title: Separability of electrostatic and hydrodynamic forces in particle electrophoresis.
abstract: By use of optical tweezers we explicitly measure the electrostatic and hydrodynamic forces that determine the electrophoretic mobility of a charged colloidal particle. We test the ansatz of O'Brien and White [J. Chem. Soc. Faraday II 74, 1607 (1978)] that the electrostatically and hydrodynamically coupled electrophoresis problem is separable into two simpler problems: (1) a particle held fixed in an applied electric field with no flow field and (2) a particle held fixed in a flow field with no applied electric field. For a system in the Helmholtz-Smoluchowski and Debye-Hückel regimes, we find that the electrostatic and hydrodynamic forces measured independently accurately predict the electrophoretic mobility within our measurement precision of 7%; the O'Brien and White ansatz holds under the conditions of our experiment.
authors: Department of Physics, Purdue University, West Lafayette, Indiana 47907, USA. batodd@purdue.edu
authors: Brian A
authors: BA
authors: Todd
authors: Joel A
authors: JA
authors: Cohen
mesh_terms: D003102:Colloids / Q000737:chemistry* / Q000528:radiation effects*; D003198:Computer Simulation; D004574:Electromagnetic Fields; D004586:Electrophoresis / Q000379:methods*; D008956:Models, Chemical; D008958:Models, Molecular; D055672:Static Electricity; D013314:Stress, Mechanical; D014867:Water / Q000737:chemistry*
chemical_list: D003102:Colloids; D014867:Water