Photo-induced Contraction of Layered Materials

MRS Advances ◽  
2018 ◽  
Vol 3 (6-7) ◽  
pp. 333-338
Author(s):  
Hiroyuki Kumazoe ◽  
Aravind Krishnamoorthy ◽  
Lindsay Bassman ◽  
Fuyuki Shimojo ◽  
Rajiv K. Kalia ◽  
...  
Keyword(s):  
Van Der Waals ◽  
Optical Excitation ◽  
Layered Materials ◽  
Van Der Waals Interactions ◽  
Electronic Charge ◽  
Quantum Molecular Dynamics ◽  
Covalent Bonds ◽  
Coulombic Interactions ◽  
Hydrogen Bond Interactions ◽  
The Impact

ABSTRACTUltrafast atomic dynamics induced by electronic and optical excitation opens new possibilities for functionalization of two-dimensional and layered materials. Understanding the impact of perturbed valence band populations on both the strong covalent bonds and relatively weaker van der Waals interactions is important for these anisotropic systems. While the dynamics of strong covalent bonds has been explored both experimentally and theoretically, relatively fewer studies have focused on the impact of excitation on weak bonds like van der Waals and hydrogen-bond interactions. We perform non-adiabatic quantum molecular dynamics (NAQMD) simulations to study photo-induced dynamics in MoS2 bilayer. We observe photo-induced non-thermal contraction of the interlayer distance in the MoS2 bilayer within 100 femtoseconds after photoexcitation. We identify a large photo-induced redistribution of electronic charge density, whose Coulombic interactions could explain the observed inter-layer contraction.

scholarly journals Thermal stability of imidazolium-based ionic liquids

2016 ◽  
Vol 4 (1) ◽  
pp. 51-64 ◽  
Author(s):  
Léa Chancelier ◽  
Olivier Boyron ◽  
Thibaut Gutel ◽  
Catherine Santini
Keyword(s):  
Thermal Stability ◽  
Ionic Liquids ◽  
Hydrogen Bonds ◽  
Alkyl Chain ◽  
Alkyl Chain Length ◽  
Van Der Waals Interactions ◽  
Alkyl Chains ◽  
Coulombic Interactions ◽  
The Impact ◽  
Thermal Stability Of

This work highlights the factors tuning the thermal stability of imidazolium-based ionic liquids (IL) associated to bis(trifluoromethanesulfonyl)imide anion [NTf2]. The decomposition temperatures (Td) were evaluated by thermogravimetric analyses (TGA) with optimized parameters to obtain reproducible Td. The impact of the alkyl chain length and of the presence of functional groups and unsaturations on Td were evaluated. The thermal behaviour was governed by Van der Waals interactions between alkyl chains, and by inter and intra coulombic interactions such as hydrogen bonds.

Tuning Coulombic interactions to stabilize nematic and smectic ionic liquid crystal phases in mixtures of charged soft ellipsoids and spheres

Soft Matter ◽  
2017 ◽  
Vol 13 (30) ◽  
pp. 5204-5213 ◽  
Author(s):  
Giacomo Saielli ◽  
Tommaso Margola ◽  
Katsuhiko Satoh
Keyword(s):  
Ionic Liquid ◽  
Liquid Crystal ◽  
Nematic Phase ◽  
Van Der Waals ◽  
Van Der Waals Interactions ◽  
Coulombic Interactions ◽  
Crystal Phases ◽  
Liquid Crystal Phases

Ionic liquid crystal phases, including the elusive ionic nematic phase, can be stabilized with an appropriate balance of electrostatic vs. van der Waals interactions.

