Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session S47: Chemical Physics of Surfaces, Interfaces and Colloids |
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Sponsoring Units: DCP GSOFT Chair: Jeff Owrutsky, Naval Research Laboratory Room: 312 |
Thursday, March 17, 2016 11:15AM - 11:27AM |
S47.00001: Effects of Oxide Surface on the Detonation Initiation of Energetic Materials from First Principles Fenggong Wang, Roman Tsyshevsky, Maija Kuklja Organic-inorganic interface provides both intrigues and opportunities for designing systems possessing properties and functionalities inaccessible by individual component. The electronic, catalytic, and defect properties of inorganic surfaces can affect the adsorption, chemical reaction, and photo-responsive properties of organic molecules. In particular, the presence of a particular oxide additive prompts the energy absorption for detonation initiation. Here, we choose the highly catalytic oxide TiO$_{2}$ and explosive trinitrotoluene (TNT) as prototypical examples to explore the role of oxide surface on the detonation initiation of explosives from first principles. We show that the TNT-TiO$_{2}$ (110) interface induces optical transitions between TiO$_{2}$ and TNT, shifting the light absorption edge to lower energy. This helps to control the detonation initiation by laser light with a modest optical energy. In addition, the presence of surface oxygen vacancies leads to electron transfer from surface to molecule, facilitating the decomposition of TNT. Our results not only provide guidelines for designing a controllable oxide-explosive formulation that can be initiated by available lasers, but also help to understand interfaces with target properties and functionalities. [Preview Abstract] |
Thursday, March 17, 2016 11:27AM - 11:39AM |
S47.00002: Effect of surface morphology on kinetic compensation effect Nayeli Zuniga-Hansen, Leonardo E. Silbert The existence of the kinetic compensation effect, observed in many fields of science, continues to be debated and believed to be a mathematical artifact. Recently, we performed a computational study of the thermal desorption of interacting adsorbates from an energetically homogeneous surface and we observed that the kinetic compensation effect indeed occurs to varying degrees depending on interaction strength. However, other factors which may lead to a kinetic compensation effect have yet to be explored. In the present work, using kinetic Monte Carlo simulations, we study the effects of substrate topology on thermal desorption. We focus on differences between ordered and disordered surfaces at a fixed site coordination number. The rates of desorption depend on surface configuration due to the inherent differences in the local environments of adsorbing sites. While the compensation effect persists for the disordered substrate, it is more strongly influenced by variations in the preexponential factor rather than the activation energy which dominates in the ordered lattice. We expect our results to provide a deeper insight into the microscopic events that originate compensation effects in our system of study but also in other fields where these effects have been reported. [Preview Abstract] |
Thursday, March 17, 2016 11:39AM - 11:51AM |
S47.00003: Thermodynamics of catalytic nanoparticle morphology Michael Zwolak, Renu Sharma, Pin Ann Lin Metallic nanoparticles are an important class of industrial catalysts. The variability of their properties and the environment in which they act, from their chemical nature {\&} surface modification to their dispersion and support, allows their performance to be optimized for many chemical processes useful in, e.g., energy applications and other areas. Their large surface area to volume ratio, as well as varying sizes and faceting, in particular, makes them an efficient source for catalytically active sites. These characteristics of nanoparticles -- i.e., their morphology -- can often display intriguing behavior as a catalytic process progresses. We develop a thermodynamic model of nanoparticle morphology, one that captures the competition of surface energy with other interactions, to predict structural changes during catalytic processes. Comparing the model to environmental transmission electron microscope images of nickel nanoparticles during carbon nanotube (and other product) growth demonstrates that nickel deformation in response to the nanotube growth is due to a favorable interaction with carbon. Moreover, this deformation is halted due to insufficient volume of the particles. We will discuss the factors that influence morphology and also how the model can be used to extract interaction strengths from experimental observations. [Preview Abstract] |
Thursday, March 17, 2016 11:51AM - 12:03PM |
