Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session D26: Focus Session: Water and Liquid Dynamics |
Hide Abstracts |
Sponsoring Units: DCP Chair: David Chandler, Sandia National Laboratories Room: 204A |
Monday, March 2, 2015 2:30PM - 2:42PM |
D26.00001: ABSTRACT WITHDRAWN |
Monday, March 2, 2015 2:42PM - 2:54PM |
D26.00002: New insights into the femtosecond-to-picosecond dynamics of liquid water from temperature dependence using terahertz spectroscopy studies and molecular dynamics simulations Chola Regmi, Deepu George, Shengfeng Cheng, Nguyen Vinh Water plays an active and complex role in sustaining life. The hydrogen bonds between the water molecules exhibit the unique physical properties that distinguish water from other molecular liquids. Nevertheless, there is little agreement regarding the femtosecond to picosecond relaxation dynamics of water. In response, we have used the state-of-the-art terahertz spectroscopy (frequency-domain and time-domain) and molecular dynamics simulation techniques to study the molecular relaxation of water at different temperatures in the femtosecond to picosecond time scale. We show that the two-Debye model is insufficient to explain the observed relaxation dynamics of water and our results on the terahertz dielectric relaxation of water are best described as the sum of three-Debye processes. We compute the time autocorrelation function of the dipole moment of water molecules at different temperatures with molecular dynamics simulations and compare the calculations with the experimental data. [Preview Abstract] |
Monday, March 2, 2015 2:54PM - 3:06PM |
D26.00003: Exploring the nonlocal dielectric susceptibility of liquid water in the terahertz regime - propagating modes, Debye relaxation and overscreening Daniel Elton, Marivi Fernandez-Serra There is great interest in the dielectric and infrared spectra of water between 1-1000 cm$^{-1}$ (.03-30 THz). To gain insight into this region we study the nonlocal (wavelength dependent) dielectric susceptibility. A curious feature of water is the presence of a propagating mode in the librational region. For the first time we study the temperature dependence of this mode and its range of propagation. We show that the librational band has two components - non-dispersive and dispersive. Previously this mode was suggested to be analogous to an optical phonon propagating along the H-bond network. We suggest a possible alternative - that it is the dipolaron mode predicted for dipolar systems.\footnote{PRL {\bf 46}, 950 (1981).} Next we study the region of .1-10 THz which is relevant to understanding the coupling between proteins and water. We show that in addition to H-bond vibrations, intramolecular inertial relaxations also contribute. We find that the Debye peak is dispersive, confirming its long range cooperativity. We report the first temperature dependent study of the static nonlocal susceptibility, which exhibits a negative region, a phenomena called overscreening. We compare a rigid model (TIP4P/$\varepsilon$), a flexible model (TIP4P/2005f) and a polarizable model (TTM3-F). [Preview Abstract] |
Monday, March 2, 2015 3:06PM - 3:18PM |
D26.00004: A Dataset of First-Principles Molecular Dynamics Simulations of Water Francois Gygi, William Dawson We present a dataset of first-principles molecular dynamics simulations [1] of water performed using Density Functional Theory. A set of 32 independent 64-molecule samples was used in separate, parallel simulations for a duration of 58 ps. An analysis of atomic trajectories is given focusing on correlations of the Kohn-Sham energy, ionic kinetic energy, pair correlation functions, diffusion coefficient, and vibrational spectrum. The availability of 32 independent simulations allows for an estimation of the variance of averaged quantities, both within MD runs and between samples. The variability of oxygen pair correlation functions across samples provides a measure of the uncertainty associated with that quantity. We observe several instances of large fluctuations in the oxygen pair correlation functions that can be associated with increases in the local structure index (LSI) proposed by Shiratani and Sasai [2] supporting the hypothesis that water undergoes frequent changes to locally highly structured configurations. Complete atomic trajectories and simulation output files are available online[3]. \\{} [1] Qbox code, http://eslab.ucdavis.edu/software/qbox \\{} [2] E. Shiratani and M. Sasai, J.\ Chem.\ Phys.\ {\bf 104}, 7671 (1996) \\{} [3] http://www.quantum-simulation.org \\ [Preview Abstract] |
