Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session D15: Monolayers, Membranes and Microemulsions |
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Sponsoring Units: DFD Chair: Erik Luijten, Northwestern University Room: 316 |
Monday, March 16, 2009 2:30PM - 2:42PM |
D15.00001: Nanoparticle--induced domain formation in zwitterionic lipid membranes Meenakshi Dutt, Erik Luijten Charged nanoparticles have been found to induce coexistence of gel and fluid states in a pure zwitter\-ionic membrane\footnote{Wang et al., Proc.\ Natl.\ Acad.\ Sci.\ (in press).} due to electrostatic interactions between the nanoparticle and the adjacent membrane monolayer. Analogies can be drawn between this system and biological membranes, where domains in the vicinity of charged peripheral proteins play an important role in regulating cell activity.\footnote{Bergelson et al., Mol.\ Memb.\ Biol.\ \textbf{12}, 1 (1995).} To understand the differences in the structural and dynamical properties of coexisting domains in lipid membranes, we develop a coarse-grained model that represents the monolayer as a quasi two-dimensional plane of dipoles. The electrostatic interactions between the charged nanoparticle and the adjacent membrane monolayer, as well as the steric interactions within the monolayer, are incorporated explicitly. We will discuss our model and present results on the thermodynamic and structural changes in the model membrane induced by the presence of the nanoparticle. [Preview Abstract] |
Monday, March 16, 2009 2:42PM - 2:54PM |
D15.00002: ABSTRACT HAS BEEN MOVED TO Y36.00013 |
Monday, March 16, 2009 2:54PM - 3:06PM |
D15.00003: Langmuir films of chiral lipid molecules and Pattern Formation . Prem Basnet, Elizabeth Mann, Sahraoui Chaieb Langmuir films of 1,2-bis(10,12 Tricosadiynoyl)-sn-Glycero-3-Phosphoethanolamine form spiral and target patterns when compressed between two movable barriers in a Langmuir trough above 30$^{0}$C, up to the chain-melting transition at $\sim $37$^{0}$C. The critical pressure, at which spirals appear, increases with temperature. The patterns themselves also depend on temperature, with single-armed spirals with many defects forming near 30$^{0}$C and defect-free target patterns at higher temperatures. The mechanism of spiral formation could be a competition among elasticity, chirality, and the boundary conditions at the core of the domains. Optical anisotropy and the growth rate of internal structures test this suggested mechanism. . [Preview Abstract] |
Monday, March 16, 2009 3:06PM - 3:18PM |
D15.00004: Phase behavior of a binary phospholipid/cholesterol Langmuir monolayer: comparison of Brewster angle and fluorescence microscopy Fanindra Bhatta, Pritam Mandal, David Allender, Elizabeth Mann, Yasmin Isler, Edgar Kooijman, Andrew Bernoff The binary mixture of dihydrocholesterol and dimyristoyl phosphatidylcholine exhibits two liquid phases at the air/water interface: a cholesterol-rich and a phospholipid-rich phase, with a well-known critical point at a critical composition. Approaching that point with increasing monolayer pressure, the differences between phases disappear, along with the line tension between phases. In our experiments, the line tension is determined through comparison of the relaxation of domain shapes towards equilibrium with a compact, numerically tractable boundary integral model for the system hydrodynamics. We use both fluorescence microscopy and Brewster angle microscopy to visualize the lipid monolayer, and find the two methods have significant differences in monolayer behavior near the critical point. [Preview Abstract] |
Monday, March 16, 2009 3:18PM - 3:30PM |
D15.00005: Large-scale free-standing monolayer membranes of nanoparticles: preparation and properties Jinbo He, Laszlo Frazer, Xiao-Min Lin, Adam Weis, Heinrich Jaeger Two-dimensional arrays of close-packed nanoparticles can be stretched across tens-micrometre-size holes. The resulting freestanding monolayer membranes extend over hundreds of particle diameters without crosslinking of the ligands or further embedding in polymer. In our previous results of dodecanethiol-ligated 6-nm-diameter gold nanocrystal monolayers, we find a Young's modulus of the order of several GPa. This remarkable strength is coupled with high flexibility, enabling the membranes to bend easily while draping over edges. Recently we found that oleic-acid-covered cobalt nanoparticcles ($\sim $9 nm in diameter) self-assemble at toluene/ethylene glycol interfaces and form large two-dimensional arrays. These membranes stretch across tens-of-micrometer holes after drying of ethylene glycol. The mechanical and diffusion properties of these membranes are tested and the response of these membranes under external fields is also investigated. [Preview Abstract] |
Monday, March 16, 2009 3:30PM - 3:42PM |
D15.00006: Casimir force between inclusions in a strechable fluid membrane Hsiang-Ku Lin, Roya Zandi, Leonid Pryadko We calculate the entropic fluctuational force, a finite- temperature analogue of the Casimir force, between foreign inclusions in a strechable fluid membrane. Specifically, we consider the fluctuations of a planar membrane governed by the full Helfrich Hamiltonian, including the surface tension and both bending rigidity terms. The inclusions are introduced as circular regions where the surface tension and/or bending rigidities are modified from their values on the non-perturbed membrane. Results for arbitrarily-strong perturbations of the membrane, including holes, rigid disks, and edges will be presented. [Preview Abstract] |
