Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session U30: Glassy Materials: Colloids, Traffic, Disordered Crystals, Etc. |
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Sponsoring Units: DCMP Chair: Peter Schall, University of Amsterdam Room: 338 |
Thursday, March 21, 2013 11:15AM - 11:27AM |
U30.00001: Criticality in dynamic arrest: Correspondence between glasses and traffic Daniel Miedema, Astrid De Wijn, Bernard Nienhuis, Peter Schall Dynamic arrest is a general phenomenon across a wide range of dynamic systems including glasses, traffic flow, and dynamics in cells, but the universality of dynamic arrest phenomena remains unclear. We connect the emergence of traffic jams in traffic flow to the dynamic slow down in glasses. A direct correspondence is established by identifying a simple traffic model as a kinetically constrained model. In kinetically constrained models, the formation of glass becomes a (singular) phase transition in the zero temperature limit. Similarly, using the Nagel-Schreckenberg model to simulate traffic flow, we show that the emergence of jammed traffic acquires the signature of a sharp transition in the deterministic limit, corresponding to overcautious driving. We identify a true dynamical critical point marking the onset of coexistence between free flowing and jammed traffic, and demonstrate its analogy to the kinetically constrained glass models. [Preview Abstract] |
Thursday, March 21, 2013 11:27AM - 11:39AM |
U30.00002: Glass-like dynamics of a structural colloidal crystal in a disordered potential landscape Kevin Aptowicz, Tim Still, Matthew Gratale, Ye Xu, Arjun Yodh Disordered solids exhibit a boson peak at low frequencies, where many more modes appear than is expected for sound modes behavior. The origin of the boson peak remains unclear, although two explanations have risen to the forefront: (i) the boson peak is composed of quasi-localized modes arising from peculiarities of the interatomic forces in amorphous materials and (ii) the boson peak is the amorphous equivalent of the Van Hove singularity in crystalline systems. We experimentally explore these two possible explanations by studying a quasi-two-dimensional colloidal structural crystal residing in a disordered potential landscape. The potential landscape is generated by non-uniform heating of the sample. Thermophoretic effects lead to a heterogeneous force distribution that is tunable with temperature. With this experimental geometry, we explore the evolution of the density of vibrational states as a function of the strength of the disorder potential landscape. [Preview Abstract] |
Thursday, March 21, 2013 11:39AM - 11:51AM |
U30.00003: Correlations Between Structure, Vibrational Modes and Collective Motion in Dense Attractive 2D Colloidal Packings Matthew Lohr, Tim Still, Kevin Aptowicz, Ye Xu, Matthew Gratale, Arjun Yodh In this work, we investigate the microscopic dynamics of quasi-2D dense attractive colloidal systems. We confine bidisperse polystyrene spheres between glass coverslips in a suspension of water and 2,6-lutidine; as we increase the temperature of the sample into a critical regime, lutidine wets the colloids, creating a strong attractive interaction (\textgreater 4kT). We specifically study suspensions in the ``dense gel'' regime, i.e., at a volume fraction high enough that the attractive particles form a spanning cluster, yet just low enough that there exists some structural heterogeneity larger than the individual particle size. We track the particle locations via bright-field video microscopy and analyze the dynamics of both lower-volume-fraction gel states and higher-volume-fraction glassy states. Despite similarities in local structure, we find several consistent differences in the dynamic and vibrational properties of these two extreme systems. Specifically, we observe a drastic change of the presence of low-frequency modes between the two states. These modes appear to be coupled to collective motion of large groups of particles. By investigating the correlation between these collective motions and local packing structures, we gain further insight into the origins of dynamic heterogeneity in disordered systems. [Preview Abstract] |
Thursday, March 21, 2013 11:51AM - 12:03PM |
