Slow anomalous dynamics close to MCT higher order singularities. A numerical

study of short-range attractive colloids.

(and some additional comments)

Francesco Sciortino

Email: francesco.sciortino@phys.uniroma1.it

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) (sowhsin@mit.edu)Francesco Mallamace (U of Messina) (mallamac@mail.unime.it)

Francesco Sciortino (U of Rome La Sapienza) (francesco.sciortino@phys.uniroma1.it) 

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

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