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In a recent paper [J. Chem. Phys. 2005, 122, 124318], a full-dimensional quantum method, designed to efficiently compute the rovibrational states of triatomic systems with long-range interactions, was applied to the benchmark Li - (H 2 ) ion-molecule system. The method incorporates several key features in order to accurately represent the rovibrational Hamiltonian using only modestly sized basis sets: (1) exact analytical treatment of Coriolis coupling; (2) a single bend-angle basis for all rotational states; (3) phase space optimization of the vibrational basis; (4) G 4 symmetry adaptation of the rovibrational basis. In this paper, the same methodology is applied for the first time to a van der Waals complex system, He(H 2 ). As in the Li - (H 2 ) study, all of the rovibrational bound states, and a number of resonance states, are computed to very high accuracy (1/10 000 of a wavenumber or better). Three different isotopologues are considered, all of which are found to have a single bound state with a very low binding energy. Several extremely long-lived Feshbach resonances are also reported.

In an earlier paper, 1 we detailed the current status of the comparison between experimentally observed reaction crosssections and product HF(v,J) vibration-rotation state populations and corresponding results obtained using quantum scattering theory on current state-of-the-art potential energy surfaces (PESs) for the title reaction. More recently, a paper from the Skodje group has appeared 2 that offers an even more up-todate evaluation and an excellent overview. The latter paper points out that remaining experimental-theoretical differences are unlikely to arise from the treatment of the quantum dynamics or through contributions of the 2 P1/2 excited state of fluorine, which is in line with what we said in ref 1. Reference 2 also emphasizes that differences in the HF product vibrational populations likely arise from an incorrect exothermicity of the theoretical PES and that there seem to be errors in this PES in the region of the product-channel FH‚‚‚H van der Waals well. The main emphasis of ref 2 was to introduce corrections to the Stark and Werner 3 PES, which is the best global threedimensional (3D) PES presently available, and to improve its descriptions of the exothermicity and of the FH‚‚‚H van der Waals well. Although great progress has been made on both the experimental and theoretical (PES and reaction dynamics) fronts in the past 20 years, there remain differences between the theoretical and experimental findings suggesting that small errors (ca. 0.5-1.0 kcal mol -1 ) remain in even the very best current

sCO2 power cycle is the most investigated and most promising technology for replacing conventional steam cycle in CSP plants. Nevertheless, the efficiency of sCO2 power cycle is strongly penalized by high ambient temperatures which are typical of favourable CSP locations. This paper focuses on a new working fluid for power cycles which consists of CO2 blended with C6F6. The addition of C6F6 increases the fluid critical temperature allowing for a condensing cycle for ambient temperatures up to 45 °C. The calculated gross mechanical efficiency of the innovative cycle is around 42% when adopting a typical Peng Robinson equation of state with van der Waals mixing rules for a maximum operating temperature of 550 °C and a minimum cycle temperature of 51 °C. This performance varies just of ±0.1% if the prediction of the binary interaction parameter of the Peng Robinson is over- or under-estimated by 50%, but more significantly if other equations of states are adopted (up to 1% points). Moreover, a detailed analysis on the operating conditions of the cycle components highlighted that components design is affected by the adopted EoS. A sensitivity analysis is then performed to identify where the largest differences in predicting the efficiency of the cycle occur.

It is the forces between the microscopic constituents of materials which to a large extent determine the macroscopic properties. For example, it is the differences in bonding between the carbon atoms which determines the different physical properties of carbon and graphite. The same is true in colloidal systems. In colloidal systems, there are three common types of long-range interactions between particles: van der Waals forces, electrical double layer forces and steric forces. In this paper, examples as to how these forces can be modified and even manipulated will be given. To convincingly demonstrate these effects, it is necessary to measure these interaction forces. We have achieved this by using the principles of atomic force microscopy (AFM). The principle is simple, a small particle, 5–30 μm, is attached onto a small weak cantilever spring. The interaction between this particle and another particle or a surface is measured by monitoring the deflection of the spring as the two particles are moved together. In this paper, I shall give examples of direct measurements of van der Waals, electrical double layer and steric forces and show how they can be modified and how these modifications affect the properties of bulk suspensions. Similar principles are involved in the interactions of biological materials. However, nature is much cleverer than man such that many of the macromolecules on cell surfaces are able to specifically recognise only one other molecule. An example of this recognition-type interaction, namely, cholera toxin interacting with the glycolipid Gm1, will also be presented. Finally, the adhesion of cells to surfaces of different surface chemistries has been determined; this is of significance in many fields ranging from fouling of filtration membranes on the one hand to the biocompatibility of surgical implants on the other.

This paper discusses the role of the structural disjoining pressure exerted by nanoparticles on the spreading of a liquid film containing these particles. The origin of the structural disjoining pressure in a confined geometry is due to the layering of the particles normal to the confining plane and has already been traced to the net increase in the entropy of the system in previous studies. In a recent paper, Wasan and Nikolov (Nature, 423 (2003) 156) pointed out that the structural component of the disjoining pressure is strong enough to move a liquid wedge; this casts a new light on many applications-most notably, detergency. While the concept of spreading driven by the disjoining pressure is not new, the importance of the structural disjoining pressure arises from its long-range nature (as compared to the van der Waals' force), making it an important component of the overall force balance near the contact line. In this paper, we report on a parametric study of the spreading phenomena by examining the effects of nanoparticle size, concentration and polydispersity on the displacement of an oil-aqueous interface with the aqueous bulk containing nanoparticles. The solution of the extended Laplace-Young equations for the profile of the meniscus yields the position of the nominal contact line under the action of the structural disjoining pressure. Simulations show that the displacement of the contact line is greater with a high nanoparticle volume fraction, small particles for the same volume fraction, monodispersed (in size) particles rather than polydispersed particles and when the resisting capillary pressure is small, i.e., when the interfacial tension is low and/or the radius of the dispersed phase drop/bubble is large.

In this paper, the study of the properties of L-leucine crystal is carried out using the density functional theory with PBE exchange-correlation functional with consideration of the van der Waals forces according to the Grimme scheme in option D3 (BJ). The calculations are based on the linear combination method of atomic orbitals and performed using the CRYSTAL’17 software package. The structural and electronic properties of L-leucine crystal under pressure are investigated, and the equation of state for the pressure ranges from 0 to 4 GPa is obtained. The constructed equation of state shows that anomalies are observed due to changes in the unit cell parameter a directed across the layers of molecules, as well as due to the angle p. It has been suggested that a possible complication of the structure of L-shaped amino acid molecules by functional groups is associated with the bulk modulus B0 and its first derivative B1. Using the calculated compressibility modulus as an example, it is shown that the highest compressibility is observed along the c axis, which directed along the orientation of the molecules in the unit cell of the L-leucine crystal. The observed compressibility is four and five times higher than the compressibility in L-alanine and L-threonine, respectively. An analysis of the dependence of electronic properties on pressure, such as the effective charges of functional groups, the band gap, and the location of the peaks of the density of states, demonstrates that the above properties do not undergo noticeable changes in the pressure range from 0 to 4 GPa.

