Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session H43: Aging in the Jammed StateFocus

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Sponsoring Units: GSNP GSOFT Chair: Stefan Boettcher, Emory University Room: 346 
Tuesday, March 15, 2016 2:30PM  2:42PM 
H43.00001: A TimeTemperature Transistor  An Application of Aging Dynamics Gregory Kenning Aging dynamics occur as systems far from thermodynamic equilibrium evolve towards equilibrium. We have produced a magnetic nanoparticle system composed of Co nanoparticles, which selfassemble during Co deposition on Sb. At a particular time in the formation of the nanoparticles, they are encased in a layer of Sb producing a system far from equilibrium. Magnetization vs. temperature measurements as well as Magnetic Force Microscopy (MFM) indicates that the nanoparticles initially have a large magnetic moment. We observe, as a function of time, an approximately 80{\%} decay in the sample magnetization and an approximately 50{\%} decay in the DC electrical resistivity. MFM suggests that the magnetization decay proceeds from the magnetic nanoparticles losing their net moments possibly due to spin rearrangement. Evidence also suggests that the initial magnetic moments, drive the Sb layer semiconducting. As the net moments of the magnetic nanoparticles decrease, the Sb reverts back to its semimetal behavior with the accompanying decrease in the electrical resistivity. The magnetization and resistance decays follow the same Arrhenius type behavior. By varying the Co layer thickness, the Arrhenius parameters can be tuned. We have been able to tune the parameters making these materials excellent candidates for sensors for electronically monitoring the age and lifetime of perishable foods. [Preview Abstract] 
Tuesday, March 15, 2016 2:42PM  2:54PM 
H43.00002: ABSTRACT WITHDRAWN 
Tuesday, March 15, 2016 2:54PM  3:06PM 
H43.00003: Aging and memory effects in the spin jam states of densely populated frustrated magnets Anjana Samarakoon, SeungHun Lee, Taku Sato, Haidong Zhou, Ryan Sinclair, Junjie Yang, Tianran Chen, GiaWei Chern, Israel Klich Defects and randomness has been largely studied as the key mechanism of glassiness find in a dilute magnetic system. Even though the same argument has also been made to explain the spin glass like properties in dense frustrated magnets, the existence of a glassy state arise intrinsically from a defect free spin system, far from the conventional dilute limit with different mechanisms such as quantum fluctuations and topological features, has been theoretically proposed recently. We have studied field effects on zerofield cooled and field cooled susceptibility bifurcation and memory effects below freezing transition, of three different densely populated frustrated magnets which glassy states we call spin jam, and a conventional dilute spin glass. Our data show common behaviors among the spin jam states, which is distinct from that of the conventional spin glass. We have also performed Monte Carlo simulations to understand the nature of their energy landscapes. [Preview Abstract] 
Tuesday, March 15, 2016 3:06PM  3:18PM 
H43.00004: Time Dependence of the freezing temperature for thin film spin glasses Raymond Orbach There have been many measurements of the dependence of the ``freezing temperature", $T_f$, on the thickness $\mathcal {L}$ of thin film spin glasses. $T_f$ decreases with decreasing $\mathcal {L}$, but never vanishes. This contribution suggests that the dependence of $T_f$ on $\mathcal {L}$ is a time dependent relationship. Because the lower critical dimension of a spin glass, ${d_\ell}\approx 2.5$, when the spin glass correlation length $\xi(t, T)$ grows to $\mathcal {L}$, the spin glass dimensionality crosses over from $d = 3$ to $d = 2$. What remains are spin glass correlations for length scales $\leq \mathcal {L}$. The time dependence of the magnetization dynamics are then activated, with activation energy equal to a largest barrier ${\Delta_{\text {max}}}({\mathcal {L}})$, and an associated activation time $\tau$. For measurements at time scales such that $\xi(t, T) < \mathcal {L}$, the effective dimension $d = 3$, and the characteristic cusp and knee of a spin glass is observed. For experimental time scales greater than $\tau$, with $\xi(t, T) \approx \mathcal {L}$, the zerofield cooled magnetization has grown to the fieldcooled value of the magnetization, leading to the identification of $T_f$. Quantitative agreement with experiment is exhibited. [Preview Abstract] 
Tuesday, March 15, 2016 3:18PM  3:30PM 
H43.00005: Intermittent Aging Dynamics in a Metallic Glass Studied by Xray Photon Correlation Spectroscopy Zach Evenson, Beatrice Ruta, Simon Hechler, Moritz Stolpe, Eloi Pineda, Isabella Gallino, Ralf Busch Although physical aging is a universal feature of glasses and other nonequilibrium matter, the atomiclevel processes involved still remain a puzzling mystery. Here we study the microscopic aging dynamics of a metallic glass using coherent Xrays. Contrary to the common assumption of a steady slowing down of the dynamics usually observed in macroscopic studies, we show that the structural relaxation processes underlying aging in this metallic glass are intermittent and highly heterogeneous at the atomic scale. Moreover, physical aging is triggered by cooperative atomic rearrangements, driven by the relaxation of internal stresses. These results strengthen the similarities between metallic glasses and nonequilibrium soft materials and a suggest a common microscopic origin stemming from from a complex energy landscape. [Preview Abstract] 
