Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session S17: Colloids II |
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Sponsoring Units: GSOFT Chair: Sharon Gerbode, Harvey Mudd College Room: 276 |
Thursday, March 16, 2017 11:15AM - 11:27AM |
S17.00001: Brownian dynamics simulations of optical blasting technique for manipulating colloidal crystal grain boundaries Jeremy Wang, Maya Martirossyan, Caitlin Cash, Kemper Ludlow, Alejandro Baptista, Sharon Gerbode We use Brownian Dynamics simulations to explore the new experimental ``optical blasting'' technique, in which a 1064 nm laser creates repulsive gradient forces on index-mismatched colloidal crystal particles. In the simulations, laser-induced forces are approximated using ray optics to calculate momentum transfer to the colloidal particles. Like our colloidal experiments, we find that the simulated optical blast forms small holes in 2-D colloidal crystals. When these holes form near grain boundaries (GB) the subsequent recovery of the crystal attracts the GB toward the location of the blast. By recreating this experimental setup \textit{in silico}, we systematically study how the effective attraction between the blast and the GB depends on the relative orientations of the crystal grains and the GB. [Preview Abstract] |
Thursday, March 16, 2017 11:27AM - 11:39AM |
S17.00002: Probing colloidal grain boundary dynamics using a novel optical blasting technique Maya Martirossyan, Jeremy Wang, Caitlin Cash, Kemper Ludlow, Alejandro Baptista, Sharon Gerbode We introduce an ``optical blasting'' technique that allows for grain boundary manipulation of colloidal crystals. Like an inverted optical tweezer, optical blasting employs a 1064 nm laser to create repulsive gradient forces on index mismatched colloidal particles, producing a hole within monolayer colloidal crystals. We find that optical blasting near grain boundaries in polycrystalline monolayer crystals of 1.2 micron silica spheres causes asymmetric melting near the blast. The subsequent recrystallization pulls the grain boundary toward the blast. We study this effective attraction between the blast and the grain boundary, and use the technique to deform grain boundaries and ultimately create new grains within an existing crystal. [Preview Abstract] |
Thursday, March 16, 2017 11:39AM - 11:51AM |
S17.00003: Strong ion-driven depletion causes Nano-particle assembly Yaohua Li, Jaime Millan, Meng Shen, Trung Nguyen, Monica Olvera Ion mediated interaction between Nanoparticles (NPs) have been extensively utilized in experiments such as protein crystallization. At high ionic concentration, strongly correlated ions can form short chains which induce depletion-type attraction between charge or non-charged nanoparticles. In this regime, previous theoretical and numerical efforts such as DLVO theory or the primitive model breaks down because they either neglect excluded volume of ions or solvent-induced correlation like hydration effects, which have non-trivial contribution to NP-NP interactions. To include these effects, we perform multi-scale molecular dynamics simulation to obtain the potential of mean-force between NPs immersed in 0.3M-3M NaCl solution. Ion pair potentials that reproduce radial distribution function from atomistic simulation are derived and used for implicit solvent simulation. The attractive interaction between NPs is of order of several kT (thermo energy) and scales with NP size and ionic strength. The functional form of the potential matches with classical depletion theory. Our results suggest that ion-induced depletion dominate interaction between NPs at high ionic strength. [Preview Abstract] |
Thursday, March 16, 2017 11:51AM - 12:03PM |
S17.00004: Deposition kinetics of colloidal particles at high ionic strengths Cesare Cejas, Fabrice Monti, Marine Truchet, Jean-Pierre Burnouf, Patrick Tabeling Using microfluidic experiments, we describe the deposition of a fluid suspension of weakly brownian particles transported in a straight channel at small Reynolds numbers under conditions of high ionic strengths. Our studies fall in a regime where electrostatic interactions are neglected and particle-wall van der Waals interactions govern the deposition mechanism on channel walls. We calculate the deposition kinetics analytically for a wide range of physical parameters. We find that the theory agrees with numerical Langevin simulations, which both confirm the experimental results. From this analysis, we demonstrate a universal dimensionless deposition function described by contributions from advection-diffusion transport and adhesion interactions (Hamaker constant). Results show that we accurately confirm the theoretical expression for the deposition kinetics. From a surface science perspective, working in the van der Waals regime enables to measure the Hamaker constant, a task that would take much longer to perform with the standard AFM. [Preview Abstract] |
