Nanoslit Pores Research Articles

Molecular Dynamics Study of Water Transport Property in Micro Hydrophobic Pore

In this study, the transport property of a water droplet in the nano hydrophobic pore was clarified by molecular dynamics simulation. The size dependence of the transport property of the water droplet in a nano slit pore was focused. Considering several models of the nano pore, the differences of the structures of water droplets were shown and these differences were discussed from the viewpoint of the interaction between hydrophobic walls. Furthermore, forces by the hydrophobic walls were evaluated. From these results, the dependence of the width of the pore and the size of the droplet were clarified. Moreover, the effect of the liquid-vapor interface was considered.

Lateral Pressure Tensor of Confined Fluids in Nanoslit Pores

Full text available. Keywords: Lateral pressure tensor, Lennard-Jones confined fluid, hard-sphere confined fluid, nanoconfined fluid, nanoslit pore, transverse pressure tensor, Pressure Tensor

Population Inversion of Binary Lennard-Jones Mixtures in Nanoslit Pores (A Density Functional Theory Study)

The aim of this work is to investigate the population inversion of binary asymmetric Lennard-Jones mixtures inside nanoslit pores due to confinement effects for both vapor and liquid phases. For this purpose we have used mean field fundamental measure theory, and the effect of different parameters such as interaction strength and size ratios of the components, confinement size, and thermodynamic state on the population distribution of molecules have been studied. It has been shown that in the case of bulk liquid mixtures, increasing the role of confinement effects can lead to preferential adsorption of the component with larger size and weaker intermolecular interactions into the nanopore in spite of its minority in the bulk which is referred as population inversion. This population inversion phenomenon is terminated by a sudden condensation which, interestingly, involves a simultaneous adsorption and desorption for more and less bulk concentrated species, respectively. We have demonstrated that this condensation phenomenon shifts to higher bulk densities with increasing the role of confinement effects such that in some cases population inversion is observable for the whole range of densities. In consideration of the conditions in which vapor Lennard-Jones mixtures undergo capillary condensation, the population distribution of components in the vapor- and liquidlike phases was studied. It has been shown that variation of parameters such as interaction strength and size ratios, temperature, and confinement size can lead to conditions in which capillary condensation is accompanying with a population inversion phenomenon. In these cases, whereas the composition of vaporlike phases is the same as bulk fluid, liquidlike phases are richer in the component with less bulk concentration.

Attractive energy contribution to nanoconfined fluids behavior: the normal pressure tensor

The aim of our research is to demonstrate the role of attractive intermolecular potential energy on normal pressure tensor of confined molecular fluids inside nanoslit pores of two structureless purely repulsive parallel walls in xy plane at z = 0 and z = H, in equilibrium with a bulk homogeneous fluid at the same temperature and at a uniform density. To achieve this we have derived the perturbation theory version of the normal pressure tensor of confined inhomogeneous fluids in nanoslit pores: $$ P_{ZZ} = kT\rho \left( {Z_{1} } \right) + \pi kT\rho \left( {Z_{1} } \right)\int\limits_{ - d}^{0} {\rho \left( {Z_{2} } \right)} Z_{2}^{2} g_{Z,H} (d){\text{d}}Z_{2} - \frac{1}{2}\iint {\int\limits_{0}^{2\pi } {\phi^{\prime } \left( {\vec{r}_{2} } \right)\rho \left( {Z_{1} } \right)\rho \left( {Z_{2} } \right)g_{Z,H} (r_{2} )} }{\frac{{Z_{2}^{2} }}{{(R_{2}^{2} + Z_{2}^{2} )^{{\frac{1}{2}}} }}}R_{2} {\text{d}}R_{2} {\text{d}}Z_{2} {\text{d}}\Uptheta ;\quad \left| {\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {r}_{2} } \right| > d $$ In which R, Θ, Z are the cylindrical coordinate’s notations and \( \left| {\vec{r}_{2} } \right| = \sqrt {R_{2}^{2} + Z_{2}^{2} }\). Assuming the truncated-Lennard-Jones potential, the third term represents the attractive intermolecular potential energy contribution to the normal pressure tensor. We report solution of this equation for the truncated-Lennard-Jones confined fluid in nanoslit pores, and we demonstrate the role of attractive potential energy by comparing the results of Lennard-Jones and hard-sphere fluids. Our numerical calculations show that the normal pressure tensor has an oscillatory form versus distance from the walls for all confined fluids. The oscillations increase with reduced bulk density and decrease with fluid–fluid attraction. It also becomes broad and smooth with pore width at constant temperature and density. In comparison with hard-sphere confined fluids, the values of the normal pressure for LJ fluids at all distances from the walls are less than the hard-sphere fluids. This analytic pressure tensor equation is a useful tool to understand the role of attractive and repulsive forces in the normal pressure tensor and to predict phase behavior of nanoconfined fluids.

