title: Osmotic Bulk Modulus of Charged Colloids Measured by Ensemble Optical Trapping.
abstract: The optical-bottle technique is used to measure osmotic bulk moduli of colloid suspensions. The bulk modulus is determined by optically trapping an ensemble of nanoparticles and invoking a steady-state force balance between confining optical-gradient forces and repulsive osmotic-pressure forces. Osmotic bulk moduli are reported for aqueous suspensions of charged polystyrene particles in NaCl solutions as a function of particle concentration and ionic strength, and are compared to those determined by turbidity measurements under the same conditions. Effective particle charges are calculated from the bulk moduli and are found to increase as a function of ionic strength, consistent with previously reported results.
authors.affiliation: Department of Physics, Lehigh University , Bethlehem, Pennsylvania 18015, United States.
authors.forename: Joseph
authors.initials: J
authors.lastname: Junio
authors.affiliation: Department of Physics, University of Massachusetts , Amherst, Massachusetts 01003, United States.
authors.forename: Joel A
authors.initials: JA
authors.lastname: Cohen
authors.affiliation: Department of Physics, Lehigh University , Bethlehem, Pennsylvania 18015, United States.
authors.forename: H Daniel
authors.initials: HD
authors.lastname: Ou-Yang