Tuesday, March 15, 2016 3:30PM  3:42PM 
H43.00006: Record Dynamics and the Parking Lot Model for granular dynamics Paolo Sibani, Stefan Boettcher Also known for its application to granular compaction (E. BenNaim et al., Physica D, 1998), the Parking Lot Model (PLM) describes the random parking of identical cars in a strip with no marked bays. In the thermally activated version considered, cars can be removed at an energy cost and, in thermal equilibrium, their average density increases as temperature decreases. However, equilibration at high density becomes exceedingly slow and the system enters an aging regime induced by a kinematic constraint, the fact that parked cars may not overlap. As parking an extra car reduces the available free space,the next parking event is even harder to achieve. Records in the number of parked cars mark the salient features of the dynamics and are shown to be well described by the logPoisson statistics known from other glassy systems with record dynamics. Clusters of cars whose positions must be rearranged to make the next insertion possible have a length scale which grows logarithmically with age, while their lifetime grows exponentially with size. The implications for a recent cluster model of colloidal dynamics,(S. Boettcher and P. Sibani, J. Phys.: Cond. Matter, 2011 N. Becker et al., J. Phys.: Cond. Matter, 2014) are discussed. [Preview Abstract] 
Tuesday, March 15, 2016 3:42PM  4:18PM 
H43.00007: Nonequilibrium phenomena in disordered colloidal solids Invited Speaker: Peter Yunker Colloidal particles are a convenient tool for studying a variety of nonequilibrium phenomena. I will discuss experiments that investigate the aging and nonequilibrium growth of disordered solids. In the first set of experiments, colloidal glasses are rapidly formed to study aging in jammed packings. A colloidal fluid, composed of micronsized temperaturesensitive pNIPAM particles, is rapidly quenched into a colloidal glass. After the glass is formed, collective rearrangements occur as the glass ages. Particles that undergo irreversible rearrangements, which break nearestneighbor pairings and allow the glass to relax, are identified. These irreversible rearrangements are accompanied by large clusters of fast moving particles; the number of particles involved in these clusters increases as the glass ages, leading to the slowing of dynamics that is characteristic of aging. In the second set of experiments, we study the role particle shape, and thus, interparticle interaction, plays in the formation of disordered solids with different structural and mechanical properties. Aqueous suspensions of colloidal particles with different shapes evaporate on glass slides. Convective flows during evaporation carry particles from drop center to drop edge, where they accumulate. The resulting particle deposits grow heterogeneously from the edge on the airwater interface. Three distinct growth processes were discovered in the evaporating colloidal suspensions by tuning particle shapedependent capillary interactions and thus varying the microscopic rules of deposition. Mechanical testing of these particulate deposits reveals that the deposit bending rigidity increases as particles become more anisotropic in shape. [Preview Abstract] 
Tuesday, March 15, 2016 4:18PM  4:30PM 
H43.00008: Correlated Clusters in Aging Colloidal Glass Dominic Robe, Stefan Boettcher, Peter Yunker A numerical model of correlated domains in glassy colloids is recreated, following its development by Becker, et. al.\footnote{N Becker, et. al. Mesoscopic model of temporal and spatial heterogeneity in aging colloids 2014 \textit{J. Phys.: Condens. Matt.} \url{http://arxiv.org/abs/1401.6521v1}}. The model is a course grained representation of 2D colloidal systems inspired by record dynamics, and produces emergent dynamic heterogeneity and aging. Results from the original development are reproduced, and compared to the same observables in an experimental system of bidisperse microgel spheres studied by Yunker, et. al.\footnote{P Yunker, et. al. Irreversible rearrangements, correlated domains, and local structure in aging glasses 2009 \textit{Phys. Rev. Lett.} \url{http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.103.115701}}. Basic observables such as particle persistence and mean square displacement are measured at different waiting times to observe aging. Fourpoint correlation lengths are also examined for signs of dynamic heterogeneity. Results from both the numerical and experimental systems are consistent with the predictions of record dynamics, that aging systems evolve on a logarithmic time scale. [Preview Abstract] 
Tuesday, March 15, 2016 4:30PM  4:42PM 
