Bulletin of the American Physical Society
2014 Annual Meeting of the Far West Section of the APS
Volume 59, Number 14
Friday–Saturday, October 24–25, 2014; Reno, Nevada
Session H2: Applied Physics and Life Science |
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Chair: Hendrik Ohldag, SLAC National Accelerator Laboratory Room: JCSU 423 |
Saturday, October 25, 2014 2:00PM - 2:12PM |
H2.00001: Particles on the interface of oil and water: Topological Defects Produced by Anisotropic Particles Charles Melton, Linda Hirst Topological defects have been the subject of many fascinating studies in soft condensed matter physics. The ability to control the onset of topological defects would prove to be invaluable to fields that benefit from defects such as electronics, the food industry, and pharmaceutical applications. In this study, the topological defects are studied in an oil/water emulsion system stabilized by polystyrene particles. The particles have varying aspect ratios, thus allowing for defects to be formed as a function of anisotropy. Fluorescence microscopy is used to image the particles on the interface between oil and water. Confocal microscopy is then used to image the particles in 3D space, allowing for a 3D mapping of the particles and reconstruction the oil/water interface. We observe spontaneous curvature of the interface when anisotropic particles are used and attribute this phenomenon to topological defects formed as a result of particle packing. Being able to visualize how particle packing and defect formation correlates to induced curvature of a deformable interface can aid in forming models that can explain the formation of topological defects in other systems, such as lipid bilayers and liquid crystal films. [Preview Abstract] |
Saturday, October 25, 2014 2:12PM - 2:24PM |
H2.00002: Determination of Surface-Substrate Adsorption Energy using the Exchange-Hole Dipole Moment Matthew Christian, Alberto Otero de la Roza, Erin Johnson Calculated surface-substrate binding energies are usually underestimated because conventional density functionals do not include dispersion, which is necessary to capture the van der Waals interactions that lead to weak physiadsorption. The exchange-hole dipole moment (XDM) model is a non-empirical density-functional approach to model dispersion. Adsorption energies for several aromatic molecules and nuclebases on noble metal surfaces were calculated using B86bPBE-XDM. In this talk, I compare the calculated adsorption energies with experiment and present implications for future applications to modeling surface interactions. \\[4pt] [1] A.\ Otero-de-la-Roza and E.\ R.\ Johnson, \textsl{J.\ Chem.\ Phys.} \textbf{138} 204109 (2013).\\[0pt] [2] A.\ Otero-de-la-Roza and E.\ R.\ Johnson, \textsl{J.\ Chem.\ Phys.} \textbf{137} 054103 (2012).\\[0pt] [3] A.\ Otero-de-la-Roza and E.\ R.\ Johnson, \textsl{J.\ Chem.\ Phys.} \textbf{136} 204109 (2012). [Preview Abstract] |
Saturday, October 25, 2014 2:24PM - 2:36PM |
H2.00003: Calculating thermal transport coefficients of reverse micelles using molecular dynamics simulations and normal mode analysis Hari Pandey, David Leitner Ultrafast vibrational studies of reverse micelles reveal that energy transfer from the water inside the reverse micelle to non-polar solvent can be more rapid than energy transfer from the surfactant directly to the solvent [1]. To address computationally the flow of heat in this system, we have calculated thermal transport coefficients for a reverse micelle formed by sodium di-2-ethylhexylsulfosuccinate (AOT) in isooctane over the temperature range 200 K--350K. Because of a ``glassy'' topology of the reverse micelle we adopted Allen-Feldman theory [2] to calculate thermal transport coefficients, which we have applied to calculate thermal transport coefficients for other soft matter in the past [3]. At room temperature, the thermal conductivity and thermal diffusivity of the reverse micelle was found to be 0.13 W/mK and 5.86 {\AA}$^{2}$/ps respectively, the former agreeing well with experimental values in polyalphaolefins solvent. \\[4pt] [1] J. C. Deak, Y. Pang, T. D. Sechler, Z. Wang, D. D. Dlott, \textit{Science} \textbf{306}, 473 (2004).\\[0pt] [2] P. B. Allen, J. L. Feldman, \textit{Phys. Rev. B} \textbf{48}, 12581 (1993).\\[0pt] [3] D. M. Leitner, \textit{J. Chem. Phys}. \textbf{130}, 195101 (2009). [Preview Abstract] |
Saturday, October 25, 2014 2:36PM - 2:48PM |
H2.00004: Interplay between group function of kinesin based transport and the planar lipid bilayer's recovery time after photobleaching Joseph Lopes, Jing Xu, Linda Hirst Motor proteins, discovered in recent decades, are important building blocks to life. These molecular machines transport cargo and although indispensable to cell function, are not well understood at present. Single kinesin transport properties have been documented, but their group function remains unknown. In this project, the properties of kinesin-based transport by multiple motors are investigated in-vitro to establish a link between travel distance and lipid diffusion in the vesicle membrane. In the experiments, silica beads coated in a supported lipid membrane and giant lipid vesicles are transported along a microtubule by embedded kinesin motors. To measure the diffusion properties of the membrane a planar lipid bilayer is prepared on a silica slide supported by bovine serum albumin protein. To establish a diffusion constant at room temperature for the lipid membrane we use the FRAP technique (fluorescence recovery after photobleaching). Using this method we can investigate if there is any interplay between group travel function and membrane fluidity. [Preview Abstract] |
Saturday, October 25, 2014 2:48PM - 3:00PM |
