  Dense suspensions of model hard-sphere-like colloids, with different particle
sizes, are examined experimentally in the glass state, under shear and
extensional rheology. Under steady shear flow we detect Discontinuous Shear
Thickening (DST) above a critical shear rate. Start-up shear experiments show
stress overshoots in the vicinity of the onset of DST related with a change in
microscopic morphology, as the sample shows dilatancy effects. The analysis of
the normal stress together with direct sample observation by high speed camera,
indicates the appearance of positive N1 and dilation behavior at the shear
thickening onset. Dilatancy effects are detected also under extensional flow.
The latter was studied through capillary breakup and filament stretching
experimental setups, where liquid-like response is seen for strain rate lower
than a critical strain rate and solid like-behavior for higher strain rates.
Monitoring the filament thinning processes under different conditions (volume
fractions and strain rates) we have created a state diagram where all responses
of a hard-sphere suspension (Newtonian, shear thinning, shear thickening,
dilatant) are shown. We finally compare the shear thickening response of these
hard-sphere-like suspensions and glasses in shear with that in extensional
flow.