The fundamental ideas for a non-local density functional theory -- capable of reliably capturing van der Waals interaction -- were already conceived in the 1990's. In 2004, a seminal paper introduced the first practical non-local exchange-correlation functional called vdW-DF, which has become widely successful and laid the foundation for much further research. However, since then, the functional form of vdW-DF has remained unchanged. Several successful modifications paired the original functional with different (local) exchange functionals to improve performance and the successor vdW-DF2 also updated one internal parameter. Bringing together different insights from almost two decades of development and testing, we present the next-generation non-local correlation functional called vdW-DF3, in which we change the functional form while staying true to the original design philosophy. Although many popular functionals show good performance around the binding separation of van der Waals complexes, they often result in significant errors at larger separations. With vdW-DF3, we address this problem by taking advantage of a recently uncovered and largely unconstrained degree of freedom within the vdW-DF framework that can be constrained through empirical input, making our functional semi-empirical. For two different parameterizations, we benchmark vdW-DF3 against a large set of well-studied test cases and compare our results with the most popular functionals, finding good performance in general for a wide array of systems and a significant improvement in accuracy at larger separations. Finally, we discuss the achievable performance within the current vdW-DF framework, the flexibility in functional design offered by vdW-DF3, as well as possible future directions for non-local van der Waals density functional theory.

The rupture of thin liquid films driven by the van der Waals force is of significance in many engineering processes, and most previous studies have relied on the lubrication approximation. In this paper, we develop a smoothed particle hydrodynamics (SPH) representation for the van der Waals force and simulate the rupture of thin liquid films without resort to lubrication theory. The van der Waals force in SPH is only imposed on one layer, i.e., the outermost layer of fluid particles, where a weighting function is deployed to evaluate the contributions of particles on or near the interface. However, to obtain an accurate hydrostatic pressure in reaction to the van der Waals force, a smaller smoothing length is used for the calculation of the weighting function than that used for SPH discretizations of the bulk fluid. The same surface particles are also used to model the surface tension. To deal with the rupture of a thin liquid film with a very small aspect ratio e (e = thickness/length), a coordinate transformation is introduced to shrink the length of the liquid film to achieve accurate numerical resolution with a manageable number of particles. As verifications of our physical model and numerical algorithm, we simulate the hydrostatic pressure in a stationary film and the relaxation of an initially square droplet and compare the SPH results with the analytical solutions. The method is then applied to simulate the rupture of thin liquid films with moderate and small aspect ratios (e = 0.5 and 0.005). The convergence of the method is verified by refining particle spacing to four different levels. The effect of the capillary number on the rupture process is analyzed.

The paper presents theoretical studies of the adsorption of pollutant gases on the surface of cadmium-containing polyacrylonitrile (Cd-polyacrylonitrile) in the absence and presence of water molecules and oxygen molecules in the environment. The list of gases to which the Cd-polyacrylonitrile surface may have the highest sensitivity is determined. Nitrogen dioxide, methane, ammonia, sulfur oxide (II), hydrogen sulfide, ozone, carbon monoxide, carbon oxide (II), chlorine were chosen as pollutant gases. The following software packages are used for modeling: HyperChem, Gaussian 09, Сhemoffice 2010. Polyacrylonitrile macromolecule models were obtained from HyperChem, Gaussian 09, from which a pentamer macromolecule was chosen to produce a Cd-polyacrylonitrile cluster. Then, implementing the molecular mechanics method in Сhemoffice 2010, namely in the Chem3D subroutine, the Cd-polyacrylonitrile cluster model is constructed. Further, using the molecular modeling method, the following thermodynamic parameters were determined: «Cd-polyacrylonitrile cluster – gas molecule», «Cd-polyacrylonitrile cluster – oxygen molecule», «Cd-polyacrylonitrile cluster – water molecule», «Cd-polyacrylonitrile cluster – oxygen molecule gas molecule», «Cd-polyacrylonitrile cluster – water molecule – gas molecule». As a result of molecular modeling, it was established that Cd-polyacrylonitrile in the atmospheric air exhibits selective sensitivity to gaseous chlorine and carbon monoxide; in an oxygen-free environment – also to hydrogen sulfide. The results of molecular modeling confirm the previously obtained experimental data on the evaluation of the gas sensitivity of Cd-polyacrylonitrile and indicate the presence of van der Waals forces between the Cd-polyacrylonitrile and the adsorbed gas molecule. The presence or absence of water molecules in atmospheric air should not affect the change in the sensitivity of Cd-polyacrylonitrile to pollutant gases.

Explicit solutions are derived to study the equilibrium distance as well as potential energy between graphene and its derivative forms. Since the application of explicitly analytical solutions is limited to homogenous deformation and cannot capture the edge effect, Gaussian quadrature is presented to overcome these problems. The two key elements, i.e., truncation distance and the size of integration element, which are closely related to the computational efficiency and accuracy have been systemically studied. Fitting functions in terms of the above-mentioned two key elements are also provided to easily evaluate the difference of Gaussian quadrature. This paper provides a good understanding of the van der Waals interaction between graphitic nanostructures, and should be of great help for fabricating nano devices and simulating their mechanical behaviors such as spontaneous buckling.

Abstract The present paper investigated the effects of the electrostatic and non-electrostatic interactions on the water wettability of a surface. Based on this aim, examinations are performed on the molybdenum disulfide (MoS2) as possible nanostructure surface. The results obtained through calculating the water contact angle on the MoS2 surface indicate which this surface is a weak hydrophobic substrate. The present simulations illustrate that the electrostatic interactions have little impact on the wettability amount of the MoS2 substrate. However, the molybdenum disulfide is composed of two charged parts with significant values. In addition, it is observed that the relation between density, van der Waals and electrostatic interactions is different from each other. It have been observed that the van der Waals interactions have direct relationship with water density while there is not anything between the electrostatic interactions and water density peak. The Obtained results via simulation demonstrate that the effectiveness of electrostatic interactions on the wettability depends on the sigma in the Lennard–Jones equation. In the other words, the role of electrostatic and van der Waals interactions on the wettability are not indissociable from each other and this method is sufficient in nanostructure systems. Graphic abstract

Inverse gas chromatography at infinite dilution is a powerful technique that can be advantageously used to characterize the surface physicochemical properties of solid substrates as oxides and polymers in both forms of powder or fibres. In the case of polymer, this technique can be used to determine the second order transition phenomena temperatures. This paper was devoted to the determination of the glass transition temperature of polylactide polymer. The dispersive component of the surface energy of polylactides was determined by inverse gas chromatography at infinite dilution. Various theoretical models were used to deduce the dispersive component of the surface energy of the solid substrates. These models are based on the calculation of the molecular areas of adsorbed molecules on the polymer surface: geometrical model, cylindrical molecular model, liquid density model, BET method, Kiselev results and the two-dimensional Van der Waals and Redlich-Kwong equations. The curves relative to the variation of as a function of the temperature showed a specific graph with a maximum value of at a certain particular temperature characteristic to the investigated polylactide polymer. In fact, the maxima of indicated the presence of glass transition temperature Tg of polylactide whatever the molecular model used. This study showed a glass transition temperature equal to 64°C confirming that obtained by other studies.

