Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session R54: Colloids |
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Sponsoring Units: GSOFT DFD Chair: Subhalakshmi Kumar, University of Illinois at Urbana-Champaign Room: LACC 514 |
Thursday, March 8, 2018 8:00AM - 8:12AM |
R54.00001: Predicting colors from multiply-scattering structures of disordered colloids Victoria Hwang, Anna Stephenson, Solomon Barkley, Vinothan Manoharan Disordered packings of colloidal spheres can display structural colors that arise from constructive interference of scattered light. These colors are independent of the angle between light source and observer, in contrast to the angle-dependent, or iridescent, colors of colloidal crystals. The locations of the color peaks in the spectrum can be accurately predicted by single scattering models, but these systems also have weak multiple scattering that contributes to the reflected intensity, making it difficult to quantitatively predict or design colors from these colloidal packings. To model the multiple scattering, we use a Monte Carlo approach, which simulates photon trajectories in a multiply-scattering medium. To validate the model, we use Bayesian analysis to infer the most probable sample parameters that produce a particular experimental reflection spectrum, and we compare these values against precise measurements of the sample parameters. We find good agreement between experimental reflection spectra and the multiple scattering model. Thus, the model helps us understand the effect of multiple scattering on reflection spectra of disordered colloidal packings, and gives us the ability to predict the sample parameters needed to achieve specific colors. |
Thursday, March 8, 2018 8:12AM - 8:24AM |
R54.00002: Determining degree of scattering in structurally-colored colloidal glasses Anna Stephenson, Victoria Hwang, Solomon Barkley, Vinothan Manoharan The reflection spectra produced by colloidal glasses comes from both single and multiple scattering. Interference between the waves scattered from these structures results in reflection peaks that we perceive as colors, termed structural colors because they come from the nanoscale structure rather than from absorption. While the location of the primary structural resonance can be predicted using a single-scattering theory, other features of the spectrum, such as the increase in reflection at small wavelengths, cannot be explained by single scattering alone. To experimentally measure how much light is multiply-scattered in these systems, we detect light reflected from colloidal glasses through crossed polarizers, which only pass light that has been scattered more than once. To extract the degree of multiple scattering, we use a Monte Carlo approach to simulate photons traveling through the glass, tracking the number of scattering events before photons exit the sample. By fitting the model to the experimental data, we can gain new insight into how the degree of scattering affects the off-resonant features of the reflectance spectra of colloidal glasses. |
Thursday, March 8, 2018 8:24AM - 8:36AM |
R54.00003: Visualization of Electron and or Energy Transfer in Redox Active Polymeric Colloids Subing Qu, Zihao Ou, Yavuz Savsatli, Yu Cao, Jeffrey Moore, Qian Chen, Paul Braun Under the scenario of size-exclusion mechanism flow battery, viologen-based polymeric colloids demonstrate efficient and reversible charge transport in aqueous and non-aqueous environments. We believe there is tremendous power in visualization of the corresponding contact-mediated electron and or energy transfer between these colloids, which will provide a more intuitive understanding of the unique dynamics as well as facilitate redox-state mapping in the system. Intrinsic electrofluorochromism of the redox active colloids (RAC) was discovered and exploited to serve the purpose. Via coupling a distinct fluorescent contrast with the respective redox state we successfully in-situ imaged intra- and inter-colloid energy transfer processes during electrochemical cycling. This system also displayed a greater than hundred-fold amplification of the sensitivity to fluorescence quenching. Photophysics of the amplification was further investigated and we attributed it to fast electron hopping among neighboring redox groups. |
Thursday, March 8, 2018 8:36AM - 8:48AM |
R54.00004: Numerical Study of Biased Brownian Motion in Narrow Asymmetric Channel with Anisotropy Ki-Wing To Recently experiments [Zheng Peng and Kiwing To, PRE 94, 022902 (2016)] showed that a Brownian particle in a narrow channel with asymmetric walls maybe biased to drift uni-directionaly by the presence of anisotropy in the longitudinal and transverse directions. Here we perform Brownian dynamics simulations of the experiments to study the physics behind the phenomenon. We verify that the driving force of the drift is indeed originated by the anisotropy the channel walls. Furthermore, the drift velocity is proportional to the mean-square velocity in the transverse direction. |
Thursday, March 8, 2018 8:48AM - 9:00AM |
R54.00005: "Spin" Dynamics in Buckled and Frustrated Quasi-two-dimensional Colloidal Crystals Analisa Hill, Xiaoguang Ma, A. G. Yodh We experimentally study the structure and dynamics of quasi-two-dimensional (2D) colloidal crystals [Nature 456, 898 (2008)] with frustrated interparticle interactions. The 2D triangular lattice is formed by confining a monolayer of close-packed micro-spheres between two parallel cover glass plates. The wall separation is slightly larger than one particle diameter, facilitating formation of a buckled monolayer of particles. While each particle can occupy either up or down position (“spin” direction) on its lattice site, neighboring particles favor opposite positions, which frustrates a third neighboring particle in a triangular lattice (analogous to the Ising antiferromagnet on a triangular lattice). With video microscopy and particle tracking we determine the in-plane and vertical motion of each particle. Then, using Markov state models, we extract the equilibrium distribution of ground states and the transition rates between them. Preliminary results reveal a hierarchy of time scales associated with relaxation in this frustrated system. |
