Bulletin of the American Physical Society
2008 Joint Spring Meeting of the Texas Sections of APS, AAPT, and Zone 13 of SPS
Volume 53, Number 1
Thursday–Saturday, March 6–8, 2008; Corpus Christi, Texas
Session APS3: Condensed Matter Physics |
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Chair: Paul Cox, Texas A and M Kingsville Room: Omni Corpus Christi Hotel Marina Tower Padre B |
Friday, March 7, 2008 2:30PM - 2:42PM |
APS3.00001: Polymer-Conducting Polymer Composites Juan Monrreal, Heinrich D. Foltz , Elsa Garcia, Karen Lozano, Marcos Villareal, Steven C. Tidrow, Magdalena Dorina Chipara, Mircea Chipara Polyaniline is a conducting polymer with high electrical conductivity, good thermal and thermo-oxidative resistance, and poor mechanical properties. To overcome these weaknesses, the conducting nanoparticles were dispersed within polymeric matrices characterized by high mechanical strength or high elasticity. Such composite materials found applications as lightweight antistatic materials (at low doping levels) and electromagnetic shielding capabilities (at high doping levels, typically above the percolation threshold for electrical conductivity) and exhibit potential applications as metamaterials. Nanosized particles of polyaniline were dispersed within polymeric matrices (polystyrene, polyvinylchloride, and polyethylene). The thermal properties were investigated by Thermal Analysis and Differential Scanning Calorimetry. FTIR/ATR, Raman spectroscopy, and Electron Spin Resonance spectroscopy provided additional information about the effect of nanofiller on the polymeric matrix. Electrical (dc) measurements confirmed the increase of the electrical conductivity as the concentration of conducting nanoparticle is increased and revealed a broad percolation behavior. The effect of the conducting nanofiller on the mechanical properties is reported. [Preview Abstract] |
Friday, March 7, 2008 2:42PM - 2:54PM |
APS3.00002: Assessment of Bone Microstructural Changes by NMR Qingwen Ni, Xiaodu Wang Previous studies have shown that age related increases in bone porosity without significant changes in bone mineral density (BMD) (without bone microstructural information) result in a decrease in bone strength. Bone fracture toughness is also significantly correlated to changes in porosity, microarchitecture, collagen integrity, microdamage, and water distribution, all of which are measures of bone quality. Unfortunately, current technology does not allow the non-destructive and non-invasive detection of bone water distribution or other measures of bone quality including microporosity. On the other hand, Nuclear Magnetic Resonance (NMR) proton spin-spin (T2) relaxation time measurements and computational analytical method have been used to determine microstructural characteristics of various types of fluid filled porous materials. The study in here is to demonstrate that non-destructive and non-invasive NMR proton spin-spin (T2) relaxation techniques has been developed and applied to quantify the porosity, pore size distribution and water distribution in human cortical bone. This new bone microstructural information can then be used as descriptions of bone quality and, along or in combination with existing method (BMD) to more accurately assess bone fracture risk, and the results could help doctors and researchers to detect osteoporosis and other conditions related to weak bones in persons. [Preview Abstract] |
Friday, March 7, 2008 2:54PM - 3:06PM |
APS3.00003: Ultraviolet, Infrared, and Raman Spectra of Pyridine and Its Fluoro Derivatives Jaan Laane, Praveen Boopalachandran, Kathleen McCann The vapour-phase infrared and ultraviolet absorption spectra of pyridine, pyridine-d$_{5}$, 2-fluoropyridine, and 3-fluoropyridine have been recorded. The high-temperature Raman spectra of these vapour phase samples have also been collected. DFT and ab initio calculations for each molecule were carried out for both the ground and S$_{1}$(n,$\pi $*) electronic excited states in order to calculate the molecular structures and vibrational frequencies, and this facilitated the assignment of the vibrational data. Comparison of the assignments for the S$_{1}$(n,$\pi $*) states with the electronic ground state provided an understanding of how the bonding of the molecules changes in the electronic excited states, where the molecules become much less rigid and floppy. Investigation of the $\nu _{18}$ out-of-plane ring-bending mode for pyridine-d$_{0}$ and --d$_{5}$ allowed their potential energy function to be determined, and this demonstrated that pyridine is quasi-planar with a barrier to planarity of 3 cm$^{-1}$ in the S$_{1}$(n,$\pi $*) state. The decrease from 403 cm$^{-1}$ (S$_{0})$ to 59.5 cm$^{-1}$ (S$_{1})$ for the $\nu _{18}$ vibration of pyridine reflects the decreased rigidity in the excited state. [Preview Abstract] |
