Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session D20: Invited Session: Physics of Glass-Forming Liquids: Challenges and Surprises II |
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Sponsoring Units: DPOLY Chair: Sindee Simon, Texas Tech University Room: Ballroom B |
Monday, March 2, 2015 2:30PM - 3:06PM |
D20.00001: The structure of glass as revealed by dynamical large deviation methods Invited Speaker: Juan P. Garrahan The dynamics of many-body systems is often richer than what one can directly infer from their static properties. This dynamical richness is revealed by considering strictly dynamical observables. The full statistical characteristics of such quantities encode the dynamical properties of the system at hand. By considering their large deviations it is possible to derive a statistical mechanics of trajectories, which is to trajectories of the dynamics what equilibrium statistical mechanics is to configurations of the statics. In this talk I will describe this approach and how it can be applied to the glass transition problem. I will show how the underlying kinetic phenomenon of glass formation is a novel class of order-disorder transitions in trajectory, rather than configuration, space. I will consider the connection between the inactive dynamical phases this approach reveals and glasses prepared by more standard means. A significant prediction from this approach is the emergence of non-trivial correlations that distinguish glass from its reversible melt. Time permitting I will discuss how these ideas extend to the area of quantum glasses. [Preview Abstract] |
Monday, March 2, 2015 3:06PM - 3:42PM |
D20.00002: Approaching the Glass Transition from Various Directions Invited Speaker: Jane Lipson In recent years a significant amount of experimental work has appeared on glassy systems, both polymeric and small molecule. However, this rich explosion in data has not been met with a concomitant leap in fundamental understanding. We have developed a number of approaches to elucidate some of the underlying mechanisms of behaviour in bulk and confined glassy systems. Using our Limited Mobility (LM) coarse-grained simulation model we have characterized the dynamic heterogeneity associated with approaching the glass transition, explored interfacial behaviour when layering materials of differing mobility, and analyzed the effect of a free surface on a supported thin film. Approaching related problems from a different direction we have modified a simple thermodynamic description of the bulk to account for missing interactions at a film surface, and substrate interactions in the case of supported films. Characterizing the systems via bulk data alone, we find our film-averaged predictions for the effects of confinement agree well with experimental data on several freestanding and supported polymer films. That work deals with confined systems; a fundamental understanding of bulk glass transitions also remains incomplete. Most recently we have been applying our Locally Correlated Lattice (LCL) equation of state model, which has met with success in modeling polymer melt and mixture behaviour, to reveal hints of the underlying glassy nature of a bulk polymer sample, even while above its transition temperature (Tg). Correlations between Tg and a variety of equilibrium bulk quantities have lead us to make connections not only with a substantive amount of experimental data on a wide range of polymers, but also with other models of glassy polymeric systems. This talk will comprise an efficient summary of past progress from these different directions, and will then focus on our most recent results and current understanding. [Preview Abstract] |
Monday, March 2, 2015 3:42PM - 4:18PM |
D20.00003: Simple aging in molecular glasses Invited Speaker: Kristine Niss The glass transition takes place when the structural (alpha) relaxation freezes in and the liquid enters a non-equilibrium solid state. This usually happens when the relaxation time, $\tau$, reaches a timescale of 1000 seconds, and $\tau=1000$ s is pragmatically used as a definition of the glass transition temperature $T_g$. However, if the glass is studied on a long enough time scale then relaxation is still seen as physical aging. Aging is a non-linear signature of the alpha relaxation in which the relaxation dynamics changes as a function of how far the system has relaxed. If the system is studied well below $T_g$ then equilibrium will not be achieved, but just below or around $T_g$ it is possible to systematically monitor the non-linear relaxation all the way to equilibrium. We have developed a micro crystat which is optimized for making fast changes in temperature and keeping temperature stable over days and even weeks. Combining this micro cryostat with a small dielectric cell it is possible to monitor non-linear relaxation in a dynamical range of more than 4 decades from 10 seconds to a $10^5$ seconds. The aging is monitored after a fast temperature jump. This means that the aging itself is isotherm, and the data therefore directly shows, how the relaxation-rate changes as volume and structure change on the isotherm. We have studied several molecular liquids and find that the data to a very large extend can be understood in terms of a TNM formalism. This implies time-aging-time superposition and suggests a simple picture where the out of equlibrium ``states'' correspond to equilibrium states - at an other temperature. If the alpha relaxation is dynamically heterogeneous as it is commonly believed, then the aging results show that fast and slow ``modes'' of the relaxation are governed in the same way by structure and volume. We hypothesize that aging according to TNM formalism is an intrinsic property of Roskilde Simple liquids. [Preview Abstract] |
Monday, March 2, 2015 4:18PM - 4:54PM |
D20.00004: Colloidal liquids and glasses: Insights from microscopy Invited Speaker: Eric R. Weeks What would we learn if we could clearly see individual atoms deep inside materials? My group studies colloidal suspensions, which are solid micron-sized particles in a liquid. In many ways, these particles are analogous to atoms. At high particle concentration, the sample is a good model system for a glassy material, with the particles randomly packed together. We use an optical confocal microscope to view the motion of these colloidal particles in three dimensions to see how the motion is changed as the glass transition is approached. In particular, we will discuss two puzzles. First, we'll examine how rotational and translational diffusion of tracers differ as the glass transition is approached. Second, we'll study how how the behavior of glassy samples change when they are confined, and how this depends on the nature of the confining boundaries. [Preview Abstract] |
Monday, March 2, 2015 4:54PM - 5:30PM |
D20.00005: Fluids with short-range attractions and longer-range repulsions Invited Speaker: Thomas Truskett Many complex fluids comprise particles with effective interactions that include short-range attractions and longer-range repulsions. In this talk, I explore---using a simple theoretical model---what behaviors one should expect to find in such systems, including the possibility of equilibrium ``cluster'' formation and its associated implications for dynamics near structural arrest. I also discuss how one might predict the onset of cluster formation from the static structure factor. Finally, some implications for concentrated liquid formulations of therapeutic proteins are addressed. [Preview Abstract] |
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