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Paper based thermoresistive sensors are fabricated by rubbing WS2 powder against a piece of standard copier paper, like the way a pencil is used to write on paper. The abrasion between the layered material and the rough paper surface erodes the material, breaking the weak van der Waals interlayer bonds, yielding a film of interconnected platelets. The resistance of WS2 presents a strong temperature dependence, as expected for a semiconductor material in which charge transport is due to thermally activated carriers. This strong temperature dependence makes the paper supported WS2 devices extremely sensitive to small changes in temperature. This exquisite thermal sensitivity, and their fast response times to sudden temperature changes, is exploited thereby demonstrating the usability of a WS2-on-paper thermal sensor in a respiration monitoring device., 6 main text figures, 1 table, 6 supp. info. figures

We fabricate paper-supported semiconducting devices by rubbing a layered molybdenum disulfide (MoS2) crystal onto a piece of paper, similarly to the action of drawing/writing with a pencil on paper. We show that the abrasion between the MoS2 crystal and the paper substrate efficiently exfoliates the crystals, breaking the weak van der Waals interlayer bonds and leading to the deposition of a film of interconnected MoS2 platelets. Employing this simple method, that can be easily extended to other 2D materials, we fabricate MoS2-on-paper broadband photodectectors with spectral sensitivity from the ultraviolet (UV) to the near-infrared (NIR). We also used these paper-based photodetectors to acquire pictures of objects by mounting the photodetectors in a homebuilt single-pixel camera setup., Comment: 6 main text figures + 4 Supp Info figures

Metal oxide nanostructures of TiO2, ZnO, Fe2O3/Fe3O4, Bi2O3, CeO2, ITO, SiO2, MoO2, and WO3 have shown great potential for applications in various fields such as piezoelectric, magnetic, gas sensors, and dye sensitized solar cells due to their unique optical, electronic, conductivity, catalytic and antimicrobial properties. However, recovery and reuse of these nanostructures pose big threats from cost and environmental perspectives. Thus, various substrates have been employed for incorporating or immobilizing them but finding suitable substrate is still a big challenge. Paper, being a natural biopolymer, has been used recently to incorporate/immobilize various metal oxide nanostructures. The metal oxide nanostructures are normally adhered to the cellulose matrices through weak interactions such as van der Waals force and hence, usually have retention related issues. This was circumvented to a great extent by using suitable linkers, binders, or retention aids for the incorporation/immobilization of the nanostructures in paper matrices. Although these reagents improve retention, as well as some of the properties, they ultimately add cost to the final product. Additionally, these retention aids and linkers hinder accessibility of active surface sites of metal oxide nanostructures for their various applications. Very recently our group developed an in situ single step hydrothermal method to immobilize metal oxide nanostructures such as TiO2, ZnO, and Bi2O3 without using any binder, linker or retention aid. In this review a comprehensive account of the development of methodology for incorporation/immobilization of metal oxide nanostructures is discussed. Furthermore, how the immobilization of nanostructures evolved without using any binder, linker or retention aid is thoroughly discussed based on the chemistry of the cellulose and metal oxides. Applications of nanostructure immobilized paper matrices are highlighted and critical challenges are discussed along with directions for future research.

Self-supporting carbon nanotube (CNT) Bucky-Papers have unique structural and surface properties which can be utilised in many applications. In this work we characterised pure self-supporting CNT membranes, where CNTs were held together only by Van der Waals forces, and evaluated their potential and performance in direct contact membrane distillation. The membranes were found to be highly hydrophobic (contact angle of 113°), highly porous (90%), and to exhibit a thermal conductivity of 2.7 kW/m2 h. We demonstrate, as a proof of concept, that self-supporting CNT Bucky-Paper membranes can be used for desalination in a direct contact membrane distillation setup with 99% salt rejection and a flux rate of 12 kg/m2 h at a water vapour partial pressure difference of 22.7 kPa. Ageing of the membranes by delamination is a main factor limiting their performance and work is currently under way to address this issue by investigating composite material structures.

This article reviews Advances in Thermodynamics of the van der Waals Fluid. by David C. Johnston 118 pp. , 2014. Price: $50 (paper). ISBN 978-1-627-05531-4.

N‐Heteropolycycles are among the most promising candidates for applications in organic devices. For this purpose, a profound understanding of the low‐energy electronic absorbance and emission characteristics is of crucial importance. Herein, we report high‐resolution absorbance and fluorescence spectra of pentacene (PEN) and 6,13‐diazapentacene (DAP) in solid neon obtained using the matrix‐isolation technique. Accompanying DFT calculations allow the assignment of specific vibrationally resolved signals to corresponding modes. Furthermore, we present for the first time evidence for the formation of van der Waals dimers of both substances. These dimers exhibit significantly different optical characteristics resulting from the change of electronic properties evoked by the incorporation of sp2 nitrogen into the molecular backbone., High‐resolution and fluorescence spectra of pentacene and 6,13‐diazapentacene isolated in solid neon are presented. In alliance with quantum‐chemical calculations, the spectra give valuable information about the monomeric compounds. In addition, the matrix‐isolation technique was used to generate weakly bound dimers which were spectroscopically studied for the first time, providing information about the electronic coupling therein.

