Bulletin of the American Physical Society
2016 Annual Meeting of the Far West Section
Volume 61, Number 17
Friday–Saturday, October 28–29, 2016; Davis, California
Session S2: Material Science and Molecular Transport |
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Chair: Hope Ishii, University of Hawaii Room: Ball Room A |
Saturday, October 29, 2016 2:00PM - 2:12PM |
S2.00001: Assembling Nanoparticles at The Isotropic to Nematic Phase Transition Sheida T Riahinasab, Ahmed Elbaradei, Amir Keshavarz, Benjamin Stockes, Linda Hirst Liquid crystal (LC) self-assembly allows for the controlled dispersion of quantum dots (QDs), creating new types of material -- liquid crystal nanocomposites. Our current research explores the properties of these materials to understand the underlying physics of mixing hard and soft matter. We report the use of a liquid crystal host phase in a new process for the generation of micron-scale, vesicle-like, nanoparticle shells stabilized by ligand-ligand interactions. Mesogenic ligands are used to provide control over the dispersion and stabilization of nanoparticles in liquid crystal phases. The mesogenic ligand's flexible arm structure enhances ligand alignment with the local LC director, promoting QDs dispersion in the isotropic and nematic phases. We have used nuclear magnetic resonance (NMR), polarized optical microscopy and X-ray scattering to characterize QDs dispersion on different length scales. We created a robust shell of controllable size composed of closely packed quantum dots (QDs) and stabilized by local crystallization of the mesogenic ligands. [Preview Abstract] |
Saturday, October 29, 2016 2:12PM - 2:24PM |
S2.00002: Morphology-Dependent Optical Energy Band Gap in Copper- and Manganese- Phthalocyanine Thin Films. Anh Nguyen, Carl Cosue, Thomas Gredig Metallo-phthalocyanines thin films have been used widely in applications, such as electronic and photonic devices, organic photovoltaic devices, and gas sensors. Copper phthalocyanine (CuPc) and manganese phthalocyanine (MnPc) thin films have been deposited on clean glass substrates by using thermal evaporation at several deposition temperatures to modify the crystal growth. Generally, electrical, and optical properties of CuPc and MnPc thin films depend on the morphology, which includes the grain size distribution (size, shape, and the orientation of stacked molecules), and film surface roughness. The energy band gap is estimated from the optical spectrum of the transmission data and found to vary with deposition temperature. The fundamental energy band gap of MnPc thin films increases for higher deposition temperatures. It has one energy band gap near 3.6 eV, which is in the Q-band region, whereas CuPc thin films have two energy band gaps in both the Soret band region and Q-band region. At low deposition temperatures, CuPc films have gaps at 1.71(2) eV, and 3.05(5) eV. But for higher deposition temperatures, the energy gap decreases to 1.64 eV and 2.93 eV. Consequently, the energy band gap in the Q-band is higher for MnPc than for CuPc. [Preview Abstract] |
Saturday, October 29, 2016 2:24PM - 2:36PM |
S2.00003: Using Block Co-Polymers to Create a Metal Oxide Hard Mask for Etching Silicon and Silicon Dioxide Omar Cervantes, Luis Castro, Noel Arellano Moore's Law has been achievable using lithography techniques for decades. However, lithography techniques are getting more expensive and difficult due to the wavelength of light and the limitations of optical systems currently used to pattern transistors. Our proposal involves using block-copolymers (BCP) to create the patterns necessary to achieve a line width which defines the critical dimension of a transistor. BCP have been shown to create patterns with line widths around 10 to 14 nanometers. Our specific internship goal was to develop an etch-resistant metal oxide mask defined by a lamellae BCP pattern. We began the process by creating fingerprint BCP patterns using spin casting techniques on surface of a silicon or silicon dioxide wafer. Then, we removed one of the polymers after they have self-assembled using an oxygen plasma etch. After, the empty space was filled with a metal oxide using an atomic layer deposition (ALD) tool. Next, we removed the top layer of metal oxide to reveal the remaining polymer block. Finally, we remove the remaining polymer block leaving behind the metal oxide mask. This allowed us to selectively etch into the silicon or silicon dioxide. This technique can achieve spacing smaller than being used today. [Preview Abstract] |
Saturday, October 29, 2016 2:36PM - 2:48PM |
S2.00004: Snap-Acting Bimetallic Disc (SABMD) Behavior and Fabrication Process Maureen Smith, Chris Wong, Moira Foster, Matthew Moelter, Thomas Gutierrez, Nathan Heston Shallow bimetallic shells rapidly transition between concave and convex equilibrium states with variations in temperature which can be described by a hysteresis cycle. They are widely used as low-cost temperature control devices, and are commonly referred to as snap-acting bimetallic discs (SABMDs). Despite their popular application, experimental literature is lacking that describes the relationship between their shape and temperature. Here, we describe a fabrication process that we've used to create large ($\sim$75 mm) SABMDs, and share the results of our heat treatment study that suggest a method to fine tune a disc's snapping temperatures. We present profile measurements that show the thermal deformation of a disc as its temperature varies prior to transitioning. Finally, we offer the first experimental evidence showing the dependence of characteristic snapping temperatures on original room temperature disc shape and compare these results to the Wittrick model. [Preview Abstract] |
Saturday, October 29, 2016 2:48PM - 3:00PM |
