Effect of Ethanol on the Micellization and Gelation of Pluronic P123

Abstract

In certain applications copolymer P123 (E21P67E21) is dissolved in water-ethanol mixtures, initially to form micellar solutions and eventually to gel. For P123 in 10, 20, and 30 wt % aqueous ethanol we used dynamic light scattering from dilute solutions to confirm micellization, oscillatory rheometry, and visual observation of mobility (tube inversion) to determine gel formation in concentrated solutions and small-angle X-ray scattering (SAXS) to determine gel structure. Except for solutions in 30 wt % aqueous ethanol, a clear-turbid transition was encountered on heating dilute and concentrated micellar solutions alike, and as for solutions in water alone (Chaibundit et al. Langmuir 2007, 23, 9229) this could be ascribed to formation of wormlike micelles. Dense clouding, typical of phase separation, was observed at higher temperatures. Regions of isotropic and birefringent gel were defined for concentrated solutions and shown (by SAXS) to have cubic (fcc and hcp) and hexagonal structures, consistent with packed spherical and elongated micelles, respectively. The cubic gels (0, 10, and 20 wt % ethanol) were clear, while the hex gels were either turbid (0 and 10 wt % ethanol), turbid enclosing a clear region (20 wt % ethanol), or entirely clear (30 wt % ethanol). The SAXS profile was unchanged between turbid and clear regions of the 20 wt % ethanol gel. Temperature scans of dynamic moduli showed (as expected) a clear distinction between high-modulus cubic gels (G'max approximately 20-30 kPa) and lower modulus hex gels (G'max<10 kPa).

Effect of ethanol on the gelation of aqueous solutions of Pluronic F127

“…We note that broadly consistent results have been reported for gels of related Pluronic copolymers in ethanol/water solutions, e.g. P123 (E 21 P 67 E 21 ) [10][11][12], P105 (E 37 P 58 E 37 ) [13] and F88 (E 97 P 39 E 97 ) [14].…”

“…A similar increase in particle size with increase in alcohol concentration has been observed by Bharatiya et al for copolymer P123 in aqueous solutions of various alkanols, and has been ascribed to solvation of the alcohols by the micelles [17]. Swelling of the cores of the micelles of related copolymers is known to lead to formation of elongated (wormlike) micelles [12] and, given recent evidence of the formation of such micelles in dilute solutions of F127 in water [18], this may be so in the present case.…”

Natural product mixture analysis by matrix-assisted DOSY using Brij surfactants in mixed solvents

“…For Brij 78, these solutions were in 20% DMSO-d 6 -80% D 2 O (v/v) and for The CMC behavior of various PEO-block copolymers has been investigated in water-ethanol mixed solvents. [33][34][35] These studies have shown that the CMC increased aer addition of ethanol. The addition of DMSO-d 6 to D 2 O seems to show the same tendency, providing better solvent conditions for the Brij 78 and 98 compared to pure D 2 O and disfavoring the formation of micelles (self-assembly).…”

The effect of n-, s- and t-butanol on the micellization and gelation of Pluronic P123 in aqueous solution

“…As described previously for solutions of P123 in aqueous ethanol [10], the onset of turbidity can be assigned to the formation of elongated micelles. Any additive which enlarges the cores of spherical micelles, whether by solubilization in the core or by modifying the water structure in such a way as to increase the association number (N) of the micelles, can cause overstretching of the core chains and promote the sphere-to-cylinder transition.…”

“…We associate the formation of turbid fluids at higher temperatures with the formation of worm-like micelles, as discussed in Section 3.1. Worm-like micelles have been identified in a closely related turbid fluid, 11 wt.% P123 in 10 wt.% ethanol/ water at 55°C, by observation of the characteristic plateau region in its flow curve [10], and elongated micelles have been confirmed in other solutions of P123 in ethanol/water by use of scattering and viscometric techniques [14].…”