Heat‐Induced Phase Transitions from an Aqueous Solution to Precipitates in a Poly(sodium 4‐styrenesulfonate)/Tetradecyltrimethylammonium Bromide System

Abstract

For the first time, temperature-induced phase transitions upon heating and cooling an aqueous solution that contained oppositely charged polyelectrolyte and surfactant mixtures was observed. The phase transition from micelles to vesicles, then to the coexistence of vesicles and superstructures that have the morphology of melon seeds, and finally to precipitates was determined by means of turbidity measurements and transmission electron microscopy images. These phase transitions were shown to be reversible and reproducible after several heating and cooling cycles were performed on the same sample. The novel observations for the temperature-induced phase transition from primary aggregates, such as micelles, to superstructures (i.e., vesicles) should provide new understanding for surfactant sciences, and in particular for self-assembled amphiphilic systems.

New observation of near-reversible behaviors for the redox couple in vesicular solution

“…The electrode was polished with chamois and was cleaned ultrasonically in 95% ethanol prior to use. The electrochemical behaviors of K 4 [Fe(CN) 6 ] were examined using cyclic voltammetry (equipment, 600B CHI electrochemistry analytical instrument, USA) under a nitrogen atmosphere. A saturated calomel electrode (SCE) and a Pt plate were used as the reference and the counter electrodes, respectively.…”

“…However, while adding K 4 [Fe(CN) 6 ] in salt catanionic surfactant system, many precipitates came into being.…”

“…A pair of welldefined redox peaks of ½FeðCNÞ 6 3À=4À is observed in TTAOH/LA vesicular solution only with DE p = 61 mV at a scan rate of 0.001 V/s. For further understanding and determining the superiority of the electrochemical behaviors of ½FeðCNÞ 6 3À=4À in salt-free TTAOH/LA vesicle phase solution, the cyclic voltammograms of K 4 [Fe(CN) 6 ] in SDS, TTABr/SDS (r TTABr/SDS = 1/99) and TTAOH/LA micelle phase solutions were also studied. …”

“…Based on the detailed research on the phase behavior of salt-free catanionic surfactant system of TTAOH and LA [14], the electrochemical behavior of K 4 [Fe(CN) 6 ] in TTAOH/LA vesicle phase solutions was studied. In this salt-free catanionic surfactant system, no precipitates appeared after adding K 4 [Fe(CN) 6 ]. What is more, new observation of near-reversible behaviors for the ½FeðCNÞ 6 3À=4À redox couple in this vesicle phase solution was obtained.…”

“…Depending on the strength of intra-and intermolecular interactions, the relative fractions of different groups within the surfactant molecules and the shape of the surfactant molecules, the mixtures of anionic and cationic surfactants can also self-assemble into these various microstructures [1,2]. Mixtures of anionic and cationic surfactants in water produce the so-called ''catanionic" mixed solutions, which are the fascinating subject of extensive investigations recently [3][4][5][6][7][8]. Among the catanionic surfactant mesophases, there has been much interest in studying the microstructures and properties of the spontaneous vesicles at thermodynamic equilibrium, which was demonstrated for the first time by Kaler et al [9] in 1989.…”