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Physical Gels and strong liquids

5th International Discussion Meeting on Relaxations in Complex Systems New results, Directions and Opportunities. Physical Gels and strong liquids. Wednesday … last talk. Francesco Sciortino. Outline. Irreversible (Chemical) Gelation in a simple model Thermoreversible (Physical) Gelation

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Physical Gels and strong liquids

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  1. 5th International Discussion Meeting on Relaxations in Complex Systems New results, Directions and Opportunities Physical Gels and strong liquids Wednesday … last talk Francesco Sciortino

  2. Outline • Irreversible (Chemical) Gelation in a simple model • Thermoreversible (Physical) Gelation • Gels (strong liquids) and Glasses • Other gels…..(water, DNA-gels)

  3. Irreversible Gelation Ivan HS gel Simple Model for Chemical Gels [with HS g(r)] V(r ) s s+D r

  4. Behavior of the density autocorrelation functions F dependence

  5. Irreversible Gelation fq Signatures of percolation at fixed q

  6. Finite Lifetime…. V(r ) s s+D r See also Del Gado works

  7. Square Well 3% width What on cooling ? Generic Phase Diagram for Square Well (3%)

  8. The dream

  9. The quest The quest for the ideal (thermoreversible) gel….model 1) Long Living (but reversible) bonds 2)No Phase Separation Are 1 and 2 mutually exclusive ? Long Bond Lifetime LowTemperature Condensation

  10. Surface Tension How to stay at low T without condensation ? Reasons for condensation (Frank, Hill, Coniglio) Physical Clusters at low T if the infinite cluster is the lowest (free)energy state How to make the surface as stable as the bulk (or more)? The quest

  11. Nmax on a Bethe lattice Nmax=12 Nmax=5 Nmax=2 E=0 E=-1 E=-Nmax E=-Nmax S.Sastry and E. La Nave

  12. Maximum Valency Geometric Constraint: Maximum Valency V(r ) SW if # of bonded particles <= Nmax HS if # of bonded particles > Nmax r

  13. Phase Diagram et al NMAX-modifiedPhase Diagram

  14. It is possible to equilibrate at low T !

  15. The structure of the gel

  16. What is the gel dynamics (in this model) ? • Bond lifetime (Arrhenius along isochores)

  17. What is the gel dynamics (in this model) ? • Bond lifetime • R2 vs t (along isochores)

  18. Gel vs Glass - MSD

  19. What is the gel dynamics (in this model) ? • Bond lifetime • R2 vs t • Fq(t)

  20. D along isochores… D along isoterms D vs isochores and isotherms

  21. Dynamic Arrest Lines The possibility of observing strong-liquid behavior intimately connected to reduction of bonding

  22. Pair-wise model (geometric correlation between bonds) (PMW, I. Nezbeda)

  23. Colloidal Gels, Molecular Gels, …. and DNA gels Four Arm Ologonucleotide Complexes as precursors for the generation of supramolecular periodic assemblies JACS 126, 2050 2004 Palindroms in complementary space

  24. Conclusions….. • Gel propensity: Initial understanding of the ingredients requested to generate an “ideal” gel • Gels and Glasses (two different faces of the arrest dynamics). Percolation not seen… • Molecular and Atomic gels - Strong ! • Interesting questions…. Where is the MCT line ?

  25. C. De Michele, E. La Nave, P. Tartaglia, E. Zaccarelli (U. La Sapienza, Roma, Italy)I. Saika-Voivod (U. Saskatchewan, Canada)A. Moreno (Donostia International Center, Spain)S. Bulderyev (DMD code) (Yeshiva U., USA) S. Sastry (Bethe) (JNCASR, India)F. Starr (DNA-Gels) (Wesleyan U., USA)

  26. Gel vs Glass: Density Autocorrelation Functions fq

  27. Fq gel vs glass

  28. Bond Lifetime.. Several more decades..

  29. Stoke

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