Thursday, March 8, 2018 9:00AM - 9:12AM |
R54.00006: Scalable Production of Polymer Nanocolloids with Complex Internal Structures and Amphiphilic Properties via Flash NanoPrecipitation Victoria Lee, Chris Sosa, Rui Liu, Brian Wilson, Robert Prud'homme, Rodney Priestley Polymer nanocolloids with complex internal structures, including anisotropic Janus nanocolloids and patchy particles, have generated significant interest for their potential applications in medicine and optics and for their unique self-assembly behavior. However, nanocolloids with such complex internal structures often require highly specific chemistries and multiple processing steps with long residence times, making a processing platform which can generate kilograms of such structured nanocolloids per day highly desirable. Here, we demonstrate the ability to produce these structured polymer nanocolloids using Flash NanoPrecipitation (FNP). During FNP, nanocolloids form when polymers precipitate and phase separate upon rapid mixing of a polymer blend in a good solvent with a poor solvent, and the resulting nanocolloid morphology is determined by the minimization of the surface free energy of the system. We are able to produce core-shell, spherical Janus, and snowman Janus polymer nanocolloids by tuning interactions between the polymers and the solvent environment. Additional functionality can be incorporated by adding inorganic nanoparticles and reacting hydrophilic moieties onto one half of the nanocolloid, making them amphiphilic for potential application as solid surfactants. |
Thursday, March 8, 2018 9:12AM - 9:24AM |
R54.00007: Controlling soft matter with intermediate-plane holography Argha Mondal, Aaron Yevick, Lauren Blackburn, Nikitas Kanellakopoloulos, David Grier We introduce an approach to phase-only holography that substantially improves the ability of holographic trapping systems to project propagation-invariant modes of light. This technique, which we call intermediate-plane holography, improves the diffraction efficiency of phase-only holograms by up to 400 times, and extends the range of non-diffracting propation by up to a factor of 1000. The resulting holograms are particularly well suited for projecting accelerating modes of light and long-range tractor beams for transporting colloidal particles and aerosols. We present meter-class tractor beams projected with centimeter-scale optical elements. |
Thursday, March 8, 2018 9:24AM - 9:36AM |
R54.00008: Universal diagram of particle deposition kinetics Cesare Cejas, Fabrice Monti, Marine Truchet, Jean-Pierre Burnouf, Patrick Tabeling Using microfluidics, we present a comprehensive description of particle deposition on solid surfaces for a broad range of experimental conditions (velocity, geometry, particle size, salt concentration). Here, we use microchannels where near the channel wall, particles are subject to different forces that control their trajectories: hindered diffusion, hydrodynamic forces, electrostatic forces, and adhesion. By coupling microfluidic experiments, theoretical analysis, and numerical simulations, we succeed in establishing a general description of particle deposition phenomenon by demonstrating the existence of three regimes: (attractive) van der Waals, (repulsive electrostatic) Debye, and Diffusive. In a certain coordinate system, the universal diagram that embodies these regimes can be represented by a cantilever beam, in which the vertical support is defined by a dimensionless number incorporating the properties of the Debye layer with respect to adhesion and the horizontal beam is determined by the comparison between an effective Peclet number (advection-diffusion transport) and the Hamaker constant (adhesion forces). Results show that the theory is supported quantitatively by experiments and numerics. |
Thursday, March 8, 2018 9:36AM - 9:48AM |
R54.00009: Lattice Dynamics in Quasi-Two-Dimensional Attractive Colloidal Crystals Xiaoguang Ma, Wei-Shao Wei, Piotr Habdas, Arjun Yodh We experimentally study lattice dynamics and phonon properties in quasi-two-dimensional (2D) colloidal crystals composed of hard-spheres with short-range attractions. The 2D colloidal crystal is formed by confining a monolayer of close-packed micron-sized polystyrene latex beads between two parallel cover glasses. The interparticle attraction is controlled via a temperature-tunable depletion interaction and the attractive potential is increased from 0 to 5 kBT . Using video microscopy and particle tracking techniques, we obtain individual particle trajectories and investigate their dynamics as a function of interparticle attractions. By measuring the displacement correlations between particles, we extract the vibrational properties of an equivalent "shadow" system, and we show that while the lattice becomes more rigid with increasing attractions, surprisingly the microscopic spring constants become more heterogeneous across the lattice. |
Thursday, March 8, 2018 9:48AM - 10:00AM |