T0501-1-4 ナノ細孔内における液滴の移送現象([T0501-1]マイクロ・ナノスケールの熱流体現象(1))

In this research, we reported the dependence of pore size on the characteristics of transport phenomena of confined water in a nano slit pore by molecular dynamics (MD) simulation. The two surfaces were made of graphite, whose distance was set at 15, 30, and 60 A. The interaction potential between water and carbon was Lennard-Jones potential, and that between water molecules was SPC/E. The water formed a film in each system. The film moved when constant fictitious force parallel to the walls was given to water molecules in the pore. From the results, we examined dependence on width of the velocity of water in the slit pores.

0307 グラファイト細孔内を移動する水の界面張力(OS302 ナノスケールの熱流動現象,オーガナイズドセッション)

In this research, we reported the dependence of pore size on the characteristics of transport phenomena of confined water in a nano slit pore by molecular dynamics (MD) simulation. The two surfaces were made of graphite, whose distance was set at 15 and 30 Å. The interaction potential between water and carbon was Lennard-Jones potential, and that between water molecules was SPC/E. The water formed a film in each system. The film moved when pressure gradient parallel to the walls was given to water molecules in the pore. From the results, we examined dependence of the velocity of water in the slit pores on pore width.

Behavior of confined fluids in nanoslit pores: the normal pressure tensor

The aim of our research is to develop a theory, which can predict the behavior of confined fluids in nanoslit pores. The nanoslit pores studied in this work consist of two structureless and parallel walls in the xy plane located at z = 0 and z = H, in equilibrium with a bulk homogeneous fluid at the same temperature and at a given uniform bulk density. We have derived the following general equation for prediction of the normal pressure tensor Pzz of confined inhomogeneous fluids in nanoslit pores: $$ P_{zz} = kT\rho \left( {r_{1z} } \right)\left[ {1 + \frac{1}{kT}\frac{{\partial \phi_{\text{ext}} }}{{\partial r_{1z} }}{\text{d}}r_{1z} } \right] - \frac{1}{2}\int\limits_{v} {\varphi^{\prime}(\vec{r}_{12} )\rho^{(2)} \left( {\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {r}_{12} ,\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {r}_{1} } \right)} \frac{{(r_{12z} )^{2} }}{{\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {r}_{12} }}{\text{d}}\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {r}_{12} , $$ where \( \vec{r}_{12} \equiv \vec{r}_{1} - \vec{r}_{2} \) is the intermolecular position vector of molecule 2 with respect to molecule 1 and \( r_{12z} = |\vec{r}_{12} |_{z} \) is the projection of distance of molecule 1 from molecule 2 in the z-direction. This equation may be solved for any fluid possessing a defined intermolecular pair-potential energy function, \( \varphi \left( {\vec{r}_{12} } \right) ,\) confined in a nanoslit pore and with a given fluid molecules—wall interaction potential function ϕext. As an important example of its application we have solved this equation for the hard-sphere fluid confined between two parallel–structureless hard walls with different nanometer distances and at various uniform bulk densities. Our results indicate the oscillatory form of the normal pressure tensor versus distance from the wall at high densities. As the density of the nanoconfined fluid decreases, the height and depth of the normal pressure tensor oscillations are reduced.

BEHAVIOR OF THE CONFINED HARD-SPHERE FLUID WITHIN NANOSLITS: A FUNDAMENTAL-MEASURE DENSITY-FUNCTIONAL THEORY STUDY

A property of central interest for theoretical study of nanoconfined fluids is the density distribution of molecules. The density profile of the hard-sphere fluids confined within nanoslit pores is a key quantity for understanding the configurational behavior of confined real molecules. In this report, we produce the density profile of the hard-sphere fluid confined within nanoslit pores using the fundamental-measure density-functional theory (FM-DFT). FM-DFT is a powerful approach to studying the structure and the phase behavior of nanoconfined fluids. We report the computational procedure and the calculated data for nanoslits with different widths and for a wide range of hard-sphere fluid densities. The high accuracy of the resulting density profiles and optimum grid-size values in numerical integration are verified. The data reveal a number of interesting features of hard spheres in nanoslits, which are different from the bulk hard-sphere systems. These data are also useful for a variety of purposes, including obtaining the shear stress, thermal conductivity, adsorption, solvation forces, free volume and prediction of phase transitions.

Pore Size or Geometry: Which Determines the Shape and Inverse-Shape Selective Adsorption of Alkane Isomers?

The adsorption of pure pentane (C(5)) isomers and their ternary mixture is simulated in a series of carbon nanoslits. With decreasing nanoslit pore size, shape selective adsorption first occurs in the order of nC(5) > or = iC(5) > neoC(5) due to the configurational entropy effect, then inverse-shape selective adsorption occurs in the order of nC(5) < iC(5) < or = neoC(5) due to the area entropy effect, and finally no adsorption occurs. The entropy effects lead to a large adsorptive separation among the C(5) isomers from their mixture. Similar behavior has been observed from the simulation of C(5) adsorption in carbon nanotubes with variation in pore size. These results reveal that pore size rather than geometry determines the shape and inverse-shape selective adsorption of alkane isomers in nanopores.