Thomas W. Healy

Mutual coagulation of colloidal dispersions

A quantitative theory is presented which describes the kinetics of coagulation of colloidal systems containing more than one dispersed species. A general expression has been derived to describe the potential energy of interaction between dissimilar spherical colloidal particles, using the linear (Debye-Huckel) approximation for low surface potentials. An overall stability ratio has been defined which takes into account the possibility of interactions between like, as well as unlike, particles in the system. The errors introduced by the use of the linear approximation have been assessed in terms of their effects on the stability ratio, and found to be quite small. The theory has been used to describe the behaviour of a hypothetical system under various conditions.

The effect of crystal structure on the surface properties of a series of manganese dioxides

Abstract The zero-points-of-charge for a series of manganese dioxides have been determined by both electrophoretic and coagulation-sedimentation techniques. The zpc was found to increase from pH 1.5 for the amorphous δ form of MnO 2 up to pH 7.3 for β-MnO 2 , the most well-defined crystalline form. This variation is interpreted in terms of, and is shown to be in agreement with, the electrostatic field strength concept modified to describe more complex solids. The change in cation-anion spacing, as derived from the volume per unit cell per cation in the crystal lattice, corresponds to a change in the polarization of the water dipoles and their subsequent dissociation to establish the electrochemical double layer at the oxide-water interface.

The energetics of flocculation and redispersion by polymers

Abstract The theory of polymer flocculation and of the filtration of colloidal dispersions flocculated by polymers has been extended to a molecular level. Maximum flocculation occurs at half surface coverage of the solid by adsorbed polymer. A Langmuir type isotherm describes the process of adsorption of individual polymer segments with surface sites. An energy profile is presented for the system of colloidal solid and polymer solution as the system undergoes change from dispersed to flocculated to redispersed.

Adsorption of alkylbenzene sulfonate (A.B.S.) surfactants at the alumina-water interface

Abstract The detailed adsorption isotherms of five isomers of sodium dodecylbenzene sulfonate at the alumina-water interface have been determined as a function of concentration and pH. Branching decreases the contribution of hydrophobic interactions to two-dimensional condensation (hemi-micelle formation) at the solid-liquid interface. The benzene ring contributes a hydrophobic adsorption energy equivalent to 3.2 CH2 groups, which is the same contribution that is observed in micelle formation in bulk solution. The detailed application of the hemi-micelle model to alkylbenzene sulfonate (A.B.S.) adsorption is considered and evidence is presented that branching displaces the shear plane out from the interface and that vertical orientation for adsorbed molecules is more likely than horizontal orientation.

The oxide-water interface—Interrelation of the zero point of charge and the heat of immersion

Abstract A quantitative linear relation between the heat of immersion and the pH of the zero point of charge (zpc) of inorganic oxides has been derived. The validity of the derivation has been substantiated by literature values of the two quantities for the inorganic oxides. The basis of the correlation is examined in terms of the electrostatic field strengths of the oxide surfaces, and the role of this field strength in determining both heat of immersion and zpc phenomena is discussed. The field is considered to control both the adsorption and dissociation of water molecules at the solid-liquid interface.

Diffusional mixing in an ideal system

Abstract A quantitative theory is presented which describes the mixing of two identical powders in a horizontal barrel mixer. It is proposed that when two components are loaded end-to-end in a simple barrel mixer, mixing can occur only by diffusion. By application of the equations of diffusion, theoretical expressions for the kinetics of the process have been derived. An experimental system has been devised for studying the mixing of essentially identical components. The progress of mixing is followed by a sampling and assaying technique which allows quite accurate determination of concentration with minimal disturbance of the charge. Excellent agreement is obtained when comparing the experimental data to the theoretical predictions.

The mechanism of adsorption of fatty acids and other surfactants at the oxide—water interface

Abstract The technique of microelectrophoresis was used to obtain electrochemical evidence of any specific adsorption of saturated and unsaturated fatty acids and other surfactants at the Al 2 O 3 and Fe 2 O 3 —water interfaces. The adsorption of alkyl sulfonates and sulfates on both of these oxide colloids resulted from simple physisorption together with subsequent hydrophobic interaction at higher adsorption densities. Lauric acid also adsorbed on alumina by simple physisorption plus hydrophobic interaction whereas on Fe 2 O 3 it showed not only hydrophobic adsorption but also specific chemisorption. In contrast, potassium octyl hydroxamate showed very strong specific chemisorption but no hydrophobic interaction. Oleic acid appears to chemisorb on both Fe 2 O 3 and A1 2 O 3 , but it is complicated by deterioration of the oleic acid.

The transport of water through monolayers of long-chain n-paraffinic alcohols

The importance of the chain length of the monolayer-forming molecule on evaporation resistance and spreading rate has been emphasized. n nEvaporation resistance-surface pressure isotherms show that n-hexane as the spreading solvent does not have a deleterious effect on the resistance; whereas benzene, since it is retained to some extent in the monolayer, reduces the resistance of a monolayer at all pressures. Kerosene, although retained at low pressures, is effectively squeezed out of the monolayer at high pressures. n nWe have used resistance-pressure isotherms of high-purity materials to show more conclusively that the forces involved in the formation of a hole in a close-packed monolayer are primarily those of repulsion between the chains. n nFinally we have shown how the Columbia University quiescent evaporation resistance-surface pressure apparatus (Evaporimeter) is a valuable tool for specifying materials suitable for field tests in respect to many properties.

The aggregation of colloidal alumina dispersions by adsorbed surfactant ions

Abstract The stability ratios of suspensions of α-alumina in aqueous solutions of sodium dodecyl sulfonate at constant ionic strength were determined at pH 6.9 and 7.2 at 25°C. and at pH 6.9 at 45°C, by measuring the rate of change of turbidity. Measurements of adsorption of surfactant by alumina and of electrophoretic mobilities of alumina particles and the extent of coagulation of the same system gave isotherms of the same general form. This indicates that coagulation in this system results mainly by reduction in diffuse layer potential because of surfactant adsorption. The dependence of surfactant adsorption and coagulation on pH is extremely marked; there is a much lesser dependence on temperature. Stability ratios were also calculated from the electrophoretic mobility data, and the variation of the ratios with concentration was compared with that evaluated from turbidity measurements.

Effects of alkyl amine surfactants on the corrosion of a rotating copper cylinder

Abstract The corrosion of a rotating copper cylinder in saline solution has been studied in terms of the rest potential and the limiting current density for optimum cathodic protection of the metal. A comparison of these electrochemical parameters has been made in the absence and the presence of alkyl amine surfactants of various chain lengths. Alkyl amines were found to reduce both the tendency of the metal to corrode and the current requirement for cathodic protection. An attempt has been made to explain the inhibition phenomenon and its dependency on such variables as the electrode rotational speed, surfactant concentration and chain length.