Friday, March 7, 2008 3:06PM - 3:18PM |
APS3.00004: Characterization and Optical Tuning of CdSe {\&} ZnS Quantum Dots Generated by Laser Ablation of Microparticles Ignacio Gallardo, Kay Hoffmann, John Keto CdSe and ZnS core-shell nanoparticles made by LAM (Laser Ablation of Microparticles) show photoluminesence (PL) peaks in a region of wavelengths below 400nm. Control over the size and PL peak position is obtained by irradiating the nanoparticles multiple times. In LAM, micropaticle powder passes through an aerosol generator and then into a laser ablation glass cell, where a laser pulse (high energy excimer laser) ablates the microparticle aerosol. Nanoparticles are formed after condensation. At this stage the nanoparticles can be covered with a second material or irradiated multiple times to change their size. Using TEM (Transmission Electron Microscopy) measurements, CdSe particles have shown a size range that goes from 3.1$\pm $0.17nm (one ablation) to a mean radius of 2.5$\pm $0.19nm (after a second radiation). PL blue shifts are seen as the mean size decreases. A thermodynamic numerical calculation based on evaporation models and Mie absorption during the LAM process supports the blue shifting of the PL peaks by showing a decrease in particle size as they are exposed to multiple laser irradiations. [Preview Abstract] |
Friday, March 7, 2008 3:18PM - 3:30PM |
APS3.00005: Photonic Band Gap and Negative Refraction in Two-dimensional Photonic Crystals with Centered Rectangular Symmetry Kris Ohlinger, Yuankun Lin We report photonic band gaps in two-dimensional photonic crystals with centered rectangular lattices of elliptical air rods in a silicon background for both transverse electric and transverse magnetic polarizations. The calculations have revealed the existence of large complete photonic band gaps in those photonic crystals. Negative refractive behaviors have also been studied in these two-dimensional centered rectangular elliptical-rod photonic crystals. [Preview Abstract] |
Friday, March 7, 2008 3:30PM - 3:42PM |
APS3.00006: Photonic Band Gap Calculation and Holographic Fabrication of Orthorhombic and Tetragonal 3D Photonic Crystals Kris Ohlinger, Yuankun Lin, Di Xu, Kevin Chen We report a photonic band gap (PBG) and fabrication of both orthorhombic and tetragonal photonic crystals. 3D photonic crystal structures were formed by a double-exposure of photoresist SU8 through a phase mask. Lattice structures and PBG can be controlled by the rotational angles of the phase mask between two exposures. PBG computation predicts that the photonic crystal structure with the optimized bandgap can be realized when the rotational angle is set between 50 and 70 degrees. A photonic crystal template by 60-degree phase mask rotation was fabricated in SU8. [Preview Abstract] |
Friday, March 7, 2008 3:42PM - 3:54PM |
APS3.00007: Functionalized Nanomaterials to Sense Toxins/Pollutant Gases Using a Resonant Cavity James Roberts, Jai Dahiya, Aman Anand This paper provides an overview of the techniques and methods involving electromagnetic resonators to study the interactions of gas molecules with substrates. A resonant cavity operating in TE$_{011}$ mode was employed to characterize the nature of interactions of a range of weakly polar to non-polar gas molecules with carbon nanotubes loaded in the cavity. Resonant cavities are special electromagnetic resonators which can have a very high quality factor; which enhances the sensitivity of the apparatus as compared to standard electrical tank circuits. Shifts in the resonant frequency of these circuits for gas pressure changes provides a highly effective means to quantify the nature of agents perturbing the cavity. By functionalizing the nanomaterials with specific anti-bodies and loading them as wicks in these cylinders, the technique can be engineered into a very sensitive and unique chemical and biological sensor prototype. [Preview Abstract] |
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