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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

Thermochemical heat storage materials for space heating applications such as, ZnSO4 offer high energy storage density, low cost and clean mean of long-term solar energy storage. Herein, we studied the ZnSO4 hydrated salt as potential heat storage material at low temperature and furthermore observed the impact of temperature and concentration on the dehydration/hydration process and enthalpy. The thermal behavior of ZnSO4•7H2O was investigated by applying various dehydration temperatures. The results showed that 85% of water loosed at 100 °C temperature, which released 699 J/g (1.37 GJ/m3) in the dehydration process. The hydration process of ZnSO4.7H2O at 100 °C recovered 541 J/g enthalpies, which delivered 1.1 GJ/m3. Similarly, the dehydration result obtained at 150 °C was the same as showed at 100 °C. However, the enthalpy of hydration was 20% less than prior. The XRD result showed that at higher temperatures agglomeration appeared followed by Van der Waals forces which affect the hydration rate. The result of good cyclability and larger water sorption performance of ZnSO4 make them a promising and suitable for heat storage in space heating application, which can be used as thermochemical heat storage material for thermal storage devices.

The phenomenon of 'wet pick' during printing is well known to paper coating and printing technologists. Recent work has highlighted the reversible effect of water on the tensile strength of coating layers, and has shown that the mineral and vegetable oils commonly used in ink formulations have a similar, if smaller, detrimental effect on strength. In this study, we show that the coating strength decreases as the dielectric constant of the penetrating fluid increases. In the adhesive science literature, a similar correlation has been observed for various types of adhesive joints, and can be explained in terms of ion-pair bonding. We have tested this theory for mineral-based paper coatings containing latex adhesive, and found that it underestimates the loss of strength observed experimentally. In the latex–mineral bond, contributions from other mechanisms such as van der Waals forces are also likely. This knowledge should ultimately allow the design of more effective pigment–binder combinations better able ...

In the fields of smart materials there is still a demand for a material featuring high modulus, low density and large strain. Carbon materials catch enormous scientific attention not only since carbon fibers were used for highperformance composite structures. But more and more the scientific attention moves from the macroscale to the nanoscale. This paper focuses with a adaptive point of view on one of the carbon allotropes: carbon nanotubes (CNTs). Beside excellent electromechanical properties another interesting feature was first mentioned 1999 - the active behavior of paper-like mats (bucky-papers) made of CNTs. CNT-papers are electrically activated using a double-layer interaction of ions provided by an electrolyte and the charged, high specific surface area of the paper formed by carbon nanotubes. Until now the detailed mechanism behind the strain/force generation of CNT-based architectures is unknown. A clarification of this principle reveals the potential of carbon tubes to be or not to be a resilient smart material in order to use their strong covalent carbon bonds instead of weak van der Waals force as tube-linking. This paper presents further investigations about the composition of CNT-papers and their performance in contrast to vertical aligned CNT-arrays using an actuated tensile test set-up. For better comparison the experiments of both specimen-types are carried out in dry, wet and wet/charged conditions. Especially in the case of CNT-arrays it is essential to preload the specimens because the curly CNT-structure superimposes the vertical orientation. While the CNT-paper is tested in an aqueous solution of one molar sodium chloride, the hydrophobic character of CNT-arrays requires an ionic liquid (IL) as electrolyte. It is found that the mechanical properties of CNT-papers drop significantly by wetting and can be controlled by charging what indicates an electrostatic dominated effect. In contrast the CNT-arrays show identical results regardless of the test conditions and furthermore an active, reversible behavior of tube elongation by charging. These results indicate strongly a quantum mechanical effect as reason of a CNT-array actuation.

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.

We developed a facile method to transfer vertically aligned carbon nanotubes (VACNT) onto a carbon fiber paper (CFP) substrate using silicone as an adhesion layer. The resulting VACNT–CFP hybrid structure displays a very low interface resistance of 0.006 Ω as a result of the Van der Waals interaction at the VACNT–CFP interface. We demonstrated in this work that the VACNT–CFP can be used as a supercapacitor electrode with excellent rate performance and cycling stability, which could be attributed to the vertically alignment and chemical stability of CNTs in the hybrid structure. Further, we found that VACNT–CFP showed good resistance to the impact of flowing water when tested as a capacitive deionizer electrode, owing to superior mechanical robustness of the hybrid structure.

