Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session A54: Soft Interface Mechanics I |
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Sponsoring Units: GSOFT DBIO DPOLY Chair: John Kolinski, Ecole Polytech Fed de Lausanne Room: LACC 514 |
Monday, March 5, 2018 8:00AM - 8:12AM |
A54.00001: Smectic Capsids Robijn Bruinsma, Sanjay Dharmavaram, Joseph Rudnick We develop the theory of capsids that are in a smectic liquid crystal state. The capsids of the double-tailed Archaeal viruses are able to execute a large shape change, while maintaining their integrity with respect to capsid tension generated by osmotic pressure. We propose that these capsids are in a smectic liquid crystalline state, consistent with the spiral molecular organization of the capsid proteins. We show that smectic capsids have a strong restoring force against the formation ofaneurysm-type bulge formation while still allowing for large scale cooperative shape changes, consistent with the observations on the Archaeal viruses. |
Monday, March 5, 2018 8:12AM - 8:24AM |
A54.00002: Structural Evolution and Spatial Heterogeneity in Mucin Layers Tristan Hormel, Tapomoy Bhattacharjee, Christopher O'Bryan, Gregory Sawyer, Thomas Angelini Mucous layers formed by epithelial cell excretions perform a variety of biologically essential functions, including anti-microbial protection, lubrication, and environmental resistance. These beneficial attributes may be enabled by the rheological and physical properties of an entangled mesh of a variety of mucin glycoprotein species. While the chemical identity of these glycoproteins is known for many epithelial cell types, the mesoscale structure of the layer they produce is not well understood. We investigate the spatiotemporal dynamics of the mucous network produced by corneal epithelial cells in vitro using antibody staining and confocal fluorescence microscopy, which allows us to determine the location in 3D of individual mucin species within the mucous layer as it evolves. Correlation functions of the different fluorescently labeled mucin species reveal spatial heterogeneity that evolves over time. These results illuminate the structure of the mucous layer, and may inform our understanding of its functioning. |
Monday, March 5, 2018 8:24AM - 8:36AM |
A54.00003: Viral Capsid Assembly and Orientational Phase Transitions Sanjay Dharmavaram, Fangming Xie, Joseph Rudnick, William Klug, Robijn Bruinsma The Landau theory of orientational phase transition has successfully been used to investigate liquid crystals, quasicrystals, metallic glasses and Fermi liquids. In this talk, we explore its connection to the assembly of icosahedral viruses. The theory predicts two kinds of ordering transition: (i) a robust first-order transition with states dominated by achiral even spherical harmonics (ii) a transition to icosahedral states formed by a mixture of even and odd spherical harmonics, where chirality plays an important role. In the latter case, the transition is either continuous or weakly first-order and the icosahedral state is in strong competition with tetrahedral, octahedral and five-fold symmetric states. |
Monday, March 5, 2018 8:36AM - 8:48AM |
A54.00004: Role of Gaussian Curvature in the Budding of HIV-1 Viruses Baochen She, Sanjay Dharmavaram, Ioulia Rouzina, Robijn Bruinsma In the immature stage of HIV-1 life cycle, the exocytosis of the viron begins when cone-shaped Gag polyproteins assemble into a shell beneath the surface of the infected cell membrane. The detailed mechanism of this process is still insufficiently understood. As the protein assembles, this shell is observed to possess large irregular holes and the budding process pauses at certain phase. In human cells, exocytosis is completed only when the virus hijacks the cell's fission-inducing (ESCRT) machinery. The presence of large irregular holes, implying a very small line-tension for the Gag assembly, precludes the classical Lipowsky mechanism for budding. In this talk, we propose a new mechanism for viron budding based on the role of Gaussian curvature coupling between the lipid membrane and the Gag-protein shell. We show that this term plays a crucial role in the initial stages of budding. During the later stages, however, formation of buds with pronounced neck are inhibited, thus offering an explanation for the observed pausing. |
Monday, March 5, 2018 8:48AM - 9:00AM |
A54.00005: Force vs separation for axisymmetric nearly minimal surfaces Thomas Powers, Steven Pei, Leroy Jia, Robert Pelcovits Motivated by the desire to understand the shapes exhibited by colloidal membranes, we study the shape of a surface with bending stiffness and fixed surface tension, stretched between two circular boundaries. The boundary circles lie in parallel planes and have axial symmetry. We work in the limit of large bending stiffness, in which the surface shapes are nearly catenoids, and calculate the force required to hold the rings apart at a fixed separation. We find the the force-separation curve has two branches, with one branch corresponding to the stable branch of shapes observed in catenoidal soap films. As in the case of the soap film, we find a maximal separation of the rings for this branch. We also find a low branch of solutions, as in the case of a soap film, but we do not find an upper limit to the separation. |
