Transition from dilute to concentrated electrokinetic behavior in the dielectric spectra of a colloidal suspension.
Dielectric spectroscopy is used to measure the complex permittivity of 200 and 100 nm diameter polystyrene latex suspended in potassium chloride (KCl) solutions over the frequency range 10(4)-10(7) Hz as a function of particle volume fraction (ϕ) and ionic strength. Dilute suspension dielectric spectra are in excellent agreement with electrokinetic theory. A volume fraction dependence of the dielectric increment is observed for low electrolyte concentrations (0.01, 0.05, and 0.1 mM) above ϕ ≈ 0.02. This deviation from the dilute theory occurs at a critical frequency ω* that is a function of volume fraction, particle size, and ionic strength. The dielectric increment of suspensions at the highest salt concentration (1 mM) shows no volume fraction dependence up to ϕ = 0.09. Values of ω* are collapsed onto a master curve that accounts for the length and time scales of ion migration between neighboring particles. The measured conductivity increment is independent of volume fraction and agrees with theory after accounting for added counterions and nonspecific adsorption.
Department of Chemical and Biomolecular Engineering and Center for Molecular and Engineering Thermodynamics, University of Delaware, 150 Academy St., Newark, Delaware 19716, United States.
Peter J
PJ
Beltramo
Eric M
EM
Furst
D003102:Colloids / Q000737:chemistry; D058266:Dielectric Spectroscopy; D007700:Kinetics; D010316:Particle Size; D011137:Polystyrenes / Q000737:chemistry*; D011189:Potassium Chloride / Q000737:chemistry; D012996:Solutions; D013499:Surface Properties
D003102:Colloids; D011137:Polystyrenes; D012996:Solutions; D011189:Potassium Chloride