U30.00004: Resolving structural modifications of colloidal glasses by combining x-ray scattering and rheology Dmitry Denisov, Triet Dang, Bernd Struth, Gerard Wegdam, Peter Schall Glasses have liquid-like structure, but exhibit solid-like properties. A central question concerns the relation between the structure and mechanical properties of glasses, but structural changes remain difficult to resolve. We use a novel combination of rheology and x-ray scattering to resolve structural changes in colloidal glasses and link them directly to their mechanical behavior. By combining stress and structure factor measurements, we resolve shear induced changes in the nearest neighbor configuration as a function of applied stress, allowing us to elucidate the structural origin of the genuine shear banding transition of glasses. Our results reveal a coupling between structural parameters and the applied shear that underlies this instability: the non-monotonic behavior of the flow curve is directly mirrored in simple structural measures such as the position, the width, and the height of the nearest neighbor peak of the structure factor. Besides small changes in the nearest neighbor distances, our results underscore the importance of anisotropy in the structure of out of-equilibrium systems, in agreement with structure analysis of jammed and unjammed granular packings. [Preview Abstract] |
Thursday, March 21, 2013 12:03PM - 12:15PM |
U30.00005: Free energy transition of sheared colloidal glasses Minh Triet Dang, Rojman Zargar, Daniel Bonn, Peter Schall Glasses have liquid-like structure, but solid-like properties. An important question concerns the relation between the macroscopic flow behavior and the microscopic structure. However, for atomic glasses, microscopic configurations are prohibitively difficult to visualize due to the small molecular length scales. Here, we use a colloidal glass to directly visualize and analyze particle configurations of quiescent and sheared colloidal glasses. We determine the free volumes of the particles, and relate this free volume distribution directly to the free energy of the glass. This allows us to obtain novel insight into the relation between rigidity/flow and changes in the amorphous structure. We identify a clear change in the free energy at the transition from homogenous to inhomogenous flow. [Preview Abstract] |
Thursday, March 21, 2013 12:15PM - 12:27PM |
U30.00006: Phonon Dispersion and Elastic Properties of Two-Dimensional Soft Particle Colloidal Crystals and Glasses Tim Still, Ke Chen, Peter J. Yunker, Carl P. Goodrich, Samuel Schoenholz, Andrea J. Liu, A.G. Yodh We investigate phonon dispersion relations and associated mechanical properties of two-dimensional colloidal glasses and crystals composed of soft, thermoresponsive microgel particles whose temperature-sensitive size facilitates in-situ variation of particle packing fraction. The phonon modes were measured using particle tracking and displacement covariance matrix techniques. Measurements of the hexagonal crystal served to check our methodology and, as expected, the observed phonon dispersion was largely in agreement with theoretical expectations. Measurements of phonon dispersion in the glassy colloids, as a function of packing fraction above the jamming transition, permitted study of the scaling of bulk and shear moduli as a function of packing fraction. We performed numerical simulations and were able to recover the experimental findings. Moreover, the obtained shear moduli are in good agreement with rheological measurements. [Preview Abstract] |
Thursday, March 21, 2013 12:27PM - 12:39PM |
U30.00007: Aggregation, Gelation and Glass Transition in Mixed Suspension of Polystyrene Microsphere and Poly(N-isopropyl-acrylamide) Microgel Guangcui Yuan, Chuanzhuang Zhao, Charles C. Han Poly(N-isopropylacrylamide) microgel is adsorbable to the polystyrene microsphere surface. The saturated adsorption concentration of microgel ($\Phi *_{\mathrm{MG}})$ is in a linear relationship with the given concentration of microsphere ($\Phi_{\mathrm{MS}})$. Depending on the concentration of microgel ($\Phi_{\mathrm{MG}})$ added into the suspension microspheres, the microgel can induce bridging ($\Phi _{\mathrm{MG}}$ \textless $\Phi *_{\mathrm{MG}})$, stabilizing ($\Phi _{\mathrm{MG}} = \Phi *_{\mathrm{MG}})$ and depletion ($\Phi _{\mathrm{MG}}$ \textgreater $\Phi *_{\mathrm{MG}})$ effect. With combination of various $\Phi_{\mathrm{MS}}$ and $\Phi _{\mathrm{MG}}$/$\Phi *_{\mathrm{MG}}$, different structures including stable solution, bridging and depletion cluster, bridging and depletion gel, attractive glass and repulsive glass, were obtained. The transitions between these states were investigated by rheology and microscopy. Two-step yielding behavior was observed in attractive glass, which was contributed from bridging bonds of microgels and caging effect of dense microspheres. [Preview Abstract] |
Thursday, March 21, 2013 12:39PM - 12:51PM |
