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The dispersion type Bi···π arene interaction is one of the important structural features in the assembly process of arylbismuth compounds. Several triarylbismuth compounds and polymorphs are discussed and compared based on the analysis of single crystal X-ray diffraction data and computational studies. First, the crystal structures of polymorphs of Ph3Bi (1) are described emphasizing on the description of London dispersion type bismuth···π arene interactions and other van der Waals interactions in the solid state and the effect of it on polymorphism. For comparison we have chosen the substituted arylbismuth compounds (C6H4-CH═CH2-4)3Bi (2), (C6H4-OMe-4)3Bi (3), (C6H3-t-Bu2-3,5)3Bi (4) and (C6H3-t-Bu2-3,5)2BiCl (5). The structural analyses revealed that only two of them show London dispersion type bismuth···π arene interactions. One of them is the styryl derivative 2, for which two polymorphs were isolated. Polymorph 2a crystallizes in the orthorhombic space group P212121, while polymorph 2b exhibits the monoclinic space group P21/c. The general structure of 2a is similar to the monoclinic C2/c modification of Ph3Bi (1a), which leads to the formation of zig-zag Bi–arenecentroid ribbons formed as a result of bismuth···π arene interactions and π···π intermolecular contacts. In the crystal structures of the polymorph 2b as well as for 4 bismuth···π arene interactions are not observed, but both compounds revealed C–HPh···π intermolecular contacts, as likewise observed in all of the three described polymorphs of Ph3Bi. For compound 3 intermolecular contacts as a result of coordination of the methoxy group to neighboring bismuth atoms are observed overruling Bi···π arene contacts. Compound 5 shows a combination of donor acceptor Bi···Cl and Bi···π arene interactions, resulting in an intermolecular pincer-type coordination at the bismuth atom. A detailed analysis of three polymorphs of Ph3Bi (1), which were chosen as model systems, at the DFT-D level of theory supported by DLPNO-CCSD(T) calculations reveals how van der Waals interactions between different structural features balance in order to stabilize molecular arrangements present in the crystal structure. Furthermore, the computational results allow to group this class of compounds into the range of heavy main group element compounds which have been characterized as dispersion energy donors in previous work.

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.

Modern approaches to modelling dispersion forces are becoming increasingly accurate, and can predict accurate binding distances and energies. However, it is possible that these successes reflect a fortuitous cancellation of errors at equilibrium. Thus, in this work we investigate whether a selection of modern dispersion methods agree with benchmark calculations across several potential-energy curves of the benzene dimer to determine if they are capable of describing forces and energies outside equilibrium. We find the exchange-hold dipole moment (XDM) model describes most cases with the highest overall agreement with reference data for energies and forces, with many-body dispersion (MBD) and its fractionally ionic (FI) variant performing essentially as well. Popular approaches, such as Grimme-D and van der Waals density functional approximations (vdW-DFAs) underperform on our tests. The meta-GGA M06-L is surprisingly good for a method without explicit dispersion corrections. Some problems with SCAN+rVV10 are uncovered and briefly discussed.

Adhesion forces between functionalized gold colloidal nanoparticles (Au NPs) and scanning probe microscope silicon tips were experimentally investigated by atomic force microscopy (AFM) equipped with PeakForce QNM (Quantitative Nanoscale Mechanics) module. Au NPs were synthesized by a seed-mediated process and then functionalized with thiols containing different functional groups: amino, hydroxy, methoxy, carboxy, methyl, and thiol. Adhesion measurements showed strong differences between NPs and silicon tip depending on the nature of the tail functional group. The dependence of the adhesion on ligand density for different thiols with identical functional tail-group was also demonstrated. The calculated contribution of the van der Waals (vdW) forces between particles was in good agreement with experimentally measured adhesive values. In addition, the adhesion forces were evaluated between flat Au films functionalized with the same molecular components and silicon tips to exclude the effect of particle shape on the adhesion values. Although adhesion values on flat substrates were higher than on their nanoparticle counterparts, the dependance on functional groups remained the same.

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.

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.

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.

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 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.