Thursday, March 16, 2017 12:03PM - 12:15PM |
S17.00005: Particle Size Effects in Flow-Stabilized Colloidal Solids Scott Lindauer, Robert Riehn, Karen Daniels Flow-stabilized solids (FSS) are a class of fragile matter that forms when a dense suspension of colloids accumulates as it flows against a semi-permeable barrier in a micron-sized Hele-Shaw cell. It has previously been observed that FSS form above a critical flow rate. In order to probe the effect of particle size on the formation of FSS, we perform experiments with monodisperse spherical particles of five distinct sizes. When appropriately scaled by the height of the channel, we observe the expected power law relationship between Péclet number and pile area for all particle sizes. However, the critical Péclet number does not control the onset of pile formation; an additional particle size effect is present. Finally, we characterize the thermal fluctuations of the FSS with respect to the Péclet number. [Preview Abstract] |
Thursday, March 16, 2017 12:15PM - 12:27PM |
S17.00006: Colloidal diffusion over a quasicrystalline-patterned substrate Yun Su, Pik-Yin Lai, Bruce Ackerson, Penger Tong We report a systematic study of colloidal diffusion over a quasicrystalline-patterned substrate. The sample substrate is made of a flat thin layer of photoresist and contains identical cylindrical holes of diameter $d_h$, which are arranged on a quasicrystal lattice. A monolayer of silica spheres of diameter comparable to $d_h$ diffuse over the rugged quasicrystalline-patterned substrate and experience a gravitational potential $U(x,y)$. With optical microscopy and the particle tracking method, we measure $U(x,y)$ and particle's diffusion trajectories, which are found to undergo two distinct states: a trapped state when the particles are inside the holes and a free diffusion state when they are over the flat portion of the substrate. The dynamic properties of the diffusing particle, such as its mean dwell time, mean square displacement, and long-time diffusion coefficient $D_L$ are obtained from the particle trajectories. The measured $D_L$ is found to be in good agreement with the prediction of two theoretical models proposed for diffusion over a quasicrystal lattice. The experiment demonstrates the applications of this newly constructed colloidal potential landscape. This work was supported by the Research Grants Council of Hong Kong SAR. [Preview Abstract] |
Thursday, March 16, 2017 12:27PM - 12:39PM |
S17.00007: An Experimental Study of the Equation of State of Nano Colloids Using a Novel Dielectrophoresis Osmometer Chong Shen, Krittanon Sirorattanakul, Hao Huang, H. Daniel Ou-Yang This talk reports a novel method to measure equation of state (EOS) relating the colloidal osmotic pressure with particle concentration. Recent theories and simulations have made predictions for such EOS for various particle interactions, but measurements are rare. Conventional methods to determine the osmotic pressure in colloid suspensions use gravity or centrifugation. However, the nano colloidal system requires a long time to reach equilibrium when the particle sizes are small or their mass densities are close to that of the solvent. Here, we propose a new method involving electric bottle that will solve all such challenges. In the equilibrium under dielectrophoresis (DEP) force field, the spatial distribution of the particle density can be determined from fluorescent microscopy. According to Einstein’s osmotic equilibrium theory, the osmotic pressure of the colloid suspensions can be calculated. Then, the DEP force field is calibrated using the well-established EOS of colloidal hard spheres. Using the known force field, we determine the EOS for other particles with various interactions and compare the results with theoretical predictions. [Preview Abstract] |
Thursday, March 16, 2017 12:39PM - 12:51PM |
