Robert D Vold

The effect of lauryl alcohol on the stability of oil-in-water emulsions

Abstract The effect of addition of lauryl alcohol was determined on the rate at which oil was separated in an ultracentrifuge from emulsions of Nujol and of olive oil in water, stabilized with 0.2% or 0.4% sodium dodecyl sulfate (SDS). In a Nujol-water-0.2% SDS emulsion with a specific interfacial area of 1.08 × 10 4 cm 2 /ml emulsified oil the stability increases with added lauryl alcohol up to 56% on the basis of the SDS, after which it remains constant. The stability of the olive oil-water-SDS emulsions is unaffected by addition of lauryl alcohol. Calculations show that the increase in stability of the Nujol emulsions can be attributed to adsorption of lauryl alcohol on areas of the oil-water interface not occupied by adsorbed SDS. The absence of any stabilizing effect in the case of the olive oil emulsions is attributed to the greater solubility of lauryl alcohol in olive oil than in Nujol.

The effect of electrolytes on the ultracentrifugal stability of emulsions

Abstract The rate of separation of oil from 50 volume per cent Nujol-50 volume per cent water emulsions stabilized with either 0.2% or 0.4% sodium dodecyl sulfate (SDS) on the basis of the aqueous phase was determined on ultracentrifugation at 113,200 g over a range of concentrations of sodium chloride from zero to 0.1 M. The oil-water interfacial area of these emulsions and the effect of added salt on the adsorption of SDS at the interface were also determined. At equilibrium concentrations of SDS in the aqueous phase both larger and smaller than the critical micelle concentration (cmc) the rate of separation of oil varies inversely as the logarithm of the total concentration of sodium ion supplied by the added sodium chloride and the SDS. Adsorption of dodecyl sulfate at the oil-water interface increases directly with the logarithm of the total concentration of sodium ion. Both with and without added salt the rate of separation of oil decreases linearly with increasing fractional saturation of the interface with adsorbed dodecyl sulfate, thus indicating that under ultracentrifugal conditions the rate of coalescence is directly proportional to the area of “bare” oil-water interface. The functional dependence of the rate of separation of oil on the concentration of added salt does not appear to be consistent with rate of drainage of water from the emulsion, or rate of sedimentation or diffusion of micellar SDS, as rate-determining steps in the coalescence process under ultracentrifugal conditions.

Differences between fact and theory in the stability of carbon suspensions in heptane

Abstract In order to test the adequacy of the present theories of the stability of nonaqueous suspensions, rates of flocculation of Graphon suspensions were determined in heptane from the change of optical density with time in the presence and absence of Triton X-35 and dodecylbenzene (DDB). Viscosities of the solutions and the adsorption isotherm for each of the additives on Graphon were also determined. In the DDB system, the reduced stability ratio calculated from the balance of the van der Waals attraction and the entropic repulsion between particles increases rapidly as a function of the DDB concentration. However, the experimental value increases gradually to an apparent limiting value reached at a mole fraction of DDB corresponding to about 3/4 surface coverage as inferred from the adsorption isotherm. Since the viscosity measurements show a positive value for the second virial coefficient, it is possible that the observed enhancement of stability in this system is due to osmotic rather than entropic effects. Triton X-35 neither increased nor decreased the stability of carbon suspensions in heptane. At lower concentrations, assuming the adsorbed molecules to be flat on the surface so there would be no entropic repulsion, calculation showed that the adsorbed film did not make sufficient change in the van der Waals attraction to change the value of the reduced stability ratio, either because the thickness of the film is too small or because its Hamaker constant is too close to that of the solvent itself. Judging from the viscosity data, the second virial coefficient of the solutions is so close to zero at the concentrations used that no osmotic repulsion would be expected.

Polymorphic transformations of calcium stearate and calcium stearate monohydrate

Abstract Anhydrous calcium stearate undergoes transformations at 65°, 86°, 123°, 150°, and 195°C. It melts with decomposition at 350°C. The substance can be obtained at room temperature either as a stable crystal, an unstable crystal (by quenching from between 123° and 150°), or a vitreous form (by quenching from above 150°). Differential heating and cooling curves and X-ray diffraction patterns of quenched samples at room temperature are presented. The set of transformations is partially analogous to that for sodium stearate, the resemblance being greater at low temperatures and less marked at high temperatures where, with the hydrocarbon chains irregularly packed and relatively mobile, the difference in binding power between sodium and calcium ions becomes important. Calcium stearate forms a monohydrate whose decomposition temperature at atmospheric pressure is about 110°C. Calcium stearates of technical quality resemble the pure material but tend to assume the vitreous form more readily and to crystallize completely only with difficulty.

