Measuring colloid interactions and dynamics with digital holographic microscopy and multi-particle scattering theory

ORAL

Abstract

We describe an \textit{in situ}, nonperturbative optical technique for measuring the pair potential between two colloidal particles in bulk suspension. We image clusters of colloidal spheres at or near contact with digital holographic microscopy and fit the resulting holograms to the exact numerical solution for electromagnetic scattering from the clusters. We measure the depletion interaction between two 1 $\mu$m polystyrene spheres in a bulk suspension by studying the thermal fluctuations of their $\sim$ 50 nm separation distance with $\sim$ 5 nm spatial resolution. Our method does not require the use of optical tweezers and thus may be useful for studying interactions between colloids that are too small or too nearly index-matched to be optically trapped. We also use our methods for recording and fitting holograms to simultaneously measure the 3D translational and rotational Brownian motion of sphere clusters.

–

Authors

  • Jerome Fung

    • Dept. of Physics, Harvard University

  • David Kaz

    • Dept. of Physics, Harvard University

  • Ryan McGorty

    • Dept. of Physics, Harvard University
    • Harvard University, Physics Department
    • Harvard University

  • Guangnan Meng

    • Dept. of Physics, Harvard University

  • K. Eric Martin

    • Dept. of Physics, UC Santa Barbara

  • Vinothan Manoharan

    • Dept. of Physics and SEAS, Harvard University
    • Harvard SEAS
    • Harvard University
    • Harvard Physics and SEAS
    • Harvard University, Physics \& SEAS