S17.00008: Effect of Confinement Induced Structures on Colloidal Suspension Viscosity Meera Ramaswamy, Christopher Ness, Andrew Fiore, Neil Lin, James Swan, Itai Cohen Confined systems occur at widely separated length scales from the atomic to granular. In confined atomic and granular systems there is complex relationship between the microstructure and the rheology. While the same relationship in colloidal systems is interesting due to the range of structures formed, such studies are also extremely challenging because of the system size scale. Here we use a custom built confocal rheoscope to image the particle configuration in a microsphere suspension while measuring its stress response. We find a non-monotonic trend in the viscosity under confinement that is strongly correlated with the microstructure. Further, we use two simulations techniques, the first, a Stokesian dynamics simulation that calculates the full hydrodynamic stress and the second uses a lubrication approximation for the hydrodynamics and allows a repulsive particle contact contribution to the stress. The use of these techniques enables us make comparisons with experiments and determine the contributions of the different stresses (hydrodynamic and contact) to the rheology. These results provide new insights to the unique rheology of confined suspensions. [Preview Abstract] |
Thursday, March 16, 2017 12:51PM - 1:03PM |
S17.00009: Transformation dynamics of colloidal assemblies from shape-shifting MOF particles Xiaohui Song, Qian Chen This study presents three consecutive demonstrations on realizing programmable colloidal assembly transformation based on shape-shifting ZIF-based MOF colloids: (1) preparation of monodisperse colloidal ZIF crystals with excellent controllability both in shape and size, (2) morphology transformation of a single ZIF particle monitored in-situ upon doping of fluorescent dye molecules on its surface, and (3) the in-situ transition of the assembled structures from one kind of closed packing to another which is based on single ZIF particle crystal transformation. Furthermore, we studied mutual interactions of neighboring MOF colloids whose attractive and repulsive forces are different upon their shape transformation. Our study will open new doors to align MOF colloids adaptively in multi-dimensionality for various applications in different fields, such as gas sorption and separation, catalysis, sensing, and biomedicine. [Preview Abstract] |
Thursday, March 16, 2017 1:03PM - 1:15PM |
S17.00010: Preparation and assembly of magnetic patchy colloids. Laura Rossi, Peter Schall The preparation of novel materials with specific functional properties calls for the design of colloidal building blocks that are able to rationally (self-)assemble into precise and adaptable structures and at the same time have the potential to be mass produced. In this talk, I will show that introducing magnetic patches into otherwise symmetric particles allows us to promote asymmetric directional and selective interactions between colloidal polymer spheres. Such colloidal building blocks can be engineered either by embedding dipolar units into polymerizable oil droplets or by using a novel combination of wet chemistry and photolithography. These magnetic patchy colloids make the ideal model system for the rational design of large 2D bonded structures with predefined and tunable architecture. [Preview Abstract] |
Thursday, March 16, 2017 1:15PM - 1:27PM |
S17.00011: Aging and Glassy Behaviors in a Model Soft Colloidal System Qi Li, Xiaoguang Peng, Gregory McKenna In the vicinity of glass transition, colloidal and molecular systems share similar behaviors. Inspired by temperature jump aging experiments in molecular systems, volume fraction up-jump experiments (induced by temperature down-jumps) were used to study both aging responses and equilibrium dynamics for a thermoresponsive PS-PNIPAM/AA soft colloidal system using light scattering (diffusing wave spectroscopy, DWS). Long-term aging responses were investigated under both equilibrium and non-equilibrium conditions. In the equilibrium state, liquid-to-glass transitions were observed as effective volume fraction increases. For the equilibrium $\alpha $-relaxation processes, the $\alpha $-relaxation time of the samples aged into equilibrium deviate from the Vogel-Fulcher-Tammann (VFT)-type expectations and the super-Arrhenius signature disappears below the glass transition volume fractions. The non-equilibrium aging responses of the samples show decoupling of the $\alpha $-relaxation time and the time for the structural evolution into equilibrium. As a microrheological method, DWS was found to probe the dynamics of the investigated colloidal systems differently from macroscopic rheology when in non-equilibrium regimes. [Preview Abstract] |
Thursday, March 16, 2017 1:27PM - 1:39PM |
