The introduction of the 2D materials in recent years has resulted in an emerging type of the constructed structures called van der Waals heterostructures (vdWHs) that take advantage of the 2D materials in forming atomically thin components and devices. The vdWHs are constructed by the stacking of 2D materials by van der Waals interactions or edge covalent boning. The electron orbitals of the 2D layers in vdWHs extend to each other and influence the electronic band structures of the constituent layers. The tunable optical response over a wide range of the wavelengths (NIR to visible) can be obtained by assembling vdWHs through combining of the monolayers. By application of 2D layers in vdWHs, p-n heterojunctions without lattice mismatch can be formed. The photodiodes based on the van der Waals interactions could be considered as promising candidates for future optoelectronic devices. Furthermore, on-chip quantum optoelectronics can move to the next generation by using 2D materials in vdWHs. In this review, the vdWHs are introduced and their properties and applications in light-emitting diodes (LEDs) have been discussed. The vdWHs allow bandgap engineering, and hence, LEDs working in a range of the wavelengths can be realized. The applications of vdWHs in forming atomically thin components in optoelectronic devices and LEDs have been addressed.

This paper is devoted to investigate the thermodynamic stability of a generic cosmological fluid known as Van der Waals fluid in the context of flat FRW universe. It is treated as a perfect fluid that obeys the equation of state $P=frac{gammarho}{1-betarho}-alpharho^{2}, 0leqgamma<1$, where $rho$ stands for energy density and $P$ stands for pressure of the fluid. In this regard, we discuss the behavior of physical parameters to analyze the evolution of the universe. We investigate whether the cosmological scenario fulfills the third law of thermodynamics using specific heat formalism. Next we discuss the thermal equation of state and by means of adiabatic, specific heat and isothermal conditions from classical thermodynamics we examine the thermal stability.

Effect of interparticle force on the hydrodynamic of gas-solid fluidized beds was investigated using the combined method of computational fluid dynamics and discrete element method (CFD-DEM). The cohesive force between particles was considered to follow the van der Waals form. The model was validated by experimental results in terms of bed voidage distribution and Eulerian solid velocity field. The results revealed that the incorporated model can satisfactorily predict the hydrodynamics of the fluidized bed in the presence of interparticle forces. Effect of interparticle force on bubble rise characteristics such bubble stability, bubbles diameter and bubble velocity, was investigated. It was shown that emulsion voidage increases with the interparticle force in the bed and it can hold more gas inside its structures. In addition by increasing interparticle force, the bubble size and bubble rise velocity increase while the average velocity of particles decreases.

In this work the improved van der Waals equation of state which has been used for vapour-liquid equilibria of polymer-solvent mixtures by previous workers, is extended to consider liquid-liquid equilibria by calculating and evaluating its third parameter (c) for several solvents and polymers such as benzene, cyclohexane, methylacetate, ethylacetate, propylacetate, acetone, polystyrene, polyisobutylene, polyvinylacetate. Also solvent activity in binary mixtures such as benzene-polyisobutylene, cyclohexane-polyisobutylene, ethylacetate-polyvinylacetate, propylacetate-polystyrene, and acetone-polystyrene at various concentrations is evaluated and compared with the experimental results and that of UNIFAC-FV results. The molar volume and activity calculation indicated that this equation has a higher predictability in phase equilibria calculation compared with methods such as UNIFAC-FV. The results showed that the improved van der Waals equation of state can give both upper and lower critical solution temperatures in liquid-liquid equilibria calculations, and this can be considered as an advantage over similar calculation procedures which can only give upper critical solution temperature. It has become evident, however, that using a suitable temperature functionality for the adjustable parameter, k(ij), can improve the results.

In this study a simple and general chemical association theory is introduced.The concept of infinite equilibrium model is re-examined and true mole fractions of associated species are calculated. The theory is applied to derive the distribution function of associated species. As a severe test the application of presented theory to the van der Waals mixture model is introduced in order to perform Vapor-Liquid Equilibrium (VLE) calculations of aqueous ternary mixtures.The calculations are shown to be consistently improving the prediction over the non-associating case. Also, well known empirical models of NRTL and UNIQUAC are applied on the studied systems and their results are compared with proposed model.