Field effect transistors (FETs) based on 2D materials are of great interest for applications in ultrathin electronic and sensing devices. Here we demonstrate the possibility to add optical switchability to graphene FETs (GFET) by functionalizing the graphene channel with optically switchable azobenzene molecules. The azobenzene molecules were incorporated to the GFET channel by building a van der Waals heterostructure with a carbon nanomembrane (CNM), which is used as a molecular interposer to attach the azobenzene molecules. Under exposure with 365 nm and 455 nm light, azobenzene molecules transition between cis and trans molecular conformations, respectively, resulting in a switching of the molecular dipole moment. Thus, the effective electric field acting on the GFET channel is tuned by optical stimulation and the carrier density is modulated., Optically switchable graphene FET: Via van der Waals assembly of an approximately 1 nm thick azobenzene functionalized molecular nanosheets with single layer graphene, optically responsive field‐effect transistors are demonstrated. The electrical carrier density of these devices can be modulated using optical stimuli, 365 nm and 455 nm light.

Recently, combinations of 2D van der Waals (2D vdW) materials and organic materials have attracted attention because they facilitate the formation of various heterojunctions with excellent interface quality owing to the absence of dangling bonds on their surface. In this work, a double negative differential resistance (D‐NDR) characteristic of a hybrid 2D vdW/organic tunneling device consisting of a hafnium disulfide/pentacene heterojunction and a 3D pentacene resistor is reported. This D‐NDR phenomenon is achieved by precisely controlling an NDR peak voltage with the pentacene resistor and then integrating two distinct NDR devices in parallel. Then, the operation of a controllable‐gain amplifier configured with the D‐NDR device and an n‐channel transistor is demonstrated using the Cadence Spectre simulation platform. The proposed D‐NDR device technology based on a hybrid 2D vdW/organic heterostructure provides a scientific foundation for various circuit applications that require the NDR phenomenon., In this work, a double negative differential resistance (D‐NDR) characteristic of a hybrid 2D van der Waals (2D vdW)/organic tunneling device consisting of a hafnium disulfide/pentacene heterojunction and a 3D pentacene resistor is reported. Then the operation of a controllable‐gain amplifier configured with the D‐NDR device and an n‐channel transistor is demonstrated using the Cadence Spectre simulation platform.

The characteristics of interaction between six transition-metal porphyrines and the Ag(111) surface are detailed here as resulted from DFT calculations. Van der Waals interactions as well as the strong correlation in 3d orbitals of transition metals were taken into account in all calculations, including the structural relaxation. For each system we investigate four relative positions of the metallic atom on top the surface. We show that the interaction between the transition metal and silver is the result of a combination between the dispersion interaction, charge transfer and weak chemical interaction. The detailed analysis of the physical properties, such as dipolar and magnetic moments and the molecule–surface charge transfer, analyzed for different geometric configurations allows us to propose qualitative models, relevant for the understanding of the self-assembly processes and related phenomena.

Under ambient conditions, surfaces are rapidly modified and contaminated by absorbance of molecules and a variety of nanoparticles that drastically change their chemical and physical properties. The atomic force microscope tip–sample system can be considered a model system for investigating a variety of nanoscale phenomena. In the present work we use atomic force microscopy to directly image nanoscale contamination on surfaces, and to characterize this contamination by using multidimensional spectroscopy techniques. By acquisition of spectroscopy data as a function of tip–sample voltage and tip–sample distance, we are able to determine the contact potential, the Hamaker constant and the effective thickness of the dielectric layer within the tip–sample system. All these properties depend strongly on the contamination within the tip–sample system. We propose to access the state of contamination of real surfaces under ambient conditions using advanced atomic force microscopy techniques.

The chemistry of organic adsorbates on surfaces is often discussed in terms of Pauli repulsion as limiting factor regarding the packing of molecules. Here we show that the attractive part of the van der Waals potential can be similarly decisive. For the semiconductor surface Si(001), an already covalently bonded molecule of cyclooctyne steers a second incoming molecule via dispersion interactions onto the neighbouring adsorption site. This helps in understanding the nonstatistical pattern formation for this surface–adsorbate system and hints toward an inclusion of dispersion attraction as another determining factor for surface adsorption.

Among the various flow assurance problems that the petroleum industry faces, the deposition of paraffin waxes on to the wall of the pipeline is the most challenging. The challenge arises when the crude oil temperature decreases below the wax appearance temperature (WAT) which leads to the wax crystal in the crude oil to crystallize. An efficient method in remedying paraffin wax deposition is the utilization of chemical inhibitors. However, currently used chemical inhibitors are costly and environmentally harmful if a spillage occurs. Therefore, the use of biodegradable or environmently friendly inhibitors as potential chemical inhibitors are being studied by various researchers. This study investigated oleic acid, poly (ethylene-co-vinyl acetate) (EVA) and triethanolamine (TEA) as inhibitors that perform based on the van der Waals intermolecular interaction between the main wax component molecule eicosane C20H42 using the molecular dynamics simulation (MD) procedure via Material Studio 8.0 software package. In order to analyse the desired structural property which is the Radial Distribution Function (RDF), COMPASS force field was used. The RDF and g(r) function portrayed the functional atoms which aid in inhibiting the agglomeration and crystallization of the wax crystal formation. The presence of a carbonyl oxygen in oleic acid plays a vital role to inhibit the wax formation through the van der Waals interaction between active hydrogen atoms in eicosane molecule. Therefore, the chances of wax inhibition in eicosane is higher by introducing oleic acid as an inhibitor as compared to EVA and TEA. The results were then validated experimentally utilizing a cold finger technique under static condition.