S2.00005: Microtubule defects influence kinesin-based transport in vitro. Winnie Liang, Qiaochu Li, K M Faysal, Stephen King, Ajay Gopinathan, Jing Xu Microtubules are protein polymers that form ``molecular highways'' for long-range transport within living cells. Molecular motors actively step along microtubules to shuttle cellular materials between the nucleus and the cell periphery; this transport is critical for the survival and health of all eukaryotic cells. Structural defects in microtubules exist, but whether these defects impact molecular motor-based transport remains unknown. Here, we report a new, to our knowledge, approach that allowed us to directly investigate the impact of such defects. Using a modified optical-trapping method, we examined the group function of a major molecular motor, conventional kinesin, when transporting cargos along individual microtubules. We found that microtubule defects influence kinesin-based transport in vitro. The effects depend on motor number: cargos driven by a few motors tended to unbind prematurely from the microtubule, whereas cargos driven by more motors tended to pause. To our knowledge, our study provides the first direct link between microtubule defects and kinesin function. The effects uncovered in our study may have physiological relevance in vivo. [Preview Abstract] |
Saturday, October 29, 2016 3:00PM - 3:12PM |
S2.00006: Quantitative Determination of the Probability of Multiple-Motor Transport in Bead-Based Assays Qiaochu Li With their longest dimension typically being less than 100 nm, molecular motors are significantly below the optical-resolution limit. Despite substantial advances in fluorescence-based imaging methodologies, labeling with beads remains critical for optical-trapping-based investigations of molecular motors. A key experimental challenge in bead-based assays is that the number of motors on a bead is not well defined. Particularly for single-molecule investigations, the probability of single versus multiple-motor events has not been experimentally investigated. Here, we used bead travel distance as an indicator of multiple-motor transport and determined the lower-bound probability of bead transport by two or more motors. We limited the ATP concentration to increase our detection sensitivity for multiple- versus single-kinesin transport. Surprisingly, for all but the lowest motor number examined, our measurements exceeded estimations of a previous model by $\ge $2-fold. To bridge this apparent gap between theory and experiment, we derived a closed-form expression for the probability of bead transport by multiple motors, and constrained the only free parameter in this model using our experimental measurements. Our data indicate that kinesin extends to \textasciitilde 57 nm during bead transport, suggesting that kinesin exploits its conformational flexibility to interact with microtubules at highly curved interfaces such as those present for vesicle transport in cells. To our knowledge, our findings provide the first experimentally constrained guide for estimating the probability of multiple-motor transport in optical trapping studies. [Preview Abstract] |
Saturday, October 29, 2016 3:12PM - 3:24PM |
S2.00007: Understanding the role of transport velocity in bio-motor powered microtubule spool assembly Amanda Tan, Dail Chapman, Linda Hirst, Jing Xu Microtubules and their associated motor proteins, such as kinesin are widely used to study active self\textunderscore assembly of higher order structures. Kinesin motors convert ATP to energy through hydrolysis and walk along microtubules. In gliding assays, kinesin are immobilized on the surface and propel microtubules forward when they hydrolyze ATP. Microtubules functionalized with biotin and streptavidin will bind together and form bundles and spools when gliding. The spools are able to maintain its shape and continue to rotate in the presence of ATP. We examined the sensitivity of microtubule spools to transport velocity (by varying ATP concentration). We determined that the steady-state number and size of spools remained constant over a seven-fold range of velocities. Our data on the kinetics of spool assembly further suggest that the main mechanisms underlying spool growth vary during assembly. [Preview Abstract] |
Saturday, October 29, 2016 3:24PM - 3:36PM |
S2.00008: Effect of membrane coupling on multiple-kinesin transport Joseph Lopes, Dail Chapman, Linda Hirst, Jing Xu Molecular motor-based transport is critical for all eukaryotic cell function and health. Although traditionally examined in the context of single motor experiments, molecular motors often work in small teams together to transport the same cargo in vivo. Factors that control and regulate the group function of multiple motors has remained unclear. Here we used a simple lipid bilayer to couple kinesin motors together, and used microtubule gliding assay to examine the effect of this membrane coupling on the group function of multiple kinesin motors. [Preview Abstract] |
Saturday, October 29, 2016 3:36PM - 3:48PM |
S2.00009: Geometric space - the extension of extremely dense unit cells Antony J Bourdillon The Quasicrystal is a relatively new kind of solid, intermediate between crystals and compound glasses. It has many peculiar properties including non-Drude conductivity; geometric electronic band structures; peculiar mechanical and magnetic effects etc. However the greatest benefit they have taught us is the fact of geometric space with sharp coherence [1]. This provides opportunities for finite element simulations with fast convergence and avoidance of subsidiary maxima or minima. As Einstein's curved space is locally Euclidean; dense atomic space is locally icosahedral and geometric in extension. Intermediate linear periodicity, in crystals, is constrained by unit cells that are less dense at short range. [1] Diffraction line width in quasicrystals -- sharper than crystals, A.J. Bourdillon, (2016) Journal of Modern Physics, in press. [Preview Abstract] |
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