Biomedical subjects

BR Midmore

Publications and source records attributed to BR Midmore.

3 recordsLinked to original sources

PubMed1999

Effect of Aqueous Phase Composition on the Properties of a Silica-Stabilized W/O Emulsion.

A high volume fraction silica stabilized w/o emulsion with small droplet size ( approximately 3 µm) has been prepared using a commercially available hydrophobic silica. Addition of hydroxypropyl cellulose to the dispersed aqueous phase was found to improve the monodispersity of the emulsion by suppressing the production of larger droplets. The droplet size distribution showed complex behavior as the silica concentration was varied, which was explained using a simple kinetic argument. The effect of varying the acidity and ionic strength of the internal water phase was investigated. It was found that the presence of strong acid or strong alkali in the internal aqueous phase increased the gelation of the emulsions by promoting flocculation. This could be explained by acid- and alkali-catalyzed cleavage of surface siloxane groups increasing the number of surface silanol groups. If emulsions of strong acid and strong alkali were mixed, substantial additional gelation (again caused by flocculation) occurred. A possible explanation, preferred by the author, was an electrostatic one involving the interaction of dipoles in close proximity in the flocculated emulsion. Copyright 1999 Academic Press.

Journal Article↗

PubMed1996

Evidence for the Validity of Electrokinetic Theory in the Thin Double Layer Region

Mobility vs potassium chloride concentration data in the thin double layer region has been determined for three untreated commercial polystyrene latices. Using classical thin double layer electrokinetic theory, it has been possible to fit these plots theoretically if it is assumed that there is a constant electrokinetic charge and no anomalous surface conduction. Calculating the zeta potential using the same theory gave data that when plotted against log10 [electrolyte concentration] gave linear plots with slopes approximately equal to the Nernst constant. The calculated electrokinetic charge was almost constant across the electrolyte concentration range, and for the lowest charged latex it was close to the titration charge. As a result, it was concluded that these latices, at least in the electrolyte concentration range studied, do not exhibit anomalous surface conduction inside the shear plane and that their behavior may be described as almost ideal. The data therefore provide further evidence for the validity of classical electrokinetic theory.

Journal Article↗

PubMed1996

Surface Rheological Data for a Polymeric Surfactant Using a Pulsed Drop Rheometer.

Measurements of dynamic interfacial tension of adsorbed layers of the oil-soluble polymeric surfactant E5 have been made using a pulsed drop rheometer. The pulsed drop rheometer is based on the instantaneous expansion of a water droplet in oil. After perturbation an interfacial relaxation occurs and is followed from the drop profile. The difference in pressure across a curved interface and the interfacial tension are directly related. The decay of pressure change, and hence the interfacial tension decay, is followed as a function of time using a sensitive pressure transducer. Concentrations of E5 above and below the CMC were investigated at the n-decane/water and Isopar M/water interfaces. The interfacial tension decays obtained were fitted to known relaxation mechanisms. Fourier transforms were calculated over a complete frequency spectrum to obtain the dilational elasticity and viscosity. Above the CMC, the interfacial relaxation of E5 at both the n-decane/water and Isopar M/water interfaces was shown to be due to the diffusion of micelles to the interface and the subsequent lowering of the interfacial tension. From the calculated diffusion coefficient and micelle size, the micellar aggregation number could be calculated. Below the CMC, both diffusion and reorientation contribute to the interfacial relaxation. It was not possible to determine the parameters for each process because the characteristic frequencies for the two processes are of similar magnitude.

Journal Article↗