Presentation on theme: "Slow anomalous dynamics close to MCT higher order singularities. A numerical study of short-range attractive colloids. (and some additional comments) Francesco."— Presentation transcript:
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@example.com Titolo ! UCGMG Capri, June 2003
In collaboration with ….. Giuseppe Foffi Piero Tartaglia Emanuela Zaccarelli Wolfgang Goetze, Thomas Voigtman, Mattias Sperl Kenneth Dawson collaboratori
riassunto Outline of the talk -The MCT predictions for SW (repetita juvant) -Experiments -Simulations A3, A4 ? Glass-Glass ? Hopping Phenomena ? Gels in SW ?
The MCT predictions for short-range attractive square well MCT predictions for short range attractive square-well hard-sphere glass (repulsive) Short-range attractive glass fluid Type B A3A3 Fluid-Glass on cooling and heating !! Controlled by Fabbian et al PRE R1347 (1999) Bergenholtz and Fuchs, PRE 59 5708 (1999)
Depletion Interactions Cartoons Depletion Interaction: A Cartoon
Science Pham et al Fig 1 Glass samples Fluid samples MCT fluid- glass line Fluid-glass line from experiments Temperature
Berths PRL (no polymer-with molymer) 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 ) Adding short-range attraction T. Eckert and E. Bartsch
MCT IDEAL GLASS LINES (PY) - SQUARE WELL MODEL - CHANGING PRE-63-011401-2001 Role of the width A3A3 A4A4 V(r)
Isodiffusivity Isodiffusivity curves (MD Binary Hard Spheres) Zaccarelli et al PRE 66, 041402 (2002).
Tracing the A4 point Tracing the A 4 point: Theory and Simulation D 1.897 PY -0.3922 T MD 0.5882T PY - 0.225 PY PY + transformation FS et al, cond-mat/0304192 PY-MCT overestimates ideal attractive glass T by a factor of 2
A summary 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) (firstname.lastname@example.org) Francesco Mallamace (U of Messina) (email@example.com) Francesco Sciortino (U of Rome La Sapienza) (firstname.lastname@example.org) 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/ Pubblicita’ Advertisement
van Megen and S.M. Underwood Phys. Rev. Lett. 70, 2766 (1993) HS e MCT (t) HS (slow) dynamics
HS 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) The MSD in HS log(t) (0.1 ) 2 MSD
Non ergodicity parameters for the two glasses 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)
Correlatori lungo la linea Density-density correlators along the iso-diffusivity locus
Non-ergodicity factor Non ergodicity parameter along the isodiffusivity curve from MD
Sub diffusive ! ~(0.1 ) 2 R2 lungo la linea
Volume Fraction Temperature Liquid Repulsive Glass Attractive Glass Gel ? Glass-glass transition Non-adsorbing -polymer concentration glass line Summary 2 (and open questions) ! Activated Processes ? Fig 2 of Natmat
The cage effect (in HS) Explanation of the cage and analysis of correlation function Rattling in the cage Cage dynamics log(t) (t) fqfq
Log(t) Mean squared displacement repulsive attractive (0.1 ) 2 Figure 1 di Natmat A model with two different localization length How does the system change from one (glass) to the other ?
What if …. 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 ? Attractive Glass lowering T