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Slow anomalous dynamics close to MCT higher order singularities. A numerical
study of short-range attractive colloids.
(and some additional comments)
Francesco Sciortino
Email: [email protected]
UCGMG Capri, June 2003
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In collaboration with …..
Giuseppe Foffi Piero TartagliaEmanuela Zaccarelli
Wolfgang Goetze, Thomas Voigtman, Mattias SperlKenneth Dawson
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Outline of the talk
-The MCT predictions for SW (repetita juvant)
-Experiments
-Simulations
A3, A4 ?
Glass-Glass ?
Hopping Phenomena ?
Gels in SW ?
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MCT predictions for short range attractive square-well
hard-sphere glass
(repulsive)
Short-range attractive glass
fluid
Type B
A3
Fluid-Glass on cooling and heating !!
Controlled by
Fabbian et al PRE R1347 (1999)Bergenholtz and Fuchs, PRE 59 5708 (1999)
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Depletion Interaction:A Cartoon
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Glass samplesFluid samples
MCT fluid-glass
line
Fluid-glass line from
experiments
Tem
pera
ture
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Colloidal-Polymer Mixture with Re-entrant Glass Transition in a Depletion Interactions
T. Eckert and E. Bartsch
Phys.Rev. Lett. 89 125701 (2002)
HS (increasing )
Addingshort-rangeattraction
T. Eckert and E. Bartsch
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Temperature
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MCT IDEAL GLASS LINES (PY) - SQUARE WELL MODEL - CHANGING
PRE-63-011401-2001
A3
A4
V(r)
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Isodiffusivity curves (MD Binary Hard Spheres)
Zaccarelli et al PRE 66, 041402 (2002).
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Tracing the A4 point: Theory and Simulation
D 1.897PY-0.3922TMD 0.5882TPY - 0.225
PYPY +transformation
FS et al, cond-mat/0304192
PY-MCT overestimates ideal attractive glass T by a factor of 2
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Slope 1
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q(t)=fq-hq [B(1) ln(t/) + B(2)q ln2(t/)].
Same T and, different
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q(tq(t)-fq)/hq^
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X(t)=fX-hX [B(1) ln(t/) + B(2)X ln2(t/)].
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Reentrance (glass-liquid-glass) (both experiments and simulations) √
A4 dynamics √ (simulation)
Glass-glass transition
Check List
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low T
high T
t
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Jumping into the glass
Zaccarelli et al, cond-mat/0304100
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The attractive glass is not stable !low T
high T
Zaccarelli et al, cond-mat/0304100
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dfasdd
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t
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Nice model for theoretical and numerical simulation
Very complex dynamics - benchmark for microscopic theories of super-cooled liquid and glasses (MCT does well!)
Model for activated processes For the SW model, the gel line cannot be
approached from equilibrium (what are the colloidal gels ? What is the interaction potential ?)
A summary
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Structural Arrest Transitions in Colloidal Systems with Short-Range Attractions
Taormina, Italy, December 2003.
A workshop organized by
Sow-Hsin Chen (MIT) ([email protected])Francesco Mallamace (U of Messina) ([email protected])
Francesco Sciortino (U of Rome La Sapienza) ([email protected])
Purpose: To discuss, in depth, the recent progress on both the mode coupling theory predictions and their experimental tests on various aspects of structural arrest
transitions in colloidal systems with short-range attractions.
http://server1.phys.uniroma1.it/DOCS/TAO/
Advertisement
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van Megen and S.M. Underwood Phys. Rev. Lett. 70, 2766 (1993)
(t) HS (slow) dynamics
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BMLJ SiO2
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Hard Spheres
•at =0.58, the system freezes forming disordered aggregates.
MCT transition=51.6%
1. W. van Megen and P.N. Pusey Phys. Rev. A 43, 5429 (1991)
2. U. Bengtzelius et al. J. Phys. C 17, 5915 (1984)
3. W. van Megen and S.M. Underwood Phys. Rev. Lett. 70, 2766 (1993)
Potential
V(r)
r
(No temperature, only density)
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The mean square displacement
(in the glass)
log(t)
(0.1 )2
MSD
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Wavevector dependence of the non ergodicity parameter
(plateau) along the glass line
Fabbian et al PRE R1347 (1999)Bergenholtz and Fuchs, PRE 59 5708 (1999)
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Density-density correlators along the iso-diffusivity locus
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Non ergodicity parameter along the isodiffusivity curve from MD
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Sub diffusive !
~(0.1 )2
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Volume Fraction
Tem
pera
ture
Liquid
RepulsiveGlass
Attractive Glass
Gel
?Glass-glass transition
Non
-ads
orbi
ng -
poly
mer
con
cent
rati
on glass line
Summary 2 (and open questions) !
Activated Processes ?
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Equations MCT !
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The cage effect
(in HS)
Rattling in the cage
Cage dynamics
log(t)
(t)
fq
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Log(t)
Mean squared displacement
repulsiveattractive
(0.1 )2
A model with two different localization length
How does the system change from one (glass) to the other ?
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Hard Spheres Potential
Square-Well short range attractive Potential
Can the localization length be controlled in a different way ?
What if we add a short-range attraction ?
lowering T
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MD simulation
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Comparing MD data and MCT predictions for binary HS
See next talk by G. Foffi