Monday, March 5, 2018 9:00AM - 9:12AM |
A54.00006: Interfacial tension of motility-induced phases Adam Patch, David Yllanes, Daniel Sussman, M Cristina Marchetti A striking feature of motility-induced phase separation (MIPS) is the apparent negative interfacial tension that arises during spinodal decomposition. In equilibrium, a negative interfacial tension indicates an ever-expanding surface and dividing volumes, but active Brownian particles (ABPs) with purely repulsive interactions are different. Using ABP simulations, we study interface height fluctuations for different system sizes and persistence lengths. We find that the statistics of this interface are surprisingly equilibrium-like, and that interface rigidity increases with motility persistence. Using local frames of reference, we study particle orientations relative to the normal and find that this negative value of interfacial tension is due to strong tangential currents, which seem to help stabilize the interface. |
Monday, March 5, 2018 9:12AM - 9:24AM |
A54.00007: Wrinkle-Fold Coexistence and Stress Propagation in Nanoparticles at the Oil-Water Interface Andres Mariano, Joe Forth, Jaffar Hasnain, Anju Toor, Phillip Geissler, Thomas Russell We present the behavior of nanoparticle surfactant monolayers, assembled at the oil-water interface, in response to uniaxial compression by a movable barrier. These systems are formed by the binding of nanoparticles and polymers at the oil-water interface. Upon compression, the films buckle with a characteristic wavelength and a spatially decaying amplitude. Increasing strain leads to the presence of folds near the barrier, and wrinkle formation further away from it. The size of the folded region grows with increasing strain, whilst the wrinkled region exists over a characteristic lengthscale. Remarkably, when compression ceases, the folded region expands and wrinkles propagate away from the compressing barrier. This relaxation occurs on the timescale of hours to days, depending on the size of the particles that make up the assembly. We combine theory and experiment to characterize this behavior using a range of model systems, including particles of differing sizes and chemical constituents. |
Monday, March 5, 2018 9:24AM - 9:36AM |
A54.00008: Tension in a Floating film Deepak Kumar, Thomas Russell, Benjamin Davidovitch, Narayanan Menon We describe a simple experiment to extract the in-plane stress in a thin sheet floating at a liquid/vapour interface. This allows us to determine what combination of solid-liquid, solid-vapor and liquid-vapour surface energies affect the in-plane stress. We address this question by pulling one edge of the floating sheet upward, such that part of the sheet is rigidly suspended, while the remainder floats on the liquid. We determine the tensile stress in the sheet from the two-sided meniscus that is thus formed: one side is covered by the sheet and the other side is a liquid-vapor interface. The observed symmetry between the two sides of the meniscus shows that the tensile stress in the sheet is equal to the liquid-vapor surface tension, and is independent of the solid-liquid or solid-vapor surface energy. We confirm this result by repeating the experiment with different sheets and liquids. |
Monday, March 5, 2018 9:36AM - 9:48AM |
A54.00009: Elastohydrodynamic wake in a thin elastic film floating on water Kari Dalnoki-Veress, Jean-Christophe Ono-dit-Biot, Miguel Trejo, Elsie Loukiantchenko, Maximillian Lauch, Elie Raphael, Thomas Salez Waves can be formed at the surface of water by a moving disturbance. These waves are known as gravity-capillary waves and have been extensively studied both experimentally and theoretically. In this study, the surface of water is covered with a thin elastic film (hundreds of micrometers in thickness). A large tank filled with water is rotated at constant speed and a stationary air jet perturbs the surface of the covering film, thereby producing an elastohydrodynamic wake. The waves are characterized as a function of the speed using a high-resolution cross-correlation method. In particular, we experimentally probe the dispersion relation and compare to the theoretical expression. We find excellent agreement, revealing that gravity, tension and bending all contribute in our system. This study might have implications in geology, ice floes, as well as energy harvesting at the surface of the ocean. |
Monday, March 5, 2018 9:48AM - 10:00AM |
A54.00010: Rheological variability of P. aeruginosa pellicles Lingjuan Qi, Gordon Christopher A current trend in biofilm research uses changes in biofilm viscoelasticity to evaluate how biological mechanisms adapt to environment. However, it can be difficult to interpret results due to un-quantified variability in biofilm propertie, making comparison between different growth conditions, strains, mutant, or species nearly impossible. To interpret biofilm viscoelasticity requires understanding the statistical variance in biofilm mechanical properties. |
