Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session L52: Liquids, Bio, and Interfacial Science |
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Sponsoring Units: DCP Chair: Timothy Zwier, Purdue Univ Room: LACC 512 |
Wednesday, March 7, 2018 11:15AM - 11:27AM |
L52.00001: State Variables for the Glassy State: Numerical Studies of Amorphous Ice Nicolas Giovambattista, Francis Starr, Peter Poole The potential energy landscape (PEL) formalism is a valuable approach within statistical mechanics for describing supercooled liquids and glasses. We use the PEL formalism and computer simulations to study the transformation between low-density (LDA) and high-density amorphous ice (HDA). We employ the ST2 water model that exhibits a LDA-HDA first-order phase transition, as observed in experiments. We prepare samples of LDA and HDA following completely uncorrelated thermodynamic paths and study the evolution of these LDA and HDA samples during compression and decompression at temperatures sufficiently low that annealing is absent. It is found that the evolution of these LDA/HDA glasses, during the compression and decompression processes, is uniquely determined by a few quantities associated of the starting glass: (i) the thermodynamic variables (N,V,T) and (b) a few properties of the PEL. In other words, for isothermal compression/decompression processes, these few quantities define the ‘glass state’ of amorphous ice. We interpret our results in terms of the PEL formalism and suggests that the identified “state variables” may be applicable to amorphous solids in general. |
Wednesday, March 7, 2018 11:27AM - 11:39AM |
L52.00002: Anomalous Diffusivity of Aqueous Polyatomic ions: A Mode-coupling Theory Study Biman Bagchi, Puja Banerjee Unlike simple monatomic ions, biologically and industrially relevant complex polyatomic ions like nitrate, acetate etc. have not been studied in any great detail. Experiments have shown that some polyatomic ions with larger size show anomalously high diffusivity in water. We simulate nitrate and acetate ions in water to find that polyatomic ions exhibit jump rotations in water that is coupled to the jump dynamics of water. We show that the charge distribution decides the rate of rotational jump which is again coupled to their translational motion. A symmetric ion like nitrate undergoes faster rotational jump that enhances its diffusivity where an asymmetric ion like acetate with hindered rotational motion exhibits lower diffusivity. |
Wednesday, March 7, 2018 11:39AM - 11:51AM |
L52.00003: Solvation Dynamics of Several Choline Chloride-based Deep-Eutectic Solvents Adam Turner, Doseok Kim Deep-eutectic solvents (DES), formed by mixing two or more components of pure materials, show deeply suppressed melting points and are in the liquid state at room temperature. Intermolecular hydrogen bonding, crystal lattice frustration, and entropy gain upon mixing have been considered responsible for this phenomenon. Dynamic solvation responses of coumarin 153 in a range of choline chloride-based DES were investigated with time-resolved fluorescence emission spectroscopy at room temperature. Time-resolved Stokes shifts were used to quantify dynamic solvation, with the solvation response function in DES found to be a biexponential function of time in contrast to the single exponential commonly observed in molecular solvents. This biexponential character of the solvation response is similar to that previously observed for ionic liquids, while solvation times are similar or slightly faster in DES than in ionic liquids of comparable viscosity. Average solvation times obtained from the dynamic Stokes shifts showed a partial correlation with viscosity suggesting that a model that only takes viscosity into account is not suitable for describing DES solvation. |
Wednesday, March 7, 2018 11:51AM - 12:03PM |
L52.00004: Understanding the vibrational solvatochromism of the carbonyl stretch in dilute PCBM solutions Liang Shi PCBM, a fullerene derivative, is widely used as an electron transport material in electronic devices, such as organic solar cells. It is known that the electron transfer efficiency in amorphous PCBM films is greatly affected by the underlying nanoscale disorder, which gives rise to the broad IR spectra of the carbonyl stretch of PCBM in these systems. In order to understand the heterogeneity in PCBM-containing systems and its manifestation in the IR spectra, we develop an efficient mixed quantum/classical model for the spectral simulations, which are based on classical molecular dynamics simulations and extensive quantum calculations. With this spectroscopic model we reproduce the unusual vibrational solvatochromism in dilute PCBM solutions, and the origin of the solvatochromism is discussed. Some approximations for spectral simulations are evaluated with the goal of employing them in the modeling of nonlinear vibrational spectra. |
Wednesday, March 7, 2018 12:03PM - 12:15PM |