Modeling novel van der Waals (vdW) heterostructures is an emerging field to achieve materials with exciting properties for various devices. In this paper, we report a theoretical investigation of GaN–MX2 (M = Mo, W; X= S, Se) van der Waals heterostructures by hybrid density functional theory calculations. Our results predicted that GaN–MoS2, GaN–MoSe2, GaN–WS2 and GaN–WSe2 van der Waals heterostructures are energetically stable. Furthermore, we find that GaN–MoS2, GaN–MoSe2 and GaN–WSe2 are direct semiconductors, whereas GaN–WS2 is an indirect band gap semiconductor. Type-II band alignment is observed through PBE, PBE + SOC and HSE calculations in all heterostructures, except GaN–WSe2 having type-I. The photocatalytic behavior of these systems, based on Bader charge analysis, work function and valence and conduction band edge potentials, shows that these heterostructures are energetically favorable for water splitting.

The C–H⋯π interaction and the C–H⋯Cl–C van der Waals interaction play a crucial role in the crystallization of nanoclusters. In this paper, we present an example of a crystal system transformation of Au11(PR3)7Cl3 from monoclinic (M) to trigonal (T) by surface modification. Atomically-resolved gold nanoclusters containing tris(4-chlorophenyl)phosphine and chloride ligands were synthesized and determined to be Au11(p-ClPPh3)7Cl3 (p-ClPPh3 = tris(4-chlorophenyl)phosphine) by X-ray crystallography. Crystal data demonstrated that the C–H⋯Cl–C interaction is dominant in a trigonal crystal system of Au11(p-ClPPh3)7Cl3 with a R space group. However, the C–H⋯π interaction is the major driving force to form a monoclinic crystal system of Au11(PPh3)7Cl3 (PPh3 = triphenylphosphine) with a P2(1)/n space group. Moreover, UV-vis absorption spectra and X-ray photoelectron spectra reveal that the electronic structure of the Au11(p-ClPPh3)7Cl3 nanocluster is greatly influenced by p-ClPPh3. This work provides critical implications for the crystallization of metal nanoclusters, as well as a better understanding of the non-covalent interaction on the nanocluster assembly and the crystal engineering by surface modification.

AM2X4 crystalline materials display important technological electronic, optical and magnetic properties that are sensitive to general stress effects. In this paper, the behavior under hydrostatic pressure of the ambient condition rhombohedral phase of MgIn2Se4 is investigated in detail for the first time. We carried out first-principles calculations within the density functional theory framework aimed at determining the pressure-induced polymorphic sequence of this selenide. To accurately evaluate transition pressures at room temperature, thermal corrections have been included after the computation of phonon dispersion curves in potential candidate phases, namely the initial rhombohedral Rm one, inverse and direct spinels, LiTiO2-type and defective I structures. Only the transition from the Rm to the inverse spinel phase was found to fulfill the thermodynamic and mechanical stability criteria. The direct spinel could appear as metastable if kinetic effects hinder the above transition. Additionally, electronic band structures and chemical bonding properties were analyzed from the outcome of our quantum-mechanical solutions reporting band gap values and ionicity and noncovalent interaction indexes. It is shown that the investigated compound keeps behaving as a semiconductor, loses its van der Waals interactions, and becomes more covalent as hydrostatic pressure is applied.

Additive manufacturing (AM) is a rapid and flexible technique for the production of metal parts and prototypes from metal powders. The quality of parts manufactured using AM is a strong function of powder physical and mechanical properties. Previous work has shown that powders with a large fraction of fine particles produce better parts in terms of smooth finished surface and high mass density. However, an excessive fine fraction in the source powder causes serious flowability issues, leading to unexpected voids or discontinuities in the finished product. This effect of the fine fraction on the flowability of metal powder is widely encountered but poorly understood in the AM industry. This study presents a three-dimensional (3D) discrete element method (DEM) model to simulate the microscale mechanisms of powder flow considering the effects of van der Waals force. This microscale force has a negligible influence on the flowability of coarse grains, but the effect becomes the dominant factor governing the behavior of fine fractions (micrometer scale). The results show that the numerical model presented in this paper is capable of reproducing the experimental dependency of the powder flowability on the fine fraction. Moreover, it also successfully captures the characteristics of particle flow under the influence of microscale van der Waals force.

In this research paper, the equilibrium isotherms for the adsorption of cobalt(II)nitrate and cobalt(II)chloride on tetrakis(4-tolylphenyl)porphyrin (H2TTPP) were obtained at four temperatures for modeling analysis. The experimental data describing the adsorbed quantity of cobalt particles were measured using the quartz crystal microbalance (QCM) strategy. Then, statistical physics formalism was employed to interpret the complexation mechanism by applying the real gas law that contemplates the interaction between the adsorbate particles in the free state. Advanced models treated with the law of van der Waals were applied for the single and L.B.L adsorptions of Co2+ at various temperatures (288–318 K). The experimental adsorption data of CoCl2 on porphyrins were satisfactorily fitted with the monolayer equation, showing that the chlorine particles had no effect on the complexation system, while the nitrate particles were involved in the adsorption of Co(NO3)2 and contributed to the layer formation. The physicochemical parameters of statistical physics models were estimated and used to compare the complexation mechanisms of both adsorbates. The study of the cohesion pressure (a) and the co-volume (b) confirmed that cobalt chloride guaranteed more stability during the formation of the vitamin B12 nucleus. Deeper energetic analysis demonstrated that cobalt ions were complexed by ionic or covalent bonds in the case of cobalt chloride (complexation energy (–E1/2) varies from −48.2 to −50.3), while a physisorption process took place in the case of cobalt nitrate ((–E1) varies from −33.6 to −36.1), thus indicating that CoCl2–H2TTPP was the most stable complex. The statistical physics models were also used to investigate two thermodynamic functions that govern the adsorption mechanisms, namely, the configurational entropy and the Gibbs free enthalpy.

In this paper, we consider the singular limit of an energy minimizing problem which is a semi-limit of a singular elliptic equation modeling steady states of thin film equation with both Van der Waals force and Born repulsion force. We show that the singular limit of energy minimizers is a Dirac mass located on the boundary point with the maximum curvature.

Elemental 2D materials have emerged as promising candidates for electrochemical applications that require miniaturized devices and superior performance. These atomically thin materials are derived primarily from bulk-layered materials that consist of strong in-plane covalent bonding and weak interlayer van der Waals bonding. Their large surface areas, high degrees of variability in structure, and electronic properties make them distinctly superior for energy storage systems (ESSs). This review introduces elemental 2D nanomaterials and describes their properties and electrochemical applications such as gas sensing, catalysis, and ESS. This paper also highlights promising routes for the synthesis and characterization of elemental 2D materials.

