Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session V54: Membranes, Micelles and Vesicles |
Hide Abstracts |
Sponsoring Units: GSOFT Chair: Radhakrishna Sureshkumar, Syracuse Univ Room: LACC 514 |
Thursday, March 8, 2018 2:30PM - 2:42PM |
V54.00001: Plate Models for Buckling Analysis David Robinson, Draga Pihler-Puzovic, Matthias Heil The Föppl-von Kármán equations are widely used to model the buckling of thin elastic sheets. We demonstrate two significant shortcomings of these equations when used to analyse the pre- and post-buckling behaviour of inflated circular sheets. Specifically, we show that the equations (i) over-estimate the sheets' overall stiffness, and (ii) that they predict non-axisymmetric buckling to occur with a universal azimuthal wavenumber, independent of the sheet thickness, in contrast with experimental observations. We identify the origin of these shortcomings and demonstrate that they can be alleviated by using the nonlinear, large-strain Koiter plate model. |
Thursday, March 8, 2018 2:42PM - 2:54PM |
V54.00002: The curious case of the misbehaving colloidal sheet Ruo-Yu Dong, Wei Wang, Shankar Ghosh, Steve Granick Colloidal sheets were created such that 2D layers of polystyrene spheres were levitated in deionized water far above the bottom of the sample cell and then allowed to sediment. The curious observation is that as time elapses the sheet retains its 2D shape; in some circumstances it becomes convex, in other circumstances it buckles, but in all circumstances the 2D character persists during the sedimentation process. This talk describes the phenomenon and presents tentative explanation. |
Thursday, March 8, 2018 2:54PM - 3:06PM |
V54.00003: Stabilization of Immiscible Liquids using Surfactant / Fatty Acid Mixtures that Self-Assemble into Nanostructured Interfaces Zahra Niroobakhsh, Mo Segad, Robert Hickey, Andrew Belmonte Great efforts have been made to stabilize immiscible liquid interfaces or to compartmentalize discrete domains using surfactant molecules, in most cases focusing on equilibrium morphology. Here we present work highlighting how to use surfactants to create liquid columns that are composed of an aqueous cationic surfactant, cetylpyridinium chloride (CPCl), and a fatty acid, oleic acid (OA), via the formation of a self-assembled nanostructured interfacial layer under non-equilibrium conditions. The interfacial layer or column wall exhibits particular elastic behavior such as wrinkling, buckling, or rupture. The resulting interfacial layer forms owing to rapid self-organization of CPCl and OA molecules, which is similar to established surfactant systems. We determine that the morphology of the interfacial layer formed during the flowing column experiment is lamellar, and exhibits a domain spacing on the order of 20 nm using small angle X-ray scattering (SAXS). Furthermore, we find that the viscoelastic response is one of a soft-solid with gel-like properties using interfacial rheology. The characteristics are studied as a function of CPCl solution concentration, followed by a comparison with the bulk equilibrium phases in the mapped-out ternary phase diagram (water, OA, and CPCl). |
Thursday, March 8, 2018 3:06PM - 3:18PM |
V54.00004: Microfluidic-SANS Study of Micellar Shape and Interactions in Mixed Solvents Marco Adamo, Joao Cabral, Lionel Porcar, Anne Martel We report a microflow approach to perform small angle neutron scattering (SANS) of contrast variation and phase mapping of multicomponent liquid mixtures, focussing on surfactant systems. We integrate a low scattering microfluidic device in a SANS beamline to yield a reconfigurable liquid flow cell. By contrast with conventional techniques, our approach continually varies solution composition during SANS acquisition. We demonstrate our contrast variation approach with model systems, including sodium dodecyl sulphate (SDS) and a block-copolymer (F127) in isotopic aqueous mixtures during linear composition ramps with 5 s time resolution. The form and structure factor are quantitatively determined with a global fit of the dataset, leading to unprecedented robustness and precision. Ternary and quaternary phase mapping of surfactant systems is then demonstrated by dynamically scanning across the phase space. We first validate the approach with a diluting of micellar 10% SDS in D2O, then study the effect of 1-butanol addition in the shape and interactions of micelles. The generality of the microflow-SANS approach, ensuring component mixing yet minimal composition dispersion is then demonstrated with a quaternary system of two surfactants, solvents and polymer. |