U30.00008: Dynamics of concentrated dicolloid particles Mark M. Panczyk, Norman J. Wagner, Eric M. Furst Nonspherical colloidal particles exhibit a variety of equilibrium structures, including colloidal crystals. However, with increasing concentration, particle dynamics in these suspensions slow, and the creation of equilibrium close-packed structures may be ultimately inhibited by the presence of a glass transition. For dicolloid particles, dimer particles with asymmetric or symmetric lobes, suspension dynamics have been studied using Stokesian dynamics simulations [1] and mode-coupling theory [2], and the glass transitions have been determined using rheology [3]. In this study, the dynamics of polystyrene dicolloids in water are measured by diffusing wave spectroscopy (DWS) at particle concentrations between 1 and 60 volume percent. Relaxation times of the dicolloid particle suspensions are determined as a function of particle concentration and shape. Strong particle localization occurs at the highest concentrations. The localization lengths measured by DWS are compared to their mode coupling theory predictions.\\[4pt] [1] Kumar A, Higdon JJL\textit{. J. Fluid. Mech}. \textbf{2011}, \textit{675, 297-335.}\\[0pt] [2] Zhang R, Schweizer KS. \textit{J. Chem. Phys. }\textbf{\textit{2010}}\textit{, 133 104902.}\\[0pt] [3] Kramb R.C. et al., \textit{J. Phys.: Condens. Matter. }\textbf{\textit{2011, }}\textit{23, 035102} [Preview Abstract] |
Thursday, March 21, 2013 12:51PM - 1:03PM |
U30.00009: On the Absence of Red Structural Color in Colloidal Glasses Sofia Magkiriadou, Jin-Gyu Park, Young-Seok Kim, Gi-Ra Yi, Vinothan N. Manoharan When a colloidal glass is illuminated, the short-ranged spatial correlations between neighboring particles can give rise to constructive interference for a particular wavelength. Unlike the structural colors arising from Bragg diffraction in colloidal crystals, the colors of these colloidal glasses are independent of angle due to the disordered, isotropic microstructure. We therefore call them ``photonic glasses.'' A similar coloration mechanism is found in the feathers of certain birds. However, there are few examples of red photonic glasses either in nature or in colloidal systems. Using scattering theory, we show that the absence of red photonic glasses can be explained by the wavelength-dependence of the single-particle scattering cross-section, which can override the interference condition set by the structure. We propose ways to overcome this obstacle, and we report on experimental methods to make non-iridescent, structural red color. [Preview Abstract] |
Thursday, March 21, 2013 1:03PM - 1:15PM |
U30.00010: Structure/dynamics coupling in suspensions of microgel particles on their approach to the glass A. Fernandez-Nieves, J. Clara-Rahola, P.N. Segre, A.B. South, L.A. Lyon We measure the structure factor, S(q), and the q-dependent diffusion coefficient, D(q), of dense suspensions of pNIPAm microgel particles. We do this at different temperatures, and hence different swelling degrees, at constant generalized volume fraction, and find dramatic changes in behavior. While for certain temperatures, 1/D(q) follows the behavior of S(q), at other temperatures the behavior of these two quantities completely decouples. Interestingly, this behavior correlates with fragility: Structure/dynamics decoupling is observed for suspensions resembling strong glass formation. [Preview Abstract] |
Thursday, March 21, 2013 1:15PM - 1:27PM |
U30.00011: Evolution of dynamical facilitation approaching the glass transition Raphael Candelier, Asaph Widmer-Cooper, David Reichman, Giulio Biroli, Olivier Dauchot We investigate the relaxation dynamics of simulated dense bidimensional supercooled liquids composed of softly interacting particles. We show that the long time scale dynamical heterogeneities result from the aggregation of several elementary relaxation events, themselves formed by collective leaps. By varying the temperature, we show that for low temperatures there is a growing excess of probability to find cage jumps that are close both in space and time, and that the network of spatio-temporal facilitation evolves towards a collection of clearly defined large events. We discuss these observations and specifically the relative importance of facilitation when approaching the glass transition. [Preview Abstract] |
Thursday, March 21, 2013 1:27PM - 1:39PM |