2D transition metal dichalcogenide (2D‐TMD) materials and their van der Waals heterostructures (vdWHs) have inspired worldwide efforts in the fields of electronics and optoelectronics. However, photodetectors based on 2D/2D vdWHs suffer from performance limitations due to the weak optical absorption of their atomically thin nature. In this work, taking advantage of an excellent light absorption coefficient, low‐temperature solution‐processability, and long charge carrier diffusion length, all‐inorganic halides perovskite CsPbI3− xBrx quantum dots are integrated with monolayer MoS2 for high‐performance and low‐cost photodetectors. A favorable energy band alignment facilitating interfacial photocarrier separation and efficient carrier injection into the MoS2 layer inside the 0D–2D mixed‐dimensional vdWHs are confirmed by a series of optical characterizations. Owing to the synergistic effect of the photogating mechanism and the modulation of Schottky barriers, the corresponding phototransistor exhibits a high photoresponsivity of 7.7 × 104 A W−1, a specific detectivity of ≈5.6 × 1011 Jones, and an external quantum efficiency exceeding 107%. The demonstration of such 0D–2D mixed‐dimensional heterostructures proposed here would open up a wide realm of opportunities for designing low‐cost, flexible transparent, and high‐performance optoelectronics.

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.

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.

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.

Altres ajuts: TRF/PHD/0109/2553 Immunoassays are nowadays a crucial tool for diagnostics and drug development. However, they often involve time-consuming procedures and need at least two antibodies in charge of the capture and detection processes, respectively. This study reports a nanocomposite based on graphene oxide-coated nanopaper (GONAP) facilitating an advantageous immunosensing platform using a single antibody and without the need for washing steps. The hydrophilic, porous, and photoluminescence-quenching character of GONAP allows for the adsorption and quenching of photoluminescent quantum dots nanocrystals complexed with antibodies (Ab-QDs), enabling a ready-to-use immunosensing platform. The photoluminescence is recovered upon immunocomplex (antibody-antigen) formation which embraces a series of interactions (hydrogen bonding, electrostatic, hydrophobic, and Van der Waals interactions) that trigger desorption of the antigen-Ab-QD complex from GONAP surface. However, the antigen is then attached onto the GONAP surface by electrostatic interactions leading to a spacer (greater than ≈20 nm) between Ab-QDs and GONAP and thus hindering nonradiative energy transfer. It is demonstrated that this simple-yet highly sensitive-platform represents a virtually universal immunosensing approach by using small-sized and big-sized targets as model analytes, those are, human-IgG protein and Escherichia coli bacteria. In addition, the assay is proved effective in real matrices analysis, including human serum, poultry meat, and river water. GONAP opens the way to conceptually new paper-based devices for immunosensing, which are amenable to point of care applications and automated diagnostics.

In principle, non-contact atomic force microscopy (NC-AFM) now readily allows for the measurement of forces with sub-nanonewton precision on the atomic scale. In practice, however, the extraction of the often desired ‘short-range’ force from the experimental observable (frequency shift) is often far from trivial. In most cases there is a significant contribution to the total tip–sample force due to non-site-specific van der Waals and electrostatic forces. Typically, the contribution from these forces must be removed before the results of the experiment can be successfully interpreted, often by comparison to density functional theory calculations. In this paper we compare the ‘on-minus-off’ method for extracting site-specific forces to a commonly used extrapolation method modelling the long-range forces using a simple power law. By examining the behaviour of the fitting method in the case of two radically different interaction potentials we show that significant uncertainties in the final extracted forces may result from use of the extrapolation method.

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.

One of the main issues in the production of polymer nanocomposites is the dispersion state of filler as multilayered graphene (MLG) and carbon nanotubes (CNTs) tend to agglomerate due to van der Waals forces. The agglomeration can be avoided by using organic solvents, selecting suitable dispersion and production methods, and functionalizing the fillers. Another proposed method is the use of hybrid fillers as synergistic effects can cause an improvement in the dispersion state of the fillers. In this review article, various aspects of each process that can help avoid filler agglomeration and improve dispersion state are discussed in detail. This review article would be helpful for both current and prospective researchers in the field of MLG- and CNT-based polymer nanocomposites to achieve maximum enhancement in mechanical, thermal, and electrical properties of produced polymer nanocomposites.

