LANDSCAPE AND MEMORY LANDSCAPE AND MEMORY 1 Nonequilibrium

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LANDSCAPE AND MEMORY

LANDSCAPE AND MEMORY

LANDSCAPE AND MEMORY 1. Nonequilibrium soft matter physics 2. Lecithin/bile-salt mixtures 3. Colloidal arrest

LANDSCAPE AND MEMORY 1. Nonequilibrium soft matter physics 2. Lecithin/bile-salt mixtures 3. Colloidal arrest in binary solvents 4. The vision thing! coworkers: W. Poon, S. Egelhaaf, J. Leng, K. Stratford, I. Pagonabarraga R. Adhikari funding: EPSRC Programme Grant + e. Science Testbed Project

0. FOR THE TEN-YEAR OLDS • Soft matter = gloop • Physics question: why

0. FOR THE TEN-YEAR OLDS • Soft matter = gloop • Physics question: why does gloop? • How do the molecules or other bits inside interact to make it gloopy? • How do these interactions control when flow starts and stops? • Here are some ways: polymers: colloids: sand: molecular spaghetti molecular ping-pong balls just sand!

1. NONEQUILIBRIUM SOFT MATTER • Polymers, colloids, amphiphiles: chains, balls, bilayers nanoscale or mesoscale

1. NONEQUILIBRIUM SOFT MATTER • Polymers, colloids, amphiphiles: chains, balls, bilayers nanoscale or mesoscale structure (5 nm – 50 mm) • Low free energy density: k. BT per soft degree of freedom perturbed by weak forcing (shear flow, T– quench etc. ) • Brownian motion strives to reach equilibrium state barriers exist: arrest, jamming, glassiness • Free energy landscape can be simple (one barrier) or complex (many) • Not one glass but an ever-growing zoo of different types

Surfactant Aggregation preferred local geometries sphere rod , small disc curvature tail/head size ratio

Surfactant Aggregation preferred local geometries sphere rod , small disc curvature tail/head size ratio flat bilayer

2. LECITHIN/BILE-SALT MIXTURES Physics: preferred curvature controlled by ratio lecithin: bile salt change this

2. LECITHIN/BILE-SALT MIXTURES Physics: preferred curvature controlled by ratio lecithin: bile salt change this ratio by sudden dilution (“dialysis”) aggregates undergo shape + size transformation sphere disc with rim Physiology: digestion, lipid metabolism vesicle

2. LECITHIN/BILE-SALT MIXTURES Longstanding controversy: large end-state vesicles of pure lecithin observed. . trapped

2. LECITHIN/BILE-SALT MIXTURES Longstanding controversy: large end-state vesicles of pure lecithin observed. . trapped metastable states or equilibrium? Our answer: definitely metastable, despite indefinite lifetime How do we know? their size depends on bile salt properties!

Free energy landscape for disc closure V=r /4 E/Eves r: disc radius : rim

Free energy landscape for disc closure V=r /4 E/Eves r: disc radius : rim tension : bilayer rigidity “reaction coordinate”

Kinetic pathway from disks to vesicles small discs grow by aggregation then drives closure

Kinetic pathway from disks to vesicles small discs grow by aggregation then drives closure of large discs end-state vesicle size R depends on bile salt, p. H, [Na. Cl] etc varying these away from “realistic” levels exposes the mechanism! experiments + quantitative model: J. Leng, S. Egelhaaf, MEC, Biophys J 2003

3. COLLOIDAL ARREST IN BINARY SOLVENTS Contact angle Neutral wetting: = π/2 solid-liquid tensions

3. COLLOIDAL ARREST IN BINARY SOLVENTS Contact angle Neutral wetting: = π/2 solid-liquid tensions equal Energy gain πσa 2 k. BT colloids stick to interface π/2 ∟ COLLOIDS = IRREVERSIBLE SURFACTANTS!

DEMIXING OF SYMMETRIC BINARY FLUIDS local free energy landscape F( , ) = a

DEMIXING OF SYMMETRIC BINARY FLUIDS local free energy landscape F( , ) = a 2 + b 4 + k( )2 a < 0 in immiscible region A/B repulsion F 2 -1 = proportion of species A = order parameter SPINODAL DECOMPOSITION

late crossover, Re =50 viscous hydrodynamic, Re = 0. 5

late crossover, Re =50 viscous hydrodynamic, Re = 0. 5

spinodal decomposition under shear © University of Edinburgh 2000

spinodal decomposition under shear © University of Edinburgh 2000

DEMIXING: GLOBAL FREE ENERGY LANDSCAPES without colloidal particles: complex but always downhill complete separation

DEMIXING: GLOBAL FREE ENERGY LANDSCAPES without colloidal particles: complex but always downhill complete separation eventually “zero temperature fixed point” with colloidal particles: glassy landscape, many traps? arrested separation? strong memory effects?

LAB REALIZATIONS? P. Clegg, W. Poon, S. Egelhaaf & MEC WATCH THIS SPACE!! COMPUTER

LAB REALIZATIONS? P. Clegg, W. Poon, S. Egelhaaf & MEC WATCH THIS SPACE!! COMPUTER SIMULATIONS K. Stratford, I. Pagonabarraga, R. Adhikari & MEC Will be published soon. . .

4. SOFT MATTER: SCIENCE VISION • Beyond equilibrium self assembly: using controlled forcing (shear,

4. SOFT MATTER: SCIENCE VISION • Beyond equilibrium self assembly: using controlled forcing (shear, quench) to steer through a landscape • Arrested end-states more robust than equilibrium: memory effects can ride out changes in the here and now • To control end-state “products” we must understand free energy landscapes: not just the free energy minima that define equilibrium • “Combinatorial physics”: glasses, plus phase separation, plus shear, plus fields, plus. . HOW DO WE AVOID GETTING LOST IN THIS IMMENSE SPACE?

4. THE B–WORD AND THE N–WORD • Soft matter physics can contribute to biology,

4. THE B–WORD AND THE N–WORD • Soft matter physics can contribute to biology, and already does • Soft matter physics can contribute to nanotechnology, and already does • The central problems of soft matter involve nonequilibrium and forcing in systems with complicated free-energy landscapes • Soft matter will lose its relevance to biology, nanotechnology, and all other fields, if these central problems are not rigorously addressed THEREFORE • We should not all have to constantly invoke bio– and/or nano–relevance • We cannot apply this new physics without understanding it first