Aging in short-ranged attractive colloids

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Aging in short-ranged attractive colloids

• G. Foffi
• INFM, Universita La Sapienza, Roma

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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

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Simulated system

• N700
• 50-50 concentration
• ? 1.2
• ? 3

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The numerical experiment

• We prepared 60 independent configurations
  equilibrated at T0.6
• We quenched the system at two point state
• T1.2 in the repulsive glass
• T0.3 in the attractive glass
• After that the system evolves at constant
  temperature.

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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

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Energy evolution

• After the quench the system present two different
  evolution of the energy
• _at_T1.2 the energy increase and can be fitted with
  a log.
• _at_T0.3 the energy decrease and follows a power
  law

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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

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Density-density correlation function
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Scaling
Theoretical studies (Cugliandolo
cond-mat/0210312) 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)
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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.
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Mean Squared Displacement
_at_T1.2 There is a clear plateau that grows with
the waiting time
_at_T0.3 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)
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Experimental Findings
T1.2
T0.3
Pham et al. cond-mat/0308250, to be published on
PRE
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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.

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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/0311621 submitted to JCP