S47.00004: Support- dependent evolution of oxidation state and nanoassembly formation of subnanometer copper clusters under carbon dioxide conversion conditions Avik Halder, Bing Yang, Karthika L. Kolipaka, Michael Pellin, Soenke Seifert, Stefan Vajda Size- and support- dependence of the properties of copper clusters have been investigated during carbon dioxide conversion with hydrogen at high reactant concentrations and atmospheric pressure. The model catalyst systems were prepared by depositing size-selected Cu$_{\mathrm{n}}$ clusters (n $=$ 3, 4, 12 and 20) on various amorphous metal oxide (Al$_{\mathrm{2}}$O$_{\mathrm{3}}$, ZnO, and ZrO$_{\mathrm{2}})$, and carbon-based (UNCD $=$ ultrananocrystaline diamond) supports. During the temperature ramp, the evolution of the chemical state and size of the particles were characterized by \textit{in situ} grazing incidence X-ray absorption near edge structure (GIXANES), and grazing incidence small angle X-ray scattering (GISAXS) respectively. Under reaction conditions the initially oxidized Cu clusters reduced at various temperatures depending on cluster size and support. Clusters supported on ZnO and UNCD were found to be sinter-resistant under reactive gases at elevated temperatures and atmospheric pressures, whereas on ZrO$_{\mathrm{2}}$ support the clusters formed stable aggregates. Clusters on Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ support demonstrated unique properties, where a formation of a nanostructure was observed during heating, which then disintegrated during the cool down. Under applied conditions, Cu$_{\mathrm{4}}$ clusters on Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ were found to be the most efficient in methanol formation. [Preview Abstract] |
Thursday, March 17, 2016 12:03PM - 12:15PM |
S47.00005: Molecular Imprinting of Silica Nanoparticle Surfaces via Reversible Addition-Fragmentation Polymerization for Optical Biosensing Applications Zehra Oluz, Sana Nayab, Talya Tugana Kursun, Tuncer Caykara, Basit Yameen, Hatice Duran Azo initiator modified surface of silica nanoparticles were coated via reversible addition-fragmentation polymerization (RAFT) of methacrylic acid and ethylene glycol dimethacrylate using 2-phenylprop 2-yl dithobenzoate as chain transfer agent. Using L-phenylalanine anilide as template during polymerization led molecularly imprinted nanoparticles. RAFT polymerization offers an efficient control of grafting process, while molecularly imprinted polymers shows enhanced capacity as sensor. L-phenylalanine anilide imprinted silica particles were characterized by X-Ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM). Performances of the particles were followed by surface plasmon resonance spectroscopy (SPR) after coating the final product on gold deposited glass substrate against four different analogous of analyte molecules: D-henylalanine anilide, L-tyrosine, L-tryptophan and L-phenylalanine. Characterizations indicated that silica particles coated with polymer layer do contain binding sites for L-phenylalanine anilide, and are highly selective for the molecule of interest. [Preview Abstract] |
Thursday, March 17, 2016 12:15PM - 12:27PM |
S47.00006: Sum Frequency Generation at the Al$_{\mathrm{2}}$O$_{\mathrm{3}}$-H$_{\mathrm{2}}$O Interface: An Effective Bond Polarizability Model Mark DelloStritto, James Kubicki, Jorge Sofo Sum Frequency Generation (SFG) is a powerful tool for extracting the vibrational spectrum of an interface as it is a second-order optical process and therefore prohibited in centrosymmetric bulk media. When calculating the spectrum, it is often desirable to write the response as a sum over components of the system, such as atoms or molecules. This can pose a number challenges however, as the response depends upon the total polarizability, which is in general not an additive quantity. We employ a Thole-type model to assign polarizabilities to the bonds of a system, which allows us to treat the contribution of molecules and surface groups to the spectrum. Local field effects are then taken into account using modified Ewald sums. Following the time-dependent approach of Morita, we are able to produce the SFG spectrum at an interface from molecular dynamics simulations ranging in size and detail from small ab-initio to large classical simulations. We tested our method on ab-initio simulations of the Al$_{\mathrm{2}}$O$_{\mathrm{3}}$(0001)-H$_{\mathrm{2}}$O interface as Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ has a low dissolution rate, a well-known surface structure, and thoroughly studied surface-water interactions. We were able to successfully reproduce the experimental spectrum and decompose it in terms of molecular motions and local correlations. [Preview Abstract] |
Thursday, March 17, 2016 12:27PM - 12:39PM |
S47.00007: Electrokinetic Stabilization of Thin Surfactant Films Soumyadip Sett, Rakesh Sahu, Alexander Yarin Ionic surfactant solutions were used to study gravitational drainage from thin vertical planar films supported on a frame with the upper and lower parts being electrodes. The imposed electric field resulted in the following physical phenomena: (i) surface charge redistribution, (ii) electroosmotic flow in the diffuse layer, and (iii) pressure build-up near the electrode to which the electroosmotic flow is directed. The interplay of these phenomena stabilized the film drainage irrespectively of polarity. Similar effects were observed with foams. [Preview Abstract] |
