It has recently been demonstrated  that nearly hard sphere PMMA colloids carry a small but significant charge when suspended in certain organic solvents. The effective range of the electrostatic interaction can be tuned by the addition of an appropriate amount of salt. I will present results from confocal microscopy studies showing that this weak but long ranged repulsion has a detrimental effect on the gelation transition in colloid polymer mixtures, resulting in a long lived and stable cluster phase.  A. Yethiraj and A. van Blaaderen, Nature 421, 513 (2003)
This is a weekly series of informal talks given primarily by members of the soft condensed matter and statistical mechanics groups, but is also open to members of other groups and external visitors. The aim of the series is to promote discussion and learning of various topics at a level suitable to the broad background of the group. Everyone is welcome to attend..