This paper focuses on the actuation mechanisms of CNT-papers and CNT-arrays. CNT-papers represent architectures of CNTs which are connected by van der Waals forces or structural entanglement. In contrast CNT-arrays are vertically aligned CNTs. Single CNTs are favored for investigation of the active behavior of the hexagonal carbon structure formed by covalent C-bonds. CNT-arrays feature contiuous tubes of 3 mm length which allows the test the tubes themselves. Thus they are clamped at each end they represent samples for testing covalent bonds. Both sample types are tested within an actuated tensile test set-up under different conditions to identify the specific influence. Furthermore different electrolytes are used to investigate the influence of the ion-radius on the CNT-paper. CNT-papers are tested in water-based electrolytes CNT-arrays are tested in an ionic liquid. It was found that the performance of CNT-papers strongly depends on the conditions which indicates ion-diffusion as actuation mechanism. However, CNT-arrays are almost unaffected by the conditions, considering their active response and sample composition quantum mechanical reasons seem to be the most appropriate explanation for the array actuation.

Self-supporting film of single-walled carbon nanotubes (SWNTs), also known as SWNT paper, is held together by Van der Waals force without any chemical binders. Prepared by vacuum filtration method, SWNT paper was then decorated wirh polypyrrole (PPy) through pulsed potentio amperometric polymerization. The results indicated that the SWNT paper had a typical network structure, after polymerizing PPy, cauliflower-like structure was observed on the surface of SWNT ropes. The composite thin film has good cyclic voltammetry (CV) property and the specific capacitance wass ca.420Fg-1, which was much larger than that of pure SWNT paper.

We fabricated large-scale anisotropic carbon nanotube (CNT) paper sheets by stacking long-lasting multiwalled CNT (MWCNT) webs without using binder materials. The MWCNTs are highly aligned in the webs and they retain their alignment in the fabricated paper. Although MWCNTs are just connected by van der Waals force, tensile strength is as strong as 75.6 MPa. In addition, resistivity and thermal conductivity is as good as 2.5 × 10−3 Ω cm and 70 W/m K, respectively. The present high anisotropy ratios of 7.3 in resistivity and of 8.1 in thermal conductivity are due to the high alignment of the ultra-long MWCNTs which have lengths of millimeters. High-speed web drawing with a draw speed of over 10 m/s enables very rapid fabrication. The material properties of CNT structures can be measured by conventional methods for macroscopic samples rather than methods designed for nanomaterials. CNT web technology will enable CNTs to be used in new applications.

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.

Supramolecular chemistry now has become a central part of the research activities. Basically, it mostly concerns molecular recognition and self aggregation by non-covalent weak intermolecular interactions, such as hydrogen bonding, .π-π. stacking, and van der Waals interactions. The computational applications on such large systems are limited for their structural complexity. Several examples of the computational approaches to understand molecular recognition and self-aggregation are discussed. Firstly, bifunctional (fluorescence and visible light absorption) anion sensing mechanism is supported by the DFT calculations. Secondly, an experimentally observed selective recognition of Cu2+ by an azobenzeneappended receptor, which can exhibit Cu2+ selectivity by color change, is discussed based on computational approach. Finally, the intermolecular interaction, which is useful for predicting the self-assembled structures, can be understood by replicating the monomer unit and manipulating the translation and rotation.

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.

