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Gelation Routes in Colloidal Systems

Gelation Routes in Colloidal Systems. Dipartimento di Fisica & SOFT Complex Dynamics in Structured Systems Università La Sapienza , Roma Italy Bangalore, 30/06/2004. Emanuela Zaccarelli. Outline of the Talk. Simple Model of attractive colloids

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Gelation Routes in Colloidal Systems

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  1. Gelation Routes in Colloidal Systems Dipartimento di Fisica & SOFTComplex Dynamics in Structured Systems Università La Sapienza, Roma Italy Bangalore, 30/06/2004 Emanuela Zaccarelli

  2. Outline of the Talk • Simple Model of attractive colloids to describe asymmetric colloid-polymer mixtures Introduce “Gelation problem” • Necessity of model for “reversible • gelation” • Two different approaches: • Take into account Charge Effects • Introduce a geometrical constraint on • Bond Formation

  3. Simple model of Attractive Colloids (eg Square Well potential)Phase Diagram at high densities…. MCT predictions Dawson et al. PRE 2001 confirmed by experiments Mallamace et al. PRL (2000) Pham et al. Science (2002) Eckert and Bartsch PRL (2002) and simulations Puertas et al PRL (2002) Zaccarelli et al PRE (2002) F. Sciortino, Nat. Mat. 1, 145 (2002).

  4. … simulations at low densities… A phase separation occurs Gels can be only obtained via spinodal decomposition EZ, F.Sciortino, S. Buldyrev and P. Tartaglia condmat/0310765

  5. Necessity of new models for thermo-reversibleGELS incorporating: • No phase Separation • Long-Lived Bonds • Additional charge • Maximum Number of Bonds

  6. 1. Competition between short-range attraction and long-range repulsion 2n-n potential (n=100) Yukawa potential (screened electrostatic interactions)

  7. Ground State Clusters Energy per particle

  8. Ground State Clusters gyration radius

  9. Ground State ClustersStructures for A=0.05, =2.0

  10. “Structural Phase Diagram” at T=0 S. Mossa, F. Sciortino, P. Tartaglia, EZ, condmat/0406263.

  11. Effect of Cluster-Cluster Interactions Renormalize Yukawa form

  12. Flow in the phase diagram N=1 F. Sciortino, S. Mossa, EZ, P. Tartaglia, condmat/0312161; PRL in press.

  13. Flow in the phase diagram N=1 N=2 F. Sciortino, S. Mossa, EZ, P. Tartaglia, condmat/0312161; PRL in press.

  14. Flow in the phase diagram N=1 N=2 N=4 F. Sciortino, S. Mossa, EZ, P. Tartaglia, condmat/0312161; PRL in press.

  15. Flow in the phase diagram N=1 N=2 N=4 N=8 F. Sciortino, S. Mossa, EZ, P. Tartaglia, condmat/0312161; PRL in press.

  16. Flow in the phase diagram N=1 N=2 N=4 N=8 N=16 F. Sciortino, S. Mossa, EZ, P. Tartaglia, condmat/0312161; PRL in press.

  17. Flow in the phase diagram N=1 N=2 N=4 N=8 N=16 N=32 F. Sciortino, S. Mossa, EZ, P. Tartaglia, condmat/0312161; PRL in press.

  18. Flow in the phase diagram N=1 N=2 N=4 N=8 N=16 N=32 N=64 F. Sciortino, S. Mossa, EZ, P. Tartaglia, condmat/0312161; PRL in press.

  19. Snapshots from simulations

  20. Cluster glass transition

  21. Static structure Factor

  22. Dynamical density correlators (q~2.7)

  23. Main Results Evidence of an equilibrium cluster phase experimentally observed in weakly charged colloid/polymer mixtures Segre et al. PRL (2001), Sedgwick et al. (to be published) and protein solutions Stradner&Schurtenberger, Chen et al. (to be published) Gel interpreted in terms of glass transition of clusters

  24. 2. Maximum Number of BondsNMAXper particle • Model for particles with fixed number of sticky points (eg. Manoharan, Elsesser and Pine, Science 2003) • Simple modification of square well potential, weakening phase separation, enhancing more ramified structure formation

  25. NMAX-modifiedPhase Diagram

  26. Diffusivity along special isochores

  27. Bond Lifetime (NMAX=3, =0.20)

  28. Energy per Particle

  29. Viscosity(preliminary results)

  30. Static structure factor NMAX=3

  31. reminder:at the Glass Transition(BMSW =0.58, T=2.0)

  32. … while for the NMAX model(NMAX=3, =0.20, T=0.1)

  33. … looking in more details… … gel transition

  34. Conclusions Moreover, the model appears to be a GOOD candidate of a strong Liquid, i.e. highly degenerate ground state and absence of a (finite) Kauzmann temperature We have introduced a model with ideal gel features: • increase of relaxation times by orders of magnitude • density autocorrelation functions with non-glassy (but percolative) behaviour.

  35. Many Thanks to my Collaborators Francesco Sciortino and Piero Tartaglia Stefano Mossa ESRF Grenoble Sergey Buldyrev Boston Ivan Saika-Voivod, Emilia LaNave, Angel Moreno Roma

  36. Configurational Entropy(preliminary results)

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