Phillip V. Nelson

An ultrasound velocity and attenuation scanner for viewing the temporal evolution of a dispersed phase in fluids

Ultrasound scanning using the group velocity of sound to determine the concentration of a liquid or solid phase dispersed in a fluid has been used for many years to characterize dispersions with regard to their long-term stability. The technique has the twin advantages of speed and operation in concentrated, optically opaque dispersions. In this work, the group velocity technique is combined in a single instrument with phase velocity and attenuation spectroscopy measurements to give valuable additional information about particle size and the microscopic particle distribution, related to important destabilization phenomena such as particle flocculation. This provides earlier evidence of the processes that finally lead to gravitational destabilization and reduced shelf life of fluid dispersions such as emulsions. A further advantage is the ability to compare the measured spatial and temporal variation with computer models. The technique works in optically opaque materials and in concentrated colloids, giving a quantitative picture of the macroscopic spatial distribution of the dispersed phase and a semiquantitative picture of microscopic particle aggregation processes. Since these microscopic particle rearrangements are often responsible for the ultimate gravitational destabilization of colloidal systems, the Acoustiscan, as we have called the ultrasonic scanner described herein, may indicate product instability long in advance of visual evidence. New data are presented for protein containing sunflower oil-in-water emulsions, destabilized with Tween 20, in order to exemplify the use of the Acoustiscan for the characterization of food emulsions. The Acoustiscan instrument provides quantitative information about the destabilization of emulsions,dispersions, and colloidal systems in a rapid and informative manner. It simultaneously measures changes in the dispersed phase and follows microscopic changes in the arrangement of particles. The instrument has many other uses, for example, for characterizing crude oil, pharmaceuticals, cosmetics, and agrochemicals. It can also be used to follow crystallization processes. It does all this in materials over an extremely wide concentration range, from a few percent up to the highest concentrations obtainable. Moreover, when data are compared with computer models, it is possible to infer the presence of gels whose yield stress is far lower than any measurable by contemporary rheological equipment. This makes the Acoustiscan ideal for the study of the new soft solid materials currently in development.

Dynamic colloidal interactions between protein-stabilised particles—experiment and simulation

Experimental n data are compared with computer simulation of interactions between two colloidal particles in a laminar n shear field, when one particle is fixed to a wall and a second particle is freely mobile in the shear field n in the narrow gap formed by a second parallel, moving wall. Both colloidal and hydrodynamic interactions n are taken into account in simulating the scattering of the mobile particle by the fixed particle. A detailed explanation is given of the experimental procedure required to perform and observe such particle collisions successfully, n in order to extract the information required to compare with the simulated results. Polystyrene latex particles and n oil droplets of diameter ca. 5 μm, stabilised by pure β-casein, αs1-casein, sodium caseinate or gelatine, were studied in water over a range of pH values and ionic strengths. Within experimental error, the scattering in these systems could not be detected as varying markedly, due mainly to random noise introduced by n Brownian motion, in agreement with the simulation results for a wide range of DLVO plus simple steric-type colloidal n interaction potentials. It is concluded that the dynamic n steric interactions for all the different protein layers, as measured by this technique, may n be quite similar, n or that a more complex n type of dynamic interaction may be involved.

A versatile scanning acoustic platform

We present a versatile and highly configurable scanning acoustic platform. This platform, comprising a high frequency transducer, bespoke positioning system and temperature-regulated sample unit, enables the acoustic probing of materials over a wide range of length scales and with minimal thermal aberration. In its bare form the platform acts as a reflection-mode acoustic microscope, while optical capabilities are readily incorporated to extend its abilities to the acousto-optic domain. Here we illustrate the capabilities of the platform through its incarnation as an acoustic microscope. Operating at 55 MHz we demonstrate acoustic imaging with a lateral resolution of 25 ?m. We outline its construction, calibration and capabilities as an acoustic microscope, and discuss its wider applications.

Chapter 25:Coalescence of Expanding Bubbles: Effects of Protein Type and Included Oil Droplets

Air may be viewed as a renewable, cheap, ‘zero-calorie’ replacement for fat in food products, where it can provide the desired bulk volume, texture, stability and appearance. Air bubbles are a traditional structural component of many foodstuffs such as mousses, ice cream, whipped toppings, etc. Howe...

Determination of protein foam stability from time-dependent pressure monitoring

Abstract An apparatus is described for the determination of protein foam stability from time-dependent measurements of the small pressure changes above the collapsing foam in a closed chamber. Experimental data are reported for foams made with a fixed concentration (0.1% wt) of bovine serum albumin (BSA) and various concentrations of the nonionic polysaccharide dextran at neutral pH. The results show a loss of foam stability at low dextran contents, an increase in stability at high contents, and a minimum level of stability at a dextran:bovine serum albumin (BSA) molar ratio of ~2. The trends in the data obtained with the new pressure monitoring apparatus are consistent with those obtained by visual observations of the rate of foam volume decay.