Aging in short-ranged attractive colloids G. Foffi INFM, Universita’ “La Sapienza”, Roma

Overview We study a short-ranged attractive system in the reentrant region of the glass phase diagram We quench the system deep in the glass by lowering and increasing the temperature The aging properties of this two states have been studied by molecular dynamics

Simulated system N=700 50%-50% concentration  = 1.2  = 3%

The numerical experiment We prepared 60 independent configurations equilibrated at T=0.6 We quenched the system at two point state:  T=1.2 in the repulsive glass  T=0.3 in the attractive glass After that the system evolves at constant temperature.

Aging We are studying an out-of-equilibrium process! Time translational invariance does not hold One time observable (i.g. energy and static structure factors) will depend on the waiting time Correlation function will depend on the observation time and the waiting time:

Energy evolution After the quench the system present two different evolution of the energy: the energy increase and can be fitted with a log. the energy decrease and follows a power law:

Static structure factors The overall shape of the S(q) does not change with a waiting time Only a slightly increase (decrease) in the first peak is present

Density-density correlation function

Scaling Theoretical studies (Cugliandolo cond-mat/ ) suggest the possibility of rescaling the correlators ad different waiting time For example: Simple aging case Proposed for BMLJ with   0.88 [1] [1] Kob and Barrat PRL 78, 4581 (1997)

Scaling for the attractive glass Even if the scaling time can be fitted with a power law (with approx.   0.38) the collapse of the correlators into a master curve is not satisfactory.

Mean Squared There is a clear plateau that grows with the waiting There is no clear plateau but rather a power law increase in that follows a power law (with an exponent that grows with waiting time)

Experimental Findings T=1.2T=0.3 Pham et al. cond-mat/ , to be published on PRE

Conclusion The repulsive and the attractive glasses aging scenario has been numerically investigated Static structure factors do not change significantly with time Density-density correlation functions evolves with the waiting time in a completely different way No scaling properties with waiting time Good agreement with experimental results.

Collaborators: E. Zaccarelli, F. Sciortino and P.Tartaglia (Roma) S. Buldyrev (Boston) Acknowledgment: W.C.K. Poon and K.N. Pham for useful discussions and for bringing their results to our attention. Reference: G. Foffi et al. cond-mat/ submitted to JCP