H43.00009: Universal Scaling in the Aging of the Strong Glass Former SiO2 Katharina VollmayrLee, Horacio Castillo, Christopher Gorman We show that the aging dynamics of a strong glass former displays a strikingly simple scaling behavior. Using molecular dynamics simulations, we quench the system from high temperature to 2500 K, below the glass transition and investigate dynamic heterogeneities as function of waiting time, the time elapsed since the quench. We find that both the dynamic susceptibility and the probability distribution of the local incoherent intermediate scattering function can be described by simple scaling forms in terms of the global incoherent intermediate scattering function. The scaling forms are the same that have been found to describe the aging of several fragile glass formers. Furthermore we find that the aging dynamics is controlled by a unique aging clock which is the same for Si and O atoms. [Preview Abstract] 
Tuesday, March 15, 2016 4:42PM  4:54PM 
H43.00010: Aging near the wall in colloidal glasses Cong Cao, Xinru Huang, Eric Weeks In a colloidal glass system, particles move slower as sample ages. In addition, their motions may be affected by their local structure, and this structure will be different near a wall. We examine how the aging process near a wall differs from that in the bulk of the sample. In particular, we use a confocal microscope to observe 3D motion in a bidisperse colloidal glass sample. We find that flat walls induce the particles to organize into layers. The aging process behaves differently near the boundary, especially within the first three layers. Particle motion near the wall is noticeably slower but also changes less dramatically with age. We compare and contrast aging seen in samples with flat and rough walls. [Preview Abstract] 
Tuesday, March 15, 2016 4:54PM  5:06PM 
H43.00011: Thermal fluctuations and elastic relaxation in the compressed exponential dynamics of colloidal gels Mehdi Bouzid, Jader Colombo, Emanuela Del Gado Colloidal gels belong to the class of amorphous systems, they are disordered elastic solids that can form at very low volume fraction, via aggregation into a rich variety of networks. They exhibit a slow relaxation process in the aging regime similar to the glassy dynamics. A wide range of experiments on colloidal gels show unusual compressed exponential of the relaxation dynamical properties. We use molecular dynamics simulation to investigate how the dynamic change with the age of the system. Upon breaking and reorganization of the network structure, the system may display stretched or compressed exponential relaxation. We show that the transition between these two regimes is associated to the interplay between thermally activated rearrangements and the elastic relaxation of internal stresses. In particular, ballisticlike displacements emerge from the non local relaxation of internal stresses mediated by a series of "microcollapses". When thermal fluctuations dominate, the gel restructuring involves instead more homogeneous displacements across the heterogeneous gel network, leading to a stretched exponential type of relaxation. [Preview Abstract] 
Tuesday, March 15, 2016 5:06PM  5:18PM 
H43.00012: Powerlaw creep and residual stresses in carbopol microgels Pierre Lidon, Sebastien Manneville We report on the interplay between creep and residual stresses in carbopol microgels. When a constant shear stress $\sigma$ is applied below the yield stress $\sigma_\text{c}$, the strain is shown to increase as a power law of time, $\gamma(t)=\gamma_0 + (t/\tau)^\alpha$, with and exponent $\alpha\simeq 0.38$ that is strongly reminiscent of Andrade creep in hard solids. For applied shear stresses lower than some characteristic value of about $\sigma_\text{c}/10$, the microgels experience a more complex creep behavior that we link to the existence of residual stresses and to weak aging of the system after preshear. The influence of the preshear protocol, of boundary conditions and of microgel concentration on residual stresses is investigated. We discuss our results in light of previous works on colloidal glasses and other soft glassy systems. [Preview Abstract] 
Tuesday, March 15, 2016 5:18PM  5:30PM 
H43.00013: Creep and aging in jammed granular materials Ishan Srivastava, Timothy Fisher Granular materials flow (or unjam) when stressed above the Coulomb yield stress, but a slow creep is observed when the applied stresses are low. In this work, using a recently introduced enthalpybased variablecell simulation method, we will present results on the creep and slow aging dynamics in granular systems comprised of soft particles of varying shape that are hydrostatically jammed and subjected to an external stress. We observe a twostage creep with an initial fast exponential evolution followed by a slow logarithmic evolution over long time scales. We correlate the slow creeping dynamics with micromechanical evolution at the grain scale, such as increasing dynamical heterogeneity and forcechain rearrangements. Results will also be presented on the effect of grain shape (faceted vs.~spherical) on the creep and aging dynamics. Finally, a continuum granular fluidity model is developed to rationalize these observations. [Preview Abstract] 
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