Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session S54: Colloids, Emulsions and Foams |
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Sponsoring Units: GSOFT DFD Chair: Gerd Schroeder-Turk, Murdoch Univ Room: LACC 514 |
Thursday, March 8, 2018 11:15AM - 11:27AM |
S54.00001: Attractive and repulsive interactions in joined pairs of floating bubbles Klebert Feitosa, Nicholas Hagans, Brian Seymour, Parviz Shabane, Shengfeng Cheng When bubbles floating on water come in contact, they experience both an attractive force, due to capillarity, and a repulsive force, due to elastic deformations. We perform an experiment to investigate the nature of these interactions in a joined pair of bubbles and their dependence on bubble size and bubble size ratio. The experiment consists of placing two floating bubbles in close proximity on a water tank and tracking their collision and subsequent oscillations. By fitting the oscillations to a simple damped-spring model, we extract the effective spring constant and the damping coefficient of the joined pair as a function of bubble size. We find that the natural frequency of oscillation has a power-law dependence with bubble diameter of the form ω0 ∝ D-0.5. |
Thursday, March 8, 2018 11:27AM - 11:39AM |
S54.00002: Foams in microfluidics Ilham Maimouni, Maria Russo, Joshua Ricouvier, Pavel Yazhgur, Patrick Tabeling Foams are investigated to be self-assembled materials exhibiting interesting photonic properties. We experimentally build 3D foams by packing air bubbles in aqueous solution containing a monomer. The bubbles are produced in a PDMS (Polydimethylsiloxane) microfluidic chip and directly assembled in a microfluidic channel giving birth to highly tunable 3D foam. Indeed, by varying fluid pressures, the foam composition and fabrication process, we manage to sharply control bubbles production and thereby govern the structural properties of the obtained material: porosity, pores size, connectivity and polydispersity. Electromagnetic simulations are then performed to study wave propagation in such materials over an important range of frequencies and different relevant transmission regimes are distinguished. |
Thursday, March 8, 2018 11:39AM - 11:51AM |
S54.00003: Stepwise Thinning and Nanoscopic Thickness Variations in Foam Films formed by Aqueous Sodium Napthenate Solutions Chrystian Ochoa, Subinuer Yilixiati, Yiran Zhang, William Yang, Vivek Sharma Sodium Napthenates found in crude oils can act as surfactants, and self-assemble in aqueous solutions to form micelles and liquid crystals. Understanding and controlling the drainage kinetics of thin films is an important problem that underlies the stability, lifetime and rheology of pertroleum foams and emulsions. Here we show that foam films formed by aqueous solutions of sodium napthenates exhibit step-wise thinning or stratification, due to the influence of non-DLVO forces, including supramolecular oscillatory structural forces. We utilize Interferometry, Digital, Imaging, Optical Microscopy protocols, previously developed by our group, to investigate the drainage and stratification in micellar foam films (< 100 nm) with high spatial (thickness < 10 nm) and temporal resolution (< 1 ms). We determine how the concentration of added sodium napthenates influences the nanoscopic topography, stratification kinetics and step size of foam films and contrast the results with behavior observed with stratifying foams made with sodium dodecyl sulfate (SDS) solutions. |
Thursday, March 8, 2018 11:51AM - 12:03PM |
S54.00004: Experimentally Testing the Border-Crossing Model for Coarsening of Quasi-Two-Dimensional Wet Foams Anthony Chieco, Cody Schimming, Douglas Durian In dry foams, a bubble’s area grows or shrinks according only to its number of sides, dA/dt=K0(n-6). This von Neumann law is increasingly violated for wetter foams, where Plateau borders are inflated with liquid and this has been assumed to block the available film area across which gas diffuses. Recently it was predicted that a surprisingly large amount of gas actually crosses the borders, and that this modifies the von Neumann law such that bubble size and shape now matter [1]. To test this experimentally, we measure the growth rate of individual bubbles in quasi-2d foams of variable wetness confined between parallel plates. Interestingly, some 6-sided bubbles are found to grow, and others are found that shrink -- in violation of the usual von Neumann law. These results, and similar data for bubbles with other numbers of sides, appear to agree with the generalization of the von Neumann law that incorporates the effects of border crossing [1]. |
Thursday, March 8, 2018 12:03PM - 12:15PM |
S54.00005: Structural Anisotropy in Periodically Sheared Colloidal Suspensions Sam Wilken, Rodrigo Guerra, David Pine, Paul Chaikin Periodically sheared dilute, non-Brownian suspensions explore new configurations through collisions in an otherwise reversible flow. Below a critical strain, the particles remain active until they find a configuration with no collisions and reach an absorbing state. Recent simulations by Hexner and Levine have shown that the configuration of particles in the critically absorbing state is hyperuniform. The structure factor ( S(q) ) of a hyperuniform system goes to zero at q=0 (as opposed to a constant positive value for the same suspension away from the critical state). We built a compact, uni-axial shear cell in order to shear colloidal suspensions while using small-angle light scattering to measure S(q) from angles of 0.03\degree to 1.5\degree. We observe a strong anisotropy in S(q) due to the anisotropy of the imposed strain. For a suspension of volume fraction 0.25, the critical strain is near 2; the structure factor along the shear does not decrease while S(q) along the vorticity direction decreases by almost an order of magnitude from the structure at thermal equilibrium. |