A highly periodic electrostatic potential, even though established in van der Waals bonded organic crystals, is essential for the realization of a coherent band electron system. While impurity doping is an effective chemical operation that can precisely tune the energy of an electronic system, it always faces an unavoidable difficulty in molecular crystals because the introduction of a relatively high density of dopants inevitably destroys the highly ordered molecular framework. In striking contrast, a versatile strategy is presented to create coherent 2D electronic carriers at the surface of organic semiconductor crystals with their precise molecular structures preserved perfectly. The formation of an assembly of redox‐active molecular dopants via a simple one‐shot solution process on a molecularly flat crystalline surface allows efficient chemical doping and results in a relatively high carrier density of 1013 cm−2 at room temperature. Structural and magnetotransport analyses comprehensively reveal that excellent carrier transport and piezoresistive effects can be obtained that are similar to those in bulk crystals., The surface of organic single crystals is chemically doped via a simple one‐shot solution process, and the resulting 2D electronic system with a high carrier density serves as a multi‐functional, conductive nanosheet.

Using molecular dynamics simulations, the adsorption and diffusion of doxorubicin drug molecules in boron nitride nanotubes are investigated. The interaction between doxorubicin and the nanotube is governed by van der Waals attraction. We find strong adsorption of doxorubicin to the wall for narrow nanotubes (radius of 9 Å). For larger radii (12 and 15 Å), the adsorption energy decreases, while the diffusion coefficient of doxorubicin increases. It does, however, not reach the values of pure water, as adsorption events still hinder the doxorubicin mobility. It is concluded that nanotubes wider than around 4 nm diameter can serve as efficient drug containers for targeted drug delivery of doxorubicin in cancer chemotherapy.

New insight into the nature of protein crystal lattices is proposed., Until recently, the occurrence of conformational entropy in protein crystal contacts was considered to be a very unlikely event. A study based on the most accurately refined protein structures demonstrated that side-chain conformational entropy and static disorder might be common in protein crystal lattices. The present investigation uses structures refined using ensemble refinement to show that although paradoxical, conformational entropy is likely to be the major factor in the emergence and integrity of the protein condensed phase. This study reveals that the role of shape entropy and local entropic forces expands beyond the onset of crystallization. For the first time, the complete pattern of intermolecular interactions by protein atoms in crystal lattices is presented, which shows that van der Waals interactions dominate in crystal formation.

Graphene produced by chemical vapor deposition (CVD) is a promising candidate for implementing graphene in a range of technologies. In most device configurations, one side of the graphene is supported by a solid substrate, wheras the other side is in contact with a medium of interest, such as a liquid or other two-dimensional material within a van der Waals stack. In such devices, graphene interacts on both faces via noncovalent interactions and therefore surface energies are key parameters for device fabrication and operation. In this work, we directly measured adhesive forces and surface energies of CVD-grown graphene in dry nitrogen, water, and sodium cholate using a modified surface force balance. For this, we fabricated large (∼1 cm(2)) and clean graphene-coated surfaces with smooth topography at both macro- and nanoscales. By bringing two such surfaces into contact and measuring the force required to separate them, we measured the surface energy of single-layer graphene in dry nitrogen to be 115 ± 4 mJ/m(2), which was similar to that of few-layer graphene (119 ± 3 mJ/m(2)). In water and sodium cholate, we measured interfacial energies of 83 ± 7 and 29 ± 6 mJ/m(2), respectively. Our work provides the first direct measurement of graphene surface energy and is expected to have an impact both on the development of graphene-based devices and contribute to the fundamental understanding of surface interactions.

A new, facile, low cost, environmentally safe process is demonstrated for the production of few layer graphene by liquid phase exfoliation of graphite using extracts of medicinal plants in water. Plant extracts possibly function as bio-surfactants by creating a barrier in the aggregation by adsorbing on to the exposed surfaces of the graphite, weakening the attraction between the layers created by the van der Waals forces and allowing the graphite to slowly exfoliate in the form of undamaged flakes.

We theoretically study the optical advantages of graphene on boron nitride for advanced materials. Firstly, the optical absorption properties of graphene and the boron nitride are investigated theoretically, respectively. It is found that there is a strong optical absorption in the visible and SW-NIR regions for graphene; while the optical absorption of boron nitride is in the deep-ultraviolet region. For the two layer complex of graphene on the boron nitride, theoretical calculations further reveal that the optical property of graphene in the visual region is almost not influenced by boron nitride. The three dimensional charge difference densities reveal the optical properties of electron–hole distribution on the optical excitation for the single layer graphene. The ground state interaction between the graphene and the boron nitride is mainly the van der Waals interactions via edge atoms between two layers. Furthermore, charge difference density reveals that there is no charge transfer between graphene and boron nitride in the visual region on electronic transitions. So, the optical properties of graphene are not influenced by boron nitride in the visible region, which reveals that the boron nitride is one of the best substrates for graphene-based nano-photonic devices.