L52.00005: Revealing the crucial role of molecular rigidity on the fragility evolution of glass-forming liquids Matthieu Micoulaut, Jean-Yves Raty, Can Yildirim If quenched fast enough, a liquid is able to avoid crystallization and will remain in a metastable supercooled state down to the glass transition, with an important increase in viscosity upon further cooling. There are important differences in the way liquids relax as they approach the glass transition, rapid or slow variation in dynamic quantities under moderate temperature changes, and a simple means to quantify such variations is provided by the concept of fragility. Here, we report molecular dynamics simulations of a typical network-forming glass, Ge–Se, and find that the relaxation behaviour of the supercooled liquid is strongly correlated to the variation of rigidity with temperature and the spatial distribution of the corresponding topological constraints, which ultimately connect to the fragility minima. This permits extending the fragility concept to aspects of topology/rigidity, and to the degree of homogeneity of the atomic-scale interactions for a variety of structural glasses. |
Wednesday, March 7, 2018 12:15PM - 12:27PM |
L52.00006: Heavy Anionic Complex Shows Unexpected Adsorption Behavior Coupled with Unique Interfacial Water Structure at a Soft Charged Interface Ahmet Uysal, William Rock, Baofu Qiao, Tiecheng Zhou, Aurora Clark, Wei Bu, Binhua Lin The molecular-scale behavior of ions at aqueous charged interfaces is coupled with their hydration, and is fundamentally important to many macroscopic phenomena, including biophysics, atmospheric chemistry and chemical separations. Although lighter ions have been widely studied in this context, heavy anionic complexes, that are crucial for modern energy and lighting technologies, are underexplored. Here, we study the adsorption of PtCl62- at a positively charged Langmuir monolayer. Surface-sensitive x-ray techniques show that PtCl62- adsorbs in the diffuse layer and the Stern layer at low and high bulk concentrations, respectively [1]. This is contrary to the expectations from classical mean-field theories. Sum frequency generation spectroscopy shows that PtCl62- partially retains its hydration sphere after adsorption in the Stern layer. This unique interfacial hydration is likely responsible for its unexpected adsorption behavior. Our experimental and computational studies provide important clues to solving the mystery of specific ion effects. |
Wednesday, March 7, 2018 12:27PM - 12:39PM |
L52.00007: Ion Motion in Electrolytic Cells: Anomalous Diffusion Evidences Luiz Evangelista, Ervin Lenzi, Rafael Zola, Haroldo Ribeiro, Denner Vieira, Federica Ciuchi, Alfredo Mazzulla, Nicola Scaramuzza We argue that ion motion in electrolytic cells containing Milli-Q water, weak electrolytes, or liquid crystals may exhibit unusual diffusive regimes that deviate from the expected behavior, leading the system to present anomalous diffusion. The Poisson-Nernst-Planck (PNP) diffusional model is used with extended boundary conditions to simulated the charge transfer, accumulation and adsorption - desorption at the electrodes surfaces. We analyze the relation between the electrical conductivity and ionic motion from the experimental data obtained via electrical impedance spectroscopy. We establish the contribution of the surface and bulk effects for the diffusive regimes present in these systems by considering the connection between the impedance and the conductivity, thus enabling the use of Einstein's generalized relation between mobility and diffusion coefficient. We then obtain the frequency dependent diffusion coefficient and relate it with the mean square displacement that characterizes the diffusive process. We also use the PNP model to connect the behavior of the conductivity with the surface or bulk contribution, according to the frequency range. |
Wednesday, March 7, 2018 12:39PM - 12:51PM |
L52.00008: Adsorption of different trivalent ions on fatty acid Langmuir monolayer Sona Krem, Woongmo Sung, Doseok Kim Counterion binding to Langmuir monolayer is an important process in all areas of soft matter phenomena, ranging from biology, suspensions, colloids, and atmospheric processes. Langmuir monolayers, consisting of fatty acid molecules, were prepared on solutions of FeCl3 and LaCl3 to investigate adsorption of trivalent metal ions on carboxylic headgroups by sum-frequency vibrational spectroscopy. Fe3+ ions bound to the fatty acid headgroups only in the form of hydroxide complexes (Fe(OH)x+3-x), and sum-frequency intensity of water stretch modes increased markedly upon adsorption of ion hydroxide. On the other hand, La3+ ions bound to the charged anionic headgroups (at high pH subphase) as bare trivalent ions, and reached saturation adsorption at 10 mM bulk concentration. |
Wednesday, March 7, 2018 12:51PM - 1:03PM |
L52.00009: Salt promotes protonation of amine groups at air/water interface Doseok Kim, Woongmo Sung, Zaure Avazbaeva Interfacial water reorientation caused by protonation/deprotonation of primary fatty amine (octadecylamine, ODA) headgroup was investigated by interface-selective vibrational sum-frequency generation spectroscopy. Sum-frequency intensity from ODA monolayer on neutral pH water was very small implying only small portion of protonated amine group (-NH3+) initially existed. By increasing the ionic strength, however, SF intensity of water OH band was enhanced markedly up to ~1 mM, and then decreased in both NaCl and NaI solutions. By measuring the phase of the sum-frequency spectra, it was found that water dipoles under the ODA headgroup point downward indicating the surfaces were always positively charged. This demonstrated that increasing ionic strength facilitates protonation of primary amine headgroups. Simple model based on Poisson-Boltzmann (PB) theory explained this protonation behavior of primary amines. |