A Comparative Study of Un-Modified and Modified Acrylate-SiO2 Nanocomposites

MRS Advances ◽  
2017 ◽  
Vol 2 (49) ◽  
pp. 2737-2743
Author(s):  
Mireya L. Hernández-Vargas ◽  
Rubén Castillo-Perez ◽  
Oscar Hernández-Guerrero ◽  
Bernardo F. Campillo-Illanes ◽  
Osvaldo Flores-Cedillo
Keyword(s):  
Physical Properties ◽  
Van Der Waals ◽  
Chemical Properties ◽  
Class Ii ◽  
Decomposition Temperature ◽  
Van Der Waals Interactions ◽  
Class I ◽  
Covalent Bonds ◽  
Neat Polymer ◽  
Hybrid Compounds

ABSTRACTBased on the nature of the links and interactions existing at the hybrid interface, hybrid materials can be broadly classified in two main designations: a) Hybrid compounds Class I, that include all systems with electrostatic forces, hydrogen bonding or Van der Waals interactions and b) Hybrid compounds Class II, showing that the inorganic and organic components are linked through strong covalent or ionic-covalent bonds. The physico–chemical properties of nanostructured copolymer acrylates based on butyl acrylate (BA), methyl methacrylate (MMA) and acrylic acid (AA) has been investigated employing un-modified SiO2 (Class I) and modified SiO2 particles (Class II) using 3-(trimethoxysilyl) propyl methacrylate (MPS) as compatibilizing agent. The synthesis was carried out using seeded batch emulsion polymerization system. Metastable nanostructured emulsions containing 1 wt% nanoparticles were obtained. Films casted from the in-situ nanostructured latex exhibited excellent optical transparency suggesting good nanoparticles dispersion. However, the mechanical properties showed by SiO2-MPS nanocomposite, are better than the Class I hybrid compounds. Therefore, SiO2-MPS surface treatment prior to polymerization enhances the physical properties of copolymer BA-MMA-AA film. The mass loss derivative traces for the polyacrylic nanocomposites and the neat polymer obtained by thermogravimetric analysis showed that the onset temperature for thermal decomposition was shifted towards a higher temperature than the neat polyacrylic, indicating the enhancement of thermal stability of the un-modified SiO2 nanocomposite. However, there is a decrease of 40°C in the decomposition temperature for the modified polyacrylic nanocomposite. The results obtained so far have shown that weak Van der Waals and H-bonding interactions may be sufficient to enable improvement of the physical properties of the acrylate nanocomposites.

scholarly journals Highly Sensitive CO Gas Sensor from Defective Graphene: Role of van der Waals Interactions

2015 ◽  
Vol 2015 ◽  
pp. 1-7 ◽  
Author(s):  
Yingda Jiang ◽  
Sha Yang ◽  
Shuang Li ◽  
Wei Liu ◽  
Yonghao Zhao
Keyword(s):  
Gas Sensor ◽  
Density Functional ◽  
Van Der Waals ◽  
Density Functional Theory Calculations ◽  
Layered Materials ◽  
Van Der Waals Interactions ◽  
Graphene Layers ◽  
Co Gas Sensor ◽  
Defective Graphene ◽  
Co Gas

Layered materials, such as graphene, have attracted increasing interests since they can be extensively used in gas sensors, spintronic devices, and transparent electrodes. Although larger size of graphene sheets has been fabricated, in reality, the existence of the defects in layered materials is almost inevitable during the manufacturing process. Here, we performed the state-of-the-art density-functional theory calculations to study the interactions between CO molecule and the pristine and defective graphene layers, with the aim of designing a CO gas sensor with higher sensitivity. The van der Waals interactions predominate the binding between the CO gas and the sensor, and also significantly enhance the stability of the system. The defective graphene strongly interacts with CO, and thus enhances the sensitivity of the graphene and further tunes the electronic and magnetic properties of the entire system. Our computed results clearly demonstrate that the defective graphene could be a good sensor for gas molecules.

