MEASUREMENT OF PARTICLE INTERACTIONS IN COLLOIDAL SYSTEMS USING FIBER OPTIC DOPPLER ANEMOMETRY (FODA) AND VISCOMETRY
Abstract
Fiber Optic Doppler Anemometry (FODA) has been validated for directly determining the particle size of colloidal dispersions using standard monodisperse polymeric latexes. The use has been further extended for direct measurement of colloidal particle interactions by using the integrated area under the curve (AUC) from the power spectrum output of the modified Lorentzian function, which can be directly related to the colloidal fraction that exhibits Brownian motion. From the AUC monitoring, together with viscometric measurements, several factors affecting particle interactions have been identified through the use of two model disperse systems, monodisperse polymeric latexes with a permanent surface charge and polydisperse aluminum hydroxide suspension with a pH-dependent surface charge. The colloidal particle interactions were favored by increased disperse phase volume fraction and by decreased particle size. The addition of electrolyte caused increased particle interaction in agreement with DLVO theory. For pH-dependent aluminum hydroxide suspensions, the maximal particle interaction, thus the minimal AUC, was found when the pH of the suspension was adjusted to the zero point of charge (ZPC). Shearing caused the pH to shift toward the ZPC of the aluminum hydroxide suspension, thereby enhancing the particle interactions. The shearing effect under controlled pH was found dependent on the volume fraction of the disperse phase and the pH with respect to the ZPC. The colloidal stability of a dispersion can also be monitored by the AUC from FODA. Small particle size and high surface charge lead to stable dispersions. The particle interactions determined by the AUC from FODA were confirmed: (1) by rheological data including apparent viscosity, yield value and Power Law parameters; and (2) from agreement with the Schulze-Hardy rule and the DLVO theory.
Degree
Ph.D.
Subject Area
Pharmacology
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.