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.

A series of azobenzene–cholesterol organogel compounds (M0–M12) with different spacers were designed and synthesized. The molecular structures were confirmed by 1H NMR and 13C NMR spectroscopy. The rapid and reversible photoresponsive properties of the compounds were investigated by UV–vis spectroscopy. Their thermal phase behaviors were studied by DSC. The length of the spacer plays a crucial role in the gelation. Compound M6 is the only one that can gelate in ethanol, isopropanol and 1-butanol and the reversible gel–sol transitions are also investigated. To obtain visual insight into the microstructure of the gels, the typical structures of the xerogels were studied by SEM. Morphologies of the aggregates change from flower-like, network and rod with different sizes. By using IR and XRD characterization, it is found that intermolecular H-bonding, the solvents and van der Waals interaction are the main contributions to the specific superstructure.

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).

We present a simulation environment, dForce, which can be used for a better understanding of dynamic force microscopy experiments. The simulator presents the cantilever-tip dynamics for two dynamic AFM methods, tapping mode AFM and bimodal AFM. It can be applied for a wide variety of experimental situations in air or liquid. The code provides all the variables and parameters relevant in those modes, for example, the instantaneous deflection and tip-surface force, velocity, virial, dissipated energy, sample deformation and peak force as a function of time or distance. The simulator includes a variety of interactions and contact mechanics models to describe AFM experiments including: van der Waals, Hertz, DMT, JKR, bottom effect cone correction, linear viscoelastic forces or the standard linear solid viscoelastic model. We have compared two numerical integration methods to select the one that offers optimal accuracy and speed. The graphical user interface has been designed to facilitate the navigation of nonexperts in simulations. Finally, the accuracy of dForce has been tested against numerical simulations performed during the last 18 years., This work was funded by the European Research Council ERC-AdG-340177 (3DNanoMech) and the Spanish Ministry of Economy (MINECO) through grant CSD2010-00024.

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.

In the present study, our aim is to investigate the preferential binding mode and encapsulation of the flavonoid fisetin in the nano-pore of β-cyclodextrin (β-CD) at the molecular level using various theoretical approaches: molecular docking, molecular dynamics (MD) simulations and binding free energy calculations. The molecular docking suggested four possible fisetin orientations in the cavity through its chromone or phenyl ring with two different geometries of fisetin due to the rotatable bond between the two rings. From the multiple MD results, the phenyl ring of fisetin favours its inclusion into the β-CD cavity, whilst less binding or even unbinding preference was observed in the complexes where the larger chromone ring is located in the cavity. All MM- and QM-PBSA/GBSA free energy predictions supported the more stable fisetin/β-CD complex of the bound phenyl ring. Van der Waals interaction is the key force in forming the complexes. In addition, the quantum mechanics calculations with M06-2X/6-31G(d,p) clearly showed that both solvation effect and BSSE correction cannot be neglected for the energy determination of the chosen system.

The wet-transfer of graphene grown by chemical vapor deposition (CVD) has been the standard procedure for transferring graphene to any substrate. However, the nature of the interactions between large area graphene and target substrates is unknown. Here, we report on measurements of the traction-separation relations, which represent the strength and range of adhesive interactions, and the adhesion energy between wet-transferred, CVD grown graphene and the native oxide surface of silicon substrates. These were determined by coupling interferometry measurements of the separation between the graphene and silicon with fracture mechanics concepts and analyses. The measured adhesion energy was 357 ± 16 mJ/m(2), which is commensurate with van der Waals interactions. However, the deduced traction-separation relation for graphene-silicon interactions exhibited a much longer range interaction than those normally associated with van der Waals forces, suggesting that other mechanisms are present.

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.

