Two kinds of transitions can occur when an emulsified water-oil-ethoxylated nonionic surfactant system is cooled under constant stirring. At a water-oil ratio close to unity, a transitional inversion takes place from a water-in-oil (W/O) to an oil-in-water (O/W) morphology according to the so-called phase-inversion-temperature method. At a high water content, a multiple w/O/W emulsion changes to a simple O/W emulsion. The continuous monitoring of both the emulsion conductivity and viscosity allows the identification of several phenomena that take place during the temperature decrease. In all cases, a viscosity maximum is found on each side of the three-phase behavior temperature interval and correlates with the attainment of extremely fine emulsions, where the best compromise between a low-tension and a not-too-unstable emulsion is reached. The studied system contains Polysorbate 85, a light alkane cut oil, and a sodium chloride brine. All transitions are interpreted in the framework of the formulation-composition bidimensional map.
A large variety of amphiphilic polylactide-grafted dextrans has been synthesized with controlled architecture through a three-step procedure: partial protection of the dextran hydroxyl groups by silylation; ring-opening polymerization of D,L-lactide initiated from remaining hydroxyl groups on partially silylated dextran; and silyl ether deprotection under very mild conditions. Throughout the synthesis, detailed characterizations of each step led to the control of copolymer architecture in terms of graft number and lengths of graft and backbone. Depending on their proportion in polylactide, these copolymers were either water-soluble or soluble in organic solvents. The potential of these amphiphilic grafted copolymers as surfactants was estimated. Their organization at air/water or dichloromethane/water interfaces was investigated by interfacial tension measurements. Self-organization in water or toluene was evaluated using fluorescence spectroscopy. Depending on its solubility, each copolymer showed noticeable surfactant properties and was able to produce either hydrophobic or hydrated microdomains in water or toluene solutions, respectively.
The surface activity of a series of partially fluorinated amphiphiles with a dimorpholinophosphate polar head, a perfluoroalkyl terminal and a hydrocarbon spacer, C n F 2n1 (CH 2 ) m OP-(O)[N(CH 2 CH 2 ) 2 O] 2 (FnCmDMP, m 1 ± 11, n 4 ± 10), was investigated, and the contributions of the CF 2 and CH 2 groups to the energies of adsorption and micellization of the amphiphiles were determined. In the literature, such data are only available for amphiphiles with either totally fluorinated or totally hydrogenated hydrophobes. We determined the impact of the fluorocarbon segment on the contribution of the hydrocarbon spacer to the adsorption and micellization processes. DG mic and DG ads were evaluated as À 4.2 AE 0.5 and À 4.1 AE 0.6 kJ mol À1 per CF 2 group, consistent with results reported on totally fluorinated surfactants (À 3.3 to À 5.2 kJ mol À1 ). In contrast, the values for DG mic and DG ads per CH 2 group (À 1.0 AE 0.4 and À 1.0 AE 0.6 kJ mol À1 , respectively) were substantially lower than those measured for hydrocarbon analogues of the FnCmDMPs (À 2.4 AE 0.4 and À 2.5 AE 0.5 kJ mol À1 ), which fall in the range observed for standard hydrocarbon amphiphiles (À 2.4 to À 3.05 kJ mol À1 ). These results show that a hydrocarbon chain grafted to a fluori-nated chain does not fully participate in the micellization and adsorption processes, and behaves as if it were shorter by a factor of about three. Thus it is primarily the length of the fluorinated chain that controls micellization and adsorption of such surfactants; the spacer plays only a minor role, and great caution must be exercised when applying the 1 CF 2 % 1.5 CH 2 rule. It is proposed that the hydrocarbon spacer adopts a folded conformation in order to better occupy the void volume which results from the difference in crosssections between fluorocarbon and hydrocarbon chains (ca. 30 vs. 20 2 , respectively).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.