Accessing colloidal systems: TIRM, Videomicroscopy and Confocal Microscopy
Christian Klix (Universität Konstanz)

Title: Accessing colloidal systems: TIRM, Videomicroscopy and Confocal Microscopy

Abstract: Investigating colloidal (model) systems, microscopy has proven to be an essential tool. Over the years, different setups, tailored to the system and physical properties one is interested in, have evolved. Accordingly, we used TIRM (Total Internal Reflection Microscopy), a technique developed by Prieve et. al. [1] in the late eighties of the past century, to accurately measure forces exerted on a single colloid close to a wall [2]. Wu et. al. [3] combined TIRM with videomicroscopy to monitor colloidal ensembles. We used a similar setup to access new, complex systems like asymmetric colloids or the intriguing TonB-protein.
If interested in bulk phenomena, confocal microscopy is the method of choice [4]. Materials with competing interactions have an intrinsically complex energy landscape, resulting in a intriguing phase behaviour [5]. In the investigated colloidal model system strong electrostatic repulsions and short-ranged polymer-induced depletion attractions lead to a variety of dynamically arrested states, namely a Wigner glass, a cluster glass and a gel. Utilizing confocal microscopy to access the system on the single particle level, dynamical and structural information are obtained providing a fascinating image of such colloidal systems. In the cluster glass, a novel aging mechanism in the form of cluster fission is revealed.

[1] D. C. Prieve, F. Luo and F. Lanni, Brownian motion of a hydrosol particle in a colloidal force field, Faraday Discussions of the Chemical Society 83, p. 297 (1987)
[2] L. Helden, G. H. Koendreink, P. Leiderer and C. Bechinger, Direct measurement of entropic forces induced by rigid rods, Physical Review Letters 90, p. 048301 (2003)
[3] H.-J. Wu and M. A. Bevan, Direct measurement of single and ensemble average particle-surface potential energy profiles, Langmuir 21, p. 1244 (2004)
[4] V. Prasad, D. Semwogerere and E. R. Weeks, Confocal microscopy of colloids, Journal of Physics: Condensed Matter 19, p. 113102 (2007)
[5] A. I. Campbell, V. J. Anderson, J. S. van Duijneveldt and P. Bartlett, Dynamical arrest in attractive colloids: The effect of long-range repulsion, Physical Review Letters 94, p. 208301 (2005)