Thursday, March 8, 2018 3:18PM - 3:30PM |
V54.00005: Geometrical Pinning and Anti-Mixing in Scaffolded Lipid Vesicles Melissa Rinaldin, Piermarco Fonda, Luca Giomi, Daniela Kraft Cellular membranes are highly compartmentalized structures comprised of specialized lipid domains. Unraveling the physical mechanisms behind the organization lipid domains is a central goal in membranes biophysics, while the ability of reproducing them in synthetic structures holds great potential for applications in self-assembly, bio-sensing and drug delivery. Previous studies on multi-component vesicles and supported lipid bilayers have unveiled a fundamental interplay between the membrane geometry and lipid composition. However, the detailed mechanisms behind this coupling and their role in the organization of lipid domains remain incompletely understood, because of the impossibility of independently controlling the membrane geometry and composition. Here we overcome this limitation by fabricating multicomponent lipid bilayers supported by colloidal scaffolds of prescribed shape. Thanks to a combination of experiments and theoretical modeling, we demonstrate that the substrate local curvature and the global chemical composition of the bilayer determine both the amount of mixing and spatial arrangement of the lipid domains. |
Thursday, March 8, 2018 3:30PM - 3:42PM |
V54.00006: Thermodynamics of equilibrium interfaces on curved surfaces Piermarco Fonda, Melissa Rinaldin, Luca Giomi, Daniela Kraft
|
Thursday, March 8, 2018 3:42PM - 3:54PM |
V54.00007: Unified Membrane Properties Extracted from the Thermal Fluctuations of Lipid Bilayers Elizabeth Kelley, Paul Butler, Rana Ashkar, Robert Bradbury, Andrea Woodka, Michihiro Nagao Biomembranes composed of lipids and proteins are a dynamic platform that accommodate a variety of cell functions. Recent research using lipid bilayers as model biomembranes have begun to explore the hierarchy of dynamics spanning sub ps to seconds of deformations that occur in these systems. Here, we study membrane fluctuations on nanosecond time scale in mixed lipid bilayers with a same headgroup chemistry but varying alkyl tail lengths, specifically a mixture between dimyristoyl- and distearoyl-phosphatidylcholine. The equilibrium membrane dynamics, thermal bending and thickness fluctuations, were accessed using neutron spin echo (NSE) spectroscopy. The NSE results were used to calculate membrane’s viscous and elastic parameters, that is the membrane viscosity and the area compressibility and bending moduli. Combining the dynamic properties with density measurements of the mixtures and the structure determination by small-angle x-ray and neutron scattering, we successfully map out the unified dependence of each parameter on the area per molecule. The present results shed light on the synergistic structure and dynamic effects in a lipid membrane. |
Thursday, March 8, 2018 3:54PM - 4:06PM |
V54.00008: Contrasting drainage via stratification in horizontal vs. vertical micellar foam films Subinuer Yilixiati, Ewelina Wojcik, Yiran Zhang, Vivek Sharma Understanding and controlling the drainage kinetics of freestanding thin films is an important problem that underlies the stability, lifetime and rheology of foams. Ultrathin micellar foam films exhibit stratification due to confinement-induced structuring and layering of micelles that contributes non-DLVO supramolecular oscillatory structural force contribution to disjoining pressure. Stratification in micellar foam films is manifested as stepwise thinning over time, and it leads to the coexistence of flat domains with discretely different thicknesses. In this contribution, we use Interferometry Digital Imaging Optical Microscopy (IDIOM) protocols to visualize and analyze thickness transitions and variations associated with stratification in micellar foam films made with sodium dodecyl sulfate (SDS). We contrast the drainage and stratification dynamics in horizontal and vertical foam films. We experimentally study the emergence of thickness fluctuations near the borders and within thinning films, and study how buoyancy, capillarity and gravity driven instabilities and flows, are affected by the variation in bulk and interfacial physicochemical properties, that are effectively dependent on the choice of constituents, including added electrolytes. |