Wednesday, March 7, 2018 1:03PM - 1:15PM |
L52.00010: Measuring Structure and Disorder of (Cy3)2 Dimer Labeled DNA Fork-Junctions Using Two-Dimensional Fluorescence Spectroscopy (2DFS) Amr Tamimi, Dylan Heussman, Loni Kringle, Michael Raymer, Andrew Marcus DNA is commonly represented as a static B-form double helix. Biologically relevant forms of DNA, however, include single (ss) and double strands (ds), as well as various types of ss-ds junctions. DNA is not a single static conformation, but rather fluctuates over a range of conformations that deviate significantly from canonical structures. This is necessary for proteins to access functionally required structural motifs. In order to characterize such heterogeneity, we have performed absorption, circular dichroism, and two-dimensional fluorescence spectroscopic experiments on DNA constructs labelled with the fluorescent chromophore cyanine-3 (Cy3). These DNA constructs form strongly-coupled dimers (Cy3)2 which are incorporated into the backbone near the ss-ds regions of model DNA replication forks. The vibronic nature of the monomer transitions and the excitonic coupling between monomers yield rich spectra which are sensitive to the range of conformations present. Detailed analyses of the data permit the extraction of conformational parameters and characterization of the conformational disorder. |
Wednesday, March 7, 2018 1:15PM - 1:27PM |
L52.00011: Aggregation Induced Emission in Holographic Polymer Dispersed Liquid Crystals Ye Zhao, Haiyan Peng, Xiaolin Xie Holography is implemented through interference of several coherent laser beams. It can simultaneously reconstruct whole amplitude and phase information of light over a large area. This feature enables holography to prevent any illegal copying or scanning. |
Wednesday, March 7, 2018 1:27PM - 1:39PM |
L52.00012: Molecular Dynamics Simulations of Thermal and Nonthermal Processes in Amorphous Solid Water Deposited on Gold Nanoparticles Yuzi He, Rajiv Kalia, Priya Vashishta, Aiichiro Nakano Amorphous solid water (ASW) plays a crucial role in the chemistry of the interstellar medium. |
Wednesday, March 7, 2018 1:39PM - 1:51PM |
L52.00013: In situ analysis of elastic properties and structural relaxation of two polymeric materials Manon Heili, John Kieffer We report on the elastic property reconstitution in two types of polymer materials subject to strain: a two-component epoxy resin DGEBA/DETA, which has a highly cross-linked network, and polyvinylidene fluoride (PVDF), a chain-like polymer. Our setup for materials characterization combines a miniature tensile tester placed into the optical path of a Brillouin light scattering (BLS) system, to probe the elastic properties of a sample while it is uniaxially strained. BLS yields the adiabatic moduli of the materials, while their isothermal moduli are derived from the measured stress-strain curves. |
Wednesday, March 7, 2018 1:51PM - 2:03PM |
L52.00014: Multipole interactions in the molecular polarizabilities of water from ambient to high pressures Ding Pan, Marco Govoni, Giulia Galli Knowledge of molecular polarizabilities in condensed phases provides important information about molecular crystals, and in general about materials composed of molecular or nano-building blocks. We propose a first-principles method based on electronic densities to compute molecular polarizabilities in condensed phases. The method includes all multipole interactions in addition to the dipole-dipole one, and it is applicable to any semiconductor or insulator. We present results for molecular polarizabilities of liquid water in a wide pressure-temperature range. We found that at ambient conditions, the dipole-induced-dipole approximation is sufficiently accurate and the Clausius-Mossotti relation may be used, e.g. to obtain molecular polarizabilities from experimental refractive indexes. However with increasing pressure this approximation becomes unreliable and in the case of ice X, where covalent bonds are present, the dipole-induced-dipole approximation breaks down. |
Wednesday, March 7, 2018 2:03PM - 2:15PM |
L52.00015: Dielectric Enhancement from Non-Insulating Particles with Ideally Polarized Interfaces and Zero zeta-Potential I: Exact Solution Jiang Qian, Pabitra Sen We solve exactly the dielectric response of a non-insulating sphere of radius a suspended in an electrolyte solution, with ideally-polarizable interface but without signicant zeta-potential. We then use this solution to derive the dielectric response of a dilute random suspension of such spheres, with volume fraction f << 1, within the Maxwell-Garnett Eective Medium Approximation. Surprisingly, we discover a huge dielectric enhancement in this bare essential model of dielectric responses of solids in electrolyte solution: at low frequency , |
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