Adhesive interactions of suspended graphene membranes were studied by using non-contact atomic force microscopy (AFM) with a sharp silicon tip. Circular graphene membranes were prepared by transferring large-area monolayer graphene onto a perforated substrate. The non-contact AFM imaging showed a fluctuation of the graphene membrane. The maximum deflection of a 2.7- μm-diameter membrane was about 26.8 nm. The dynamic deflection of the membrane is attributed to the van der Waals interactions between the graphene membrane and the silicon tip of the AFM, and the interaction force was estimated to be about 3.0 nN.

To better understand the effects of low-level fluorine in graphene-based sensors, first-principles density functional theory (DFT) with van der Waals dispersion interactions has been employed to investigate the structure and impact of fluorine defects on the electrical properties of single-layer graphene films. The results show that both graphite-2 H and graphene have zero band gaps. When fluorine bonds to a carbon atom, the carbon atom is pulled slightly above the graphene plane, creating what is referred to as a CF defect. The lowest-binding energy state is found to correspond to two CF defects on nearest neighbor sites, with one fluorine above the carbon plane and the other below the plane. Overall this has the effect of buckling the graphene. The results further show that the addition of fluorine to graphene leads to the formation of an energy band (BF) near the Fermi level, contributed mainly from the 2p orbitals of fluorine with a small contribution from the p orbitals of the carbon. Among the 11 binding configurations studied, our results show that only in two cases does the BF serve as a conduction band and open a band gap of 0.37 eV and 0.24 eV respectively. The binding energy decreases with decreasing fluorine concentration due to the interaction between neighboring fluorine atoms. The obtained results are useful for sensor development and nanoelectronics.

In this work, the effect of two organic polyamines (spermine and spermidine) on the fluorescence intensity and activity of bovine intestinal alkaline phosphatase (BIALP) are investigated. The interaction of BIALP with spermine and spermidine was studied in a diethanolamine buffer with 0.5 mM magnesium chloride (pH 9.8) and at two temperatures by using the fluorescence quenching method. Furthermore, the activity of enzyme was studied using UV–Vis spectrophotometry in a diethanolamine buffer with 0.5 mM magnesium chloride, at 37 °C, in the absence and presence of different concentrations of each polyamine (0–5 mM). It was demonstrated that both polyamines quenched the intrinsic fluorescence of BIALP by the static quenching process. Based on these results, the values of the binding site for both polyamines were close to each other and decreased by increasing the temperature. The calculated thermodynamic parameters (ΔH°

This is an Open Access article under the terms of the Creative Commons Attribution License., There has been much interest in the past two decades to produce experimental force profiles characteristic of the interaction between nanoscale objects or a nanoscale object and a plane. Arguably, the advent of the atomic force microscope AFM was instrumental in driving such efforts because, in principle, force profiles could be recovered directly. Nevertheless, it has taken years before techniques have developed enough as to recover the attractive part of the force with relatively low noise and without missing information on critical ranges, particularly under ambient conditions where capillary interactions are believed to dominate. Thus a systematic study of the different profiles that may arise in such situations is still lacking. Here we employ the surfaces of CaF2, on which nanoscale water films form, to report on the range and force profiles that might originate by dynamic capillary interactions occurring between an AFM tip and nanoscale water patches. Three types of force profiles were observed under ambient conditions. One in which the force decay resembles the well-known inverse-square law typical of van der Waals interactions during the first 0.5-1 nm of decay, a second one in which the force decays almost linearly, in relatively good agreement with capillary force predicted by the constant chemical potential approximation, and a third one in which the attractive force is almost constant, i.e., forms a plateau, up to 3-4 nm above the surface when the formation of a capillary neck dominates the tip-sample interaction., This work was supported by the Ministerio de Economía y Competitividad (MINECO), Spain, through project MAT2012-38319-C02-01. ICN2 acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295).

A single step facile approach for grafting of long alkyl chains in the basal plane of graphene oxide and simultaneous reduction of oxygen functionalities to restore the graphitic characteristics, is reported. Chemical and structural features of the synthesized dual-layer alkylated graphene are elucidated by infrared, 13C solid state nuclear magnetic resonance, X-ray diffraction, and high-resolution transmission electron microscopy analyses. The van der Waals interaction between the octadecyl chains grafted on graphene and the alkyl chains of lube oils provided long-term dispersion stability to the alkylated graphene. The 0.02 mg mL−1 alkylated graphene as an optimized concentration in the lube oil, decreased both friction and wear significantly under the sliding contacts between steel tribo-pairs. Micro-Raman results demonstrate the deposition of graphene nanosheets on the tribo-interfaces under the sheared contact, and reduced the friction and protects the surfaces against undesirable wear.

