Transient gels in colloid-polymer mixtures studied with fluorescence confocal scanning laser microscopy

We study the structure and the time evolution of transient gels formed in colloid-polymer mixtures, by means of fluorescence Confocal Scanning Laser Microscopy (CSLM). This technique is used in conjunction with never colloidal silica particles containing a fluorescent core. The confocal micrographs reveal that there exist large differences in the local structure within a single system. At a given time there are regions where the gel structure consists of alternating patterns of colloid-rich and colloid-poor regions with a characteristic length scale and regions where the gel structure becomes disrupted by the formation of fractures. The number of fractures increases with time. It is speculated that the increase of the number of fractures leads to a weakening of the strength of the gel such that it eventually collapses under gravity. (C) 1999 Elsevier Science B.V. All rights reserved.