title: Effects of non-Gaussian Brownian motion on direct force optical tweezers measurements of the electrostatic forces between pairs of colloidal particles.
abstract: Measurements of the electrostatic force with separation between a fixed and an optically trapped colloidal particle are examined with experiment, simulation and analytical calculation. Non-Gaussian Brownian motion is observed in the position of the optically trapped particle when particles are close and traps weak. As a consequence of this motion, a simple least squares parameterization of direct force measurements, in which force is inferred from the displacement of an optically trapped particle as separation is gradually decreased, contains forces generated by the rectification of thermal fluctuations in addition to those originating directly from the electrostatic interaction between the particles. Thus, when particles are close and traps weak, simply fitting the measured direct force measurement to DLVO theory extracts parameters with modified meanings when compared to the original formulation. In such cases, however, physically meaningful DLVO parameters can be recovered by comparing the measured non-Gaussian statistics to those predicted by solutions to Smoluchowski's equation for diffusion in a potential.
authors.affiliation: Institute of Fundamental Sciences, Massey University, Palmerston North, New Zealand. A.Raudsepp@massey.ac.nz.
authors.forename: Allan
authors.initials: A
authors.lastname: Raudsepp
authors.affiliation: Institute of Fundamental Sciences, Massey University, Palmerston North, New Zealand.|MacDiarmid Institute for Advanced Material and Nanotechnology, Victoria University of Wellington, Wellington, New Zealand.
authors.forename: Martin
authors.initials: M
authors.lastname: A K Williams
authors.affiliation: Institute of Fundamental Sciences, Massey University, Palmerston North, New Zealand.|MacDiarmid Institute for Advanced Material and Nanotechnology, Victoria University of Wellington, Wellington, New Zealand.
authors.forename: Simon
authors.initials: S
authors.lastname: B Hall
mesh_terms: D003102:Colloids / Q000737:chemistry*; D004058:Diffusion; D009038:Motion; D052898:Optical Tweezers; D055672:Static Electricity
chemical_list: D003102:Colloids
keywords: Soft Matter: Colloids and Nanoparticles