Phase relations in the system: Sodium stearate-cetane

Abstract The system sodium stearate-cetane has been investigated with a polarizing microscope in a specially designed hot stage, and a partial phase, diagram constructed from these data. The change from synerectic to non-synerectic systems, together with the accompanying change in rheological properties, has been shown to be related to the existence of a unique phase transition. An attempt is made to correlate these effects with the internal structure of the phases.

Particle size from the optical properties of flocculating carbon dispersions

Abstract The reasons for the inapplicability of Mie theory to systems where the dispersed particles are aggregates of smaller primary particles are discussed. It is shown what conditions must be satisfied before two similar suspensions with the same specific optical density at a given wavelength may be asserted to have the same average floc size, and that it is not possible even to make unambiguous comparisons of relative size from such data alone. A method is developed for obtaining the relative size of the flocs in two suspensions from the specific optical densities, the exponent of the dependence of optical density on wavelength, and single independent estimate of the average size of the dispersed particles in one of the suspensions, obtained by electron microscopy. It is shown that this leads to reasonable values of the average floc radius in suspensions of colloidal carbon in nonaqueous solvents, and for the relative change of floc radius with time due to flocculation of the suspension.

Rates of flocculation and deflocculation in dispersions of carbon black in hydrocarbons

Abstract The optical density of carbon black suspensions in heptane, toluene, and solutions of polystyrene in toluene and in cyclohexane, decreases with time and ultimately reaches a steady-state value. This is interpreted in terms of the simultaneous occurrence of flocculation and deflocculation following, respectively, second- and first-order kinetic rate laws. A method is developed for obtaining an absolute value of β, the rate constant for deflocculation, from the time dependence of the optical density, assuming that optical density is proportional to floc concentration. The rate constants for both flocculation and deflocculation increase with increasing initial average size of the flocs. The specific rate of redispersion, β, increases with increasing polystyrene concentration in cyclohexane, the effect being explicable in terms of decrease of attraction between carbon particles due to the presence of tightly adsorbed polymer on the surface. In toluene, β passes through a minimum with increasing polystyrene concentration, attributable to decreased redispersion resulting from bridging of particles by extended loops of adsorbed polymer.

Crystal forms of anhydrous calcium stearate derivable from calcium stearate monohydrate

Abstract Anhydrous calcium stearate can be obtained at room temperature in any one of three forms, or mixtures thereof, by dehydration of calcium stearate monohydrate. Calcium stearate VIA is believed to be the stable modification. Calcium stearate VIH is an anhydrous crystalline powder having the same X-ray diffraction pattern as calcium stearate monohydrate. Calcium stearate VIN is relatively amorphous with respect to interchain spacings although it exhibits a crystalline long spacing. Samples of calcium stearate hydrate which yield calcium stearate VIH upon dehydration lack a second order thermal transition at 48°C. characteristic of calcium stearate hydrate samples which yield calcium stearate VIA upon dehydration. Evidence is presented supporting the interpretation that transformation of the hydrate type structure to the anhydrous type is inhibited by impurities in the calcium stearate, particularly adsorbed calcium salts and foreign fatty acid anions.

A simple method for determination of the average particle size of coarse suspensions from measurements of apparent specific turbidity

Abstract If the turbidity of a suspension of large spherical polydisperse particles is independent of the wavelength of light, the apparent specific turbidity, as measured by an inexpensive commercially available spectrophotometer, is inversely proportional to the average radius of the particle size distribution. It is shown experimentally that this relation holds for suspensions of monomodal polydisperse styrenedivinylbenzene copolymer latices of average radius from 12 to 50 μm. This observation permits development of a quick method for determination of the various average particle sizes of coarse monomodally polydisperse suspensions from apparent specific turbidity measurements using a simple spectrophotometer such as the Spectronic-20. Attempts to verify similar relations for the determination of the average floc size of suspensions of silica and carbon black were unsuccessful, since it was not possible to obtain comparison values of the floc size distributions by the Coulter Counter because of extensive deflocculation of the aggregates on passage through the aperture.

The effect of temperature on the stability of Nujol-water emulsions

Abstract The rate of separation of oil from Nujol-water emulsions stabilized with sodium dodecylsulfate (SDS), cetyl pyridinium chloride (CPyCl), Tween 20 or Triton X-100 was determined over the temperature range from 5 to 30°C in an ultracentrifuge at 39,460 rpm. The emulsions were all found to be less stable at the higher temperatures, but the change in stability with temperature was such as to suggest that it is not caused primarily by changes of the viscosity with temperature. The results with SDS could be fitted to a zero-order rate expression, leading to a calculated activation energy of 9.0 kcal, but the rate of loss of oil by the other emulsions conformed to no simple rate law.