Henri L. Rosano

Microemulsions: Formation and stabilization

The influence on the formation of water-in-oil microemulsions of the chain length and cation of the surfactant and the nature of the solvent were studied. From NMR and free energy of adsorption of the alcohol, it was concluded that the alcohol-surfactant interaction is weak. Measurement of the change in the water-oil interfacial tension (..gamma../sub i/) while alcohol was injected into one of the phases was recorded. It was found that ..gamma../sub i/ may be temporarily lowered to zero while the alcohol diffused through the interface. Therefore, it would be possible for a dispersion to occur spontaneously (while ..gamma../sub i/ = 0). The role of the surfactant would be to lower ..gamma../sub i/ and stabilize the system against coalescence. (21 refs.)

The determination of the apparent binding of counterions to micelles by electromotive force measurements

Abstract The determination of the activity of potassium and sodium ions was accomplished by measuring the e.m.f. of the following cell: calomel/KCl saturated//electrolyte/cationic glass electrode. Reproducibility of potentials (±0.1 millivolt) was obtained by using a MacInnes-Belcher calomel half-cell and five-way stopcock assembly. The cell was enclosed in a Faraday box. The measuring circuit consisted of a precision potentiometer and an electrometer in series with the cell. K caprate, K laurate, K myristate, Na caprate, and Na dodecylsulfate were investigated below and above their critical micelle concentrations. Soap solutions were maintained at a pH above 12.3. All soap solutions contained constant cation concentrations. Up to the c.m.c. the measurements indicate that the presence of long-chain anions does not affect the activity of the cations. By assuming that (1) above the c.m.c. any addition of detergent merely increases the number of micelles and (2) the number of anions per micelle is constant, the apparent degree of dissociation of the cations from the micellar unit was calculated and found to be: 0.79 (KC 10 −23°C.); 0.69 (KC 12 −24°C.); 0.24 (KC 14 −25°C.); 0.57 (NaC 10 −26°C.); 0.14 (NaDS−24°C.). These assumptions appear reasonable for solutions just above the c.m.c.

Stability of W1/O/W2 multiple emulsions: Influence of ripening and interfacial interactions

Abstract Both theoretical and experimental approaches to the stability of W 1 /O/W 2 multiple emulsions are developed. The theoretical approach emphasizes the role of Ostwald ripening in countering stability in W/O emulsions, and discusses the addition of an oil-insoluble solute to the inner water phase of the system in order to prevent this mechanism. The approach assumes complete stability of the W 1 /O/W 2 interfacial films. The oil-insoluble solute is shown to stabilize both the first W 1 /O emulsion and the inner water droplets at the O/W 2 interface. The experimental approach shows that the presence of an electrolyte in W 1 is necessary for the stability of a multiple emulsion. The behavior of W 1 /O/W 2 systems containing cetyldimethicone copolyol as low HLB emulsifier and either SDS or betaine (cocamidopropylbetaine) as high HLB emulsifiers is experimentally observed by video-microscopy. The observed variation in structures leads us to consider three possible factors influencing the stability of W 1 /O/W 2 : (1) Laplace and osmotic effects between the two aqueous phases; (2) the interactions between the low and high HLB emulsifiers at the O/W 2 interface; and (3) polymeric thickener–hydrophilic emulsifier interactions in the outer phase (W 2 ).

Determination of the critical surface tension using an automatic wetting balance

Abstract The purpose of this research was to classify fluoropolymer surfaces with regard to their wettability by various liquids. Thin solid blades, coated with various fluoropolymers, were suspended from a force transducer balance. The blades penetrated various hydrocarbon/air and hydrocarbon/water interfaces, and the curves of force acting on the blade versus displacement were recorded. The contact angles hydrocarbon/solid/air and hydrocarbon/solid/water were calculated using: COS θ = t γL and COS i θ = T i γi where θ, θ i : contact and interfacial contact angle; γ L , γ i : surface and interfacial tension; and τ, τ i : adhesion and interfacial adhesion tension. Cos θ versus γ L for various γ L were plotted and γ c (for cos θ = 1) was determined. It was found that there are two critical surface ( γ c ) and critical interfacial ( γ c i ) tensions due to contact angle hysteresis. Three different fluoropolymer surfaces were investigated. When the surface can be used in the form of a well-defined blade and when enough liquid to be tested is available, the method was found to be useful, rapid, and reproducible. Under these circumstances it can be used in place of Zismans well-known sessile drop method.

Effects of the freeze-thaw process on α amylase

Abstract Purified α amylase in an aqueous solution has been subjected to various rates of freezing and thawing. The slower rate of freezing and thawing was more detrimental to the enzyme activity than the faster process. The effect of “protective additives” has also been investgated on this enzyme. Protection was evident for high concentrations of additive but for low concentrations of additive (~0.01%) the enzyme activity was lower than the freeze-thawed enzyme water system.

Mechanism of ionic exchange with carrier molecules through non-aqueous liquid membranes

Abstract In salt “diffusion” blocked systems, “carrier” transport by ionic amphipathic molecules through nonaqueous liquid membranes is explained by an ionic exchange mechanism. “Carrier” transport versus pH was established for lauric acid, stearic acid, alkyl phosphates, and cetyl trimethyl ammonium bromide (CTAB) as well as for the phospholipids lecithin and cephalin. The ionic exchange depends upon the state of ionization of these long-chain “carrier” molecules and ion+-ion− and intramolecular ion-dipole associations at the oil-water interface. Potentiometric titration and surface tension measurements on single and dual components were performed in the presence and in the absence of 1-pentanol, and similarities between the titration and the transport curves were found. The marked influence of molecular aggregate surfaces and charged oil-water interfaces on the bulk pH is established.

Physical aging of even saturated monoacid triglycerides

AbstractThe polymorphism and kinetics of phase transformations of triglycerides have been investigated using a polarizing microscope equipped with a variable temperature gradient stage. Differential thermal analysis, X-ray, NMR, and IR data supplement the visual observations. The α-polymorphic transformation was observed to change with time in the cases of trilaurin, trimyristin, tripalmitin, tristearin, triarachidin, and tribehenin and can be described by the equation:

Competition of cations at charged micelle and monolayer interfaces

t = e^{ - K\Delta T} - 1.