An experimental characterization of the Van der Waals forces involved in volatile organic compounds (VOC) dissolved into stationary phases of gas liquid chromatography (GLC) has been started at the beginning of the seventies. This field has been reactivated from 1994 thanks to a fruitful cooperation between our CNRS team and the group of Ervin Kovats at the Federal Polytechnic School of Lausanne. The applied strategy can be summarized, in the first instance, as the experimental measurement of accurate and superabundant mutual affinities of a limited number of VOC and stationary phases and their processing using an original tool named Multiplicative Matrix Analysis (MMA). Then, in the second stage, the obtained results have been compared with molecular properties well established, as the Van der Waals molecular volume, the refraction index and the polar surface area (PSA), in order to get generalized values for any compound. The present study summarizes the positive results developed in our three last papers on this topic (2013, 2016 and 2018), as well as the attempt to overcome the negative ones using enthalpies of vaporization.

In the previous paper, a novel fine particle removal system composed of a corona-discharge neutralizer, a pulse-jet air unit and an image processing system has been developed and applied to the removal of fine particles from film surface. We have calculated the van der Waals and electrostatic forces between particle and film and then reported that the electrostatic force influenced the adhesion characteristics significantly and thus the elimination of electrostatic charge should be necessary for the effective removal of fine particles. In this paper, we have modified the corona-discharge neutralizer for getting much better removal performance. The effect of operating parameters on the removal efficiency was investigated experimentally. The ratio of fine particle remained on the film surface after removal experiment as a function of particle size was measured. It was found that fine particles smaller than 15 microm, which were impossible to remove by other conventional techniques, could be almost completely removed. This method is anticipated to be used in the capsule filling, film packaging and tabletting processes for prevention of stain on lens of video automatic inspection machines, unpredictable movement of electronic devices, and deteriorates of product quality.

T conclusion that has been drawn in the previous paper 1 regarding the importance of the electrostatics interaction of urea has been drawn on the basis of the distribution of interaction energies as well as on the hydrogen bonding interactions between the protein backbone and urea and the radial distribution functions of urea atoms around the charged side chain of protein at initial and final stages of the simulation. We have observed nearly identical situations for three different proteins namely ubiquitin, G311, and GB1. While the distribution energies differed from that reported by Berne’s group, the observations regarding the hydrogen bonds and RDF’s matched fairly well. As has been very rightly pointed out by Berne’s group in their Comment, the main difference lies in the values of bulk-water energies. While different cutoffs, simulation temperature, and strategies can account for 2-3 kcal/mol, we think the main difference arises from the difference in the definition of the interacting systems. While Bernes’ group had calculated the “potential energy” of a particular set of species [FSS-U, FSS-W, bulk-W, and bulk-U], we have calculated the “interaction energy” of a particular species with the “rest of the system”. In the presence of protein for individual snapshots from the trajectories we had (i) defined the FSS-U, FSS-W, bulk-W, and bulk-U subsets (ii) for each individual subset, computed the “INTERACTION energy” of the subset with the “REST of the system followed by averaging over per molecule of urea/water, as we had clearly mentioned in the Methods of our original paper. (iii)used the average INT-energies to generate the distributions. Please note that in the INTE command of CHARMM the interaction energy is calculated between the sets and not INTRASET. For example, interaction energy between a particular water in FSS will be calculated with atoms of protein, urea [both in FSS and bulk], water in bulk [which comes within the applied cutoff] but not with another water in FSS. So the distributions [both FSS and BULK] do not include the self-interaction energies averaged as per molecules of water or urea. In other words, the distributions that have been given in Figure 3 of ref 1 implicitly assume a common Eo for urea/water in both bulk and FSS. Hence our distributions will emphasize more on the differences in the environment. The main difference lies in the Figure 3 of our main paper as we were using a different definition of interaction energy from that of Hua et al. We have done an estimate of the self-interaction energies for water in FSS and bulk [only for ubiquitin and also for a single trajectory]. For FSS and bulk water the self-electrostatic contributions are-15.62 and-16.28 kcal/mol, respectively, while for van der Waals the contributions are 0.02 and 0.16 kcal/mol, respectively. Hence including those will shift our original distributions by nearly equal amounts, leaving previously drawn conclusions unchanged. Addition of these values to our previous distributions [-1.5, -0.51, and -1.25, -0.57 kcal/mol for electrostatic and van derWaals interaction of FSS and bulk water, respectively with “rest of the system”] leads to the total electrostatic interaction energies as-17.12 and-17.53 kcal/mol for FSS and bulk water, which are very similar to those reported by Berne’s group. The calculated average values of respective potential energies are given in Table 1. We agree that the contribution of electrostatics toward the stabilization of a single urea molecule from bulk to FSS is now decreased heavily (from -12.09 to -3.03 kcal/mol) compared to that of VDW (-2.0 to-2.36 kcal/mol); however, the contribution of electrostatic stabilization energy-3.03 kcal/mol is higher than the corresponding VDW contribution of -2.36 kcal/mol. As a result, our conclusion of ref 1 remains unaltered. Figure 1 here can replace Figure 3 of the original paper. Another source of difference could be the protein-conformational state sampling. While our trajectories are shorter [∼35 ns each and truncated after the protein lost most of the secondary structures], the protein conformations that have been sampled include native, near-native intermediates, intermediates, and the denatured forms. In the Figure 1C of ref 2 it is shown that while the native protein has a radius of gyration around 15 A , in the presence of urea [in a 1000 ns simulation] the most probable distribution of the radius of gyration of the protein lies in the range 29-33 A . This will not only control the number of water/ urea molecules in the FSS/bulk but also control the amount of exposed hydrophobic residues. The fact that this will indeed affect the overall conclusion has recently been shown by Garcia’s lab. They found that “the denaturation is driven by favorable direct interaction of urea with the protein through both electrostatic and van derWaals forces and quantified their contributions. Though the magnitude of direct electrostatic interaction of urea is larger than van derWaals, the difference between unfolded and folded ensembles is dominated by the van derWaals interaction.” Hence the distribution of the interaction energy will also be biased by the amount of folded/unfolded states sampled. We believe that our shorter trajectories are capturing the early kinetic stages of the denaturing process where protein is more globular and has predominantly polar/charged groups exposed, while Table 1. Interaction Energies in kcal/mol

In forests and membranes, Carbon nano tubes (CNT) are not individual, instead they tend to be agglomerated into bundles because of the strong van der Waals interaction. CNTs usually form into bundles containing up to hundreds or thousands of parallel CNTs named as fibres which create networks within a CNT membrane. Recently, CNT based macrostructures (yarn and membrane) have increasingly been used in various applications in electronics, medical and bioengineering. Meanwhile the volume density of CNTs impacts on mechanical and physical properties of macrostructures, the controlling of the density of membranes is very complex. Thus, in this paper, an electric processing to dilate CNT membrane is sufficiently studied and investigated by both the experiment and particle based numerical simulation. Several initially potential applications of the method are also represented not only to control the density of CNTs but also to improve the CNTs’ alignment in macro-structures.