U30.00012: Aging in dense colloids through the growth and breakup of strongly correlated clusters Skanda Vivek, Stefan Boettcher, Paolo Sibani Colloidal systems exhibit glassy behaviour under the right physical conditions that can be observed through mean square displacements in experiments. Our phenomenological model of aging in colloids is based on the growth and breakup of strongly correlated clusters, which introduces dynamical heterogeneity in the system.\footnote{Boettcher \& Sibani, J.Phys.CM \textbf{23}, 065103 (2011)} Particles move and associate into clusters that can break up with a probability that decreases with cluster size. Different colloidal density regimes correspond to different probabilities. The mean square displacements measured in this system for a low density colloid shows a linear increase in time and shows a linear increase in log-time for high densities, which matches experimental data. The cluster breakup rate was measured to be uniform in time for low densities and $\propto 1/t$ in the aging regime, which provides a clock for the slowing down of the dynamics. Measurements of the four-point susceptibility $\chi_4$ show a peak indicating the response to a growing lengthscale that satisfies a scaling relation with sample age, $t_w$. For larger $t_w$, $\chi_4$ peaks higher, and decays more slowly with time, which we hypothesize is due to the dominance of relatively stable large clusters. [Preview Abstract] |
Thursday, March 21, 2013 1:39PM - 1:51PM |
U30.00013: Pinning Susceptibility at the Jamming Transition Amy Graves, Elliot Padgett, Carl Goodrich, Andrea Liu Jamming in the presence of fixed or pinned obstacles, representing quenched disorder, is a situation of both practical and theoretical interest. We study the jamming of soft, bidisperse discs in which a subset of discs are pinned while the remaining particles equilibrate around them at a given volume fraction. The obstacles provide a supporting structure for the jammed configuration which not only lowers the jamming threshold, $\phi_J$, but affects the coordination number and other parameters of interest as the critical point is approached. In the limit of low obstacle density, one can calculate a pinning susceptibility $\chi_P$, analogous to the magnetic susceptibility, with obstacle density playing the role of the magnetic field. The pinning susceptibility is thus expected to diverge in the thermodynamic limit as $\chi_P \propto |\phi-\phi_J|^{-\gamma_P}$. Finite-size scaling calculations allow us to confirm this and calculate the critical exponent, $\gamma_P$. [Preview Abstract] |
Thursday, March 21, 2013 1:51PM - 2:03PM |
U30.00014: Probing the depinning transition: contrasting lattice and continuum models Yan-Jiun Chen, Stefano Zapperi, James P. Sethna Models of depinning are used to study a wide variety of disordered systems where there are interfaces with jerky motion, including magnetic domain wall motion, fluid imbibition, and superconductor vortex lines. Analytic results from field theories are written in continuous time and space coordinates; but efficient algorithms are often done with cellular automata (CA). The equivalence of CA rules with the continuum models were justified by the appearance of a cusp in the disorder correlator after a finite-number of RG steps, especially for avalanche behavior that involve many degrees of freedom. However, in between this abrupt behavior, there exist slower dynamics where the avalanche almost stops, involving fewer degrees of freedom, and these regions may alter the scaling, as seen in recent studies of plastic deformation in crystals and crackling noise in glasses. Also, in our simulations, we find that discretization may introduce unwanted effects or relevant perturbations, such as a broken rotational symmetry. We compare and contrast results of the spatial and temporal structure of depinning from lattice and continuum simulations, and also provide complete functional forms to describe crossovers between different model classes. [Preview Abstract] |
Thursday, March 21, 2013 2:03PM - 2:15PM |
U30.00015: Dynamical Instabilities of a Brownian Particle in Weak Adhesion. Deepak Kumar, Shankar Ghosh, Shobo Bhattacharya Dynamical processes involved in weak adhesion are explored through a single cycle of an optically trapped Brownian colloidal silica particle detaching from, and reattaching to, a glass substrate immersed in a fluid in the presence of an externally applied force. Micro-rheology, video-microscopy and Nyquist noise measurements reveal both stochastic and deterministic dynamics of the process. When analyzed in terms of the viscoelastic response of the stress coupling medium between the objects, the unsticking instability shows remarkable similarities with yielding and fracture-mechanics of macro-scale solids. The resticking dynamics demonstrates stochastic instabilities through a spatio-temporally punctuated descent of the particle down an energy landscape with a hierarchy of metastable minima. [Preview Abstract] |
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