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 c olloid-polymer mixtures, by means of fluorescence Confocal Scanning Laser M icroscopy (CSLM). This technique is used in conjunction with never colloida l silica particles containing a fluorescent core. The confocal micrographs reveal that there exist large differences in the local structure within a s ingle system. At a given time there are regions where the gel structure con sists 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 le ads to a weakening of the strength of the gel such that it eventually colla pses under gravity. (C) 1999 Elsevier Science B.V. All rights reserved.