Thursday, March 17, 2016 12:39PM - 12:51PM |
S47.00008: Tuning surface reactivity by finite size effects: role of orbital symmetry in the $d-$band model Paul Snijders, Xiangshi Yin, Valentino Cooper, Hanno Weitering Catalytic activity depends sensitively on the strength of the interactions between reactant molecules and catalyst surface: too weak and the catalyst cannot capture enough molecules to react; too strong and the reaction products do not desorb, blocking further reactions. The ability to control the binding strength of molecules to metal surfaces is thus fundamental to the design of efficient and selective catalysts. Catalyst design often relies on increasing the interaction strength on relatively non-reactive materials by introducing active sites. Here, we present a complementary approach: we exploit finite size effects in the electronic structure of ultrathin Pd(111) films grown on Ru(0001) to tune their reactivity by changing the film thickness one atom layer at a time. While bulk Pd(111) is reactive toward oxygen, we find that Pd films thinner than 6 atom layers are surprisingly inert to oxidation. This observation can be explained with the $d$-band model only when it is applied to the orbitals directly involved in the bonding. The insight into orbital specific contributions to surface reactivity could be useful in the design of catalysts. [Preview Abstract] |
Thursday, March 17, 2016 12:51PM - 1:03PM |
S47.00009: Nonequilibrium thermodynamics of an interface Thierry Savin, Marco Schweizer, Hans Christian \"{O}ttinger Interfacial thermodynamics has deep ramifications in understanding the boundary conditions of transport theories. We present a formulation of local equilibrium for interfaces that extends the thermodynamics of the ``dividing surface,'' as introduced by Gibbs, to nonequilibrium settings such as evaporation or condensation. By identifying the precise position of the dividing surface in the interfacial region with a gauge degree of freedom, we exploit gauge-invariance requirements to consistently define the intensive variables for the interface. The model is verified under stringent conditions by employing high-precision nonequilibrium molecular dynamics simulations of a coexisting vapor-liquid Lennard-Jones fluid. We conclude that the interfacial temperature is determined using the surface tension as a ``thermometer,'' and can be significantly different from the temperatures of the adjacent phases. [Preview Abstract] |
Thursday, March 17, 2016 1:03PM - 1:15PM |
S47.00010: CO$_{\mathrm{2}}$ Adsorption on ZIF-8 Aldo Migone, Brice Russell We present the results of an adsorption isotherm study of CO$_{\mathrm{2}}$ on the metal-organic framework ZIF-8. This material undergoes a structural transition (``gate-opening'') as a function of increasing pressure and sorbent loading for sorbates. Gate-opening manifests itself in the isotherm data as a quasi-vertical substep, corresponding to an increase in the amount that can adsorb in the ZIF-8. We measured ten CO$_{\mathrm{2}}$ isotherms from 133 K to 227 K. In this range, we did not find in any of the isotherms the characteristic substep indicative of the gate-opening. It is possible that the temperature range over which this transition would manifest in the data simply has not been explored in our measurements. The adsorption isotherm data was used to determine the isosteric heat of adsorption of CO$_{\mathrm{2}}$ on this sorbent as a function of sorbent loading. We have studied the adsorption kinetics for this system, i.e., how the equilibration times for adsorption change as a function of sorbent loading. Trends in the isosteric heat, and kinetics of adsorption data will be discussed. [Preview Abstract] |
Thursday, March 17, 2016 1:15PM - 1:27PM |
S47.00011: Low frequency ionic conduction across liquid interfaces. Francisco J Solis, Guillermo Ivan Guerrero, Monica Olvera de la Cruz Ionic conduction in liquid media is a central component of many recently proposed technologies. As in the case of solid state systems, the presence of heterogeneous media gives rise to interesting nonlinear phenomena. We present simulations and theoretical analysis of the low frequency ionic conduction in a two-liquid system. In the case analyzed, the conduction is driven by an electric field perpendicular to the liquid-liquid interface. We show that the dielectric contrast between the liquids produces non-linear effects in the effective conductivity of the system and discuss the effects of the ion solubility in the media. [Preview Abstract] |
Thursday, March 17, 2016 1:27PM - 1:39PM |
