State of water and surfactant in lyotropic liquid crystals

Abstract

performed with DBP in a radioactively contaminated electrodynamic balance yielded similar results except that mass losses as large as 75% and charge losses as large as 63% occurred. The mean value of q-/qRL was 0.73 for these data, which is not statistically different from the previous result. It is likely that the electric fields used to suspend the droplets affect the stability phenomenon, that random thermal fluctuations in local surface charge density can contribute only in a minor way to the instability, and that surface contamination can alter the fragmentation of the exploding droplet.Differential scanning calorimetry (DSC) and 'H NMR spectroscopy were used to study various lyotropic liquid crystalline phases of sodium bis(2-ethylhexyl)sulfosuccinate (Aerosol OT or AOT) and water. At 25 "C the lamellar liquid crystalline phase contains between surfactant bilayers bulklike water ("water l"), which has a melting point Tlm = 0 "C and an enthalpy of melting AHlm = 80 cal/g. Close to the bilayers, the lamellar liquid crystalline phase contains interfacial water, "water 2", which melts at TZm = -4 f 2 "C and has AH2" = 35 f 8 cal/g of water. After most of water 1 and 2 freezes, the surfactant and the remaining liquid water undergo a phase transition to a nonlamellar liquid crystalline phase. In this phase, "water 3" melts at T3"' = -9 1 "C and has AH3m = 12 f 5 cal/g of water. When water is in ultrathin (510 A) films in lamellar liquid crystal, then water 1 is absent and water 2 can be supercooled to -45 "C or lower. The surfactant has substantial rotational mobility even when the water is frozen at temperatures from -35 to -10 "C. Similar phase and thermal behavior is observed when initially isotropic aqueous micellar solutions of AOT are frozen or melted.

Phase behavior of the Pluronic P103/water system in the dilute and semi-dilute regimes

“…1) exhibit, in addition to those corresponding to the melting of bound (i.e., strongly structure-associated) and bulk water (peaks I and II) [37], Table 1 Onset temperatures of the CMT, MGT, and CPT, determined by various techniques, as a function of P103 concentration. three endothermic peaks that have been also detected in P84 and P85 aqueous solutions in the temperature range where spherical and elongated micelles form [9].…”

Lamellar Liquid Crystal Improves the Skin Retention of 3-O-Ethyl-Ascorbic Acid and Potassium 4-Methoxysalicylate In Vitro and In Vivo for Topical Preparation

“…The gel-liquid crystal transition as well as phase transition between different liquid crystalline phases consumed low amount of energy; therefore, only a small endothermic peak occurred at 54°C (12). The peak at −5.92°C of the COW cream must be the result of Bmelting^of the interfacial water, which Bmelts^easier than the bulk-like water (14).…”

“…The peak at −0.42°C was due to the Bmelting^of bulklike water located between the bilayers of the lamellar liquid crystals (14), and peak at 54°C represented the gel-liquid crystal transition, possibly a result of the Bmelting^of the hydrocarbon tails of the surfactant in the bilayers from an ordered structure to a more disordered state. Similar results have also been reported previously, in which this phenomenon was explained as thermal transitions in surfactant-based lyotropic liquid crystals (15).…”

Fibrillar morphologies of hydrogels obtained from a lamellar medium

“…Table 3 shows that for the macroscopic monophasic samples, the thickness of the fibrils presents a minimum for an AOT concentration around 46 wt%. In order to understand this behaviour, it should be taken into account that there is a considerable change in some physical properties of the AOT/water system around this concentration: there is a change in the sign of the birefringence [29], the conductivity reaches a maximum [31], no bulk-like water is detected [42], there is a broadening of the 1 H-NMR water resonance [43]. Additionally, the viscosity shows a minimum at this concentration, which has been explained [44] as a minimum in the coulombic interactions, resulting in weaker interactions, a decrease of connectivity among microdomains, and more structural defects.…”