Thursday, March 8, 2018 4:06PM - 4:18PM |
V54.00009: Effect of co-amphiphiles on the stiffness of lipid lamellae Radhakrishna Sureshkumar, Subas Dhakal We use coarse-grained molecular dynamics simulations to study the mechanics of lamellae and vesicles formed by the self-assembly of dodecyldimethylammoniumbromide lipids in water. We observe various ordered morphologies such as micelles, uni- and multi-lamellar vesicles as well as bilayers and lamellae with increasing lipid concentration. By fitting the vesicle-water interface in terms of spherical harmonics, we track the reduced volume and correlate it with the resulting dynamics of the vesicle in shear flow. Further, we calculate the Poisson's ratio of the lamellar structures under uniaxial extension. We discover that Poisson ratio of the lamella decreases with increasing concentration of co-amphiphilic molecules stacked parallel to the lipids. Remarkably, this is similar to salt-induced stiffening observed in micellar assemblies (Dhakal and Sureshkumar, ACS Macro Lett. 2016, 5 (1), pp 108). Finally, a shear-induced structure transition from lamellae to multi-lamellar vesicles will be discussed. |
Thursday, March 8, 2018 4:18PM - 4:30PM |
V54.00010: Interplay between structure and shear flow in micelle-nanoparticle solutions Subas Dhakal, Radhakrishna Sureshkumar, Abhinanden Sambasivam Cationic surfactant molecules exhibit rich phase behavior in water. Self-assembly results in spherical, cylindrical and flexible wormlike structures with or without branches. We employ molecular dynamics simulations to study the structure and rheology of self-assembled aggregates of cetyltrimethylammonium chloride surfactants in presence of sodium salicylate counter ions in aqueous solution. Addition of nanoparticles (NPs) to such solutions results in the formation of electrostatically stabilized NP-micelle junctions, leading to a significant increase in the solution viscosity. Distinct rheological properties are observed by changing the surfactant, co-surfactant as well as NP concentrations. Micelle branching causes the solution viscosity to vary as a non-monotonic function of the NP concentration. At higher NP volume fractions and shear rates that exceed the inverse of a characteristic structure relaxation time, flow-alignment of the microstructure causes pronounced shear thinning [Molecular Simulation: http://www.tandfonline.com/doi/abs/10.1080/08927022.2017.1387658] |
Thursday, March 8, 2018 4:30PM - 4:42PM |
V54.00011: Bulk-Interfacial Partitioning of Surfactant in Concentrated Nanoemulsions Matthew Pagenkopp, Thomas Mason We explore the partitioning of amphiphilic dodecyl sulfate (DS-) surfactant anions onto interfaces of nanodroplets in a fractionated silicone oil-in-water nanoemulsion that has a well characterized size distribution and a large surface-area-to-volume ratio. We quantify this partitioning by diluting a concentrated nanoemulsion and measuring bulk concentration across a semi-permeable membrane and measuring the concentration of DS- using conductivity and gravimetric methods. We calculate and obtain an adsorption isotherm, which compares reasonably well with one obtained through interfacial tension measurments on a macroscopic interface at different bulk concentrations of DS-. Using high flow rate emulsification, we also show that an appreciable amount of surfactant leaves the bulk continuous phase and adsorbs onto the newly formed interfacial area as microscale droplets are broken down into nanodroplets by the flow. We have developed a model to describe the change in the bulk continuous surfactant concentration before and after high flow rate emulsification. Creating a nanoemulsion at high droplet volume fractions can effectively consume surfactant from the bulk as it partitions onto the high surface area of the nanodroplets. |