R54.00010: Correlating structural recovery in colloidal and molecular glasses Sourya Banik, Gregory McKenna Jammed colloidal systems are considered as models of glass transition in molecular systems. McKenna and coworkers [1] tested this by comparing the structural recovery (physical aging) behavior in the two systems. Structural recovery in molecular glasses is well established by the three experiments suggested by Kovacs. However, the behavior from thermosensitive colloids following the Kovacs type histories were found to be vastly different. The present modelling work is carried out to figure whether the disagreements in results were due to fundamentally different aging behavior or due to differences in aging conditions/parameters in the two systems. TNM-KAHR framework is used to model the structural recovery in molecular systems in isobaric and isochoric conditions. We show that a molecular system aging under constant volume conditions following a simultaneous volume and temperature jump qualitatively mimics the structural recovery in colloidal glasses. Similarities between the model and the colloidal results suggest isochoric aging is a better analogue to structural recovery in colloids than the conventional isobaric conditions. |
Thursday, March 8, 2018 10:00AM - 10:12AM |
R54.00011: Effect of Ionic Constituents on the Propagation of Charged Nanospheres in Passivated Gel Electrophoresis Dimitri Bikos, Thomas Mason We explore the types and concentrations of ionic constituents in aqueous buffer solutions that largely determine their conductivities. These constituents, in turn, directly influence the electric field E acting on charged sulfate-stabilized polystyrene nanospheres, having diameters ranging from ≈40 nm to ≈200 nm, that propagate at velocities v through large-pore, passivated agarose gels in a sodium borate buffer. Conductivity measurements near the center of the gel region show that predictions of E based on a constitutive conductivity model closely correlate with v of propagating bands of nanospheres, as measured using time-lapse optical video recording of scattered light. Additionally, we explore v(E) influenced by two different passivation agents: nonionic polyethylene glycol (PEG) and anionic sodium dodecyl sulfate (SDS). The conductivity model leads to a refined and more accurate estimate of E as compared to the standard method of dividing applied voltage by an inter-electrode separation. Moreover, this conductivity model provides a good starting point for interpreting the complicated effects of amphiphilic ionic passivation agents, such as dodecyl sulfate anions, on the velocities of propagating nanospheres in gel electrophoresis. |
Thursday, March 8, 2018 10:12AM - 10:24AM |
R54.00012: Clarifying the Role of Thermoelectriciy and Specific Ions/Molecules Effects in the Thermodiffusion of Charged Iron Oxide Nanoparticles André Sehnem, Antônio Figueiredo Neto A temperature gradient applied to a liquid solution of ferrofluid will induce the thermodiffusion effect of electrostatically stabilized iron oxide nanoparticles. The driving mechanisms of thermophoretic migration of the particles either to the cold or to the hot side come from microscopic phenomena. They are particle localized, like the temperature dependence of electric double layer and the Brownian diffusion along the temperature gradient; or long range like the thermoelectric field due to the differential ionic heats of transport of stabilizing ions or the concentration gradient generated by the intrinsic Soret coefficient of these ions. We will present experimental results for the Soret coefficient of nanoparticles and investigate the contributions of the different mechanisms by the use of auxilliary experiments like the measument of the zeta potential, the analysis of the thermoelectric field generated by thermodiffusion and the measurement of the intrinsic Soret effect of the stabilizing ions. |
Thursday, March 8, 2018 10:24AM - 10:36AM |
R54.00013: Polycrystal Annealing and Solid-Solid Phase Transitions in Colloidal Crystals Under a Flow Wei LI, Yilong Han We experimentally drive NIPA microgel colloidal crystals under a sinusoidal oscillation and studied their polycrystal annealing, grain-boundary melting and solid-solid transitions. The oscillation anneals grains into larger sizes via step-by-step grain rotations or via grain boundary melting and recrystallization. The grains grow as a power law and become faster at stronger oscillations . The lattice orientations of the resulted grains tend to align along the flow. At higher volume fraction but below the equilibrium melting point, the shear induces melting from grain boundaries. Under appropriate volume fraction and wall confinement thickness, the shear drives the thin-film square lattice into a triangular lattice via a melting and recrystallization process. |
Thursday, March 8, 2018 10:36AM - 10:48AM |
R54.00014: Evaporation-induced stratification in colloidal solutions Jiajia Zhou, Ying Jiang, Masao Doi When a liquid film of a colloidal solution consisting of particles of different sizes is dried on a substrate, the colloids often stratify, where smaller colloids are laid upon larger colloids. This phenomenon is counterintuitive because larger colloids which have a smaller diffusion constant, are expected to remain near the surface during the drying process, leaving a layer of larger colloids on top of smaller colloids. Here we show that the phenomenon is caused by the interaction between the colloids, and can be explained by a diffusion model accounting for the interaction between the colloids. By studying the evolution equations both numerically and analytically, we derive the condition at which the stratified structures are obtained. |
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