The technique of differential electrophoresis can be used to measure subpiconewton forces between Brownian colloidal particles. Previously, this technique was limited by two factors: (1) forces could be measured only between particles with different average zeta potentials and (2) the particles had to be large enough for observation under a light microscope. This paper focuses on overcoming factor 1 by using a third particle as a "handle", allowing forces to be measured between particles with identical zeta potentials. Semianalytical solutions to the electrokinetic equations for three spheres were developed, with results similar to those for two spheres, enabling the ready interpretation of experiments. Interparticle forces were then measured for charged polystyrene latex particles 1.5 and 4.5 μm in diameter over a range of aqueous solution conditions. One important finding was that while nearly-touching particles aggregate irreversibly in the absence of the polyelectrolyte sodium polystyrene sulfonate (NaPSS), the addition of trace quantities of NaPSS enables the particles to form triplets that break with forces of O(10 pN).
All Science Journal Classification (ASJC) codes
- General Materials Science
- Condensed Matter Physics
- Surfaces and Interfaces