In this paper, we combined cavity optomechanics and quantum mechanical mechanism of van der Waals force to study the dynamic behavior of interacting bimolecules in the plasmonic localized field, and extend it to the interacting multi-molecular system. We explored how plasmonic optomechanical coupling affects the strength of intermolecular interactions. Based on our results, we propose to use optical field to modulate the intermolecular interaction potential in plasmonic cavity, which can be utilized in the enhancement of the efficiency of the molecular self-assembly process and controlling the yield of the reaction in an optical environment. This research extends molecular optomechanics from intramolecular interactions to intermolecular interactions and may has high application potential in some nanostructure synthesis.

Ionic liquids are low-temperature molten salts with almost no vapor pressure, and they are composed of organic cations and inorganic anions. Ionic liquids are characterized by the properties of good chemical stability, high solubility, designable structure, high conductivity and so on. The physicochemical properties of an ionic liquid depend on the nature and size of the cation and anion, which confer unique characteristics; hence, these reagents are also termed "designed extractants." As a new class of green solvents, ionic liquids are potential replacements to traditional volatile organic solvents used for extraction; for this reason, ionic liquids have attracted the attention of scientists. Research on the methods of preparation and applications of ionic liquids is being diversified, and they are extensively used in catalytic chemistry, photoelectron chemistry, materials chemistry, analytical chemistry, etc. By functional guiding design, the structures of ionic liquids, especially the imidazole ring cations, can be easily grafted with active groups such as hydroxyl, amino, carboxyl, and cyano groups, so that interactions between the ionic liquids and target molecules can be promoted via the formation of π-π bonds, hydrogen bonds, ionic bonds, and van der Waals forces. In addition, ionic liquids can be readily immobilized on solid carriers by physical or chemical means in order to obtain a new solid material with ionic liquids embedded internally or decorated on the surface. Furthermore, ionic liquids could be converted into ionic liquid-immobilized composite materials by impregnation, grafting, etc. The resulting composites not only suffer minimal loss of ionic liquids but also retain the typical characteristics of the ionic liquids and solid materials, thus showing improved mass transfer performance and better adsorption performance. Immobilized materials are characterized by high enrichment efficiency, high adsorption capacity, good stability, and strong extraction selectivity, as well as the presence of numerous recognition sites and high utilization rate of ionic liquids. In recent years, they have been widely used as solid-phase extraction adsorption materials for the separation of small organic molecules. This review introduces common immobilization methods and the characteristics of ionic liquid-immobilized materials, as well as their application in solid-phase extraction. In this paper, methods for the immobilization of ionic liquids with solid carriers such as silica gel, molecular sieves, molecularly imprinted polymers, graphene oxide, and magnetic nanomaterials are summarized, and the application of ionic liquid-immobilized materials in solid-phase extraction is reviewed. The target substances include alkaloids, flavonoids, polyphenols, and other natural active components as well as common drug molecules, organic pesticides, and other organic small molecular compounds. The properties, applications, and separation mechanisms of ionic liquids immobilized with various carriers are systematically introduced. Literature survey shows that the distribution of the binding active sites of ionic liquid-immobilized materials to the target molecules is more uniform, which increases the adsorption capacity of the materials. The adsorption efficiency of ionic liquid-immobilized materials is related to the type of ionic liquid, amount of adsorption material, concentration of the sample solution, adsorption temperature, solution pH, flow rate of the eluent, and type and amount of the eluting solvent. The existing disadvantages of ionic liquids, such as simple structures, insufficient basic theoretical research, and unsatisfactory extraction degree in complex matrixes would also be discussed. The corresponding solutions would be presented with the aim of providing guidance for the application of ionic liquid-immobilized materials in the separation and analysis of targets in complex matrices, thus paving the way for a new direction in the field of extraction and separation.

In a previous paper (http://www.phys.uri.edu/people/nightingale/publications.html, chem-ph/9406003) we developed a form of variational trial wave function and applied it to van der Waals clusters: five or less atoms of Ar and Ne modeled by the Lennard-Jones potential. In addition, we tested the trial functions for a hypothetical, light atom resembling Ne but with only half its mass. We did not study atoms such as He with larger de Boer parameters, i.e., systems in which the zero point energy plays a more important role relative to the potential energy. This is the main purpose of the present paper. In fact, we study clusters to the very limit where the zero-point energy destroys the ground state as a bound state. A simple picture of this un-binding transition predicts the power law with which the energy vanishes as the de Boer parameter approaches its critical value and the power of the divergence of the the size of the clusters in this limit. Our numerical results are in agreement with these predictions., Comment: text and figures TeX form, 4 pages

Powder fluidity is one of the important factors affecting the smoothness of selective laser sintered parts and the mechanical properties of sintered parts. In this paper, the angle of repose (AOR) and angle of internal friction of nylon PA3200 powder were measured by a powder comprehensive tester and a direct shear tester to evaluate the flow properties of the powder particles. Based on the discrete element method (DEM), the rolling resistance contact model and the van der Waals force model were used to describe the interaction forces between the powder particles. The rolling resistance coefficient and friction coefficient within the contact model were calibrated by the results of the AOR experiments. Based on the orthogonal experimental method, the particle size and particle size distribution (PSD) (such as uniform distribution and Gaussian distribution) were selected as the influencing factors, and the effect of particle size and PSD on the fluidity of nylon PA3200 powder was studied by numerical simulation. The results show that the PSD has a stronger influence on the AOR than particle size, and the fluidity of uniform distribution is better than that of the Gaussian distribution.

The formation of clay suspensions involves complex interactions among clay particles subjected to the geochemical environment during the sedimentation process. The structural characteristics have a major influence on the physical and mechanical behavior of the suspension. A modeling framework involving a Discrete Element Method (DEM) model with customized particle mechanical interactions is proposed in this paper for the holistic prediction of the physical structure of clay suspensions. The particle interaction force model is based on the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory that accounts for electrostatic repulsion, van der Waals attraction, contact repulsion, etc. Kaolinite is used as the model clay to demonstrate the model performance. The surface charge density of kaolinite is obtained through Atomic Force Microscope (AFM) force measurement and is implemented in the particle interaction force model in the subsequent simulations. Influencing factors, such as centrifugal acceleration, ionic concentration, platy structure of particles, and particle size, on the formation of kaolinite suspensions are studied with the numerical model and compare favorably well with the experimental data. This work lays down a unique framework consisting of computational modeling and microscale characterization of clay particles to holistically predict the characteristics of clay suspensions, which paves the basis to model and predict their bulk physical and mechanical behavior.