Composition-gradient multi-angle static light scattering (CG-MALS) is an emerging technique for the determination of intermolecular interactions via the second virial coefficient B22. With CG-MALS, detailed studies of the second virial coefficient can be carried out more accurately and effectively than with traditional methods. In addition, automated mixing, delivery and measurement enable high speed, continuous, fluctuation-free sample delivery and accurate results. Using CG-MALS we measure the second virial coefficient of bovine serum albumin (BSA) in aqueous solutions at various values of pH and ionic strength of a univalent salt (NaCl). The systematic variation of the second virial coefficient as a function of pH and NaCl strength reveals the net charge change and the isoelectric point of BSA under different solution conditions. The magnitude of the second virial coefficient decreases to 1.13 x 10(-5) ml*mol/g(2) near the isoelectric point of pH 4.6 and 25 mM NaCl. These results illuminate the role of fundamental long-range electrostatic and van der Waals forces in protein-protein interactions, specifically their dependence on pH and ionic strength.

The most stable sorption site of dimethyl ether on silicalite-1 is the sinusoidal channel. The configuration of guest molecules (linear or bent) plays an important role in determining where the stable sorption site is situated., The adsorption structures of dimethyl ether (DME) on silicalite-1 zeolite (MFI-type) are determined using single-crystal X-ray diffraction. The structure of low-loaded DME-silicalite-1 indicates that all DME molecules are located in the sinusoidal channel, which is the most stable sorption site based on the van der Waals interaction between DME and the framework. The configuration of guest molecules (linear or bent) plays an important role in determining where the stable sorption site is in the pore system of MFI-type zeolites. Bent molecules favor the sinusoidal channel, while linear molecules favor the straight channel. The contribution of DME–DME interactions is considerable in the high-loaded DME-silicalite-1 structure.

In recent years, various van der Waals (vdW) materials have been used in implementing high‐performance photodetectors with high photoresponsivity over a wide detection range. However, in most studies reported so far, photodetection in the infrared (IR) region has not been achieved successfully. Although several vdW materials with narrow bandgaps have been proposed for IR detection, the devices based on these materials exhibit notably low photoresponsivity under IR light illumination. Here, highly efficient near‐infrared (NIR) photodetection based on the interlayer optical transition phenomenon in a vdW heterojunction structure consisting of ReS2 and ReSe2 is demonstrated. In addition, by applying the gate‐control function to the two‐terminal vdW heterojunction photodetector, the photoresponsivity is enhanced to 3.64 × 105 A W−1 at λ = 980 nm and 1.58 × 105 A W−1 at λ = 1310 nm. Compared to the values reported for previous vdW photodetectors, these results are the highest levels of photoresponsivity in the NIR range. The study offers a novel device platform for achieving high‐performance IR photodetectors.

Noncovalently functionalized β-cyclodextrins (β-CDs)/graphene composite dispersions have been fabricated through layer-by-layer self-assembly. Scanning electron microscope and transmission electron microscopy characterization confirm that the β-CDs/graphene composites possess brick-like sandwich-type structure. X-ray diffraction results illustrate that β-CDs covering on the surface of graphene possess channel-type structures. Moreover, the obtained β-CDs/graphene composites exhibit good dispersibility in common polar solvents and could exist for several weeks. In particular, the composites could be dispersed well in water at concentrations up to 2 mg mL−1 and stably exist at pH values from 4 to 12. The facts indicate that there exist certain forces between graphene and β-CDs. In order to clarify the interaction between them, we adopt a molecular mechanics (MM) method to evaluate the driving force. According to MM simulations, van der Waals forces should be the driving force for the formation of the well-defined β-CDs/graphene composites, and hydrogen-bonding interaction between adjacent β-CD molecules is another driving force for the formation of this stable graphene dispersion, which is similar to that of the β-CDs/carbon nanotubes composite. But the binding energy of the β-CDs/graphene composite is larger than that of the latter, suggesting much stronger interaction between graphene and β-CD molecules due to the two-dimensional flat-structure of graphene offering more and efficient sites to interact with β-CD molecules compared to carbon nanotubes with large interfacial curvature. These theoretical data for the existence of these interactions are further confirmed by experimental results from Raman and thermogravimetric analysis-differential scanning calorimetry.

We report a new method for measuring vacuum pressures using Van der Waals (VDW) interactions between reduced graphene oxide (RGO) sheets. For this purpose, we utilized a reaction-based self-assembly process to fabricate various intercalated RGO (i-RGO) films, and monitored their electrical behavior with changing pressure and temperature. Pumping to remove gas from a vacuum chamber produced a decrease in the sheet resistance of i-RGO. With further pumping, distinctly different sheet resistance behaivors were observed depending on the measurement temperature. With increasing vacuum pressure, the resistance increased at 100 °C, whereas it decreased at 30 °C. Two types of VDW interactions are proposed to explain these features: a local VDW interaction between RGO sheets that resulted in V-shaped curves of sheet resistance with pressure changes and broad VDW interactions that occur between RGO sheets when the elastic force required to bend carbon clusters on an RGO sheet exceeds their vibrational energy at low temperatures. On the basis of the results, we propose that the resistance behavior of i-RGO as a function of vacuum pressure can be interpreted as the sum of the two different VDW interactions.

