Phase Behavior of Bicontinuous and Water/Diesel Fuel Microemulsions Using Nonionic Surfactants Combined with Hydrophilic Alcohol Ethoxylates

Bicontinuous and water-in-diesel microemulsions were formulated using single nonionic alkyl poly glycol ethers combined with hydrophilic alcohol ethoxylates. The phase behavior at temperatures ranging from 0°C to 50°C was investigated. Visual inspection as well as cross-polarizers were used to detect anisotropy. The fish phase diagrams were determined. The presence of the hydrophilic alcohol ethoxylates was necessary to initiate both types of microemulsions. Increasing the hydrophobic chain length of the surfactant led to a wider range of temperature stability at lower surfactant concentration. Meanwhile, increasing the ethylene oxide units in the headgroup by two units led to a phase diagram that is dominated by lyotropic liquid crystal. The formulated water in diesel microemulsions were tested experimentally in a 4-cylinder diesel engine. From this it is observed that the emissions of NO_x, soot, and CO₂ were reduced substantially compared to neat diesel, while for the CO the reduction occurs just at low load.      

Effects of Nonionic, Cationic, and Mixed Nonionic-Cationic Surfactants on the Acid-Base Behavior of Phenyl Salicylate

The effects of Brij 35 micelles, CTABr micelles, and mixed Brij 35–CTABr micelles on the acid–base behavior of phenyl salicylate (PST) have been studied in aqueous solution containing 2% v/v acetonitrile. The apparent pK_b (pK^app_b) of PST is decreased by 1.5 pK units with the increase in [Brij 35] from 0 to 0.02 M which is attributed to micellar medium effect. The values of pK^app_b remain almost independent of [CTABr] within its range 0.01–0.03 M. The increase in [CTABr] from 0 to 0.03 M in aqueous solution containing 0.02 M Brij 35 has not resulted in a change in pK^app_b. This shows that the characeristic structural features of nonionic Brij 35 micelles remain essentially unchanged on addition of CTABr under the present experimental conditions.     

Propylene Glycol and Ethoxylated Surfactant Effects on the Phase Behavior of Water/Sucrose Stearate/Oil System

In this work, we studied the phase behavior as function of temperature of water/sucrose stearate/propylene glycol/oil and water/sucrose stearate/ethoxylated mono‐di‐glyceride/oil systems. The oils were R (+)‐limonene, isopropylmyristate, and caprylic‐capric triglyceride. It was found that adding propylene glycol and ethoxylated mono‐di‐glyceride to the water/sucrose stearate/R (+)‐limonene and water/sucrose stearate/isopropylmyristate systems decreases the temperature and surfactants concentration needed for the formation of a microemulsion phase region and no three phase region is observed. In the case of water/sucrose stearate/caprylic‐capric triglyceride system a three phase region is observed. In the caprylic‐capric based system, it was found that increasing the propylene glycol and ethoxylated mono‐di‐glyceride contents decrease the phase inversion temperature and increases the efficiency. In the case where the mixed surfactants (sucrose stearate and ethoxylated mono‐di‐glyceride) were present in the system, the efficiencies observed are higher than those observed in the system based on the mixture of sucrose stearate and propylene glycol.     

On the Behavior of Nonionic Surfactants at the N-Heptane/Silica Gel Interface: Influence of the Presence of Interfacial Water Inferred from Adsorption Isotherms and Calorimetric Data

The behavior of two polydisperse nonionic surfactants, poly (oxyethylene) glycol alkylphenyl ether TX-35 and TX-100, at the prewetted silica gel/n-heptane and dried silica gel/n-heptane interfaces has been compared by the determination of the average adsorption isotherms of the polydisperse surfactants and of displacement enthalpies. From HPLC experiments, we could also separately quantify the adsorption of each ethyleneoxide (EO) fractions for silica gel from the polydisperse surfactant solution. The adsorption isotherms clearly indicate an incomplete preferential adsorption of the large (EO) chains over the small ones, as well on dried silica gel as on a prehydrated sample. This preferential adsorption and its driving force follow the solubility rules of the poly(oxyethylene) glycol alkylphenyl ether in an apolar solvent and support the idea of a solubility-limited adsorption: solubility in organic solvents of the smaller (EO) chains is much more significant than that of the longer ones and hence prevents adsorption of the smaller species. Consequently, it is observed that the presence of interfacial water decreases the affinity of TX-35 molecules for the hydrophilic silica surface due to the hydration of (EO) chains. In contrast, for TX-100 adsorption after the prewetting treatment the clearest trend is a drastic increase of the adsorption ascribed to the additional solubilization (and micellization) of the TX-100 molecules in the interfacial aqueous phase. The differential molar enthalpies of displacement show a change in the adsorption mechanism, depending on the presence of molecular water on the surface. In the initial part of the adsorption isotherm, a prevailing exothermic process is obtained with prehydrated silica and suggests that hydration of the polar heads of TX-35 and the solubilization of the TX-35 in interfacial water are occurring. For higher equilibrium concentrations, the enthalpies of displacement observed with the prehydrated adsorbent become slightly lower than those obtained with dry silica gel. It may be that this difference is due to the micellization phenomenon of the surfactant species with longer EO chains in interfacial water. These features emphasize the influence of interfacial water on the adsorption of EO fractions from organic solvent. Copyright 2000 Academic Press.     

Physicochemistry of Mixed Systems of Water/AOT (Surfactant)/Alkanol (Cosurfactant)/Cycloalkanone (Oil): A Detailed Study of Phase Behavior,Salt Effect,and Conductance Properties

Water in oil microemulsion (μE) systems comprising water/AOT ± alkanol (n-butanol to n-dodecanol)/cycloalkanone (cyclopentanone to cycloheptanone, CA5, CA6, and CA7) were physicochemically studied with respect to phase and conductance behaviors. In absence of alkanols, AOT produced large clear zone with the cycloalkanones, compared to linear alkanes. Clear zone was comprised of gel, viscous, and clear fluid. Alkanols increased the fluidity of μE while its clarity was reduced. A maximum two-phase region was observed for n-heptanol (also for formulations with n-octanol). Salts, which reduced the clarity of the μE, followed the order of effectivity: Na⁺ < Mg²⁺ < Al³⁺. A correlation between clarity and turbidity was found irrespective of molecular size of oil, cosurfactant and salt. The influence of water and temperature on the conductance behavior of W/O formulations was studied. The studied systems were found to be less conducting than those with linear alkanes. Energetics and other structural parameters of the studied systems were evaluated from conductance behavior and the use of scaling equations.