Van der Waals interactions induced by fluctuations of electromagnetic field bear universal nature and act between individual atoms, condensed particles or bodies of any type. Continuously growing interest to theoretical understanding as well as to precise evaluation of van der Waals forces is caused by their fundamental role in many physical, chemical, and biological processes. In this paper, we scrutinize progress in the studies of van der Waals forces, related to recent active development of Coupled Dipole Method (CDM) for the analysis of the behavior and properties of nanosized systems. The application of CDM for the analysis of thin liquid films allowed achieving substantial progress in understanding the behavior of free and wetting films. It was shown that both the macroscopic properties, such as excess free energy and Hamaker constants and the local microscopic parameters, such as polarizabilities, can be successfully calculated based only on properties of individual molecules. The impact of lateral film confinement on the specific excess free energy and the film stability was elucidated, and effect of spatial constraints on the spectrum of vibrational states for liquid film and the underlying substrate was analyzed. It was shown that van der Waals interactions between molecules represent the universal mechanism for dynamic structuring and formation of boundary layers and that the CDM allows self-consistently calculating the properties of these layers in both solid and liquid phases.

Purpose – This paper aims to assess the accuracy of Lattice Boltzmann method (LBM) for numerical simulation of the stratification of a Van der Waals (VdW) fluid subjected to a gravity field and non-uniform temperature distribution. A sensitivity analysis of the influence of the pseudopotential parameters and the grid resolution is presented. The effect of gravity force on interface densities, density profiles and liquid volume fraction is studied. Design/methodology/approach – The D2Q9 multiple-relaxation-time pseudopotential LBM for two-phase flow is proposed to simulate the phase separation. The analytical solution for density profiles in a one-dimensional problem is derived and used as a benchmark case to validate the numerical results. Findings – The numerical results reproduce the analytical density profiles with great accuracy over a wide range of simulation conditions, including variations of the gravity and temperature fields. Particularly, the numerical simulations are able to represent the effect of gravity on the existence and position of the liquid– vapor boundary of an ideal pure substance in thermodynamic equilibrium. The sensitivity of the results to variations of the calibration parameters of the VdW pseudopotential was assessed. Research limitations/implications – The numerical simulations were performed assuming a VdW fluid in a 2-D cavity with one periodic direction for which analytical solutions for benchmarking purposes are possible to obtain. Originality/value – The following fundamental question is addressed: Is the pseudopotential LBM capable of simulating accurately the liquid–vapor equilibrium under gravity forces and temperature gradients? Moreover, regarding that the pseudopotential model requires the calibration of several internal parameters to achieve thermodynamic consistency, the sensitivity of the results to variations of these parameters is assessed. Fil: Fogliatto, Ezequiel Oscar. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Clausse, Alejandro. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Grupo de Plasmas Densos Magnetizados. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Grupo de Plasmas Densos Magnetizados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; Argentina Fil: Teruel, Federico Eduardo. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Making a nanoparticle (NP) approach and interact with a plasma membrane (PM) through the receptor-ligand interaction is key for applications like targeted drug delivery, cellular imaging, and theranostics. In this paper, we show that the van der Waals (vdW) interactions dominate the electrostatics ensuring that a gold NP approached the PM more spontaneously as compared to a silica NP. The negative σ (charge density) of a PM induces a negative electrostatic potential at the surface of the approaching gold NP and the silica NP; however, there is very little difference between these induced values due to a small electric double layer at the physiological salt concentration (c∞). Hence there is very little difference in the electrostatic repulsion between the two cases, while the PM-NP vdW attraction is much more for the gold NP as a result of a larger Hamaker constant. Therefore, in comparison to the gold NP, the silica NP would (a) undergo a promotion of the specific adhesion and a prevention of the non-specific adhesion simultaneously for a larger σ − c∞ phase space including the physiological conditions, (b) necessitate a larger length of the ligands to trigger spontaneous receptor-ligand interactions, and (c) require a larger driving force for force-driven receptor-ligand interactions.

In this paper, we show that MoS2 multilayers have mechanical and electrical properties that qualify them as promising channel materials for an n-type piezoelectric FET (PZ-FET). We present extensive density functional theory calculations to investigate the effects of a compressive, out-of-plane stress on MoS2 monolayers and multilayers and extract the corresponding stiffness, as well as the sensitivity to stress of the conduction and valence band edge, and of the effective masses. Then, we use these material properties and a top-of-the-barrier ballistic transistor model to evaluate numerically the ${I}_{\textsf {DS}}$ versus ${V}_{\textsf {G}}$ characteristics of n-type PZ-FETs with an MoS2 channel material. Our results indicate that MoS2 multilayers are the best material option for n-type PZ-FETs, which can reach a subthreshold swing of about 40 mV/decade for a 5-nm-thick piezoelectric layer. This is because the weak interlayer van der Waals bonding makes the conduction band edge in MoS2 multilayers very sensitive to vertical compressive stress. The simulated MoS2 PZ-FETs exhibit large ${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ ratios at low voltage and have better subthreshold steepness compared with the counterpart device employing a 3-D semiconductor.

2D van der Waals chalcogenides such as topological insulators and transition-metal dichalcogenides and their heterostructures are now at the forefront of semiconductor research. In this paper, we discuss the fundamental features and advantages of van der Waals bonded superlattices over conventional superlattices made of 3D materials and describe in more detail one practical example, namely, interfacial phase change memory based on GeTe–Sb2Te3 superlattice structures.

This paper aims to show the characteristics of ultra-thin films for non-Newtonian fluid using Ree-Eyring model where intermolecular forces of solvation and Van der Waal's are considered in addition to the hydrodynamic action to fulfill an identified need for such a conjunction. In this case, the film thickness and pressure distribution are obtained by simultaneous solution of the modified Reynolds’ equation incorporating the effect of non-Newtonian fluid, film thickness equation including elastic deformation caused by all contributing pressures and the load balance equation using Newton-Raphson method with Gauss-Seidel iterations. Effect of changing the operating conditions of speed, load, Eyring shear stress and slide-roll ratio on the characteristic of the contact has been studied. The results show that, for the case where the hydrodynamic action is the only pressure acting to support the applied load capacity, the film thickness and the pressure gradient at the exit of the contact obtained using non-Newtonian model is different than that formed using the Newtonian model especially for the increased value of slide-roll ratio. The main results of this study are that for ultra-thin film, the film thickness formed using non-Newtonian model is smaller compared to that obtained using Newtonian case and the discretization of the film thickness as the gap is reduced occurs similar to the results obtained using Newtonian model. The pressure shape shows no difference compared to that formed using the Newtonian case in which an oscillation around the Hertizan contact pressure shape due to the solvation effect appears. The results also show that for ultra-thin film, changing the Eyring shear stress does not affect the film thickness formation.