Monday, March 5, 2018 10:00AM - 10:12AM |
A54.00011: Role of Lipid Structure in the Mechanical Properties and Stress Profiles of Lipid Biomembranes Juan Vanegas, Ben Himberg, Conner Winkeljohn Lipid membranes exhibit remarkable interfacial properties determined by the chemical structure of its molecular components. Yet, they are also subject to large scale mechanical stimuli such as membrane stretching or bending. The microscopic or local stress obtained from molecular dynamics simulations provides a unique connection between atomistic details and collective mechanical properties. Based on our recent work on central decomposition of forces (Phys. Rev. Lett. 114, 258102, 2015 and J. Chem. Theory Comput. 10, 691, 2014), we calculate lateral pressure or stress profiles of coarse-grained and atomistic lipid membranes. We show that chemical features such as double bonds or ring structures in sterols have marked effects on bilayer mechanical properties as seen by large changes in the stress profiles. The effects that one type of lipid has in the stress profile of a mixed bilayer may not be universal and depend on the structure of other lipids. This is quantified in the non-additivity of the spontaneous curvature obtained from the stress profiles of PC/sterol mixtures. Finally, we show our recent efforts to include forces from long range electrostatic interactions, calculated using Ewald methods, and quantify the error in using plain cutoffs for coulombic interactions. |
Monday, March 5, 2018 10:12AM - 10:24AM |
A54.00012: Abstract Withdrawn
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Monday, March 5, 2018 10:24AM - 10:36AM |
A54.00013: The geometrical effects of stiff film patterns on surface instability modes of elastic bilayers Tetsu Ouchi, Ryan Hayward Surface instabilities, such as wrinkles and creases, are seen in many places, and are now understood to an excellent degree for homogeneous surfaces. However, fundamental understanding of surface instabilities for systems with in-plane heterogeneity remains lacking, despite their importance in a variety of applications (e.g. metal electrodes on an elastomer surface for flexible electronic devices). In this study, we fabricated an elastic bilayer with stiff film patterns and analyzed the effects of pattern geometry on surface instabilities. We found three distinct regimes for the behavior of the bilayer regions, depending on the pattern size compared to the natural wrinkle wavelength: wrinkling, Euler buckling, and rigid rotation. In the soft substrate regions, creases were formed in all cases. Interestingly, crease formation greatly facilitates the formation of contacts between neighboring stiff regions. The strain for contact was characterized as a function of the pattern geometry, and potential applications based on reversible formation of contact between the stiff film regions were demonstrated. |
Monday, March 5, 2018 10:36AM - 10:48AM |
A54.00014: Dense Packing of Soft Phytoglycogen Nanoparticles: Insight into the Compressibility and Radial Particle Density Michael Grossutti, Hurmiz Shamana, Aidan Maxwell, John Dutcher Phytoglycogen is a natural polysaccharide produced in the form of compact 35 nm diameter nanoparticles by some varieties of plants such as sweet corn. The highly-branched, dendrimeric structure of phytoglycogen leads to interesting and useful properties that make the particles ideal as unique additives in personal care, nutrition and biomedical formulations. Equilibrium osmotic pressure measurements of aqueous phytoglycogen dispersions allow the determination of the compressional modulus of the particles and add additional insight into their internal structure. Osmotic pressure measurements of native and acid hydrolyzed particles, together with tracking of the particle diameter during acid hydrolysis, are consistent with a new model of phytoglycogen nanoparticle structure consisting of a dense core and less dense shell. These results suggest new possibilities for the attachment and encapsulation of bioactive compounds. |
Monday, March 5, 2018 10:48AM - 11:00AM |
A54.00015: Surface Wetting and Premelting of Tunable Colloidal Crystals Bo Li We discovered a dye-induced attraction between colloidal spheres which can be finely tuned by temperature. It opens the way to study surface physics in colloidal model systems. We epitaxially grew high-quality colloidal crystals with free surfaces, and observed the surface premelting, grain-boundary-mediated 2D melting and isostructural solid-solid transitions at the single-particle level for the first time. We found that monolayer and bilayer crystals have distinct premelting behaviors due to their different lattice stabilities and bulk melting behaviors. Analogues to the surface liquid in premelting, we discovered a layer of square lattice on the surface of the bulk triangular lattice. Such novel surface wetting crystal should generally exist when two crystals can form a coherent interface. The thicknesses of both the surface liquid in premelting and the surface square lattice in wetting exhibit power-law growth as approaching the melting point. |
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