Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session E58: Colloids IFocus
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Sponsoring Units: GSOFT Chair: Vivek Sharma, University of Illinois at Chicago Room: BCEC 257A |
Tuesday, March 5, 2019 8:00AM - 8:12AM |
E58.00001: Impact of extreme softness on the crystallization of ultra-low crosslinked microgels in two and three dimensions Steffen Bochenek, Andrea Scotti, Monia Brugnoni, Lucio Isa, Walter Richtering Ultra-low crosslinked poly(N-isopropylacrylamide) microgels are used to elucidate the effect of softness on crystallization in two- and three-dimensions. 2D systems are produced by compressing and depositing microgels from oil-water interfaces. Ex-situ analysis by atomic force microscopy reveals that no crystals form upon compression, as opposed to the case of stiffer microgels. Once adsorbed at a fluid interface, microgels spread into disk-like objects whose size and stiffness are a strong function of polymer content and crosslinking. Consequently, interfacial confinement exacerbates size and mechanical polydispersity, effectively suppressing crystallization. In contrast, in 3D, the microgels crystallize at high concentrations, indicating that softness per se is not sufficient to suppress the liquid-solid phase transition, unless it is coupled to induced polydispersity. Furthermore, small-angle neutron scattering with contrast matching reveals that interpenetration is dominant over deswelling and deformation when these microgels are in 3D-overcrowded environments. |
Tuesday, March 5, 2019 8:12AM - 8:24AM |
E58.00002: Influence of Softness and Internal Architecture on Microgel Deswelling in Concentrated Suspensions Andrea Scotti, Monia Brugnoni, Judith Houston, Friederike Schulte, Steffen Bochenek, Walter Richtering Micorgels are soft polymeric networks swollen in a good solvent. They can be compressed, deformed or interpenetrated in concentrated suspensions. The prevalence of one of these mechanisms depends on both the softness and the architecture of the polymer network. By probing regular, ultra-low crosslinked, and hollow-poly(N-isopropylacrylamide) based microgels we show that for the same architecture, a decrease in the amount of crosslinker during the synthesis produces a more pronounced deswelling. Small-angle neutron scattering is used to directly access the form factors of the different microgels embedded within a matrix of regular crosslinked ones. This work clarifies that to obtain compressible microgels that adapt their size in concentrated suspenions, the presence of a cavity produces higher deswelling than decreasing the amount of crosslinker during the precipitation polymerization. The latter option leads to the opposite effect and interpenetration is dominant. |
Tuesday, March 5, 2019 8:24AM - 8:36AM |
E58.00003: Influence of Softness on the Stability of Binary Crystals Ronald LaCour, Carl Simon Adorf, Sharon Glotzer Binary systems of spherical colloids have shown the ability to self-assemble into many more superlattice structures than comparable monodisperse systems. Understanding the nature of the interparticle forces in such self-assembly is critical to target specific structures for self-assembly. Here we computationally investigate the influence of “softness”, the steepness of the interaction potential, on the solid phase behavior of particles interacting with a purely repulsive, isotropic pair potential. We determine the ground state phase diagram for our model using a basin-hopping algorithm to optimize candidate structures for low enthalpy. The phase behavior of repulsive particles is often understood by looking at the packing fraction of different phases; however, we find that a very small amount of softness can change the stable ground state phase of a system away from the densest packing structure. We also find softness increases the stability of many experimentally observed structures. Our results provide further insight into why particular structures self-assemble and will be useful as a reference for experimentalists working with softly repulsive particles. |
Tuesday, March 5, 2019 8:36AM - 8:48AM |
E58.00004: ABSTRACT WITHDRAWN
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Tuesday, March 5, 2019 8:48AM - 9:00AM |
E58.00005: Self-inflating Colloidal Microcapsules Zhe Xu, Stefano Sacanna
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Tuesday, March 5, 2019 9:00AM - 9:12AM |
E58.00006: Designing plasmonic-based colloidal pH microsensors Remi Dreyfus, Celine Burel, Bertrand Donnio Many natural processes start with an alteration of their immediate environment at the microscopic level. Therefore there is a need to develop pH microsensors that can easily reveal local changes in pH in any heterogeneous system. In this presentation, we show that with a careful design of colloids made of closely packed gold nanoparticles embedded in a thin pH-responsive polymeric shells, we can synthesize sensors at the micron scales that can be dispersed into heterogeneous systems and from which we can read sensitive information on local pH. We found that at low pH, close-packed jammed gold nanoparticles experience strong coupling in their plasmonic resonance, changing the plasmonic resonance to the red part of the spectrum, and giving a strong blue color to the microparticles. As pH is increased, the polymeric crust of the particles gets charged and swells, increasing the distance between the nanoparticles, thus suppressing the plasmonic correlations and inducing a strong color change with an absorption in the blue part of the spectrum, changing the microcapsules into red. Our results demonstrate that these colloidal capsules provide us with an easy way to unambiguously detect local pH changes at the microscale level in heterogenous systems. |
