Glass transition dynamics of hard sphere like microgel colloids with short-rangedattractions

Abstract

We have studied by dynamic light scattering the glass transition dynamicsof a binary mixture of polystyrene microgel particles with a size ratio ofRsmall/Rlarge = 0.81 and a number ratio of , where a short-ranged depletion attraction () was induced by addition of linear polystyrene. This system shows a reentrantglass transition. We have determined the glass transition lines of this system inthe experimental control parameter space given by the colloid volume fractionφ and the polymerconcentration cp by employing the power law of mode coupling theory (MCT) for theα-relaxation times. We find a reentry region which is much larger thanpredicted by theory and reported for another colloidal system with depletionattractions. Analysing the fluid dynamics along the transition lines with theβ-scaling law ofMCT we extract the cp dependence of the exponent parameterλ and the non-ergodicityparameter fqc. The results are in qualitative agreement with the prediction ofMCT for increasing attraction strength. The observed ‘jump’ offqc isindicative of a change of the close by glass phase from a packing-driven to a bonding-driven glass. Theincrease of λ to 0.91 and its subsequent decrease may indicate the neighbourhood of anA4 singularity.