Various functional materials, such as metal nanoparticles, carbon nanotubes and conducting polymers were coated on polymer microspheres finding various uses in electronic and biomedical applications. Herein, we demonstrate that single graphene oxide (GO) sheets could be easily wrapped on amine-functionalized poly(glycidyl methacrylate) (PGMA-ed) microspheres (∼2.5 μm in diameter) to form a PGMA-ed/GO core-shell structure with a thickness of ca. 50 nm. Subsequently, the synthesized GO-skin microspheres were consolidated by heating them to 60 °C to form a robust self-standing paper through the formation of electrostatic and van der Waals attractive forces between the very large surfaces of the GO, together with the formation of hydrogen bonding during the dewatering and drying processes, where the GO skins are interconnected to provide an electrical path and mechanical skeletal structure. When a stabilized GO dispersion was added to the PGMA-ed microspheres, the GO sheets were uniformly self-assembled on the PGMA-ed microsphere surfaces, seemingly through dipole–dipole interactions and amine–epoxide chemical reactions. This approach provides a simple route for the large volume production of PGMA-ed/GO core-shell microspheres and large-sized self-standing paper that may find various uses in optoelectronic device materials and porous membrane applications.

This paper is to correct a mistake in the authors' previous paper (Nakaoka et al., Progress in Computational Fluid Dynamics, 2008, 8(5), 270-275), which originated in the solution procedure of the population-balance (PB) equation.

This book should prove to be the definitive work explaining van der Waals forces, how to calculate them and take account of their impact under any circumstances and conditions. These weak intermolecular forces are of truly pervasive impact, and biologists, chemists, physicists and engineers will profit greatly from the thorough grounding in these fundamental forces that this book offers. Parsegian has organized his book at three successive levels of mathematical sophistication, to satisfy the needs and interests of readers at all levels of preparation. The Prelude and Level 1 are intended to give everyone an overview in words and pictures of the modern theory of van der Waals forces. Level 2 gives the formulae and a wide range of algorithms to let readers compute the van der Waals forces under virtually any physical or physiological conditions. Level 3 offers a rigorous basic formulation of the theory.

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.

The relative zone mobilities of several protonated amino acids and two peptides have been calculated from the diffusion coefficients of the zwitterionic forms of the compounds. Good agreement with observed values was obtained if it was assumed that the Van der Waals volume of protonated α-amino acids is increased by 33 A 3 by hydration.

In order to understand the degradation mechanism of thermal aging process of insulation paperboard from the microscopic level. In this paper, molecular simulation method was used to construct the cellulose model of insulation paperboard, and different temperatures were applied to study the change process of microscopic performance indicators. The results showed that the increase of temperature will lead to the increase of the mean square displacement of molecules, accelerate the movement of molecules, increase the internal kinetic energy and potential energy of molecules, and reduce the number of hydrogen bonds and other forms of non-bonding interaction energy such as van der Waals force, thereby leading to the instability of intermolecular chemical bonds and accelerating the decomposition of cellulose. Moreover, compared with pure cellulose, the mean square displacement of cellulose in oil is larger and the number of hydrogen bonds is less, which indicates that the increase of temperature in oil will make the molecular movement more intense and easier to crack. With the increase of temperature, the shear modulus and Young's modulus of cellulose model decrease, while the Cauchy pressure increases, which indicates that the increase of temperature will increase the ductility of insulating paper, but reduce its rigidity and weaken its deformation resistance. In this paper, the effect of temperature rise on the physical and chemical properties of pressboard is explained from the microscopic point of view.

The effects of various additives to the impregnation stage of the lumen-loading procedure have been studied. For all treatments considered, the lumen surface remained negatively charged. A high level of loading of well-bonded filler was found to be associated with conditions leading to a positive charge on the filler. A low level of loading of weakly-bonded filler was associated with a negative charge on the filler. The findings are in agreement with the bonding mechanism being a combination of electrostatic and van der Waals forces as described by the DLVO theory. For a series of titanium dioxide pigments, the electrostatic charge most favourable to lumen loading was found to be developed under distinctly acidic conditions with, for some fillers, the addition of an optimum amount of aluminum sulphate. Alkaline conditions and also the addition of an anionic dispersant were found to develop a more negative charge on the filler particles and so reduce lumen loading. High concentrations of electrolyte (sodium chloride) had a screening effect and thus reduced the effectiveness of any electrostatic forces whether these were attractive or repulsive in nature.

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.

