atchy Colloids, Proteins and Network Forming Liquids: nalogies

atchy Colloids, Proteins and Network Forming Liquids: nalogies

atchy Colloids, Proteins and Network Forming Liquids: nalogies and new insights from computer simulations Lyon - CECAM - June 26-28 Francesco Sciortino

Dynamics in patchy colloids and network forming liquids: gels and strong glass-forming liquids 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.

Liquid-Gas Spinodal Glass line (D->0) Binary Mixture LJ particles Equilibrium

homogeoues arrested states only for large packing fraction The general (spherical) case

(for hard core complemented by attraction) Nmax=4 phase diagram - Isodiffusivity lines The PMW model J. Kolafa and I. Nezbeda, Mol. Phys. 161 87 (1987)

V(r) Hard-Sphere + 4 sites (2H, 2LP) Tetrahedral arrangement

r u0 (energy scale) H-LP interact via a SW Potential, of range

0.15 . (length scale) Bonding is properly defined --- Lowest energy state is well defined

The PMS Model Ford, Auerbach, Monson, J.Chem.Phys, 8415,121 (2004) Silicon

Four sites (tetrahedral) Oxygen Two sites 145.8 o

SW interaction between Si sites and O sites OO=1.6

Equilibrium phase diagram (PMW) Pagan and Gunton

JCP (2005) Equilibrium Phase Diagram PSM Critical Point of PMW

GC simulation BOX SIZE= TC=0.1095 C=0.153 Critical Point of PMS

GC simulation BOX SIZE= TC=0.075 C=0.0445 s=0.45

Potential Energy for the PMW Optimal density ! Potential Energy -- Approaching the ground state

Progressive increase in packing prevents approach to the GS E-Egs vs. 1/T

Potential Energy along isotherms Optimal density Hints of a LL CP S(q) in the phase-separation region

S(q) in the network region PMS -Potential Energy PMS E vs 1/T

PMS Structure (r-space) Structure (q-space)

Summary of static data Phase Separation Region Region of

phase separation Optimal Network Region

Arrhenius Approach to Ground State Packing Region

Packing Region Diffusion Coefficient

D along isotherms Diffusion Anomalies Isodiffusivities . (PMW) .

Isodiffusivities Si dynamic in PSM Comparing different potentials Bonded-triples angle

How to compare these (and other) models for tetracoordinated 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

Comparing E(n) at low T Comparing isodiffusivity lines Analogies with other network-forming potentials

ST2 (Poole) SPC/E Faster on compression

BKS silica (Saika-Voivod) Slower on compression

Water Phase Diagram ~ 0.34 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 Summary Two glass lines ?

Fragile Liquids Colloidal Glasses Strong liquids - Gels Arrest line Coworkers:

Cristiano De Michele (PMW,PMS) Simone Gabrielli (PMW) Piero Tartaglia Emanuela Zaccarelli http://www.socobim.de/

Gelation as a result of phase separation (interrupted by the glass transition) T

T

Density Anomalies (and possible 2nd CP) D vs (1-pb)

D vs (1-pb) --- (MC) D ~ f04 ~(Stanley-Teixeira) G. Foffi, E. Zaccarelli, S. V. Buldyrev, F. Sciortino, P. Tartaglia

Aging in short range attractive colloids: A numerical study J. Chem. Phys. 120, 1824, 2004

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