Tuesday, March 5, 2019 9:12AM - 9:24AM |
E58.00007: Improved generative models for colloidal specimens in digital holographic microscopy Ronald Alexander, Brian Leahy, Vinothan N Manoharan Digital holographic microscopy (DHM) is an important tool for characterizing colloidal specimens. Traditionally, the inverse problem of determining the size, shape, orientation and composition of an object from a hologram obtained by DHM is approached by numerical reconstruction of the incident and scattered electromagnetic fields. Recently, we have made advances by comparing holograms to predictions of a forward model for hologram formation. For systems colloidal spheres and cylinders in which multiple scattering is negligible, the scattering problem is solvable analytically and/or numerically. These calculations provide the basis for a model of image formation in DHM. We present progress highlighting improvements to a generative model for DHM of systems of colloidal particles. In particular, we show that explicit modelling of the scattering and diffraction effects in a microscope’s optical train increase the model’s predictive power. We also investigate the challenges for extending our technique of characterization through fitting of a forward model to biological systems such as bacteria and and animal cells. |
Tuesday, March 5, 2019 9:24AM - 9:36AM |
E58.00008: A Quick Method to determine ensemble averaged Translational and Rotational Diffusion coefficients Namita Shokeen, Ashis Mukhopadhyay The ensemble averaged translational diffusion of isotropic particles and coupled translational-rotational diffusion of anisotropic particles inside water and various polymer solutions were determined using dynamic differential microscopy (DDM). Initially, we applied this technique to characterize the dynamics of 25 nm radius particles within entangled high molecular weight, Mw=600 kg/mol polyethylene oxide-water solutions, which extended the scope of DDM to study the dynamics and rheological properties of soft matter at nanoscale. We will demonstrate the application of this method to characterize the motion of colloidal ellipsoids of different aspect ratios. |
Tuesday, March 5, 2019 9:36AM - 9:48AM |
E58.00009: Dynamic properties of liquid states in systems with a short-range attraction and long-range respulsion Paul D Godfrin, Peter Falus, Lionel Porcar, Kunlun Hong, Steven Hudson, Norman J. Wagner, Yun Liu Colloidal systems with a short-range attraction and long-range repulsion have been intensively studied in the past decade. A generalized phase diagram has been proposed with multiple liquid states. Using lysozyme as a model system, we have identified different liquid states of previous experimentally studied lysozyme samples within this generalized state diagram and explore the dynamic properties of each liquid state. Most lysozyme samples studied previously at low and intermediate concentrations are dispersed fluid states while a few high concentration samples are randomly percolated liquid states. In the dispersed fluid state, the short-time diffusion coefficient measured is found insensitive to the attraction strength, while it is very sensitive to the attraction strength in random percolated fluids. At high enough concentrations, the mean square displacement can be as slow as those of many glassy colloidal systems at time scales near the characteristic diffusion time even though these lysozyme samples remain in liquid states at the long-time limit. A localized glassy state is further identified by the mean square displacement. |
Tuesday, March 5, 2019 9:48AM - 10:00AM |
E58.00010: Hyperuniform defects in an isotropic liquid Rodrigo Guerra, Paul M Chaikin The concentration and organization of topological lattice defects form the basis of our theoretical understanding of the two-step melting process of two-dimensional solids, as described by Kosterlitz, Thouless, Halperin, Nelson, and Young (KTHNY). In this description, particles surrounded by anything but six nearest neighbors act as topologically charged quasi-particles, called disclinations, that interact via Coulombic pair potentials when the material is in the liquid-crystalline hexatic phase. This description is presumed to break down in the fully-isotropic liquid phase, but we find that the spectrum of topological charge density fluctuations in the liquid obeys the same spatial and temperature scaling relationships, S(q→0) ~ kBTq2, expected for an idealized fluid of oppositely charged particles: except for temperatures much larger than the isotropic-hexatic transition temperature. This suggests that the quasi-particle description may provide valuable insights into the behavior of the fluid too, particularly to the coupling of Gaussian curvature and topological charge in the fluid. |
Tuesday, March 5, 2019 10:00AM - 10:12AM |
E58.00011: Colloidal gelation as a nonequilibrium continuous phase transition Joep Rouwhorst, Chris Ness, Alessio Zaccone, Peter Schall A new view on gelation as a second-order nonequilibrium phase transition is presented using combined experiments on critical Casimir colloidal suspensions, simulations, and analytic solutions to a simplified master kinetic equation. The critical Casimir forces provide effective, short-ranged colloidal interactions that can be tuned with temperature, allowing to study gelation over a range of moderate attractive strength (bond energy between 3 and 6kBT). The experiments and simulations show cluster sizes and correlation lengths diverging with exponents ~1.6 and 0.8, respectively, consistent with growth exponents in percolation theory. Cluster masses exhibit power-law distributions with exponents -3/2 and -5/2 before and after gelation, respectively, as predicted by a master kinetic equation with single-bonded particle detachment. As detailed balance is violated in this process, our results indicate that the observed gelation is a nonequilibrium continuous phase transition (nonequilibrium percolation). These results suggest that the observed gelation process, in which fluid particles aggregate and percolate into rigid structures, is an analogue, mirror-image process of yielding, where emerging fluid-like particles percolate within a rigid matrix. |