Monday, March 2, 2015 3:18PM - 3:30PM |
D26.00005: Mutual Exclusion of Urea and Trimethylamine N-oxide from Amino Acids in Mixed Solvent Environment Pritam Ganguly, Timir Hajari, Joan-Emma Shea, Nico F. A. van der Vegt We study the solvation thermodynamics of individual amino acids in mixed urea and trimethylamine N-oxide (TMAO) solutions using molecular dynamics simulations and the Kirkwood-Buff theory. Our results on the preferential interactions between the amino acids and the cosolvents (urea and TMAO) show a mutual exclusion of both the cosolvents from the amino acid surface in the mixed cosolvent condition which is followed by an increase in the cosolvent-cosolvent aggregation away from the amino acid surface. The effects of the mixed cosolvents on the association of the amino acids and the preferential solvation of the amino acids by water are found to be highly non-linear in terms of the effects of the individual cosolvents. A similar result has been found for the association of the protein backbone, mimicked by triglycine. Our results have been confirmed by different TMAO force-fields and the mutual exclusions of the cosolvents from the amino acids are found to be independent of the choice of the strength of the TMAO-water interactions. Based on our data, a general mechanism can potentially be proposed for the effects of the mixed cosolvents on the preferential solvations of the solutes including the case of cononsolvency. [Preview Abstract] |
Monday, March 2, 2015 3:30PM - 3:42PM |
D26.00006: ABSTRACT WITHDRAWN |
Monday, March 2, 2015 3:42PM - 3:54PM |
D26.00007: Experiments on Tracer Diffusion in Water and Aqueous Mixtures Dan Spiegel We have used forced Rayleigh scattering to measure tracer diffusion coefficients in water and other liquids. The tracer molecule is the azobenzene derivative methyl red (MR). In one set of experiments diffusion was measured at different temperatures to test the Cohen-Turnbull (CT) free volume diffusion theory. It was found that eight solvents were in reasonable agreement with CT, but the relevant energy in water was smaller by an order of magnitude. We believe this is due to the ``zero-point'' free volume that water would possess, due to its H-bonds, even at the glass transition temperature, and to the ability of MR to diffuse along its plane. In a second set of experiments we studied diffusion in aqueous and non-aqueous mixtures. The non-aqueous mixtures are in good agreement with free volume theory, but the aqueous mixtures show large disagreement. We suggest this is caused by the formation of two solvent shells in the aqueous mixtures, driven by the hydrophobicity of MR and water-amphiphile hydrogen bonding. [Preview Abstract] |
Monday, March 2, 2015 3:54PM - 4:06PM |
D26.00008: Spectroscopic studies on di-pophyrin rotor as micro-viscosity sensor H. Doan, S. Raut, J. Kimbal, Z. Gryczynski, S. Dzyuba, M. Balaz In typical biological systems the fluid compartment makes up more than 70{\%} percent of the system weight. A variety of mass and signal transportation as well as intermolecular interactions are often governed by viscosity. It is important to be able to measure/estimate viscosity and detect the changes in viscosity upon various stimulations. Understanding the influence of changes in viscosity is crucial and development of the molecular systems that sensitive to micro-viscosity is a goal of many researches. Molecular rotors have been considered the potential target since they present enhanced sensitivity to local viscosity that can strongly restrict molecular rotation. To understand the mechanics of rotor interaction with the environment we have been studied conjugated pophyrin-dimer rotor (DP) that emit in the near IR. Our goal is to investigate the photo physical properties such as absorption, transition moment orientation, emission and excitation, polarization anisotropy and fluorescence lifetime in various mediums of different viscosities from ethanol to poly vinyl alcohol (PVA) matrices. The results imply the influences of the medium's viscosity on the two distinct confirmations: planar and twisted conformations of DP. Linear dichroism from polarized absorption in PVA matrices shows various orientations of transition moments. Excitation anisotropy shows similar transition splitting between two conformations. Time resolved intensity decay at two different observations confirms the two different emission states and furthermore the communication between the two states in the form of energy transfer upon excitation. [Preview Abstract] |
