The glass paradigm for colloidal glasses, gels, and other arrested states driven by attractive interactions

For some time, there has existed the idea that dense colloidal systems with repulsive interactions can be interpreted using certain approaches to glass theory. Recent advances in understanding the role of short-ranged attractive interactions in driving another type of ‘glass-transition’ have considerably extended the range of potential applications for such systems. Within this framework, particle gels are now regarded as ‘attractive’ glasses, and for some concentration regimes the details of the density correlation as we approach gellation for a broad range of experimental systems seem to be well described by glass-transition ideas and laws. Initial suggestions that this might be so came from theory, but the close collaboration between theory, simulation, and experimental science has been mutually stimulating. New advances in the theory are now to be expected, and novel systems where the ideas might be applicable are emerging. The exploration of these ideas is still at the beginning, but there is a reasonable expectation that the glass paradigm will be more generally useful in many areas of soft matter and colloid science, perhaps gathering apparently disparate phenomena of particle gellation, polymer gellation, aggregation, and other aspects of ‘solidification’ into a common interpretive scheme.