The present study reports a comprehensive molecular dynamics simulation of the effect of a) temperature (300–1073 K at intervals of every 100 K) and b) point defect on the mechanical behaviour of single (armchair and zigzag direction) and bilayer layer graphene (AA and AB stacking). Adaptive intermolecular reactive bond order (AIREBO) potential function was used to describe the many-body short-range interatomic interactions for the single layer graphene sheet. Moreover, Lennard Jones model was considered for bilayer graphene to incorporate the van der Waals interactions among the interlayers of graphene. The effect of temperature on the strain energy of single layer and bilayer graphene was studied in order to understand the difference in mechanical behaviour of the two systems. The strength of the pristine single layer graphene was found to be higher as compared to bilayer AA stacked graphene at all temperatures. It was observed at 1073 K and in the presence of vacancy defect the strength for single layer armchair sheet falls by 30% and for bilayer armchair sheet by 33% as compared to the pristine sheets at 300 K. The AB stacked graphene sheet was found to have a two-step rupture process. The strength of pristine AB sheet was found to decrease by 22% on increase of temperature from 300 K to 1073 K.

The effect the solvent and transfer pressure of graphene oxide (SLGO) Langmuir–Blodgett films on the physicochemical properties of monolayers, and on their structural and optical properties, is studied. Examination of the physicochemical properties of SLGO monolayers on subphase surfaces that are formed from SLGO dispersions in different organic solvents reveals that monolayer behavior is virtually independent of the solvent. Electron microscope and optical studies show that the monolayers formed from SLGO dispersions in DMF and acetone have the highest transfer coefficients. It is concluded that the structural heterogeneity of the surfaces of graphene oxide films results from simultaneous effect of electrostatic interactions between graphene oxide particles and Van der Waals interactions with the solvation shell of the particles. Studies focusing on the effect the pressure of transferring a graphene oxide monolayer onto the surface of a solid substrate has on structural features of LB films show that films produced at low surface pressures have more homogeneous structures.

Making full use of the unique properties of graphene has required a new route for its scalable production. Here we demonstrate a green and fast approach for preparing high-quality few-layer graphene sheets (GS) based on a microwave irradiation method. This method takes advantage of solvent-free microwaves directly and violently exfoliates pristine graphite into GS by using ammonium bicarbonate (NH4HCO3) as a peeling media. In the microwave heating process, the decomposition of NH4HCO3 into H2O steam, CO2, and NH3 can generate strong pressure that exceeds the van der Waals force between the sheet layers of graphite, achieving effective peeling off of the sheets to very large graphene with fewer defects.

In this work, we report transistors made of van der Waals materials on a mesoporous paper with a smooth nanoscale surface. The aqueous transistor has a novel planar structure with source, drain, and gate electrodes on the same surface of the paper, while the mesoporous paper is used as an electrolyte reservoir. These transistors are enabled by an all-cellulose paper with nanofibrillated cellulose (NFC) on the top surface that leads to an excellent surface smoothness, while the rest of the microsized cellulose fibers can absorb electrolyte effectively. Based on two-dimensional van der Waals materials, including MoS2 and graphene, we demonstrate high-performance transistors with a large on-off ratio and low subthreshold swing. Such planar transistors with absorbed electrolyte gating can be used as sensors integrated with other components to form paper microfluidic systems. This study is significant for future paper-based electronics and biosensors.

Graphene has led researchers to explore it due to its unprecedented physical and chemical properties. It is found that graphene, as an allotrope of carbon nanotubes, could be used to replace carbon nanotubes in the composites. It can not only enhance the composites smart features such as conductivity, electromagnetic shielding, etc, but also improves the physical properties of the composites. However, the hydrophobic property and strong van der Waals force between the layers block the uniform dispersion of graphene and keep it agglomeration in solution. The study on graphene dispersion in liquid plays an important role in its application in composite materials. Based on the existing research results, this paper reviews the methods what has been used in graphene dispersion, such as sonication, mechanical stirring, covalent modification, non-covalent modification, etc. We also give an analysis on how to obtain a stable graphene suspension in high concentration. We hope this review paper will point a rational direction for high-quality preparation of graphene suspension.

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.