Monday, March 2, 2015 4:06PM - 4:18PM |
D26.00009: High pressure Raman spectroscopy of H$_{2}$O-CH$_{3}$OH mixtures Wen-Pin Hsieh, Yu-Hsiang Chien Complex intra-molecular interactions and the hydrogen-bonding network in H$_{2}$O-volatile mixtures play critical roles in many dynamics processes in physical chemistry, biology, and Earth and planetary sciences. We used high pressure Raman spectroscopy to study the pressure evolution of vibrational frequencies and bonding behavior in H$_{2}$O-CH$_{3}$OH mixtures. We found that the presence of low CH$_{3}$OH content in H$_{2}$O increases the transition pressure where water crystallizes to ice VI, but does not significantly change the pressure where ice VI transforms to ice VII. Furthermore, the stiffening rates of C-H stretching frequencies $d\omega /dP$in CH$_{3}$OH significantly decrease upon the crystallization of water, and the softening rates of the O-H stretching frequencies of ice VII are suppressed over a narrow pressure range, after which the frequencies of these modes shift with pressure in ways similar to pure CH$_{3}$OH and ice VII, respectively. Such complex pressure evolution of Raman frequencies along with pronounced variations in Raman intensities of CH$_{3}$OH within the sample, and the hysteresis of the water-ice VI phase transition suggest pressure-induced segregation of low content CH$_{3}$OH from ice VII. [Preview Abstract] |
Monday, March 2, 2015 4:18PM - 4:30PM |
D26.00010: Discovery of Water Structural Transitions near Interfaces of Polarizable Solutes Mohammadhasan Dinpajooh, Dmitry Matyushov The standard harmonic approximation describing polarization around the solute is expected to break down with increasing solute polarizability. The focus of this study is to investigate the structure of water around dipolar-polarizable solutes by Monte Carlo (MC) simulations in the non-harmonic regime. We observe a structural transition in the water hydration shell and its condensation, which are driven by increasing the solute polarizability. There is also a crossover in the orientational structure near the point of breakdown of the harmonic approximation. At lower polarizabilities, waters in the hydration shell point their hydrogens toward the solute. The dipoles flip their orientations at the transition to the non-harmonic regime. Both the hydration shell compressibility and the electric field susceptibility display maxima in the transition region. Using the water electric field at the center of the polarizable solute as the order parameter, a Landau-type model is formulated. Its predictions are in reasonable agreement with MC simulations performed for hard sphere and Lennard Jones polarizable solutes in a TIP3P water model. The observed structural transition suggests a general crossover phenomenon driven by the stabilization energy required to polarize the solute. [Preview Abstract] |
Monday, March 2, 2015 4:30PM - 4:42PM |
D26.00011: Ionic liquid and water molecules diluted in hydrophobic solvent matrix investigated by infrared absorption spectroscopy Doseok Kim, Woongmo Sung, Jonggwan Lee Pure ionic liquids ([BMIM]: 1-butyl-3-methylimidazolium, X: Cl and I) and their aqueous solutions were loaded on top of non-polar solvent CCl$_{\mathrm{4}}$, and the infrared spectra of CCl$_{\mathrm{4}}$ phase were taken as a function of time for in-situ probing of the transfer of the ionic liquid and water molecules. We observed clear vibrational bands of methyl and methylene groups of the cations similar to that of bulk ionic liquids. On the other hand, normally strong infrared absorption from C(2)-H and C(4,5)-H vibrations was hardly observable. As these bands work as indicators