Two samples of triacylglycerols i.e., olive oil and triolein, and one sample of diacylglycerol were investigated. In the course of compression, the density of the samples was determined by measurements of the change of piston position in a pressure chamber and volume correction due to chamber expansion under pressure. The speed of sound was evaluated from the time of flight of an ultrasonic impulse between emitting and receiving transducers placed in the high pressure chamber. The adiabatic compressibility, the intermolecular free length, the molar volume, the van der Waals' constant b and the surface tension were evaluated from the density, the speed of sound and the average molecular mass. All tested liquids undergo a high-pressure phase transition. Discontinuities in the measured isotherms of the physicochemical parameters of the investigated oils indicate the presence of high-pressure phase transitions. Moreover the time dependent change of pressure at constant volume during the phase transition was measured. The fundamental difference in the molecular structure of these acylglycerols influences their behavior significantly under high pressure.

This study addresses the electrostatic and van der Waals interactions at the aqueous interface of large area CVD graphene, 1-3 layers thick on a silica support and assessed by Raman spectroscopy to have exclusive sp2 character. Ionic strength was found to substantially alter the interactions of silica microspheres with silica-supported graphene. Particles were nonadhesive at large Debye lengths but became irreversibly adherent at reduced Debye lengths about 2nm or less. This was demonstrated to be qualitatively parallel to the influence of ionic strength on silica-silica interactions. The observed ionic strength effects are best explained by negative charges in the vicinity, within a few nanometers, of the supported graphene. DLVO-based modeling of the silica-water-supported graphene interaction suggests that van der Waals interactions drive particle capture and that the surface potential at the supported graphene surface is at least -10 to -15mV (corresponding to a charge density of 0.02-0.06/nm2). This charge could result from ion adsorption or from charges on silica beneath the graphene. The conclusions are not substantially affected by inclusion of nanometer-scale interfacial roughness in the modeling.

Carbon nanomaterials can be applied to the manufacture of wood-based building materials in the solid state and paint/adhesives in the liquid state to reduce emissions of formaldehyde and volatile organic compounds (VOCs). Among carbon nanomaterials, graphite is a layered material consisting of one-atom-thick sheets of carbon. The carbon atoms are bonded covalently in a hexagonal arrangement within the layer and these layers are bonded to each other by weak van der Waals forces. The α-spacing between the carbon layers is 0.335 nm. Since the van der Waals forces are relatively weak, it is possible for a wide range of atoms, molecules and ions to intercalate between graphite layers to form the graphite intercalation compounds (GICs). Expandable graphite consisting of natural graphite flake intercalated with acid, can be expanded up to hundreds of times its initial volume at high temperature, resulting in separation of the graphene sheets at the nanoscopic level along the c axis of graphene layers. Because expanded graphite is a porous carbon material, it can be applied to building materials such as wood flooring and wood-based composite after surface treatment for multi-functional building materials. To support its application to building materials, we examined the adsorption performance of graphite using a thermal extractor (TE) and 20 L small chamber. In addition, we also conducted Fourier transform infrared spectroscopy (FT-IR) analysis to confirm the variation in accordance with the modification process of graphite.

Facile dry decoration of graphene oxide sheets with aerosol Ag nanocrystals synthesized from an arc plasma source has been demonstrated using an electrostatic force directed assembly technique at room temperature. The Ag nanocrystal-graphene oxide hybrid structure was characterized by transmission electron microscopy (TEM) and selected area diffraction. The ripening of Ag nanocrystals on a graphene oxide sheet was studied by consecutive TEM imaging of the same region on a sample after heating in Ar at elevated temperatures of 100 °C, 200 °C, and 300 °C. The average size of Ag nanocrystals increased and the number density decreased after the annealing process. In particular, migration and coalescence of Ag nanocrystals were observed at a temperature as low as 100 °C, suggesting a van der Waals interaction between the Ag nanocrystal and the graphene oxide sheet. The availability of affordable graphene-nanocrystal structures and their fundamental properties will open up new opportunities for nanoscience and nanotechnology and accelerate their applications.

The design and synthesis of 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine-2-thioaceto-(2-fluorobenzyl) hydrazone (TPTH), which self-assembled into supramolecular microfibers with blue organic light-emitting properties, is reported. This is the first occurrence of the molecular self-assembly of 1,2,4-triazolo[1,5-a]pyrimidine derivatives. Keywords: 1,2,4-Triazolo[1,5-a]pyrimidine; acetohydrazone; synthesis; self-assembly; supramolecular Introduction Recently, self-assembly of organic small molecules into supramolecules has attracted a great deal of attention [1]. These supramolecules always have three-dimensional fibrous network structures and might have potential applications in drug delivery, coatings, lithography, catalyst supporters, scaffolds for tissue engineering, the engineering of nanostructural materials and as self-supporting porous materials in the novel separation for macro-molecules, and so forth [2]. Although it is well known that the self-assembly processes is mediated by cooperative weak and noncovalent bonds, such as hydrogen bonds, ionic bonds, hydrophobic interactions, van der Waals interactions, and water-mediated hydrogen bonds, there is still no sufficient understanding about the general rules of the self-assembly mechanism [3-5]. Therefore, significant efforts have been devoted to identify novel system

