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Single-Molecule Probing of Dynamical Heterogeneity in Molecular Glass Formers T. Xia, R. Zondervan, F. Kulzer, M. Orrit Molecular Nano-Optics and Spins C. Storm, W. van Saarloos Instituut Lorentz M. Möbius, M. van Hecke Kamerlingh Onnes Laboratory LION, Leiden University (NL)
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Dr. Rob Zondervan Ted Xia Dr. Florian Kulzer
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Introduction - single-molecule microscopy - rotational diffusion, previous work Local viscosity measurements - supercooled glycerol - heterogeneity Rheology - home-built Couette cell - plate-plate geometry Discussion and Outlook Outline
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Spatial selection Collection Excitation Confocal microscope
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Color scale: 1500 to 20000 counts/s with 750 W/cm 2 exc. 514.5 nm (R. Zondervan, 2003) Room Temperature DiI in Zeonex ®
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Probing viscosity with fluorescence Fluorescence Anisotropy (during emission) Polarization fluctuations (small ensembles) Single-molecule orientation Rotational diffusion time:
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Previous Work
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T g +10 K T g +5 K T g +2 K Deschenes et al. JPC 106 (2002) 11438 Environmental exchanges Spread of diffusion rates
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Schob et al., Eur. Polym. J. 40 (2004) 1019 Similar results in polymers, with rare environmental exchanges.
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- Very small samples (1 fL) quick heating and cooling (1 s). - Many repeated cycles possible Zondervan et al., Biophys. J. 90 (2006) 2956. Thermal Cycles for Single Protein Dynamics
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Rotational diffusion of single fluorescent dyes Perylene-di-imide (a) in glycerol (b) R. Zondervan et al., P. N. A. S. 104 (2007) 12628
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Viscosity of supercooled glycerol from: Schröter & Donth, J. Chem. Phys. 113 (2000) 9101
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Agreement with rheology
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Polarized single-molecule fluorescence
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Anticorrelation of polarization channels
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Single-molecule tumbling at variable T
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T-dep. of tumbling rates for 69 molecules
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Long memory time of local tumbling rate
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Seen already for colloidal suspensions in the glass phase: E. R. Weeks et al., Science 287(2000) 627 A solid matrix should be elastic : rheology? Extremely long memory of diffusion rate: evidence for solid walls? (foam)
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Rheology of Super-Cooled Glycerol R. Edgeworth et al., Eur. J. Phys. (1984) 198 The Pitch-Drop Experiment (Ig-Nobel 2005)
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Optical probing of shear deformation R. Zondervan et al., P. N. A. S. 105 (2008) 4993
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Bulk viscosity values: Glycerol: Schröter & Donth JCP 113 (2000) 9101 o-Terphenyl Laughlin & Uhlman JPC 76 (1972) 2317 Symbols: data from Zondervan et al., PNAS 105 (2008) 4993
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Shear strain traces upon sudden load
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Thermal histories yielding solid-like rheology
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Model of mixed response M
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Exponential jump and viscous drift : liquid’s viscosity : network’s spring constant : effective viscosity (creep)
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Shear modulus and viscosities from fits
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Better fit with a stretched exponential (measurement with commercial rheometer)
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Aging and hardening (over 2 weeks)
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Ortho-Terphenyl
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Shear rejuvenation
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Viscosity with Couette cell (1mm gap) in rheometer (by M. M ö bius)
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Thermal History Slow cooling from 260 K to 195 K at 5 K/hour, anneal at 195 K for 2 hour, warm up to aging temperature at 1 K/min Monitor G’,G’’ at f =0.1 Hz at low strain γ=0.0005 (dips are dewar changes)
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Aging at T=220K Solid response sets in after 25.8 hour of aging (growth)
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Aging at T=240K
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“Slushy” appearance
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- Importance of free volume; captured in liquid lakes, fenced in by solid walls? - Mobility as a function of effective pressure (Reiser et al. Europhys. Lett. 76 (2006) 1137) - Convergence of temperature dependences to about 230 K, Tg + 40 K; MCT? Discussion
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- Relation to Fischer clusters? - Crystallization? Characterize at various stages… - Relation to glacial phase?
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Images of structure growth in triphenylphosphite: from H. Tanaka, R. Kurita, H. Mataki, PRL 92 (2004) 025701 T g + 15 K T g + 8 K Glacial phase
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- Influence of thermal history on microstructure? - Size and shape of lakes? To do: Relevance to glass transition? - General for several molecular glass formers - Seen also in colloidal models
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Conclusions Inhomogeneity and spread of local viscosity Soft Glassy Rheology of supercooled glycerol and o-TP. General for glass formers? Relation to glacial phases and microscopic picture? Outlook: SM’s and nano-probing for soft matter studies
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Rob Zondervan Meindert van Dijk Florian Kulzer Clemens Hofman n Aurélien Nicolet
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Kramers theory for bond breaking Closed Broken F : applied force Effective viscosity (plastic deformation) K : spring constant of bond
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according to model, the force on the spring is the effective viscosity decreases much slower at high forces (as 1/ F only) Applied force is reduced by liquid shear
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Shear thinning
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«… glassy dynamics is a natural consequence of two properties shared by all [ Foams, emulsions, pastes, slurries, quicksand, dense suspensions, …] soft materials: structural disorder and metastability. » P. Sollich et al., Phys. Rev. Lett. 78 (1997) 2020 Also supercooled liquids! Soft Glassy Rheology
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Crossing the Melting Temperature
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Slow warming (12K/hr). Melting around 291K – melting point of glycerol
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-Friction: local pressure and temperature, third body,... - Adhesion: role of a soft layer in between two solids, probed with different dyes Solid-solid interaction with SM’s
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