Molecular Dynamics Simulation of the Soret Effect on Two Binary Liquid Solutions with Equimolar n-Alkane Mixtures

Molecular dynamics is employed to simulate the Soret effect on two binary liquid solutions with equimolar mixtures: normal pentane (n-pentane, nC-5) and normal heptane (n-heptane, nC-7) molecules plus normal decane (n- decane, nC-10) and normal pentane molecules. Moreover, two coarse-grained force field (the CG-FF) potentials, which may depict inter-/intramolecular interactions fairly well among n-alkane molecules, are developed to fulfill such investigations. In addition, thermal diffusion for the mass fraction of each of these n-alkane molecules is simulated under an effect of a weak thermal gradient (temperature difference) exerting on solution systems from their hot to cold boundary sides. Finally, quantities of the Soret coefficient (SC) for two binary solutions are calculated by means of the developed CG-FF potentials, so as to improve the calculation rationality. As a result, first, it is found that molecules with light molar masses will migrate toward the hot boundary side, while those with heavy molar masses will migrate toward the cold boundary one ; second, the SC quantities indicate that they match relevant experimental determinations fairly well, i.e., trends of these SC quantities show inverse proportionality to the thermal gradient on the systems

Template-induced crystallization of charged colloids: a molecular dynamics study

By using a large enough number of particles and implementing a parallel algorithm on the CUDA platform, we have performed brute-force molecular dynamics simulations to study the template-induced heterogeneous crystallization in charged colloids. Six kinds of templates, whose patterns include the planes of fcc(100), fcc(110), fcc(111), bcc(100), bcc(110) and bcc(111), have been implanted into the middle of the simulation box. Except the fcc(111) template, whose structure benefits not only fcc but also hcp crystals resulting in a similar behavior to homogeneous crystallization, bcc-type templates favor the formation of bcc crystals and bcc-like precursors while fcc-type templates favor the formation of fcc crystals and fcc-like precursors. Therefore, for fcc(100) and fcc(110) templates, heterogeneous crystallization will definitely result in a fcc crystallite. However, the results of heterogeneous crystallization that are induced by bcc-type templates are subtly different at different state points. At the state points where the interaction strength of charged colloids is weak and the fcc phase is thermodynamically stable, the bcc crystals formed with the promotion of bcc-type templates are not stable so as to tend to transform into fcc or hcp crystals. When the interaction strength of charged colloids is high, the predominant bcc crystals formed with the promotion of bcc-type templates can always persist within the time scale of simulation although not bcc but fcc crystals are thermodynamically stable

Analysis of dynamic decomposition for barium dimethyl-naphthalene-sulfonate on an Al3Mg (001) surface from ab-initio molecular dynamics

One important dynamic decomposition pathway for a surface corrosion-inhibitor: barium dimethyl- naphthalene-adfonate, is investigated on a clean Al3Mg (001) binary-alloy surface using ab-initio molecular dynamics based upon density functional theory. Each inhibitor molecule is oriented its functional groups of sulfonic-oxygen bases toward the surface, starting at an initial impact velocity. The dynamic decomposition pathway occurs upon molecular collision with the surface, leading to the decomposed fragments that may clearly represent the initial formation stage of additive thin-film on the surface during a plastic substrate deformation. In addition, three important factors: initial impact speed acting on molecule (kinetic effect), substrate temperature (thermal effect) and initial molecular orientation (geometric effect) etc, are employed to analyze their influences on molecular decomposition. An approach of design-of-experiment (DOE) is applied to an analysis of relative importance for each factor and all factor interactions in above, so as to figure out the best way of surface protection. Final DOE analysis indicates that the most significant factor for promoting molecular decomposition on surface is the substrate temperature, i.e., the higher the substrate temperature, the more rapid decomposition of molecule on surface. While initial impact velocity plays a smaller role, and initial molecular orientation performs less importance to molecular decomposition

Microfluidic Synthesis, Doping Strategy, and Optoelectronic Applications of Nanostructured Halide Perovskite Materials

Halide perovskites are increasingly exploited as semiconducting materials in diverse optoelectronic applications, including light emitters, photodetectors, and solar cells. The halide perovskite can be easily processed in solution, making microfluidic synthesis possible. This review introduces perovskite nanostructures based on micron fluidic channels in chemical reactions. We also briefly discuss and summarize several advantages of microfluidics, recent progress of doping strategies, and optoelectronic applications of light-sensitive nanostructured perovskite materials. The perspective of microfluidic synthesis of halide perovskite on optoelectronic applications and possible challenges are presented

Entire crystallization process of Lennard-Jones liquids: A large-scale molecular dynamics study

By using a graphics processing unit-accelerated parallel algorithm on a compute unified device architecture platform, we perform large-scale molecular dynamics simulations in a Lennard-Jones system to observe the entire crystallization process, including metastable stage, critical nuclei formation, and the stage of crystal growth. Although the intermediated precursors that play a role in determining the polymorphs are predominantly bcc ordered, the polymorph selection is rather different at different stages. The precursors that have a relatively high orientational order will be on average in a denser region than uniform liquids, but microscopically the crystal nucleation happens without a density change. The average density of nuclei first increases significantly, and then almost keeps independent on the crystallite size after the growing post-critical nucleus becomes large enough. With such a large enough system, the crystal growth rate is able to be calculated directly by doing a linear fit to the temporal evolution of growing crystallite size. The obtained value of the growth rate indicates that the actual crystal growth in the Lennard-Jones system where the crystal-liquid interface has several kinds of structures is possibly driven by both collision-controlled and diffusion-controlled mechanisms. Published under license by AIP Publishing

Fcc -> bcc -> hcp successive phase transformations in the strained ultrathin copper film: A molecular dynamic simulation study

The phase transformation behaviors of ultrathin Cu film under uniaxial tensile stress are investigated using molecular dynamic simulation. With the stress increasing, Cu film undergoes a successive phase transformation, i.e. firstly fcc -> bcc, then bcc -> hcp. The phase transformation process is very fast and thorough, i.e., all parents phase can transit into the new phase almost instantaneously. The crystallography mechanisms of two martensitic transformations are exactly corresponding to Bain and Burgers mechanism, respectively. By examining the formation conditions of such phase transformation in Cu film, we reveal that this fcc -> bcc -> hcp successive phase transformation will be subject to the very strict simulation conditions, namely stretching along [100] ( or [010], [001] ) direction, definitive tensile speed (1 x 10(10)/s), appropriate film thickness (0.7230-18.08 nm), low temperature (T <= 10 K), and continuous stretching process without any relaxation procedure

Determination of Bulk Modulus for a Colloidal Crystal with Highly Charged Particles by DC Electric Field

In this study, bulk modulus of a colloidal crystal formed by highly charged particles is experimentally determined by applying direct current electric field. A theoretical expression is also proposed to independently predict the bulk modulus based on van't Hoffs law of osmotic pressure and the theory of Ohshima. The experimental result thus obtained agrees well with the theoretical expectation. In addition, results from both above-mentioned methods coincide with that inferred from the static structure factor