Two‐dimensional metal–organic nanostructures based on the binding of ketone groups and metal atoms were fabricated by depositing pyrene‐4,5,9,10‐tetraone (PTO) molecules on a Cu(111) surface. The strongly electronegative ketone moieties bind to either copper adatoms from the substrate or codeposited iron atoms. In the former case, scanning tunnelling microscopy images reveal the development of an extended metal–organic supramolecular structure. Each copper adatom coordinates to two ketone ligands of two neighbouring PTO molecules, forming chains that are linked together into large islands through secondary van der Waals interactions. Deposition of iron atoms leads to a transformation of this assembly resulting from the substitution of the metal centres. Density functional theory calculations reveal that the driving force for the metal substitution is primarily determined by the strength of the ketone–metal bond, which is higher for Fe than for Cu. This second class of nanostructures displays a structural dependence on the rate of iron deposition.

In this paper, we report a novel water transfer printing method, which can transfer chemical vapor deposition (CVD) graphene from copper foil to 3D surface. By the aid of surface tension and Van der Waals force, multilayer graphene film can be transferred to various substrates with smooth surface including glass sheet, colophony filament, silicon oxide micro structure, polyimide (PI) film, polymethyl methacrylate (PMMA) tube and optical fibers. As the graphene film can be selectively transferred to assigned position in 3D surface, this simple room temperature transfer method has promising application potential in flexible MEMS and device on curved surface.

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.

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°

Finite element method (FEM) simulations of the adhesive contact between a nanoscale tip and a silicon oxide substrate covered with graphene were performed, modelling experimental atomic force microscopy pull-off measurements. Simulations showed a slight increase in the pull-off force as layer number increased. This small enhancement was within reported experimental error, agreeing with the experimental findings of layer-independent adhesion forces. Pull-off forces did not vary with the elastic strain in the system for a given number of layers, but were influenced by the greater adhesive stresses for tip–graphene interaction compared with tip–substrate interactions. FEM simulations were also performed on suspended graphene and showed that the adhesive forces increased slightly beyond one layer of graphene, but then varied little from two to four layers of graphene. The results indicate that while there is some local delamination of the graphene sheets from the substrate, the adhesive stresses between the graphene layers in multilayer graphene effectively prevent out-of-plane mechanical deformation of the graphene layers that could result from tip–graphene interactions. Thus, the increased pull-off forces observed beyond one monolayer results from a change in the amount of material between the tip and substrate, or in this case the number of graphene layers, thus increasing the van der Waals force between tip and graphene.

Hierarchically organized three-dimensional (3D) carbon nanotubes/graphene (CNTs/graphene) hybrid nanostructures hold great promises in composite and battery applications. Understanding the junction strength between CNTs and graphene is crucial for utilizing such special nanostructures. Here, in situ pulling an individual CNT bundle out of graphene is carried out for the first time using a nanomechanical tester developed in-house, and the measured junction strength of CNTs/graphene is 2.23 ± 0.56 GPa. The post transmission electron microscopy (TEM) analysis of remained graphene after peeling off CNT forest confirms that the failure during pull-out test occurs at the CNT–graphene junction. Such a carefully designed study makes it possible to better understand the interfacial interactions between CNTs and graphene in the 3D CNTs/graphene nanostructures. The coupled experimental and computational effort suggests that the junction between the CNTs and the graphene layer is likely to be chemically bonded, or at least consisting of a mixture of chemical bonding and van der Waals interactions.

The adsorption of the iron tetraphenylporphyrin (FeTPP) molecule in its deckchair conformation was investigated on Au(111), Ag(111) and Cu(111) surfaces by performing spin-polarized density functional theory (DFT) calculations taking into account both van der Waals (vdW) interaction and on-site Coulomb repulsion. The deckchair conformation of the molecule favours intermolecular π–π-type interactions in a less densely packed monolayer than the saddle conformation. The activation barrier between the two stable magnetic states (high spin, S = 2 and intermediate spin, S = 1) of the molecule in vacuum disappears upon adsorption on the metal surfaces. The high-spin state of physisorbed FeTPP is stable on all adsorption sites. This result reveals that an external permanent element such as a STM tip or an additional molecule is needed to use FeTPP or similar molecules as model system for molecular spin switches.

