We study the phase behaviour of hard oblate ellipsoids with superimposed short-ranged oblate-shaped square-well attractions using the replica exchange Monte Carlo method and a simple van der Waals type perturbation theory. By fixing the square-well range (l ¼ 0.25s k ), we examine the effect of varying the oblates aspect ratio, k ¼ s t /s k , on the density profiles, vapour-liquid and isotropic-nematic phase transitions. We observe that the formation of a liquid phase with vanishing density, an empty liquid, is possible with increasing aspect ratio. Surprisingly, the increasing shape anisotropy does not shift the stability region of the nematic phase to low densities, while the oblate-shaped square-well attraction favours disordered states. For k > 1.5, the critical temperature and packing fraction monotonically decrease with k, while the isotropic-nematic phase boundary moves towards higher packing fractions with decreasing temperature for all k. Simulations show that oblates preferably orientate their faces parallel to the vapour-liquid interface when located at the liquid side of the interface region and perpendicular when located at the vapour side.

The mechanism of complex formation of two oppositely charged linear polyelectrolytes dispersed in a solvent is investigated by using dissipative particle dynamics (DPD) simulation. In the polyelectrolyte solution, the size of the cationic polyelectrolyte remains constant while the size of the anionic chain increases. We analyze the influence of the anionic polyelectrolyte size and salt effect (ionic strength) on the conformational changes of the chains during complex formation. The behavior of the radial distribution function, the end-to-end distance and the radius of gyration of each polyelectrolyte is examined. These results showed that the effectiveness of complex formation is strongly influenced by the process of counterion release from the polyelectrolyte chains. The radius of gyration of the complex is estimated using the Fox-Flory equation for a wormlike polymer in a theta solvent. The addition of salts in the medium accelerates the complex formation process, affecting its radius of gyration. Depending on the ratio of chain lengths a compact complex or a loosely bound elongated structure can be formed.

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Classical molecular dynamics (MD) and density functional theory (DFT) calculations are developed to investigate the dopamine and caffeine encapsulation within boron nitride (BN) nanotubes (NT) with (14,0) chirality. Classical MD studies are done at canonical and isobaric-isothermal conditions at 298 K and 1 bar in explicit water. Results reveal that both molecules are attracted by the nanotube; however, only dopamine is able to enter the nanotube, whereas caffeine moves in its vicinity, suggesting that both species can be transported: the first by encapsulation and the second by drag. Findings are analyzed using the dielectric behavior, pair correlation functions, diffusion of the species, and energy contributions. The DFT calculations are performed according to the BLYP approach and applying the atomic base of the divided valence 6-31g(d) orbitals. The geometry optimization uses the minimum-energy criterion, accounting for the total charge neutrality and multiplicity of 1. Adsorption energies in the dopamine encapsulation indicate physisorption, which induces the highly occupied molecular orbital-lower unoccupied molecular orbital gap reduction yielding a semiconductor behavior. The charge redistribution polarizes the BNNT/dopamine and BNNT/caffeine structures. The work function decrease and the chemical potential values suggest the proper transport properties in these systems, which may allow their use in nanobiomedicine.