Thursday, March 8, 2018 12:15PM - 12:27PM |
S54.00006: Diffusion and equilibrium structure of bi-disperse colloidal suspensions confined by a spherical cavity Emma del Carmen Gonzalez Gonzalez, Christian Aponte-Rivera, Roseanna Zia Recent simulations of monodisperse colloidal suspensions confined by a spherical cavity demonstrate that both confinement and crowding produce qualitative changes in short- and long-time transport rate processes and equilibrium material properties[1,2,3]. The theoretical and computational framework developed in these studies set the foundation for studying the dynamics of 3D micro-confined suspensions. However, particle polydispersity in size plays a role in many biophysical confined systems such as the interior of eukaryotic cells, but such effects in 3D confinement have received little to no attention in the literature. In the present work, we extend our theory and model to account for size polydispersity. We present the hydrodynamic coupling functions and computational model for a bidisperse suspension of colloids coupled by hydrodynamic interactions inside a spherical cavity. We utilize our model to study the equilibrium structure and short time transport properties of spherically confined bidisperse colloidal suspensions. |
Thursday, March 8, 2018 12:27PM - 12:39PM |
S54.00007: Topological Electric Double Layers in Charged Colloids Jeffrey Everts, Miha Ravnik Charged surfaces in contact with liquids containing ions are accompanied in equilibrium by an electric double layer consisting of a layer of surface charge and a bulk ion cloud. This screening cloud determines not only the interactions between charged particles and their self-assembly [1], but also determines, for example, how the interaction of a charged colloidal particle with an interface can be tuned from attractive to repulsive [2]. However, little is known to what spatial complexity the electric double layers can be designed. Here, we show that electric double layers of non-trivial topology -including tori, multi-tori and knots- can be realised in charged colloids with complex-shaped particles, using numerical modelling. We show that the topology of double layers can be defined via a cut-off in the ion concentration and demonstrate that the double layer topology can be tuned by changing the Debye screening length or by changing the shape and topology of the particle [3]. This work is an attempt to introduce concepts of topology in the field of charged colloids. |
Thursday, March 8, 2018 12:39PM - 12:51PM |
S54.00008: Forced-induced Diffusion in Dilute Colloidal Suspensions Piotr Habdas, Rui Zhang, Zachery Brown, Henry Chu, Roseanna Zia We use fluorescence microscopy to study the dynamics of a Brownian probe particle driven by a constant external force through dilute colloidal suspensions with hard-sphere interparticle potential. As the probe particle moves through the colloidal suspension it collides with colloidal particles deforming the equilibrium suspension microstructure. The shape and the range of this distortion is determined by the volume fraction of the colloidal suspension and by the relative strength of the external force with respect to the entropic restoring force of the colloidal particles. We find that the average velocity of the probe particle is linear with the external force and it decreases with the volume fraction. Standard deviation of the distribution of the position of the probe particle perpendicular to the direction of motion decreases with the forcing strength and saturates at strong forcing for all volume fractions studied. Colloidal particles in the vicinity of the probe particle exhibit non-Gaussian dynamics. We compare our results with force-induced diffusion measured by Brownian dynamics simulations. |
Thursday, March 8, 2018 12:51PM - 1:03PM |
S54.00009: Effective interactions from ion-ion correlations: the case of Calcium-Silicate-Hydrates Abhay Goyal, Katerina Ioannidou, Roland Pellenq, Emanuela Del Gado The spatial organization of multivalent ions in solution can strongly affect the potential of mean force (PMF) between charged surfaces, which in turn affects the self-assembly of charged aggregates or particles. We combine Grand Canonical Monte Carlo and molecular dynamics simulations with a primitive model for a complex ionic solution between charged surfaces. By implementing an explicit dipolar model for the solvent, we investigate its effect on the electrostatic interactions in these systems and obtain the PMF in the case of divalent ions in water and a high surface charge. Depending on the ion concentration and spatial organization, the PMF can feature attractive wells, pure repulsion, or even competing attractive and repulsive parts. We apply this approach to compute the effective interactions that, due to the evolving ion concentration in the solvent, drive Calcium Silicate Hydrate (C-S-H) self-assembly into cement gels during cement hydration. |
Thursday, March 8, 2018 1:03PM - 1:15PM |
S54.00010: Asphaltene adsorption on functionalized solids Philippe Bourrianne, Henri-Louis Girard, Kripa Varanasi, Robert Cohen, Gareth McKinley Asphaltenes are aromatic heavy components of crude oil. Because of their dual structure made of an aromatic-core and aliphatic side-chains, asphaltenes develop a particular affinity with interfaces. For instance, their ability to adsorb onto various solids can induce serious damage such as pipe clogging. We study the effect of the physico-chemical properties of the substrate on the extent of this adsorption. Based on chemical characterizations, wetting studies and roughness measurements, we develop different tools to investigate the deposition of those molecules. Then, we quantify the adsorption using QCM and ellipsometry. We later discuss the adsorption mechanism probing orientation and adhesion of asphaltenes molecules on a solid with force spectroscopy measurement. |