H2.00005: Hydrophobic Gating in Single Conically Shaped Nanopores William Mann, Diego Gutierrez, Laura Innes, Zuzanna Siwy Voltage-gated biological channels are understood to use hydrophobic interactions in their gating mechanism. To better understand how these interactions control ionic transport, mimics were created using single conical nanopores in 12 $\mu $m thick polyethelene terephthalate (PET) films. Pores were prepared by the track-etching technique; single ion irradiated foils were subjected to asymmetric wet-chemical etching. The pores used had a narrow opening between 3 and 11 nm, and a big opening $\sim$500 nm. This study investigates the ion transport properties of nanopores, modified with decylamine to render the PET surface hydrophobic. Modification was verified by current-voltage (I-V) curves of the pore before after attachment of decylamines. Hydrophobic pores often exhibit hydrophobic gating i.e. there is a voltage range for which there is no measurable ion current. In our experiments voltages of few hundred mV had to be applied to see finite ionic transport. The closed state of the pore is believed to correspond to a pore being filled with water vapor; a conducting indicates condensed water. Hydrophobic gating is also characterized by hysteresis: the voltage magnitude needed to open the pore for ionic current is larger than that for which the pore closes. [Preview Abstract] |
Saturday, October 25, 2014 3:00PM - 3:12PM |
H2.00006: Simulating localized surface plasmon resonance of gold nano spheres and nano rods for application in all-optical switching devices John Harvey Paredes Spherical and rod-like gold nanoparticles possess distinctive optical characteristics due to their plasmon resonance, which is the collective oscillation of the free electrons of the nanoparticles in resonance with an electromagnetic wave. By using the NanoHub's DDSCAT* software package, we simulate the scattered electric field generated by arrays of nanoparticles by using the discrete dipole approximation method. We vary the orientation and local order of the nanoparticles in an effort to optimize the array design that would allow us to develop the most efficient plasmonic switches. *https://nanohub.org/resources/dda [Preview Abstract] |
Saturday, October 25, 2014 3:12PM - 3:24PM |
H2.00007: Liquid Crystalline Orientational Control via the Electric Field of Localized Surface Plasmons Makiko Quint Collective oscillation of the electrons in gold nanoparticles (localized surface plasmon resonance (LSPR)) can produce a net electric field when excited at a resonant frequency. We have investigated the effects of LSPR-induced electric fields around self-assembled 30nm gold nanoparticles (AuNPs) on a thin film of nematic liquid crystal. Such a device configuration has the potential to act as an optically excited liquid crystal switch. We reversibly switch the spatial orientation of nematic liquid crystal molecules from homeotropic to planar in the thin films, demonstrating the action of this new device mode. We present electric field simulations for the system and control measurements for off-resonance excitation in which the switching behavior is not observed. Using polarized microscopy and optical transmission measurements, we observe switching over a temperature range starting several degrees below and up to the isotropic transition. [Preview Abstract] |
Saturday, October 25, 2014 3:24PM - 3:36PM |
H2.00008: Evolution of electride behaviour under pressure Stephen Dale, Alberto Otero-de-la-Roza, Erin R. Johnson Electrides are a unique class of ionic materials in which the anions are stoichiometrically replaced by localised electrons. The localised electron gives electrides a number of unique properties including high hyperpolarisabilities, high magnetic susceptibilities, highly variable conductivities, extremely low work functions, low-temperature thermionic emissions and very strong reducing character. However, the majority of the known electrides are unstable at room temperature and consequently experimental studies of these materials are difficult. Theoretical modelling of these systems can greatly benefit the exploration of these materials. We use density-functional theory (DFT) to show the presence of a localised electron and high lying ``electride'' valence state in all of the known electrides. Pressure calculations are then conducted to explore the stability range of electrides under pressure. This helps identify ideal crystal void sizes and is the beginning of elucidating a directed design criteria for electrides. [Preview Abstract] |
Saturday, October 25, 2014 3:36PM - 3:48PM |
H2.00009: Optical RF to mechanical coupling of a thin membrane as one end of a cylindrical cavity Alessandro Castelli, Luis Martinez, Jerry Speer, Jay Sharping, Raymond Chiao We demonstrate coupling of an 11.1 GHz radio frequency (RF) TE011 cylindrical cavity mode to the mechanical motion of a silicon nitride (Si3N4) membrane. The membrane is driven into motion through radiation pressure forces arising from the transverse magnetic field present at the membrane boundary. We use a cylindrical aluminum cavity where one end consists of a 500-nm thick Si3N4 membrane that has been sputtered with 300 nm of niobium (Nb). Cavity frequency tuning is controlled via an aluminum plunger attached to a micrometer at the other end of the cavity. The plunger was machined to leave a small air gap at the border of the cavity face in order to eliminate frequency degeneracy of the TM111 mode. The membrane is driven into motion by modulating the amplitude of the RF signal at the membrane's resonant frequency of approximately 6.7 KHz. The membrane's displacement is measured by means of a Michelson interferometer. This experiment shows that the TE011 mode gives rise to radiation pressure on the ends of a cylindrical cavity and demonstrates the feasibility of future work using high Q superconducting RF cavities to realize a dynamical Casimir effect (DCE) due to the membrane's motion at GHz frequencies. [Preview Abstract] |
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