Three kinds of molecular complexes based on tetrathiafulvalene (TTF) and dialkylviologens were prepared and their crystal structures elucidated. While TTF-dimethylviologen complex forms a mixed stack arrangement of donors and acceptors in its crystal structure, TTF donors aggregate with long alkyl groups by CH/π and/or van der Waals interactions in a couple of TTF-heptylviologen complexes. Keywords: Molecular complex; CT complex; TTF; viologen; crystal structure Introduction Considerable attention has recently been paid in the field of supramolecular and materials chemistry to the incorporation of electroactive components into supramolecular assemblies. Among them, the supramolecular and macrocyclic assemblies derived from redox-controllable TTF 1 and dialkyl-4,4’-bipyridinium dications (dialkylviologens) such as 2 , have evoked attention, not only as catenanes and rotaxanes, but also as molecular switche s and potential molecular el ectronics devices [1]. The assembly of such kinds of molecular complexes relies strongly upon non-covalent charge-transfer (CT) interactions between donors and acceptors [2]. Since a dialkylviolgen

Most Kunitz proteins like BPTI and α-dendrotoxin are stabilized by three disulfide bonds. The crystal structure shows how subtle repacking of non-covalent interactions may compensate for disulfide bond loss in a naturally occurring two-disulfide variant, conkunitzin-S1, the first discovered member of a new conotoxin family., Cone snails (Conus) are predatory marine mollusks that immobilize prey with venom containing 50–200 neurotoxic polypeptides. Most of these polypeptides are small disulfide-rich conotoxins that can be classified into families according to their respective ion-channel targets and patterns of cysteine–cysteine disulfides. Conkunitzin-S1, a potassium-channel pore-blocking toxin isolated from C. striatus venom, is a member of a newly defined conotoxin family with sequence homology to Kunitz-fold proteins such as α-dendrotoxin and bovine pancreatic trypsin inhibitor (BPTI). While conkunitzin-S1 and α-dendrotoxin are 42% identical in amino-acid sequence, conkunitzin-S1 has only four of the six cysteines normally found in Kunitz proteins. Here, the crystal structure of conkunitzin-S1 is reported. Conkunitzin-S1 adopts the canonical 310–β–β–α Kunitz fold complete with additional distinguishing structural features including two completely buried water molecules. The crystal structure, although completely consistent with previously reported NMR distance restraints, provides a greater degree of precision for atomic coordinates, especially for S atoms and buried solvent molecules. The region normally cross-linked by cysteines II and IV in other Kunitz proteins retains a network of hydrogen bonds and van der Waals interactions comparable to those found in α-dendrotoxin and BPTI. In conkunitzin-S1, glycine occupies the sequence position normally reserved for cysteine II and the special steric properties of glycine allow additional van der Waals contacts with the glutamine residue substituting for cysteine IV. Evolution has thus defrayed the cost of losing a disulfide bond by augmenting and optimizing weaker yet nonetheless effective non-covalent interactions.

A gas sensor is used to detect SF6 decomposed gases, which are related to insulation faults, to accurately assess the insulated status of electrical equipment. Graphene films (GrF) modified with Au nanoparticles are used as an adsorbent for the detection of H2S and SOF2, which are two characteristic products of SF6 decomposed gases. Sensing experiments are conducted at room temperature. Results demonstrate that Au‐modified GrF yields opposite responses to the tested gases and is thus considered a promising material for developing H2S‐ and SOF2‐selective sensors. The first‐principles approach is applied to simulate the interaction between the gases and Au‐modified GrF systems and to interpret experimental data. The observed opposite resistance responses can be attributed to the charge‐transfer differences related to the interfacial interaction between the gases and systems. The density of states and Mulliken population analysis results confirm the apparent charge transfer in Au‐modified GrF chemisorption, whereas the van der Waals effect dominates the pristine graphene adsorption systems. Calculation results can also explicate the significant SOF2 responses on Au‐modified GrF. This work is important in graphene modulation and device design for selective detection.

In the title compound, C19H19FN2O, the cyclooctene ring adopts a twisted boat–chair conformation. The dihedral angle between the plane of the fluorophenyl substituent and that of the pyridine ring is 76.39 (8)°. The F andortho-H atoms of the fluorobenzene ring are disordered, with occupancy factors of 0.226 (5) and 0.774 (5). In the crystal, no significant interactions are observed between the molecules beyond van der Waals contacts.

In the title compound, C14H11FO2, the dihedral angles beteen the central C3O ketone residue and the fluoro- and hydroxy-substituted benzene rings are 50.44 (9) and 12.63 (10)°, respectively. The planes of the benzene rings subtend a dihedral angle of 58.88 (9)° and an intramolecular O—H...O hydrogen bond closes anS(6) ring. No directional interactions beyond van der Waals packing contacts were identified in the crystal structure.

A carbohydrate-anion recognition system in nonpolar solvents is reported, in which complexes form at the B-faces of β-D-pyranosides with H1-, H3-, and H5-cis patterns similar to carbohydrate-π interactions. The complexation effect was evaluated for a range of carbohydrate structures; it resulted in either 1:1 carbohydrate-anion complexes, or 1:2 complex formation depending on the protection pattern of the carbohydrate. The interaction was also evaluated with different anions and solvents. In both cases it resulted in significant binding differences. The results indicate that complexation originates from van der Waals interactions or weak CH⋅⋅⋅A(-) hydrogen bonds between the binding partners and is related to electron-withdrawing groups of the carbohydrates as well as increased hydrogen-bond-accepting capability of the anions.

