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

Sunil K. Sainis, Vincent Germain, and Eric R. Dufresne
Phys. Rev. Lett. 99, 018303 – Published 6 July 2007

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.

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  • Received 16 February 2007

DOI:https://doi.org/10.1103/PhysRevLett.99.018303

©2007 American Physical Society

Authors & Affiliations

Sunil K. Sainis, Vincent Germain, and Eric R. Dufresne

  • Departments of Mechanical Engineering, Chemical Engineering and Physics, Yale University, New Haven, Connecticut 06511, USA*

  • *eric.dufresne@yale.edu

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Issue

Vol. 99, Iss. 1 — 6 July 2007

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