In this work, we introduced a facile approach for preparing hollow graphene oxide spheres (HGOSs). By electrostatic self-assembly polystyrene (PS)/graphene oxide (GO), core/shell microspheres were synthesized. After removal of the sacrificial PS colloidal spheres by toluene solution treatment, HGOSs were prepared successfully. Based on the DLVO theory, van der Waals force and electric double layer repulsion were proposed to quantitatively analyze the self-assembly of the composite structure. The theoretical formulation for the resultant interaction force F versus separation between the surfaces d showed a significant low energy barrier for the aggregation of the GO and PS, which predicted the favorable HGOSs formation.

The van der Waals (vdW) force dominated interface between graphene and polymer matrix creates weak points in the mechanical sense. Chemical functionalization was expected to be an effective approach in transfer of the outstanding performance of graphene across multiple length scales up to the macroscopic level, due to possible improvements in the interfacial adhesion. However, published works showed the contradiction that improvements, insensitivity, or even worsening of macro-mechanical performance have all been reported in graphene-based polymer nanocomposites. Particularly central cause of such discrepancy is the variations in graphene/polymer interfacial chemistry, which is critical in nanocomposites with vast interfacial area. Herein, O3/H2O gaseous mixture was utilized to oxidize monolayer graphene sheet with controlled functionalization degrees. Hydrogen bonds (H bonds) are expected to form between oxidized graphene sheet/poly(methyl methacrylate) (PMMA) at the interface. On the basis of in situ tensile-micro Raman spectroscopy, the impacts of bonding types (vdW and H-bonds) on both key interfacial parameters (such as interfacial shear strength and critical length) and failure modes of graphene/PMMA nanocomposite were clarified for the first time at the microscopic level. Our results show that owing to improved interfacial interaction via H bonds, the interface tends to be stiffening and strengthening. Moreover, the mechanical properties of the functionalized graphene/PMMA interface will be set by the competition between the enhanced interfacial adhesion and the degraded elastic modulus of graphene, which was caused by structural defects in the graphene sheet during the functionalization process and could lead to catastrophic failure of graphene sheets in our experimental observation. Our results will be helpful to design various nanofiller-based nanocomposites with high mechanical performance.

Colloid stability is determined by the interaction between particles during a (Brownian) encounter. The forces playing a role in encounters (van der Waals forces, double-layer interaction, interaction between adsorbed molecules, such as surfactants, polymers and small molecules) are discussed with emphasis on unsolved problems. It is pointed out in which of the papers of this Discussion the different problems are treated.

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.

Precise doping of graphene at nanoscale resolution is vital for a number of applications in nanoelectronics and sustainable energy. Although large metallic contacts are presumed to move the Fermi level of graphene above or below the Dirac point, little has been done to study these effects when graphene is in contact with nanoscale metallic objects of specific sizes and concentrations and to investigate if such phenomena are associated with some forms of doping as in conventional semiconductors. As a case study we determine here the local effect of copper nanoparticles (Cu-NPs) on the Fermi energy of graphene domains in large-area graphene thin films. Tight-binding calculations corroborate our Kelvin-probe force microscopy experiments indicating that the Fermi level shifts in the presence of Cu-NPs (corresponding to 0.2 eV at 20% graphene area coverage by Cu) which break the electron-hole symmetry of graphene due to its weak Van der Waals interactions with Cu even in the absence of chemical bonding and charge transfer, in contrast to previous predictions for large and flat metallic contacts.

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).

When the width of a graphene nanoribbon (GNR) is only a few nanometers, it possesses semiconducting properties that enable various high-end electronic applications. In this study, we report that the dense and stable dispersion of a natural graphite formed using flavin mononucleotide (FMN) as a surfactant produces GNRs as small as 10 nm in width. High-resolution transmission electron microscopy reveals GNRs with various widths, along with a graphene flake containing straight-edged GNRs and cuts, depending on substrate treatments. Such nanoribbon formation originates from sonochemical graphene unzipping with a one-dimensional FMN supramolecular ribbon as a template. Raman spectroscopy demonstrates the universal intensity ratio of D over D′ bands near 4, supporting formation of continuous edge defect. Thermal annealing enhances the optical contrast and van der Waals interactions of the graphene film, resulting in increased conductivity compared to the as-prepared graphene film, which is also better than that of reduced graphene oxide.

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.