Thursday, March 8, 2018 1:15PM - 1:27PM |
S54.00011: Towards longer, bubble-free imaging of soft materials in liquid-phase TEM Huan Wang, Hima Nagamanasa Kandula, Ye-Jin Kim, Oh-Hoon Kwon, Steve Granick In situ TEM provides a unique combination of high spatial and temporal resolution, allowing direct observation of dynamics in liquids, with advantageous single molecule tracking capability; yet, the correct interpretation of dynamical process critically relies on careful assessments of high energy electron beam influence, especially for soft materials. Bubble formation due to water radiolysis, the direct indicator of electron beam damage in aqueous solution, is ubiquitous. It causes hydrodynamic-induced motion nearby and is desirable to suppress. Here, based on analysing the relevant free radical chemistry as well as by direct imaging of macromolecules in aqueous, we explore broadly the critical variables to effectively broaden the time window for bubble-free imaging of synthetic polymers, DNA, and lipids in solution. |
Thursday, March 8, 2018 1:27PM - 1:39PM |
S54.00012: Watching macromolecules dance in real-time with liquid-phase TEM Hima Nagamanasa Kandula, Huan Wang, Steve Granick Observing single molecules in real-space and time continues to pose a challenge. Working towards overcoming this limitation, we have implemented liquid-phase TEM (transmission electron microscopy) to image individual macromolecules. Unlike static imaging with conventional TEM, this liquid-phase TEM opens opportunities to investigate dynamical features of materials with nanometer resolution. Nevertheless, imaging single molecules in liquid with TEM comes with a lot of challenges. In this talk, I will discuss how by using graphene sheets to wrap liquids, we demonstrate the possibility of investigating polymers with single molecule resolution. Moreover, our study provides a direct visualization of numerous dynamical features of polymers. We expect our work to trigger more studies to investigate various other soft and living materials with liquid-phase TEM in future. |
Thursday, March 8, 2018 1:39PM - 1:51PM |
S54.00013: The Physics of Colloidal Chains Bipul Biswas, Guruswamy Kumaraswamy Spherical colloidal particles have emerged as model systems for gaining insights into different phenomena in condensed matter and statistical mechanics, such as crystallization and the glass transition. Here we make “polymeric” colloidal chains by stringing colloidal beads together using an elegant method called ice templating. Colloidal polystyrene latex particles are coated with polymer (polyethylenimine) and are crosslinked using diepoxy compounds to form colloidal chains. We can vary the chain flexibility simply by varying crosslinking time. We use optical microscopy to observe the colloidal chains and obtain the spring constant between colloidal monomers and the chain bending rigidity. We investigate semi-flexible colloidal chains and show that their center of mass diffusion scales with N-0.6, where N is the number of beads in the chain. Surface modification of the colloidal beads lends functionality to the chains. Coating the beads with catalyst allows us to achieve out-of-equilibrium active systems that show enhanced center of mass diffusion. Grafting thermoresponsive polymers to the colloidal surface allow us to create colloidal chain assemblies that are sensitive to temperature variations. |
Thursday, March 8, 2018 1:51PM - 2:03PM |
S54.00014: Surface and Interfacial Tension of Graft Polymer Melts Michael Jacobs, Brandon Pugnet, Heyi Liang, Andrey Dobrynin Understanding the surface properties of polymer melts is crucial for design of new polymeric coatings, adhesives and composites. Here, we study the effect of chain-end fraction (defined as a ratio of the number of chain ends to the total number of monomers) on the surface and interfacial tension of melts of graft and linear polymers by computer simulations. In our simulations, a film of melt of graft polymers and a film of melt of linear chains with the same total number of monomers are put in contact. By varying the degree of polymerization of the side chains nsc and their grafting density 1/ng on the graft polymer backbone, we change the chain-end fraction of graft polymers while keeping the total number of monomers unchanged. The surface tension of the graft polymer melts γG and the interfacial tension of the interface between graft and linear polymer melts γGL are obtained by using the Bakker’s formula. The simulations show that the surface tension γG decreases linearly with increasing chain-end fraction in accordance with theoretical predictions. The interfacial tension γGL first decreases then saturates with increasing chain-end fraction. |
Thursday, March 8, 2018 2:03PM - 2:15PM |
S54.00015: Morphology and Conformation of Catenanes in Dilute Solutions Saeed Akbari, Mesfin Tsige We present analysis of the structure and dynamics of catenanes in solution through molecular dynamics simulation. Pure poly(ethylene oxide) (PEO), pure polystyrene (PS) and diblocks of PEO and PS catenanes in a select group of solvents are examined. Morphology analysis was performed upon immersion of individual polymers in their respective good solvents. The behavior of the diblock at the interface of two immiscible solvents provided additional morphological understanding. Furthermore, the orientation and position of the catenane rings with respect to each other are characterized in detail. The observed morphological and conformational properties were found to admit a molecular weight influence. |
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