Aging of a Colloidal Suspension of Thermosensitive Particles

We have studied the aging behavior of a concentrated suspension of thermosensitive particles (PNIPAM).~ We found that the characteristic time of the dynamics of the system as a function of waiting time obeys the usual power law with exponent $\sim $ 1 both after shear melting the system and after a jump in temperature which is equivalent to a jump in concentration.~ We also report for the first time the observation of an extreme asymmetry of approach in the aging behavior with respect to down jump and up jump in temperature.~ While an asymmetry effect is already known in conventional glass formers such as polymers and small molecule liquids, it is both much more pronounced in the colloidal PNIPAM suspension and of a fundamentally different character.