Reducing surface charge nonuniformity on individual particles through annealing

In the absence of molecular additives, polystyrene latex particles have been shown to be nonuniformly charged. Using the technique of rotational electrophoresis, it has been shown that the standard deviation of ζ potential on individual "bare" particles can be 50-75% of the average ζ potential. With the addition of molecular additives, the charge nonuniformity can be greatly reduced. Now, it is shown that another route to reducing the charge nonuniformity is to anneal the particles at a temperature above the glass transition temperature of the polymer. Annealing reduces the charge nonuniformity by up to 80% on individual particles. Effects on interparticle forces and stability are discussed.