We study mechanically exfoliated nanosheets of franckeite by quantitative optical microscopy. The analysis of transmission-mode and epi-illumination-mode optical microscopy images provides a rapid method to estimate the thickness of the exfoliated flakes at first glance. A quantitative analysis of the optical contrast spectra by means of micro-reflectance allows one to determine the refractive index of franckeite over a broad range of the visible spectrum through a fit of the acquired spectra to a model based on the Fresnel law., We acknowledge funding from the European Commission under the Graphene Flagship, contract CNECTICT-604391, from EU Horizon 2020 research and innovation program under grant agreement No. 696656 (GrapheneCore1 – Graphene-based disruptive technologies), from the FP7 ITN MOLESCO (project no. 606728), from the MINECO (FIS2015-67367-C2-1-P, MAT2014-57915-R, MDM-2014-0377 and Ramón y Cajal 2014 program RYC-2014-16626), from the Comunidad de Madrid (MAD2D-CM Program (S2013/MIT-3007)) and NANOFRONTMAG-CM program (S2013/MIT-2850). RF acknowledges support from the Netherlands Organisation for Scientific Research (NWO) through the research program Rubicon with project number 680-50-1515.

The Hamaker constant between graphene oxide and silica, which quantifies the strength of van der Waals forces is determined, by mimicking a “vacuum spacer” in an atomic force microscopyforce study. It is demonstrated that, a 2D spacer is expected to yield an accurately defined separation, owing to the high atom density and strength in planar direction compared with other dimensional spacers.

Unspecific adhesion of bacteria is usually the first step in the formation of biofilms on abiotic surfaces, yet it is unclear up to now which forces are governing this process. Alongside long-ranged van der Waals and electrostatic forces, short-ranged hydrophobic interaction plays an important role. To characterize the forces involved during approach and retraction of an individual bacterium to and from a surface, single cell force spectroscopy is applied: A single cell of the apathogenic species Staphylococcus carnosus isolate TM300 is used as bacterial probe. With the exact same bacterium, hydrophobic and hydrophilic surfaces can be probed and compared. We find that as far as 50 nm from the surface, attractive forces can already be recorded, an indication of the involvement of long-ranged forces. Yet, comparing the surfaces of different surface energy, our results corroborate the model that large, bacterial cell wall proteins are responsible for adhesion, and that their interplay with the short-ranged hydrophobic interaction of the involved surfaces is mainly responsible for adhesion. The ostensibly long range of the attraction is a result of the large size of the cell wall proteins, searching for contact via hydrophobic interaction. The model also explains the strong (weak) adhesion of S. carnosus to hydrophobic (hydrophilic) surfaces.

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.

Graphene has remarkable mechanical properties, and it is a very promising material for sensors. The progress of graphene diaphragm based pressure sensor was detailed firstly. Then the deflection of pressurized circular graphene diaphragm with pre-stress was discussed, an approximate solution was given to substitute Hencky's series solution. Pre-stress descends the sensitivity of the graphene diaphragm, but it also makes the deflection linear in pre-stress dominated regime, which is important for sensor applications. The pre-stress in the diaphragm caused by van der Waals force between the diaphragm and the sidewall of the substrate was studied, the results indicates that the pre-stress is associated with the adhesion energy per unit area between the diaphragm and sidewall of the substrates, and the thickness of the diaphragm. Due to the influence of the the adhesion force, multilayer (2~10 layers) graphene diaphragms are more sensitive than monolayer, as monolayer graphene is much more flexible, the adhesion energy is higher than multilayer graphene.

DOI: 10.1002/adma.201303503 Assembly of graphene into functional macroscopic objects, such as fi lms, [ 1 ] sheets, [ 2 ] fi bers, [ 3 ] foams, [ 4,5 ] and other complex architectures, [ 6 ] is of enormous research interest. How to attain desired structures in a cost effective and manufacturable manner is crucial for energy harvest/storage, catalysis, sensors and so on. Unlike fullerene or carbon nanotubes, whose assembly generally relies on weak van der Walls force or chemical modifi cation, two-dimensional graphene may straightforwardly exploit strong interlayer π – π stacking. Unfortunately, such a strong and directional interaction frequently results in graphitic stacking with minimal surface area. [ 7,8 ]