Statistics of Particle Trajectories at Short Time Intervals Reveal fN-Scale Colloidal Forces

Abstract

We describe and implement a technique for extracting forces from the relaxation of an overdamped thermal system with normal modes. At sufficiently short time intervals, the evolution of a normal mode is well described by a one-dimensional Smoluchowski equation with constant drift velocity v, and diffusion coefficent D. By virtue of fluctuation dissipation, these transport coefficients are simply related to conservative forces, F, acting on the normal mode: F=kBTv/D. This relationship implicitly accounts for hydrodynamic interactions, requires no mechanical calibration, makes no assumptions about the form of conservative forces, and requires no prior knowledge of material properties. We apply this method to measure the electrostatic interactions of polymer microspheres suspended in nonpolar microemulsions.

Dynamic analysis of a diffusing particle in a trapping potential

“…For short time intervals t < τ/10 (high frequencies), the effect of the restoring force on the particle displacement is negligible relative to the diffusion effect, and the slope approaches the value 1. The Gaussian width in this regime (derived from Taylor series expansion of S) is equal to σ 2 ≈ 2D t as expected for normal diffusion [13]. Finally, in the intermediate frequencies, the particle dynamics depends on both its free diffusion parameter D as well as the DNA applied force parameter K.…”

Surfactants with colloids: Adsorption or absorption?

“…The identity of the stabilizer polymer seems to have more of an influence, as, for example, PHSA-stabilized latexes are stable in hexadecane [28,[57][58][59][60] whereas PDMSstabilized latexes are not [52]. …”

Electrophoretic Retardation of Colloidal Particles in Nonpolar Liquids

“…Depending on the type of particles and liquid, additional theories have been developed to include, for example, surface conduction, Helmholtz layers, and soft layers on particles [8,9]. More recently, research in this field has focused on induced-charge electrokinetic phenomena for microfluidics applications [10] and interparticle or atomic force measurements to probe the double layer [11][12][13][14][15].…”