S47.00012: Protonation of octadecylamine Langmuir monolayer by adsorption of halide counterions Woongmo Sung, Zaure Avazbaeva, Jonggwan Lee, Doseok Kim Langmuir monolayer consisting of octadecylamine (C$_{\mathrm{18}}$H$_{\mathrm{37}}$NH$_{\mathrm{2}}$, ODA) was investigated by heterodyne vibrational sum-frequency generation (HD-VSFG) spectroscopy in conjunction with surface pressure-area ($\pi $-$A)$ isotherm, and the result was compared with that from cationic-lipid (DPTAP) Langmuir monolayer. In case of ODA monolayer on pure water, both SF intensity of water OH band and the surface pressure were significantly smaller than those of the DPTAP monolayer implying that only small portion of the amine groups (-NH$_{\mathrm{3}}^{\mathrm{+}})$ is protonated in the monolayer. In the presence of sodium halides (NaCl and NaI) in the subphase water, it was found that the sign of Im$\chi^{\mathrm{(2)}}$ of water OH band remained the same as that of the ODA monolayer on pure water, but there was a substantial increase in the SF amplitude. From this, we propose that surface excess of the halide counterions (Cl$^{\mathrm{-}}$ and I$^{\mathrm{-}})$ makes the solution condition near the ODA monolayer/water interface more acidic so that ODA molecules in the monolayer are more positively charged, which works to align the water dipoles at the interface. [Preview Abstract] |
Thursday, March 17, 2016 1:39PM - 1:51PM |
S47.00013: Single Molecule Mechanochemistry Shaowei Li, Yanxing Zhang, Wilson Ho, Ruqian Wu Mechanical forces can be used to trigger chemical reactions through bending and stretching of chemical bonds. Using the reciprocating movement of the tip of a scanning tunneling microscope (STM), mechanical energy can be provided to a single molecule sandwiched between the tip and substrate. When the mechanical pulse center was moved to the outer ring feature of a CO molecule, the reaction rate was significantly increased compared with bare Cu surface and over Au atoms. First, DFT calculations show that the presence of CO makes the Cu cavity more attractive toward H$_{\mathrm{2}}$ Second, H$_{\mathrm{2}}$ prefers the horizontal adsorption geometry in the Cu-Cu and Au-Cu cavities and no hybridization occurs between the antibonding states of H$_{\mathrm{2}}$ and states of Cu atoms. While H$_{\mathrm{2}}$ loses electrons from its bonding state in all three cavities, the filling of its anti-bonding state only occurs in the CO-Cu cavity. Both make the CO-Cu cavity much more effectively to chop the H$_{\mathrm{2}}$ molecule. [Preview Abstract] |
Thursday, March 17, 2016 1:51PM - 2:03PM |
S47.00014: Charge-patterning phase transition on a surface lattice of titratable sites adjacent to an electrolyte solution Joel Shore, George Thurston We discuss a model for a charge-patterning phase transition on a two-dimensional square lattice of titratable sites, here regarded as protonation sites, placed on a square lattice in a dielectric medium just below the planar interface between this medium and an aqueous salt solution. Within Debye-Huckel theory, the analytical form of the electrostatic repulsion between protonated sites exhibits an approximate inverse cubic power-law decrease beyond short distances. The problem can thus be mapped onto the two-dimensional antiferromagnetic Ising model with this longer-range interaction, which we study with Monte Carlo simulations. As we increase pH, the occupation probability of a site decreases from 1 at low pH to 0 at high pH. For sufficiently-strong interaction strengths, a phase transition occurs as the occupation probability of 1/2 is approached: the charges arrange themselves into a checkerboard pattern. This ordered phase persists over a range of pH until a transition occurs back to a disordered state. This state is the analogue of the Neel state in the antiferromagnetic Ising spin model. More complicated ordered phases are expected for sufficiently strong interactions (with occupation probabilities of 1/4 and 3/4) and if the lattice is triangular rather than square. [Preview Abstract] |
Thursday, March 17, 2016 2:03PM - 2:15PM |
S47.00015: Understanding the electronic band structure of Pt-alloys for surface reactivity Jongkeun Jung, Beomyoung Kim, Ji Sook Hong, Tae Won Jin, Ji Hoon Shim, Slavomir Nemsak, Jonathan D. Denlinger, Arita Masashi, Shimada Kenya, Changyoung Kim, Bongjin Simon Mun In polymer exchange membrane fuel cell (PEMFC), the oxygen reduction reaction (ORR) at cathode side has been continuously investigated due to its critical importance in performance of fuel cell. So far, even with best industrial catalyst made with Pt, the performance of ORR is too far below from the commercial purpose. In 2007, Stamenkovic et al. showed that Pt alloys with 3-$d $transition metal exhibited significantly improved ORR performance and pointed out the altered electronic structure of surface as the major contributing factor for enhanced ORR. Since 1990, with the advance of DFT calculation, the trend of surface chemical reactivity is explained with the analysis of $d$-band structures, known as $d$-band model. While $d$-band provides valid insight on surface chemical reactivity based on the valence band DOS, the relation between surface work function and DOS has not been well understood. The element-specific local electronic band structure of Pt alloys are identified by ARPES measurement, and the correlation between surface work function and local charge density is investigated. [Preview Abstract] |
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