S17.00012: Tunable Soft Nano Colloids: A Model System Sudipta Gupta, Joerg Stellbrink, Dieter Richter, Garrett Sternhagen, Donghui Zhang, Gerald Schneider We introduce two different class of soft colloids, namely charge neutral and charged systems, with tunable morphology and architecture at the individual particle level. They are experimentally realized by diblock-co polymer micelles exhibiting star-like core-shell architecture. For uncharged micelles, we proved that just by changing the ratio of the repetitive units of the individual block copolymer we can tune the number of arms attached to the central core, a.k.a. the aggregation number and their softness. A fascinating hyperuniform state was created where Stokes-Einstein relation was not violated on approaching gel point. The second class of charged soft colloids forms a model system for polyelectrolyte micelles based on newly synthesized polypeptoid amphiphiles. In this case we are able to tune the aggregation number, simply by placing a charged monomer at different position along the corona segment. Such a high degree of accuracy is made possible by precise precision synthesis of the amphiphilic peptoids. Both these class of micelles are characterized by state of the art neutron scattering techniques. The dynamics of the uncharged micelles was investigated in combination of DLS, rheology and BD simulation. *S. Gupta et al., Nanoscale 7, 13924 (2015); PRL 115, 128302 (2015). [Preview Abstract] |
Thursday, March 16, 2017 1:39PM - 1:51PM |
S17.00013: Self-Supporting Nanodiamond Gels: Elucidating Colloidal Interactions Through Rheology\textunderscore Prajesh Adhikari, Anurodh Tripathi, Nancy A. Vogel, Orlando J. Rojas, Sriunivasa R. Raghavan, Saad A. Khan This work investigates the colloidal interactions and rheological behavior of nanodiamond (ND) dispersions. While ND represents a promising class of nanofiller due to its high surface area, superior mechanical strength, tailorable surface functionality and biocompatibility, much remains unknown about the behavior of ND dispersions. We hypothesize that controlling interactions in ND dispersions will lead to highly functional systems with tunable modulus and shear response. Steady and dynamic rheology techniques are thus employed to systematically investigate nanodiamonds dispersed in model polar and non-polar media. We find that low concentrations of ND form gels almost instantaneously in a non-polar media. In contrast, ND's in polar media show a time-dependent behavior with the modulus increasing with time. We attribute the difference in behavior to variations in inter-particle interactions as well as the interaction of the ND with the media. Large steady and oscillatory strains are applied to ND colloidal gels to investigate the role of shear in gel microstructure breakdown and recovery. For colloidal gels in non-polar medium, the incomplete recovery of elastic modulus at high strain amplitudes indicates dominance of particle-particle interactions; however, in polar media the complete recovery of elastic modulus even at high strain amplitudes indicates dominance of particle-solvent interactions. These results taken together provide a platform to develop self-supporting gels with tunable properties in terms of ND concentration, and solvent type. [Preview Abstract] |
Thursday, March 16, 2017 1:51PM - 2:03PM |
S17.00014: Lindemann histograms as a new method to analyse nano-patterns and phases Ghaith Makey, Serim Ilday, Onur Tokel, Muhamet Ibrahim, Ozgun Yavuz, Ihor Pavlov, Oguz Gulseren, Omer Ilday The detection, observation, and analysis of material phases and atomistic patterns are of great importance for understanding systems exhibiting both equilibrium and far-from-equilibrium dynamics. As such, there is intense research on phase transitions and pattern dynamics in soft matter, statistical and nonlinear physics, and polymer physics. In order to identify phases and nano-patterns, the pair correlation function is commonly used [1]. However, this approach is limited in terms of recognizing competing patterns in dynamic systems, and lacks visualisation capabilities. In order to solve these limitations, we introduce Lindemann histogram quantification as an alternative method to analyse solid, liquid, and gas phases, along with hexagonal, square, and amorphous nano-pattern symmetries. We show that the proposed approach based on Lindemann parameter calculated per particle [2] maps local number densities to material phase or particles pattern. We apply the Lindemann histogram method on dynamical colloidal self-assembly experimental data [3] and identify competing patterns. [1] Veatch, PLoS ONE, 7, 2, 2012. [2] Chakravartya, J. Chem. Phys., 126, 2007. [3] Ilday, MRS Spring, 61, 2016. [Preview Abstract] |
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