Physical Gels and strong liquids

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

• Francesco Sciortino

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Outline

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

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Ivan HS gel
Irreversible Gelation
Simple Model for Chemical Gels with HS g(r)
V(r
)
s
sD
r
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Behavior of the density autocorrelation functions
F dependence
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Irreversible Gelation fq
Signatures of percolation at fixed q
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Finite Lifetime.
V(r
)
s
sD
r
See also Del Gado works
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Square Well 3 width
What on cooling ?
Generic Phase Diagram for Square Well (3)
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The dream
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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
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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
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Nmax on a Bethe lattice
Nmax12
Nmax5
Nmax2
E0
E-1
E-Nmax
E-Nmax
S.Sastry and E. La Nave
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Maximum Valency
Geometric Constraint Maximum Valency
V(r
)
SW if of bonded particles lt Nmax HS if of
bonded particles gt Nmax
r
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Phase Diagram
et al
NMAX-modified Phase Diagram
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It is possible to equilibrate at low T !
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The structure of the gel
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What is the gel dynamics (in this model) ?

• Bond lifetime (Arrhenius along isochores)

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What is the gel dynamics (in this model) ?

• Bond lifetime
• R2 vs t (along isochores)

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Gel vs Glass - MSD
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What is the gel dynamics (in this model) ?

• Bond lifetime
• R2 vs t
• Fq(t)

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D vs isochores and isotherms
D along isochores D along isoterms
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Dynamic Arrest Lines
The possibility of observing strong-liquid
behavior intimately connected to reduction of
bonding
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Pair-wise model (geometric correlation between
bonds) (PMW, I. Nezbeda)
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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
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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 ?

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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)
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Gel vs Glass Density Autocorrelation Functions
fq
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Fq gel vs glass
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Bond Lifetime.. Several more decades..
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Stoke