyte gel. Small and wide angle X‐ray diffraction data show that electrostatic complex formed as a result of the reaction consists of lamellar type surfactant micelles embedded in a polyelectrolyte network. It is also shown that such complexes contain equimolar amount of surfactant ions and ionized polyelectrolyte units paired with amphiphil head groups. In other words a charged network is not able to bind surplus oppositely charged surfactant ions. However, it is still able to solubilize a substantial amount of a nonionized surfactant. Chemical structure of surfactants strongly affect internal structure of lamellae and stability of the complexes.

Volume Transition and Phase Coexistence in Polyelectrolyte Gels Interacting with Amphiphiles and Proteins

“…In the year 1990, Starodubtzev et al published the first report of surfactant-rich shells in polyelectrolyte gels [17]. Shortly after, the group of Zezin and Kabanov (Z&K) reported that binding of short polyion chains and proteins could give rise to similar phenomena [18,[81][82][83][84][85][86]. The early observations of surfactant-rich shells were made on gels of macroscopic size (~1 mL), that either had been immersed for a short time in a "salt-free" surfactant solution and then transferred to pure water, or stored long times in solutions containing limited amounts of the surfactant.…”

Regular and irregular deswelling of polyacrylate and hyaluronate gels induced by oppositely charged surfactants

“…When the gel is placed in a solution containing oppositely charged surfactant of a concentration exceeding the critical association concentration (cac), but of equal ionic strength, the surfactant monomers will diffuse into the gel and there form micelles [11]. This allows the release of the counter ions previously neutralizing the polymer charges and, due to the subsequent lowering of the swelling pressure, causes the gel to collapse [1,4,6]. As micelles form in the gel, the outer part will collapse first, causing a phase separation with a dense, outer, micelle rich surface phase and a still swollen, micelle lean core [1][2][3]5].…”

“…For some of these a non-uniform deswelling with the formation of a surface phase has been reported [1][2][3]5,6,8,9]. In general, a polyelectrolyte gel, such as a crosslinked polyacrylate (PA) or hyaluronate (HA) gel, is in its reference state swollen due to the swelling pressure provided by the counter ions present inside the gel [11].…”

“…As micelles form in the gel, the outer part will collapse first, causing a phase separation with a dense, outer, micelle rich surface phase and a still swollen, micelle lean core [1][2][3]5]. As more surfactant is absorbed into the gel, the surface phase will grow at the expense of the core [1,6]. The regular deswelling behavior is that the gel continuously deswells as the collapsed surface phase grows, exerting higher pressure on the core, while the core is gradually converted to surface phase, until the entire gel has collapsed [1], see Fig.…”

“…There are several descriptions in the literature of the deswelling of both macroscopic [1][2][3][4][5][6][7] and microscopic [8][9][10] charged polymer gels in the presence of oppositely charged surfactants. For some of these a non-uniform deswelling with the formation of a surface phase has been reported [1][2][3]5,6,8,9].…”