Charge Nonuniformity on Submicron Particles

Open Access
Balasubramanian, Sruti
Graduate Program:
Chemical Engineering
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 03, 2013
Committee Members:
  • Darrell Velegol, Thesis Advisor
  • James Hansell Adair, Thesis Advisor
  • Themis Matsoukas, Thesis Advisor
  • Kyle Jeffrey Magnuson Bishop, Thesis Advisor
  • nanoparticles
  • zeta potential
  • electrophoresis
Distribution of zeta potential on the surface of a colloidal particle has been previously modeled for spherical, ellipsoidal and spheroidal particles3. The standard deviation in zeta potential distribution has been measured experimentally for micron sized spheroids using rotational electrophoresis. However, the zeta potential distribution has not been mapped on submicron sized and nano-sized particles experimentally since they are difficult to see using an optical microscope and since they are more susceptible to rotation due to Brownian motion and shear. We have devised an experimental method to study the non-uniform distribution of zeta potential on sub-micron sized latex particles. We have observed that clusters of sub-micron particles which have a non-uniform distribution of surface charges rotate to orient themselves in an electric field. We have aggregated sub-micron sized particles using the stimulus-quenching technique4 and have used rotational electrophoresis to measure the angular velocity of the clusters in an electric field. A vertical rotational electrophoresis set up has been used to reduce shear due to settling of huge clusters. Angular velocity has been measured using video microscopy techniques. Each cluster was then approximated to be a spheroid and fitted it to the existing spheroidal model proposed by Velegol and Feick to measure the non-uniformity on a patch of size L on the cluster. The non-uniformity was measured as the standard deviation from the mean zeta potential per patch. Charge non-uniformity was measured for both homo and hetero-clusters of particles.