In this paper, we consider the following elliptic problem: (0.1) − Δ u + V ( x ) u + λ ( κ α ⁎ | u | p ) | u | p − 2 u = ( κ β ⁎ | u | q ) | u | q − 2 u , x ∈ R 3 , where λ > 0 , 0 α 3 , 0 β 3 , 1 + α 3 p 3 + α , q > 1 and κ α ( x ) = | x | α − 3 , κ β ( x ) = | x | β − 3 . If V = 1 , we show the existence of a ground state solution and multiple solutions, as well as the nonexistence result for (0.1) . Furthermore, we investigate the limit behavior of ground state solutions of (0.1) as λ → 0 + . Ground state solutions are also obtained if the potential V is not a constant.

Nanotubes are easy to collapse due to van der Waals interactions and the low bending stiffness of their walls. The collapse may significantly alter the mechanical, thermal, and electronic properties of nanotubes, which can lead to many exciting applications of nanotubes in nanoelectronics and nanocomposites. In this paper, a theoretical model based on finite deformation beam theory is established to analyze the collapsing of single- and multi-wall nanotubes. Using this model, the critical diameters and the profile of collapsed nanotubes are predicted, which agree well with those obtained by molecular dynamics simulations. Furthermore, a simple scaling law of the critical collapse conditions of carbon nanotubes is built as a function of geometrical parameters, which can determine whether the carbon nanotube collapse. This scaling law can be easily extended to determine the collapsing state of other nanotube systems with different bending stiffness and binding energy.

In this paper, a comprehensive analysis of the nonlinear vibration of an electrostatic nanobeam resonator is presented based on the nonlocal strain gradient theory (NSGT) and by incorporating the Gurtin-Murdoch surface elasticity theory. The Von-Karman geometrical nonlinearity and inter-molecular dispersion forces, i.e., van der Waals and Casimir forces are included in the equation of motion. Both DC and AC components of the electrostatic actuation are regarded as the excitation terms. The nanobeam is considered to be composed of a power-law functionally graded (FG) material. Utilizing Hamilton’s principle, the size-dependent nonlinear equation of motion of the system is derived. Multiple scales technique in conjunction with the differential quadrature method (DQM) is adopted to analytically obtain the solution. Results obtained are shown to be in good agreement against available literature. Static deflection and fundamental natural frequency are obtained for different size-dependent and volume fraction index parameters. Meanwhile, the variation of the oscillation amplitude by the quality factor, excitation magnitude, and frequency is determined near the primary resonance. The acquired results revealed that the nonlocal and strain gradient parameters can significantly displace the multi-valued portions and instability thresholds of the dynamical response diagrams. It is shown that the increment of the volume fraction index reduces the pull-in voltage while increasing any of the size-dependent parameters enlarge the instability voltage. Moreover, the surface effects induce the stiffness hardening behavior, whereas the inter-molecular forces impose the stiffness softening effect.

The topological charge $\epsilon$ of AdS black hole is introduced in Ref.[1,2], where a complete thermodynamic first law is obtained. In this paper, we investigate a new phase transition related to the topological charge in Einstein-Maxwell theory. Firstly, we derive the explicit solutions corresponding to the divergence of specific heat $C_{\epsilon}$ and determine the phase transition critical point. Secondly, the $T-r$ curve and $T-S$ curve are investigated and they exhibit an interesting van der Waals system's behavior. Critical physical quantities are also obtained which are consistent with those derived from the specific heat analysis. Thirdly, a van der Waals system's swallow tail behavior is observed when $\epsilon>\epsilon_{c}$ in the $F-T$ graph. What's more, the analytic phase transition coexistence lines are obtained by using the Maxwell equal area law and free energy analysis, the results of which are consistent with each other., Comment: 11 pages, 5 figures

The use of higher vibration modes and different geometries of the atomic force microscopy (AFM) piezoelectric micro cantilever (MC) is affected by the surface topography quality in a liquid medium. Therefore, utilizing an appropriate MC geometry and vibration mode is of a great importance. This paper analyzes the effect of different types of AFM MCs on the surface topography quality in the noncontact and tapping modes in a liquid medium. The modified couple stress theory (MCS) in a liquid based on the Timoshenko beam theory is used in order to enhance the accuracy of MC dynamic modeling. In addition, the differential quadrature (DQ) method has been used to discrete the equations. Identification of environmental forces helps to measure the accurate MC vibration amplitude. Investigating the effect of geometric and force parameters on the MC vibration behavior leads to understanding the system to design it properly in a liquid medium. Based on the advanced dynamic modeling, the best MC geometry for the specific surface roughness has been determined in the liquid for the surface topography. Also, due to oscillating the MC near the sample surface, the effect of interaction forces between the sample surface and the MC, including van der Waals, contact and squeeze forces is analyzed in a liquid medium in addition to the hydrodynamic forces. Furthermore, due to the reduction of the MC amplitude caused by the squeeze force; the MC is angled in proportion to the horizontal surface.

This paper investigates the postbuckling behavior of a novel glass-protection film system under thermal environment using the element-free kp-Ritz method. The governing formulation is derived based on the first-order shear deformation plate theory considering small strains and the nonlocal elasticity theory which takes small scale effect into account. The modified Newton-Raphson method incorporated with the arc-length continuation technique is used to trace the nonlinear response of the film-foundation system. The influences of boundary conditions, nonlocal parameters, geometry and elastic foundation on the nonlinear response of glass-protection film are examined. The results show that adhesion force between graphene sheets (GSs) film and the elastic substrate can significantly enhance thermal buckling resistance of GSs film. It is also concluded that van der Waals forces between GSs film lead to consistent post-buckling behavior of individual GSs. Present study can provide suggestions on firefighting design, such as setting alarm temperature based on transition temperature.

This paper investigated three process conditions in low temperature plasma treatment using orthogonal array experiments to optimize interfacial adhesion of aramid fiber (AF) III reinforced epoxy composite. The interfacial shear strength (IFSS) of the AF III in the epoxy was measured by single-fiber fragmentation test. Based on the range analysis results, the order of significant factors for IFSS is treatment power > treatment time > treatment pressure. The IFSS increased by 35.5% to 30.44 MPa under optimal conditions, which was found to be treatment power of 67.5 W, treatment time of 11 min, and treatment pressure of 2500 Pa. The interfacial reinforcing mechanism was explored by analyzing the surface morphology, chemical composition, wettability of the AF III, and the cross-section morphology of the broken single fiber-composite. Results indicated that Van der Waals’ force, interfacial friction, interfacial wettability and chemical bonding were responsible for the interfacial improvement.

Full-band atomistic quantum transport simulations based on first principles are employed to assess the potential of band-to-band tunneling FETs (TFETs) with a 2-D channel material as future electronic circuit components. We demonstrate that single-layer (SL) transition metal dichalcogenides are not well suited for TFET applications. There might, however, exist a great variety of 2-D semiconductors that have not even been exfoliated yet; this paper pinpoints some of the most promising candidates among them to realize highly efficient TFETs. SL SnTe, As, TiNBr, and Bi are all found to ideally deliver ON-currents larger than 100{\mu}A/{\mu}m at 0.5-V supply voltage and 0.1 nA/{\mu}m OFF-current value. We show that going from single to multiple layers can boost the TFET performance as long as the gain from a narrowing bandgap exceeds the loss from the deteriorating gate control. Finally, a 2-D van der Waals heterojunction TFET is revealed to perform almost as well as the best SL homojunction, paving the way for research in optimal 2-D material combinations.