Tuesday, March 5, 2019 10:12AM - 10:24AM |
E58.00012: Evolution of a sedimenting colloidal sheet Ruo-Yu Dong, Wei Wang, Shankar Ghosh, Steve Granick A sedimenting 2D colloidal sheet shows curious stability and nonlinear behavior at small Re around 10-3, which should be in the linear Stokes regime. Small-scale mechanical instabilities develop in the form of dynamic swirling of particles in transient clusters, which generate multiple critical points and highly entangled vortex lines. This nonlinearity results from the topological nature of the fluid flow. Spatial organization of swirling motions determines the overall shape. The observed phenomena may challenge our notion of a low Reynolds number hydrodynamic problem, and holds value for understanding other dissipative dynamical systems. |
Tuesday, March 5, 2019 10:24AM - 10:36AM |
E58.00013: Electrical resistance fluctuations as a probe to monitor colloidal flows Cagatay Karakan, Kamil Ekinci Impedance measurements are widely used to detect particles or cells in a flow and to measure their various properties. The approach typically focuses on individual cell counting and sizing by passing the cells through artificial constrictions in which the channel diameter D is comparable to particle size d (D~d). Here, we explore the electrical impedance sensing technique to characterize colloidal flows in microchannels at different D/d limits. Our measurement is based on a standard four-wire probe of the mean electrical resistance Rm and its fluctuations ΔR(t) across the channel. We have applied this approach to measure flows with microbead and red blood cell suspensions in microchannels with different diameters. Flow properties such as flow rate, shear stress, concentration and composition are varied while monitoring the microchannel optically and electrically. Our results suggest that concentration can be inferred from Rm , while ΔR/Rm and its probability distribution contains information about other flow parameters, such as flow rate, particle composition and its properties. Based on our preliminary data, we will discuss how impedance sensing can be used to monitor flow parameters in vasculature networks. |
Tuesday, March 5, 2019 10:36AM - 10:48AM |
E58.00014: Solvent coarsening around laser-heated colloids and related effective forces Sutapa Roy, Juan Ruben Gomez-Solano, Anna Maciolek, Siegfried Dietrich Laser illuminating a Janus colloid which is suspended in a near-critical binary solvent leads to the formation of the concentration gradient and coarsening patterns around the colloid, which leads to its phoretic motion. Using analytical theory and numerical simulations, we investigate this non-equilibrium phenomenon under the influence of a time-dependent temperature gradient. Our predictions are also confirmed by experiments with Gold-capped Janus particles immersed in PnP-water binary liquid mixture. Time-dependent properties of the coarsening patterns for various surface adsorption properties of the Janus colloid are analyzed. We also present results for structure formation around colloidal particles kept confined in thin films with confining surfaces preferring one species of the binary liquid mixture over the other. Confinement leads to the formation of a bridge connecting the colloid and both the confining walls. It is observed that the particle starts to move much before the stationary state is achieved. Results will also be presented on the time-dependent effective interactions between two such heated colloidal particles. |
Tuesday, March 5, 2019 10:48AM - 11:00AM |
E58.00015: Reentrant Glass Transition and Cooperative Dynamics in Quasi-Two-Dimensional Attractive Colloidal Suspensions Xiaoguang Ma, Piotr Habdas, Chandan Kumar Mishra, Mathrew Gratale, Arjun G Yodh Reentrant glass transition in hard spheres systems with short-range attractions are nonmonotonic phase transitions due to the competition between repulsive and attractive forces. This phenomenon has been extensively studied in three-dimensional (3D) systems. We experimentally study the dynamics of quasi-two-dimensional (2D) bidisperse colloidal glasses using optical microscopy and particle tracking techniques. The inter-particle attractions are induced and tuned in-situ using nanometer-size micelles. As the attraction strength increases, the reentrant transition from repulsive glass to supercooled liquid and then to attractive glass is observed from ensemble dynamical quantities including mean square displacements and self-intermediate scattering functions. Contrary to studies in 3D systems, ergodic fluid is absent from our 2D experiment, suggesting a difference due to dimensionality. Moreover, the heterogenous dynamics is examined by both dynamical susceptibilities and cooperative rearrangement regions along the reentrant glass transition line; both measurements suggest dynamics becomes the most heterogeneous in supercooled liquid state, which is also distinctive from 3D systems. |
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