Bulletin of the American Physical Society
2018 Annual Meeting of the APS Mid-Atlantic Section
Volume 63, Number 20
Friday–Sunday, November 9–11, 2018; College Park, Maryland
Session D01: Chemical Physics I |
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Chair: John Fourkas, University of Maryland, College Park Room: Edward St. John 1215 |
Saturday, November 10, 2018 9:30AM - 10:06AM |
D01.00001: Structure and Dynamics of Ionic Liquids in Bulk and at Interfaces Invited Speaker: Edward Castner Ionic liquids, or molten salts that are liquid are room temperature, provide both a range of fascinating properties, as well as a wide array of uses in applications for energy technologies. All of the ionic liquids we have studied are fragile glass-formers, have negligible vapor pressures, and exhibit a significant degree of ordering in the liquid phase. This ordering results both from the strong Coulombic interactions between ions, but also from van der Waals interactions from hydrophobic functional groups attached to the molecular ions. When both hydrocarbon and fluorocarbon substituents are used to functionalize the anions and cations of the ionic liquids, a number of intriguing properties result. Results from synchrotron X-ray scattering, PG-SE NMR experiments, angle-resolved XPS experiments, and AFM experiments will be contrasted with results from molecular dynamics simulations.
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Saturday, November 10, 2018 10:06AM - 10:18AM |
D01.00002: Adsorption and Separation of CO2 and CH4 Gas Mixture in a Graphene Layer and a Graphite Surface Hind H Aljaddani, Silvina M Gatica The goal of this work is to predict the selective adsorption of CO2 from a mixture with CH4 on a graphene/graphite substrate. The substrate consists on a layer of graphene with slits suspended on top of graphite at a distance of 10 Å. Molecular dynamics was used to simulate this adsorption. In this system, methane is modeled as a single, spherical atom with one Lennard-Jones site. Carbon dioxide is modeled as a linear rigid body with three Lennard-Jones sites and three partial charges. The slits in graphene are made by deleting carbon atoms from the lattice within a region of specified width. Graphite is modeled as a 10-4-3 wall. We run the simulations at 300K and compare the selectivity of CO2/CH4 on the substrate to test the capability of the graphene/graphite to separate CO2 from CH4.The result shows that the selectivity is higher for narrow slits. |
Saturday, November 10, 2018 10:18AM - 10:30AM |
D01.00003: Determination of absolute Raman cross-section of chemicals and explosives using swept wavelength resonance Raman device Milan P Poudel, Teck Lee, Pratima Kunapareddy Multi-wavelength resonance Raman in UV has been emerged as an important spectroscopic tool for detection of chemicals and explosives. We have used SWOrRD (Swept Wavelength Optical Resonance Raman Device) to detect chemical and hazardous materials. Using these SWOrRD-derived Raman data, we have determined the excitation-energy dependence of Raman cross-section in the range 220-280 nm for various chemical samples such as KClO4, KNO3, KSO4 and CH5N3O4. We also investigated the pre-resonance and resonance Raman enhancement of these samples. The knowledge of specific excitation wavelength can be utilized to selectively enhance the desired Raman band of the molecules and help to choose the right excitation laser which is useful for real time standoff detection of explosives and chemicals. |
Saturday, November 10, 2018 10:30AM - 11:06AM |
D01.00004: Influence of the Potential Energy Landscape in Liquid Dynamics Invited Speaker: Marcus T Cicerone Microscopic molecular theories of supercooled liquids and glasses often posit the presence of long-lived "structures" of some sort in these systems. There is now evidence for these in local packing configurations, and indeed they seem necessary to produce observed heterogeneous dynamic phenomenology. On the other hand, it has long been assumed that, above the melting point, dynamics are unaffected by underlying structure - i.e., that any structure that might exist is averaged out on timescales much shorter than relaxation. By contrast, we find evidence for structures living long enough to influence relaxation not only in supercooled liquids, but in simple liquids far above the melting temperature. We present neutron scattering [1, 2], simulation [3], and ultrafast optical experiments showing that these structures and associated dynamic heterogeneities arise at much higher temperature than is typically expected. We also show that they play a very important role in overall transport and relaxation, even in the liquid state. [1] Cicerone et al., Physical Review Letters, 113:11, 117801 (2014) [2] Cicerone et al., The Journal of Chemical Physics 146:5, 054502 (2017) [3] Cicerone et al., Journal of Non-Crystalline Solids 407, 118-125 (2015) |
Saturday, November 10, 2018 11:06AM - 11:18AM |
D01.00005: Oxygen effects in photopolymerization of liquid acrylate thin films Sandra A Gutierrez Razo, Nikolaos Liaros, Adam Pranda, Gottlieb Oehrlein, John T Fourkas Oxygen concentration present during free-radical photopolymerization of liquid photoresist thin films affects polymerization efficiency. In our photoresists, oxygen is both a sensitizer and a quencher, promoting radical formation as well as chain termination. Continuous diffusion of oxygen into the films keeps the oxygen concentrations steady despite oxygen depletion through quenching. We examine how polymerization responds to this complex competition of the oxygen's roles. Here we report our recent results on the effects of oxygen concentration on the polymerization threshold and polymer feature size in liquid photoresist thin films using acrylate monomer mixtures. |
Saturday, November 10, 2018 11:18AM - 11:30AM |
D01.00006: 2-beam action spectroscopy for probing multiphoton absorption processes in semiconductors Nikolaos Liaros, Samuel Cohen, Daniel Jovinelli, John T Fourkas We recently introduced a new class of methods, called two-beam action (2-BA) spectroscopies for determining the order of effective absorptive nonlinearity in different materials. The 2-BA spectroscopy approach offers significant advantages over traditional logarithmic plots of an observable as a function of average excitation power, particularly when multiple orders of absorption are involved. To demonstrate this, we extend 2-BA concept in a technique that we call 2-beam constant-amplitude photocurrent spectroscopy (2-BCAmP) to study absorption of a tightly focused, mode-locked or continuous-wave, 800 nm laser by a GaAsP photodiode. 2-BCAmP allows us to measure the effective order of the absorption process at any desired value of the photocurrent or photovoltage, as opposed to traditional approaches that require the measurement of the observable over several orders of magnitude of input intensity. We further demonstrate how to extract the relative contributions of two different absorption orders from non-integral 2-BCAmP exponents, as well as how to use these data to validate the model of the absorption orders that are involved in photocurrent generation. |
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