The objective of this work continues to be the study of dynamics, stability, and rupture (including contact line motions) of thin liquid films, especially with heat and/or mass transfer. Following the publication of a comprehensive paper on thin-film stability and rupture, taking into account evaporation (condensation), thermocapillarity, surface tension, vapor recoil, van der Waals forces, and mass loss (gain), two follow-up papers have appeared. The first examines the conditions for a non-uniformly-heated liquid film to rupture, owing to thermocapillarity, while the second reports experimental results in excellent agreement with the theory on non-isothermal free-surface problems. Another paper extends some previous results to the case where the viscosity of the liquid is a function of temperature. By proper rescaling, it is shown that the evolution equation can be transformed into the constant-viscosity case, so that previous results can be applied directly. Another paper considers the nonlinear growth, steepening, and wavebreaking of an isothermal thin liquid film draining down an inclined plate. The competition between mean flow and evaporation gives important morphological changes that control the heat-transfer process in the wavy regime. A number of other results were obtained. 9 refs.

Nanoparticles have been claimed to contribute efficiently to e.g. the mechanical strength of composite materials when present as individual particles. However, these particles tend to aggregate. In this paper we prepare nanocrystals from chitin, a product with high potential added value for application in bio-based materials, and investigate the effect of ultrasound on de-aggregation. Chitin nanocrystals with a length ~ 200 nm and a diameter ~ 15 nm, were obtained via acid hydrolysis of crude chitin powder. Freeze drying resulted in severe aggregation and after redispersion sizes up to ~ 200 µm were found. Ultrasound treatment was applied and break up behaviour was investigated using static light scattering, dynamic light scattering, and laser diffraction. Our results suggest that the cumulative energy input was the dominant factor for chitin nanocrystal aggregate breakup. When a critical energy barrier of ~ 100 kJ / g chitin nanocrystals was exceeded, the chitin nanocrystal aggregates broke down to nanometre range. The break up was mostly a result of fragmentation: the aggregation energy of chitin nanocrystal aggregates was quantified to be ~ 370 kJ / g chitin nanocrystals and we hypothesize that mainly van der Waals interactions and hydrogen bonds are responsible for aggregation.

Molybdenum disulfide (MoS2), a typical member of the transition metal dichalcogenides (TMDs) group, is known for its excellent electronic performance and is considered a candidate next-generation semiconductor. The preparation of MoS2 nanoflakes for use as the core of semiconducting devices depends on mechanical exfoliation, but its quality has not yet been optimized. In this paper, a novel exfoliation method of achieving MoS2 nanoflakes is proposed. We find that the size and yield of the exfoliated flakes are improved after thermal treatment for 2 h at a temperature of 110°C followed by precooling for 10 min in ambient air. The new method has the advantage of a 152-fold larger size of obtained MoS2 flakes than traditional mechanical exfoliation. This phenomenon may be attributable to the differences in van Der Waals force and the increase in surface free energy at the interface induced by thermal treatment. In addition, a field-effect transistor (FET) was fabricated on the basis of multilayer MoS2 prepared according to a new process, and the device exhibited a typical depleted-FET performance, with an on/off ratio of ~105 and a field-effect mobility of 24.26 cm2/Vs in the saturated region when VG is 10 V, which is generally consistent with the values for devices reported previously. This implies that the new process may have potential for the standard preparation of MoS2 and even other 2D materials as well.

Layered van der Waals (vdW) materials grown by physical vapor deposition techniques are generally assumed to have a weak interaction with the substrate during growth. This leads to films with relatively small domains that are usually triangular and a terraced morphology. In this paper, we demonstrate that Bi2Se3, a prototypical vdW material, will form a nano-column morphology when grown on GaAs(001) substrates. This morphology is explained by a relatively strong film/substrate interaction, long adatom diffusion lengths, and a high reactive selenium flux. This discovery paves the way toward growth of self-assembled vdW structures even in the absence of strain.

Surface bubbles are present in many industrial processes and in nature, as well as in carbonated beverages. They have motivated many theoretical, numerical and experimental works. This paper presents the current knowledge on the physics of surface bubbles lifetime and shows the diversity of mechanisms at play that depend on the properties of the bath, the interfaces and the ambient air. In particular, we explore the role of drainage and evaporation on film thinning. We highlight the existence of two different scenarios depending on whether the cap film ruptures at large or small thickness compared to the thickness at which van der Waals interaction come in to play., SCOPUS: re.j, info:eu-repo/semantics/published

The aim of this paper is to study the periodic orbits of the generalized van der Waals Hamiltonian system. The tool for studying such periodic orbits is the averaging theory. Moreover, for this Hamiltonian system we provide information on its C(1) nonintegrability, i.e., on the existence of a second first integral of class C(1).

Self-driven photodetectors that can detect light without any external voltage bias are important for low-power applications, including future internet of things, wearable electronics, and flexible electronics. While two-dimensional (2D) materials exhibit good optoelectronic properties, the extraordinary properties have not been fully exploited to realize high-performance self-driven photodetectors. In this paper, a metal–semiconductor–metal (MSM) photodetector with graphene and Au as the two contacts have been proposed to realize the self-driven photodetector. Van der Waals contacts are formed by dry-transfer methods, which is important in constructing the asymmetrical MSM photodetector to avoid the Fermi-level pinning effect. By choosing graphene and Au as the two contact electrodes, a pronounced photovoltaic effect is obtained. Without any external bias, the self-driven photodetector exhibits a high responsivity of 7.55 A W−1 and an ultrahigh photocurrent-to-dark current ratio of ~108. The photodetector also shows gate-tunable characteristics due to the field-induced Fermi-level shift in the constituent 2D materials. What is more, the high linearity of the photodetector over almost 60 dB suggests the easy integration with processing circuits for practical applications.

Quantum spin Hall (QSH) insulator materials feature topologically protected edge states that can drastically reduce dissipation and are useful for the next-generation electronics. However, the nonvolatile control of topological edge state is still a challenge. In this paper, based on first-principles calculations, the switchable topological states are found in the van der Waals (vdW) heterostructures consisting of two-dimensional (2D) Bi(111) bilayer (BL) and $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ by reversing the electric polarization of the ferroelectric $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{In}}_{2}{\mathrm{Se}}_{3}$. The topological switching results from the different charge transfer associated with the two opposite polarization states of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{In}}_{2}{\mathrm{Se}}_{3}$. This new topological switching mechanism has the unique advantages of being fully electrical as well as nonvolatile. Our finding provides an unprecedented approach to realize ferroelectric control of topological states in 2D materials, which will have great potential for applications in topological nanoscale electronics.