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
Mar 31, 2015
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
In collaboration with …..
Giuseppe Foffi Piero TartagliaEmanuela Zaccarelli
Wolfgang Goetze, Thomas Voigtman, Mattias SperlKenneth Dawson
Outline of the talk
-The MCT predictions for SW (repetita juvant)
-Experiments
-Simulations
A3, A4 ?
Glass-Glass ?
Hopping Phenomena ?
Gels in SW ?
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)
Depletion Interaction:A Cartoon
Glass samplesFluid samples
MCT fluid-glass
line
Fluid-glass line from
experiments
Tem
pera
ture
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
Temperature
MCT IDEAL GLASS LINES (PY) - SQUARE WELL MODEL - CHANGING
PRE-63-011401-2001
A3
A4
V(r)
Isodiffusivity curves (MD Binary Hard Spheres)
Zaccarelli et al PRE 66, 041402 (2002).
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
Slope 1
q(t)=fq-hq [B(1) ln(t/) + B(2)q ln2(t/)].
Same T and, different
q(tq(t)-fq)/hq^
X(t)=fX-hX [B(1) ln(t/) + B(2)X ln2(t/)].
Reentrance (glass-liquid-glass) (both experiments and simulations) √
A4 dynamics √ (simulation)
Glass-glass transition
Check List
low T
high T
t
Jumping into the glass
Zaccarelli et al, cond-mat/0304100
The attractive glass is not stable !low T
high T
Zaccarelli et al, cond-mat/0304100
dfasdd
t
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
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/
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van Megen and S.M. Underwood Phys. Rev. Lett. 70, 2766 (1993)
(t) HS (slow) dynamics
BMLJ SiO2
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)
The mean square displacement
(in the glass)
log(t)
(0.1 )2
MSD
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)
Density-density correlators along the iso-diffusivity locus
Non ergodicity parameter along the isodiffusivity curve from MD
Sub diffusive !
~(0.1 )2
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 ?
Equations MCT !
The cage effect
(in HS)
Rattling in the cage
Cage dynamics
log(t)
(t)
fq
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 ?
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
MD simulation
Comparing MD data and MCT predictions for binary HS
See next talk by G. Foffi