Patchy Colloids, Proteins and Network Forming Liquids: Analogies and new insights from computer...
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Transcript of Patchy Colloids, Proteins and Network Forming Liquids: Analogies and new insights from computer...
Patchy Colloids, Proteins and Network Forming Liquids: Analogies and new insights from computer simulations
Lyon - CECAM - June 26-28
Dynamics in patchy colloidsand network forming liquids: gels and strong glass-forming liquids
Francesco Sciortino
Motivations• The fate of the liquid state…. Gels and phase separation:
essential features (Sticky colloids - Proteins, network-forming liquids)
Models of patchy particles. Why to revisit them ?
• Thermodynamic and dynamic behavior of new patchy colloids .
• Clues in understanding dynamics in network forming liquids (Silica, water….)
• Essential ingredients of “strong behavior” (A. Angell scheme) in glass-forming liquids.
Glass line (D->0)
Liquid-Gas Spinodal
Binary Mixture LJ particles
“Equilibrium” “homogeoues” arrested states only for large packing fraction
BMLJ
The PMW modelJ. Kolafa and I. Nezbeda, Mol. Phys. 161 87 (1987)
Hard-Sphere + 4 sites (2H, 2LP)Tetrahedral arrangement
H-LP interact via a SWPotential, of range 0.15 .
V(r)
r
(length scale)
(energy scale)
u0
Bonding is properly defined --- Lowest energy state is well defined
The PMS ModelFord, Auerbach, Monson, J.Chem.Phys, 8415,121
(2004)
Silicon
Four sites
(tetrahedral)
OxygenTwo sites
145.8 o
OO=1.6
SW interaction betweenSi sites and O sites
Potential Energy -- Approaching the ground state
Progressive increase in packing prevents approach to the GS
Summary of static data
OptimalNetworkRegion
-Arrhenius
Approach toGround State
Regionof
phaseseparation
Packing Region
Phase Separation RegionPackingRegion
How to compare these (and other) models for tetra-coordinated liquids ?
Focus ONLY on the # of 4-coordinated particles (other particles are “bond-mediators”) (#)
Length scale ---- nn-distance among 4-coordinated particles (l44)
Scaled Density = # (l44 )3/V
Energy scale ---- Tc
Analogies with other network-forming potentials
SPC/E ST2 (Poole)
BKS silica(Saika-Voivod)
Faster on compression
Slower on compression
Comments
• Directional interaction and limited valency are essential ingredients for offering a new final fate to the liquid state and in particular to arrested states at low
• The resulting low T liquid state is (along isochores) a strong liquid. Directional bonding is essential for being strong.
• Gels and strong liquids are two faces of the same medal.
Graphic SummaryTwo glass lines ?
Strong liquids - Gels Arrest line
Fragile Liquids - Colloidal Glasses