Toward a Reliable Description of the Lattice Vibrations in Organic Molecular Crystals: The Impact of van der Waals Interactions

2018 ◽  
Vol 14 (8) ◽  
pp. 4380-4390 ◽  
Author(s):  
Natalia Bedoya-Martínez ◽  
Andrea Giunchi ◽  
Tommaso Salzillo ◽  
Elisabetta Venuti ◽  
Raffaele Guido Della Valle ◽  
...  
Keyword(s):  
Van Der Waals ◽  
Molecular Crystals ◽  
Van Der Waals Interactions ◽  
Lattice Vibrations ◽  
Organic Molecular Crystals ◽  
The Impact

Ultralow cross-plane lattice thermal conductivity caused by Bi–O/Bi–O interfaces in natural superlattice-like single crystals

CrystEngComm ◽  
2019 ◽  
Vol 21 (41) ◽  
pp. 6261-6268
Author(s):  
Chen Di ◽  
Jia-Hui Pan ◽  
Song-Tao Dong ◽  
Yang-Yang Lv ◽  
Xue-Jun Yan ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Single Crystals ◽  
Lattice Thermal Conductivity ◽  
Van Der Waals ◽  
Van Der Waals Interactions ◽  
Plane Lattice ◽  
Natural Superlattice ◽  
The Impact

Revealing the impact of Bi–O/Bi–O interfaces with van der Waals interactions on the formation of ultralow cross-plane lattice thermal conductivity.

Charge Density Study of 2-Pyridone

1998 ◽  
Vol 54 (6) ◽  
pp. 912-920 ◽  
Author(s):  
H. W. Yang ◽  
B. M. Craven
Keyword(s):  
Charge Density ◽  
Critical Points ◽  
Van Der Waals ◽  
Van Der Waals Interactions ◽  
Electronic Charge ◽  
Charge Density Distribution ◽  
Electronic Charge Density ◽  
Molecular Dipole ◽  
X Ray ◽  
Density Study

The crystal structure of 2-pyridone has been redetermined from high-resolution X-ray data collected at 123 K. The molecule is in the lactam form. Bond lengths (corrected for rigid-body libration) and angles have been determined with s.u.'s of 0.001 Å and 0.1°, respectively. The hydrogen-bonded cyclic dimers which occur in the vapor and in solution are absent in the crystal where molecules are linked by N—H...O hydrogen bonds to form puckered chains. There also appears to be a weaker C—H...O interaction (H...O, 2.57 Å) and weak C—H...π or van der Waals interactions occurring on both sides of the pyridone ring. Following a refinement of the structure assuming Stewart's rigid pseudo-atom model, the electronic charge density distribution in the crystal and its Laplacian have been calculated for atoms at rest. The total electrostatic potential has been mapped for an isolated molecule and the molecular dipole moment has been determined [8.8 (19)  D; 1D ≃ 3.33564 × 10−30 C m]. Critical points in the electron density have been located for the bonds within the molecule and for the molecular interactions cited above. For the C—H...π interactions, only the spherical components of the valence density for the pyridone ring atoms contribute effectively at the critical points. Hence, these may be better described as van der Waals interactions.

MANY-ATOM VAN DER WAALS INTERACTIONS LEAD TO DIRECTION-SENSITIVE INTERACTIONS OF COVALENT BONDS

2008 ◽  
Vol 06 (04) ◽  
pp. 693-707 ◽  
Author(s):  
ALEXEI V. FINKELSTEIN ◽  
MICHAEL Y. LOBANOV ◽  
NIKITA V. DOVIDCHENKO ◽  
NATALIA S. BOGATYREVA
Keyword(s):  
Physical Theory ◽  
Van Der Waals ◽  
Protein Structures ◽  
Covalent Bond ◽  
Covalent Bonding ◽  
Van Der Waals Interactions ◽  
Binding Affinities ◽  
Dispersion Interactions ◽  
Energy Effect ◽  
Covalent Bonds

Strict physical theory and numerical calculations show that a specific coupling of many-atom van der Waals interactions with covalent bonding can significantly (half as much) increase the strength of attractive dispersion interactions when the direction of interaction coincides with the direction of the covalent bond, and decrease this strength when the direction of interaction is perpendicular to the direction of the covalent bond. The energy effect is comparable to that caused by the replacement of atoms (e.g. N by C or O ) in conventional pairwise van der Waals interactions. Analysis of protein structures shows that they bear an imprint of this effect. This means that many-atom van der Waals interactions cannot be ignored in refinement of protein structures, in simulations of their folding, and in prediction of their binding affinities.

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