Monday, March 16, 2009 3:42PM - 3:54PM |
D15.00007: Breathable NIPAAm Network with Controllable Hydration Supports Model Lipid Membrane Michael Jablin, Hillary Smith, Mikhail Zhernenkov, Ajay Vidyasagar, Ryan Toomey, Jessica Saiz, Boris Toperverg, Erik Watkins, Tonya Kuhl, Alan Hurd, Jaroslaw Majewski The interaction of a model lipid bilayer composed of DPPC with a surface-tethered poly(N-isopropylacrylamide) (NIPAAm) was explored with neutron reflectometry (NR). The Langmuir-Blodgett / Langmuir-Schaeffer method was used to deposit a lipid bilayer onto the polymer. NR measurements were used to probe the in- and out-of-plane structure of the system as a function of temperature. NR with fluorescence microscopy show that the polymer supports a lipid bilayer, and hydration of the support can be controlled. At low temp. the membrane develops out-of-plane undulations visible in off-specular scattering. Analysis of the off-specular reveals in-plane correlation of the bilayer fluctuations. The separation of the lipid bilayer from the solid support of a substrate constitutes a significant step towards a more realistic model of biological membranes. [Preview Abstract] |
Monday, March 16, 2009 3:54PM - 4:06PM |
D15.00008: The effects of lung surfactant peptide mimic KL4 on lipid monolayer collapse Niels Holten-Andersen, Luka Pocivavsek, Alan J. Waring, Ka Yee C. Lee We have investigated the origin of the positive effect of the peptide KL4 on lung surfactant lipid monolayers containing DPPC and POPG. Using surface balance techniques and fluorescence microscopy we have observed that KL4 rigidifies POPG containing lipid monolayers evidenced by a shift in their collapse mode. Rather than collapsing as a fluid by flowing into the sub-phase, a KL4 supported POPG monolayer instead collapses by folding. Furthermore, when KL4 is added to POPG containing monolayers they demonstrate an increased tolerance to repeated compression and expansion cycles while the opposite appears to be true for pure DPPC monolayers. We will discuss the potential role of electrostatic interactions in the rigidifying effect of KL4 on POPG containing monolayers in the context of the overall importance of collapse mode in establishing robust and reversible lipid monolayers. [Preview Abstract] |
Monday, March 16, 2009 4:06PM - 4:18PM |
D15.00009: Microrheology of protein layers at the air-water interface Myung Han Lee, Steven Cardinali, Daniel Reich, Kathleen Stebe, Robert Leheny Due to their amphiphilic nature, many proteins in aqueous solution will adsorb at the air-water interface to create a viscoelastic interfacial layer. We present an investigation of the formation and mechanical properties of interfacial protein layers formed by beta-lactoglobulin using microrheological techniques including multiple particle tracking and magnetic nanowire microrheology. We observe the interfacial rheology evolve in time through three stages: (i) an increase in viscosity, (ii) a period of spatial heterogeneity in which the interface contains elastic and viscous regions, and (iii) the development of a uniformly rigid elastic film. We evaluate the dependence of this evolution on the protein-protein interactions, which we tune by varying solution pH. As we will discuss, these studies illustrate the power of microrheological approaches to interfacial rheology. [Preview Abstract] |
Monday, March 16, 2009 4:18PM - 4:30PM |
D15.00010: ABSTRACT WITHDRAWN |
Monday, March 16, 2009 4:30PM - 4:42PM |
D15.00011: Behavior of a polymer chain confined by a membrane Fabrice Thalmann, Carlos M. Marques We consider a single polymer chain, grafted on a flat and rigid subtrate, covered by a membrane. The membrane presents some affinity for the surface, caused by non specific adhesive interactions. The challenge is to anticipate and describe the different possible relative configurations of the membrane and the polymer chain, depending on parameters such as the surface tension and curvature of the membrane, or the chain gyration radius. We propose for this system a phase diagram of the different regimes, as well as quantitative predictions for comparison with some recent experiments. [Preview Abstract] |
Monday, March 16, 2009 4:42PM - 4:54PM |
D15.00012: Critical swelling of fluctuating capsules Haim Diamant, Emir Haleva In many natural transport processes the solute molecules to be transported are encapsulated in semipermeable, flexible membrane vesicles of micron size. We study the swelling of such fluctuating capsules, as the number of encapsulated particles is increased, or the concentration of the outer solution is decreased. The approach to the maximum volume-to-area ratio and the associated buildup of membrane tension involve a continuous phase transition and follow universal scaling laws. The criticality and its features are model-independent, arising solely from the interplay between volume and surface degrees of freedom.\footnote{E.\ Haleva and H.\ Diamant, Phys.\ Rev.\ Lett.\ {\bf 101}, 078104 (2008).} [Preview Abstract] |
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