The potential energy of a pair of polystyrene spheres in alternating electric fields
- Brandeis Univ., Waltham, MA (United States)
- Wellesley College, MA (United States)
The drastic change in the viscosity of electrorheological (ER) fluids when an external electric field is applied has intrigued scientists from many different fields including engineering, chemistry, and physics for over half a century. It has been generally understood that the microscopic attractive forces between induced dipole moments of the suspended particles have important effects on macroscopic fluid properties. Great effort has been given recently to maximizing the strength of the attractive forces between the particles in ER fluids to achieve practical fluids, and important progress has been made. In the preliminary work presented here, we focus on trying to understand the strength of the microscopic interactions between colloidal particles in alternating electric fields. The system used is a model system of aqueous suspensions of monodisperse polystyrene spheres. By using digital microscopy techniques to measure the inter-particle separations between two spheres at thousands of different times and at several different field strengths, we have been able to determine the probability density function P(r) for the separation distance r between the two particle centers. We begin this paper with a theoretical discussion in which the contributions of electrostatic repulsion, electric-field-induced dipole interaction, and van der Waals attraction to the pair potential are first considered. A probability density function for the distance between a pair of particles is then obtained from the pair potential using equilibrium statistical mechanics. The theoretical discussion is followed by a detailed description of the experimental apparatus - one that allows us to isolate pairs of polystyrene spheres in an essentially two-dimensional geometry by restricting the particles to a narrow gap between parallel glass plates. Finally, we examine the results of our experiments and compare our findings with theoretical predictions.
- Research Organization:
- Brandeis Univ., Waltham, MA (United States). Dept. of Physics
- Sponsoring Organization:
- USDOE, Washington, DC (United States); Henry Luce Foundation, New York, NY (United States)
- DOE Contract Number:
- FG02-94ER45522
- OSTI ID:
- 110712
- Report Number(s):
- DOE/ER/45522-2; CONF-940813-43; ON: DE96000735; TRN: 95:007273
- Resource Relation:
- Conference: 208. American Chemical Society (ACS) national meeting, Washington, DC (United States), 21-26 Aug 1994; Other Information: PBD: Apr 1995
- Country of Publication:
- United States
- Language:
- English
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