of specific interaction between the imidazolium core and the halide anions, we concluded that ion pairs are fully dissociated and [BMIM] cations exist as monomers in CCl$_{\mathrm{4}}$. For 1 M of [BMIM]Cl and [BMIM]I aqueous solutions, water molecules transferred into CCl$_{\mathrm{4}}$ also exist mostly as monomers, with a possible existence of anion-bound water molecules inferred from the new band at 3421 cm$^{\mathrm{-1}}$ for [BMIM]Cl, and at 3452 cm$^{\mathrm{-1\thinspace }}$for [BMIM]I. Both transfer rate and saturation amount of ionic liquid molecules are larger for [BMIM]I. For this, we propose that this difference in transfer rate originates from excess ionic liquid molecules at the interface between hydrophlic (aqueous solution) and hydrophobic (CCl$_{\mathrm{4}})$ medium. [Preview Abstract] |
Monday, March 2, 2015 4:42PM - 4:54PM |
D26.00012: Electrical Conduction in Pure Water -- Trapping and Scattering of Positive Protons and Negative Proton Holes Binbin Jie, Chihtang Sah Water has been characterized by hydronium (H$_{3}$O)$^{1+}$ and hydroxide (HO)$^{1-}$ ions, which fail to explain the electrical conductivity of even pure water. Experimental formulas of pure water versus temperature (0-100C) have employed 39 empirical parameters to fit 3 measured properties: ion concentration, and electrical conductance of pure water and (H$_{3}$O)$^{1+}$ ion. We have shown (4 invited talks, 3 articles in 14 months) that electrical conduction in pure water can be represented by 5 quasi-particles in the many-body water lattice: the mobile positively charged protons p$^{+}$ and negatively charged proton holes p$^{-}$, and the 3 charge states of the immobile water molecule as amphoteric protonic trap, V$^{+}=$(H$_{3}$O)$^{1+}$, V$^{0\pm}=$(H$_{2}$O)$^{0\pm}$, and V$^{-}=$(HO)$^{1-}$; and as few as 6 physics parameters: 3 binding energies, 1 protonic density of state, and 2 Coulombic scattering strengths. Protons in water are strongly coupled to the protonic-phonons, oxygen-phonons and protonic-local modes. Impuritons and affinitons may be present in the hexagonal tunnels of the water lattices. [Preview Abstract] |
Monday, March 2, 2015 4:54PM - 5:06PM |
D26.00013: Surface-enhanced Raman mapping of chemical hot spots Dmitri Voronine Surface-enhanced Raman spectroscopy (SERS) and atomic force microscopy (AFM) are used for simultaneous chemical-topographic mapping of Raman hot spots on dielectric, semiconductor and metal surfaces. Raman signals enhanced by electromagnetic and chemical mechanisms are separated. Several approaches of nanoscale surface analysis are compared. Future experimental advances for spatiotemporal imaging of surface dynamics using ultrafast lasers and multiple tips are discussed. [Preview Abstract] |
Monday, March 2, 2015 5:06PM - 5:18PM |
D26.00014: Coupling of Solute Vibrational Modes with a Fabry-Perot Optical Cavity Mode Adam Dunkelberger, Ryan Compton, Kenan Fears, Bryan Spann, James Long, Blake Simpkins, Jeffrey Owrutsky Electronic transitions of systems confined in optical microcavities can strongly couple to cavity modes, giving rise to new, mixed-character modes. Recent studies have demonstrated similar coherent coupling between the vibrational modes of a thin polymer film and a Fabry-Perot optical cavity mode. This coupling manifests experimentally as a splitting of the transmissive cavity mode into two dispersive branches separated by the vacuum Rabi splitting. Here we present recent experimental results for the coupling of solution-phase compounds with an optical cavity. Solutions of W(CO)$_6$, Mo(CO)$_6$, and NCS$^-$ contained in cavities show strong coupling between the solute chromophores in the mid-infrared and cavity modes. We show that the methodology established with polymer-filled cavities is generally applicable to liquids but that the fluidity of the sample complicates the cavity construction. Varied cavity thicknesses can give rise to spatial gradients in coupling strength and difficulty in targeting a specific cavity-mode order. We also compare the transmission of the mixed vibrational-cavity modes in cavities constructed from either metallic or dielectric reflectors which impacts the cavity resonance line width. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700