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Due to their facile manipulation and transport property, carbon nanotubes (CNTs) are the best candidate for ions and water channels with high selectivity behaviors. In this work, water permeability and salt rejection in the water nanochannel made of CNT(12,12), CNT(13,13) and CNT(14,14) encapsulating fullerene were investigated with or without applying various hydrostatic pressures using molecular dynamics (MD) simulation. In addition to high water permeation, the water nanochannel reduced ion permeation. Based on the results, salt rejection in the channels made of CNT(12.12) and CNT(13.13) encapsulating fullerene was acquired 100%. In the water nanochannel made of CNT(14,14) encapsulating fullerene, a significant water permeability was achieved about 16.22 ± 0.85 × 10−13 cm3.s−1 which is more than the water permeability was reported for the natural water channels and a remarkable salt rejection (~91.62%) was obtained under 5 MPa hydrostatic pressure. It is elucidated that the value of water permeability in this channel was approximately doubled by increasing the hydrostatic pressure. Water and ion permeation, interaction energy of the fullerene with the carbon nanotube surface and the free energy profile for water molecules through the highly selective nanochannels were assessed. In order to study the operation of the water nanochannels, the movement pattern of the fullerene inside the CNT as well as the forces applied to the fullerene was investigated. The motion of the fullerene inside carbon nanotubes was affected by the exerted forces from water molecules on the fullerene and the interaction energy between CNT wall and fullerene. Therefore stronger interaction between fullerene and CNT wall prevents fullerene exiting the nanochannel. The CNT(14,14) encapsulating fullerene shows less energy barrier when water molecules cross the fullerene inside the nanochannel. The aforementioned results demonstrated that carbon nanotube encapsulating fullerene is a high-performance candidate water nanochannel with selective behavior to water molecules and tremendous salt rejection.

Microarray technology plays an important role in detecting the sequence of the genome. In the production of microarrays, the formation of a homogeneous and uniform spot due to biodroplet pining is of great importance. In this work, using the molecular dynamics simulation method, it is possible to create homogeneous spots on the surface of graphene-based surfaces. Hence, the behavior of five different types of DNA including homogeneous sequences of adenine, cytosine, guanine, and thymine as well as heterogeneous sequence of bases in the water droplets, was subjected to a double-layer graphene substrate with a pillar structure. The results showed that double layer graphene with pillar pattern are successful in pinning of biodroplet and this substrate leads to the differnet placement of Oligonucleotide probes. Also, the results of wettability demonstrated that the formation of hydrogen bond between a single strand and water molecules reduces the spreading and increases the contact angle and height of biodroplet containing oligonucleotides with respect to the water droplet without oligonucleotides on the surface of the double layer graphene in pillar pattern. The results of the simulation of single-stranded DNA after equilibration showed that single strand of adenine and heterogeneous single strands had the least folding compared to other single strands, and the single strand of adenine produced the most stable structure. Hence, single-stranded adenine is stretched more compared to other single strands, which is due to the lack of tendency of this single strand for internal hydrogen bonds and regular spiral structure resulting from a strong internal π-π stacking interaction. As a result, single strand of adenine is more accessible to detect target single strands for use in microarrays.

In the current investigation, reactive molecular dynamics simulation has been used to study and compare the dissociation behavior of water molecules on defect-free and defective rutile TiO2 (1 0 1) surface. According to the contour map for a water molecule on the TiO2 (1 0 1) surface, water molecules have proven to dissociate around 20 times faster in the defective surface rather than defect-free surface. In the presence of defects, the oxygen atoms near the defects have lower electrostatic potentials and therefore higher reactivity which adsorption of molecules to the defects and their vicinity increases while for the defect-free surface, water molecules are adsorbed like clusters and exhibit lower dispersion. Also investigation of the density profile has proven water molecules have better dispersion through the defective surface. Namely, presence of defects leads water molecules to be adsorbed at different spots through the surface. In addition to the density profile, dissociation of water molecules to hydroxyl groups and respective diffusion of hydrogen atoms into the surface (down to the second sub-layer) has been undertaken through inspection of contours for water molecules in the defective surface throughout the simulations.

In this work, the behavior of a water nano-droplet on hydrophilic graphene oxide (GO) is studied at high temperatures using molecular dynamics simulation. The results showed that, with increasing temperature, spreading would overcome the evaporation of water molecules on the surface of GO. At high temperatures, the regime changes from partial to total wetting. After the spreading is complete and the surface is completely covered by water, evaporation of water occurs more rapidly. Simulation results revealed that as the system temperature rises, the number of hydrogen bonds between water molecules decreases. The water molecules reorient to the GO surface as the temperature increases and the number of possible H-bonds inside the bulk of the droplet decreases. However, the formation of H-bonds between water molecules and GO increases with temperature. The results obtained in terms of the contact angle and the density of the water molecules on the surface of the GO revealed that at different temperatures more water molecules spread on the surface of GO during simulation time. Increasing the temperature leads to increase in the number of evaporated water molecules from the surface of GO. Investigations of the dipolar momentum of water molecules in different layers of GO surface showed that water molecules in the initial layers tend to approach the surface with hydrogen atoms.

Wettability of water nanodroplet on graphene and graphene-coated metals in recent years have been the subject of interest. In the present work, the wettability of mono and three-layer graphene supported on underlying platinum was investigated using molecular dynamics simulation. Furthermore, the striped patterns were generated on the substrates by parallel grooves with different widths and depths. Wetting results showed that the Cassie-Baxter state converts into the Wenzel state by increasing the width of the grooves, which was confirmed by free energy results that obtained from free energy perturbation and potential of mean force methods. A chain of water molecules forms at interface by increasing the width of the grooves, which leads to higher hydrogen bond lifetime. Water-platinum interaction in the grooves and nanodroplet pinning cause anisotropy in the wetting and nanodroplet shape. This suggests that such artificial surfaces with anisotropic wetting properties can mimic water anisotropic behavior on some natural structures, which lead water to move in a specific direction.

Nano-structures play an important role in oil-water separation, and it has recently been shown that nano-particles of titanium dioxide succeed in oil-water separation. In the current study, the behavior of oil-water mixture on a titanium dioxide substrate in the presence and in the absence of surfactant was studied using molecular dynamics simulation. Simulation results indicate that in the presence of surfactant, the oil-water interfacial tension decreases as a result of hydrogen bonding between water and the hydrophilic head of the surfactant. This is particularly illustrated by the calculation of both lifetime as well as number of hydrogen bonds and leads to the separation of water from oil.