Ultrasound propagation in colloidal dispersions

Sherman, Nigel E. (1989) Ultrasound propagation in colloidal dispersions. Doctoral thesis, City of London Polytechnic.


This thesis describes apparatus and techniques for making ultrasonic measurements in fluids and applications of them to measurements of ultrasonic parameters in colloidal dispersions.

A brief description of the properties and uses of ultrasound propagation in dispersions is followed by an extensive review of theories which relate the particulate properties of the dispersions to the measurable ultrasonic parameters, velocity (c) and attenuation (a [alpha]).

Measurement principles are outlined related to the design of near-field measurement methods and the development of three techniques is described. These are shown 10 give results which are both highly self-consistent and in excellent agreement with a far-field method.

Measurements of a[alpha] and c for model dispersions of glass spheres in Newtonian Iiquids are shown to be in good agreement with the relevant theory when particle polydispersity is taken into account. For structured fluids as the continuous phase, the a[alpha] and c data for suspensions of spheres are used to obtain the continuous phase viscosity (n). The a[alpha] data agree approximately with the macroscopic viscosity, but the velocity data requires the introduction of a shear elastic term and the revision of theory in order to obtain agreement.
Attenuation as a function of barite concentration in Newtonian liquids was investigated and the ultrasonic particle radius was found to be systematically larger than expected. This is attributed to particle rugosity.

Measurements of a[alpha] and c using non-gelling aqueous kaolinite suspensions are shown to agree well with theory when the eccentricity and the interactions of particles are taken into account. For gelling aqueous bentonite suspensions, a[alpha] and c were found to be time-dependent over a period of several days following initial dispersion. The observed increases in both a[alpha] and c are interpreted in terms of a growth in gel fraction and shear modulus, respectively. The effect of shear flow on a[alpha] and c was investigated for the above dispersions. Changes were barely resolvable but consistent with shear-degradation of structure within the fluid.

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