Nonaqueous colloid characterization

This paper is intended to review characterization methods of nonaqueous colloids, their physical properties and technological applications. 

The description of a colloid should include particle size, mobility, charge and their distributions, charge/mass ratio, electrical conductivity of the media, concentration and mobility of ionic species, the extent of a double layer, particle-particle and particle-substrate interaction forces and complete interfacial analysis. The application of classical characterization methods to nonaqueous colloids is limited and, for this reason, the techniques best suited to these systems will be reviewed. Characteristic results obtained with nonaqueous dispersions will be summarized. Physical aspects, such as space charge effects and electrohydrodynamics, will receive special attention while the relationships between chemical and physical properties will not be addressed. An application of nonaqueous colloids, the electrophoretic development of latent images, will also be discussed. 

Electrochemical methods are in general free from the difficulties associated with the current industry testing methods and present an opportunity for a relatively quick, simple, and inexpensive approach, free of temperature limitations and sample preparation issues. Electrochemistry has been previously employed to inspect lubricant condition over the life of engine oils [6, 7]. For example, electrochemical impedance spectroscopy (EIS) has been used for characterization of both engine oils [8] and nonaqueous colloidal dispersions [9]. 

EIS characterization of electrorheological fluids (ERF) represents an interesting subsegment of dielectric analysis of nonaqueous colloidal systems. Analogous to soot-contaminated lubricants (Chapter 10), ERFs can be described as... 

D. Fennell Evans is the director of the Center for Interfacial Engineering and professor of chemical engineering and materials science at the University of Miimesota. He is the author of more than 180 publications on self-assembly processes in water and nonaqueous solvents, microemulsions, diffusion in liquids and micellar solutions, and characterization of surfaces using scanning probe techniques. He has published two textbooks. The Colloidal Domain and The Fundamentals of Interfacial Engineering. 

Particle-size and mass distribution curves, along with information on particle porosity, density, shape, and aggregation, can be obtained for submicrometer- and supramicrometer-size silica materials suspended in either aqueous or nonaqueous media by field-flow fractionation (FFF). Narrow fractions can readily be collected for confirmation or further characterization by microscopy and other means. Among the silicas examined were different types of colloidal microspheres, fumed silica, and various chromatographic supports. Size distribution curves for aqueous silica suspensions were obtained by both sedimentation FFF and flow FFF and for nonaqueous suspensions by thermal FFF. Populations of aggregates and oversized particles were isolated and identified in some samples. The capability of FFF to achieve the high-resolution fractionation of silica is confirmed by the collection of fractions and their examination by electron microscopy. 

In this chapter, both colloidal silica and coarser silica materials such as chromatographic supports are examined. The particle sizes range from 0.01 to 20 pm. An arsenal of FFF subtechniques was used, including sedimentation FFF, flow FFF, and thermal FFF. Although most of these studies involve aqueous suspensions, thermal FFF is shown to be capable of fractionating and characterizing nonaqueous suspensions of silica as well. 

Valentin C., Munoz M.C., Alarcdn J. Synthesis and characterization of vanadium-containing ZrSi04 solid solutions from gels. J. Sol-Gel Sci. Technol. 1999 15 221-230 Van Helden A.K., Jansen J.W., Vrij A. Preparation and characterization of spherical monodisperse silica dispersions in nonaqueous solvents. J. Colloid Interf. Sci. 1981 81 354-368 Woodhead J.L. Sol-gel processes to ceramic particles using inorganic precursors. J. Mater. Educ. 1984 6 887-925... 

---