Thursday, March 8, 2018 4:42PM - 4:54PM |
V54.00012: Conditions on length of Ligand-Receptor pairs for nanoparticle adhesion influenced by plasma membrane surface charge Shayandev Sinha, Haoyuan Jing, Harnoor Sachar, Siddhartha Das Nanoparticle (NP) adhesion with a plasma membrane typically occurs through the formation of a receptor-ligand (R-L) bond. For this binding to occur the ligand-functionalized NP need to come within a minimum distance of separation, equal to the length of the R-L complex (dRL). Here we develop a theory to establish the significant influence of the membrane surface charges and the surrounding electrolyte environment on this process of the approach of the NP towards the membrane within the R-L complex length. The negatively charged membrane induces a negative electrostatic potential on the NP surface thereby repelling the NP from the membrane, whereas the thermal fluctuations assist the NP to come closer to the membrane. This balance leads to a critical NP-membrane separation length dg,c. Our theory establishes a design criterion on the length of the R-L complex such that to facilitate the NP-membrane adhesion, we need to have dRL> dg,c. This leads to a design space for engineering the ligands for the NPs such that the process of adhesion can be ensured in a given electrostatic environment. |
Thursday, March 8, 2018 4:54PM - 5:06PM |
V54.00013: Theory of Raft Interactions in Ternary Colloidal Membranes Chaitanya Joshi, Joia Miller, Arvind Baskaran, Zvonimir Dogic, Michael Hagan, Aparna Baskaran Colloidal membranes are a recently developed experimental system in which depletion |
Thursday, March 8, 2018 5:06PM - 5:18PM |
V54.00014: Single molecular bilayers of organic semiconductor molecules realized using geometrical frustration Shunto Arai, Satoru Inoue, Takamasa Hamai, Reiji Kumai, Tatsuo Hasegawa Single molecular bilayers (SMBs) are the fundamental form of molecular nanostructures composed of biological lipids or synthetic amphiphiles. Although the realization of air-stable artificial SMBs is expected to result in versatile applications, those formed via self-assembly of usual amphiphilic molecules have strictly limited their practical use because of the inherent instability and fragility associated with the weak intermolecular interactions. Here we demonstrate the fabrication of unprecedented large-area, uniform, and self-organized SMBs using extended π-conjugated frameworks substituted by alkyl chains of variable length; (πCore)-Cn. These SMBs were produced by simple blade-coating with a solution containing two (πCore)-Cn’s with different alkyl chain lengths. The chain-length disorder did not perturb in-plane molecular order, but acted effectively as a geometrical frustration to inhibit multiple stacking of bilayers. The obtained SMBs exhibited efficient carrier transport as channels of thin-film transistors, reflecting strong intralayer π-π interactions and the concomitant highly layered-crystalline nature. We expect that this finding should open a new route to SMB-based ultrathin super-flexible electronics capable of biomimetic functions. |
Thursday, March 8, 2018 5:18PM - 5:30PM |
V54.00015: Surfactant Exchange in Low-Symmetry Sphere Packings of Micelles Kyeong-Jun Jeong, Arun Yethiraj The hierarchical self-assembly of surfactants is an attractive route to the fabrication of functional soft materials. In this work, we study solutions of an ionic surfactant, which assembles into deformable spherical micelles in water, which further pack into low-symmetry Frank-Kasper (FK) phases. Starting with an initial structure in the experimentally observed phase we study the dynamics of surfactants using molecular dynamics simulation. We find that the diffusion of surfactant molecules is dominated by molecular exchange between micelles. Micelles temporarily touch neighbors during thermal motion, and surfactant exchange occurs via a flip-flop motion during this contact. This effect significantly enhances hopping rate of surfactant molecules, resulting in uncommonly short relaxation time for the change of the size of the micelles. We suggest this exchange mechanism makes FK phases dynamically inhomogeneous. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700