Two-dimensional diffusion of colloids in polymer solutions

Abstract

Enhanced digital videomicroscopy is used to study the two-dimensional diffusion of colloidal polystyrene spheres of diameter 0.99 µm in confined aqueous solutions of polymer PEO (polyethyleneoxide) of molecular weight 8 × 10⁶. Diffusion is found to obey the Brownian motion law of linearity of the mean square displacement with time, with a constant appropriate to two dimensions. The diffusivity is determined for various polymer concentrations ranging from zero to those corresponding to dilute and semi-dilute polymer solutions. An abrupt slope change occurs near the polymer concentration of 0.002 wt-%, which lies below the concentration at which the polymer chains begin to overlap.

Acknowledgements

This paper is dedicated to Professor Widom, who, by his personal example and crystalline papers, has been a constant source of inspiration. We are grateful to Professor John Crocker for many valuable discussions on videomicroscopy and for his assistance with image processing, to Dr Francis Mueller (Hoffman-LaRoche) for help and advice with the Mylar films, and to Dr Tai-Chou Lee and Dr Bing-Hung Chen for assistance. We thank the BP-Amoco undergraduate summer research programme for the support of one of us (G.C.), and the NSF (under grants CTS-9700147 and CTS-0327487) and the Welch Foundation for financial support. Finally, we thank the referees for their constructive criticisms.

Notes

Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139.

Current addresses: Headway Technologies, 678 South Hill view Dr Milpitas, CA 95035.

Current addresses: Headway Technologies, 678 South Hill view Dr Milpitas, CA 95035.

Department of Chemical Engineering, University of Chemical Engineering, Santa Barbara, CA 93106.

Additional information

Notes on contributors

M. Robert *

Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139. Current addresses: Headway Technologies, 678 South Hill view Dr Milpitas, CA 95035. Department of Chemical Engineering, University of Chemical Engineering, Santa Barbara, CA 93106.