In the title compound, C22H16Br2O2, which has approximate non-crystallographic inversion symmetry, the dihedral angles between the central ring and the pendant rings are 89.1 (4) and 82.4 (3)°; the dihedral angle between the pendant rings is 12.1 (4)°. In the crystal, the packing is influenced by van der Waals forces and no aromatic π–π stacking is observed.

In the mononuclear title iridium(III) complex, [Ir(C4H 8)(C15H22BN6)(C3H 9P)], which is based on the [tris(3,5-dimethylpyrazol-1-yl) hydroborato]iridium moiety, Ir[TpMe2], the IrIII atom is coordinated by a chelating butane-1,4-diyl fragment and a trimethylphosphane ligand in a modestly distorted octahedral coordination environment formed by three facial N, two C and one P atom. The iridium-butane-1,4-diyl ring has an envelope conformation. This ring is disordered because alternately the second or the third C atom of the butane-1,4-diyl fragment function as an envelope flap atom (the occupancy ratio is 1:1). In the crystal, molecules are organized into densely packed columns extending along [101]. Coherence between the molecules is essentially based on van der Waals interactions.

In the mononuclear title compound, [Ni(CH(3)COO)(2)(C(6)H(6)N(2)O)(2)], the Ni(II) atom is coordinated by two pyridine-2-aldoxime (PaoH) ligands and two acetate groups, with cis coordination for the pairs of identical ligands. While each acetate group binds to the Ni(II) atom by one O atom, each PaoH chelates the Ni(II) atom through two N atoms. The O atom on PaoH is not deprotonated and does not participate in bonding to the Ni(II) atom. Thus, the Ni(II) atom exhibits an octa-hedral environment. Intra-molecular O-H⋯O hydrogen-bonding inter-actions and inter-molecular C-H⋯O hydrogen-bonding inter-actions are present in the structure. Adjacent mol-ecules pack along [100] through van der Waals forces.

In the title compound, [U(C17H13N2O2)2O2(CH3OH)]·CH3OH, the UVIion is coordinated by seven O atoms in a distorted pentagonal–bipyramidal geometry with two 3-methyl-1-phenyl-4-benzoyl-4,5-dihydro-1H-pyrazol-5-olate groups with two O atoms in a bidentate chelating coordination mode and by three O atoms, one of which is from a methanol ligand. The crystal packing can be described by alternating layers of complex molecules along theaaxis. The structure is stabilized by O—H...N and O—H...O hydrogen bonding and van der Waals interactions.

The title compound, C34H36Cl2O7, is a by-product from the reaction of 4-chlorobenzylzinc chloride with 3,4,5-trimethoxybenzaldehyde. In each of the two 1,2-diphenylethyl moieties, the two benzene rings are arranged in atransconformation and make Car—C—C—Cartorsion angles of 163.64 (19) and 174.43 (18)°. The crystal structure is stabilized by van der Waals interactions only.

In the title molecule, C22H24OSi, the Si—O—C angle is 139.79 (11)°, the O—C—C angles of the triphenylmethoxy group are in the range 106.13 (13)–109.22 (14)° and the O—Si—C angles of the trimethylsilyloxy group are in the range 103.08 (10)–113.53 (10)°. In the crystal, face-to-face π–π interactions are observed between the phenyl rings [centroid separation = 4.194 (1) Å, interplanar spacing = 3.474 Å and centroid shift = 2.35 Å]. The three phenyl groups of the triphenylmethyl substituent are mutually nearly perpendicular, with dihedral angles in the range 80.49 (8)–81.53 (8)°. There are only weak intermolecular van der Waals interactions in the crystal.

International audience; Calcium phosphate bone substitute materials can be loaded with active substances for in situ, targeted drug administration. In this study, porous -TCP pellets were investigated as an anti-inflammatory drug carrier. Porous -TCP pellets were impregnated with an ethanolic solution of ibuprofen. The effects of contact time and concentration of ibuprofen solution on drug adsorption were studied. The ibuprofen adsorption equilibrium time was found to be one hour. The adsorption isotherms fitted to the Freundlich model, suggesting that the interaction between ibuprofen and -TCP is weak. The physicochemical characterizations of loaded pellets confirmed that the reversible physisorption of ibuprofen on -TCP pellets is due to Van der Waals forces, and this property was associated with the 100% ibuprofen release.

In the title compound, C16H16ClN, the dihedral angle between the benzene rings is 24.61 (13)°. In the crystal, only van der Waals interactions occur between neighbouring molecules.

In comparison with the previous determination [Saussine, Mimoun, MitschlerFisher (1980 ▶). Nouv. J. Chim.4, 235-237] of the title compound, [V(2)(C(4)H(10)NO)(4)O(3)], the current study reports an improved precision of the derived geometric parameters, along with the deposition of all coordinates and displacement parameters. The two V(V) atoms are each surrounded by two deprotonated N,O-bidentate diethyl-hydroxy-laminate groups, and a terminal and a bridging oxide ligand, in a distorted octa-hedral coordination geometry. The crystal packing is accomplished by van der Waals inter-actions.