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Flow separation near the fluid-solid surface has attracted attention for decades. It is critical to understand the behavior of separated flow adjacent to the solid walls to broaden its range of potential applications. Therefore, we conducted molecular dynamics investigations to consider water flow separation at the water-carbon nanotube (CNT) interface for different diameters of CNTs between 13 and 50 Å and different pressures of 0.1-1.254 GPa. Density heat maps indicated that water flow separation is observed for all CNTs under high pressures, and an empty space of water molecules or evacuation is formed behind the CNTs. It is shown that in CNTs with small diameters, (10, 10) and (20, 20), the structure of the first layer (FL) of water molecules or hydrated layer adjacent to the CNT wall is completely preserved, indicating that evacuation occurs from behind the CNTs. In (30, 30) and (40, 40) CNTs, flow separation occurred from the FL of water molecules near the solid surface, and the layered structure of water around CNTs is completely destroyed. Our findings of fluid-solid and fluid-fluid interaction energies suggested that the flow separation can be due to an attraction between the FL of water molecules and CNT and a repulsion between the water molecules in the hydrated layer and the outer layers. Moreover, analyzing the relationship between the CNT size and flow separation revealed that in the case of small CNTs, there are extra water molecules that contribute to the structural stability of the hydrated layer by strengthening the repulsive interaction in the liquid-liquid surface.

Following the exceptional electrical and optical properties of black phosphorene, its wetting behavior has attracted the attention of many researchers. In the present study, reactive molecular dynamics (MD) simulations have been used to investigate the controlled wetting behavior of black phosphorene surface. In the first step, the hydrophobic behavior of the pristine black phosphorene as well as the elliptical shape of the water droplet on this surface was investigated using MD simulations which are in agreement with the recently reported experimental data. In the next step, controlled hydrophilization of black phosphorene was performed through oxidation of the pristine black phosphorene in different sizes. The simulation results showed that oxidation of the black phosphorene surface turns it into a superhydrophilic surface by increasing the number of hydrogen bonds. It was observed that, by placing water droplets on the phosphorene oxide surfaces a wide range of wettability phenomena can be created so that a wide range of contact angles can be measured. The results indicated that the placement position of water molecules on the phosphorene oxide surface leads to two different wetting patterns. Also, in agreement with the results of the energy profile of the phosphorene surface, calculations of Helmholtz free energy showed that the energy barrier in the armchair direction of the phosphorene surface is higher than that in the zigzag direction. The results could lead to new applications of phosphorene to control wettability at the nanoscale.

In this paper, a series of equilibrium molecular dynamics simulations (EMD), steered molecular dynamics (SMD), and computational electrophysiology methods are carried out to explore water and ion permeation through mechanosensitive channels of large conductance (MscL). This research aims to identify the pore-lining side chains of the channel in different conformations of MscL homologs by analyzing the pore size. The distribution of permeating water dipole angles through the pore domains enclosed by VAL21 and GLU104 demonstrated that water molecules are oriented toward the charged oxygen headgroups of GLU104 from their hydrogen atoms to retain this interaction in a stabilized fashion. Although, this behavior was not perceived for VAL21. Numerical assessments of the secondary structure clarified that, during the ion permeation, in addition to the secondary structure alterations, the structure of Tb-MscL would also undergo significant conformational changes. It was elucidated that VAL21, GLU104, and water molecules accomplish a fundamental task in ion permeation. The mentioned residues hinder ion permeation so that the pulling SMD force is increased remarkably when the ions permeate through the domains enclosed by VAL21 and GLU102. The hydration level and potassium diffusivity in the hydrophobic gate of the transmembrane domain were promoted by applying the external electric field. Furthermore, the implementation of an external electric field altered the distribution pattern for potassium ions in the system while intensifying the accumulation of Cl

In this study, we introduce a superfast biomimetic water channel mimicking the hydrophobicity scales of the Aquaporin (AQP) pore lining. Molecular dynamics simulation is used to scrutinize the impact of hydrophilic doping level in the nanotube and the water-wall interaction strength on water permeability. In the designed biomimetic channel, the constructive interplay of Lennard-Jones (LJ) e parameters and hydrophilic doping levels increased the possibility of ultrafast water transport. Moreover, a unique set of LJ parameters is discovered for each biomimetic channel with different hydrophilic doping levels, enhancing water permeation. Inside high-performance biomimetic channels, water distribution surprisingly implies a varying pore geometry that narrows down in the middle, mimicking the pattern obtained from GplF pore analysis, evoking the narrow pore induced by the aromatic/arginine selectivity filter. This exciting accordance occurred as a result of tailoring specific hydrophilic arrays within the hydrophobic channel backbone by mimicking the AQP pore interior. The main takeaway of hydrophilic doping arrays implanted within the hydrophobic nanotube is to break the large barrier in the water-wall vdW energy profile into multiple reduced ones to increase water conduction. Consequently, the "water jumping" phenomenon in the middle of the biomimetic channel occurs under specific circumstances. The biomimetic channel with the highest value of water permeability of about 13.67 ± 0.66 × 10-13 cm3·s-1 exhibits the best mechanism for artificial water channels (AWCs), serving superfast water transport considering the low entrance barrier and weak water-wall interaction.

In this paper, we analyze the shape of two-dimensional and three-dimensional drops on flat and curved substrates by minimizing free energy with the variational approach. The process initiated from the flat substrate and has proved the drop shape equation. Then, the drop shape equation for these models has been determined by extending the method to curved substrates. The constraints in 2D and 3D models are constant surface area and volume, respectively. The Euler–Lagrange differential equation can be solved analytically in the two-dimensional case and the drop height as a function of x has been driven which is the equation of a circle. In the 3D model, a fundamental partial differential equation (PDE) has been obtained but it cannot be solved analytically and has been solved through a numerical method. This PDE becomes a first-order ordinary differential equation (ODE) after two reduction steps and is solved by the Euler explicit method. Six different systems are simulated and a logical algorithm is introduced to compare the results of the simulation, numerical, and analytical. The simulation results determined there is an iso-density curve or surface that is closest to the analytical result. It has revealed the solution of the three-dimensional case is not a sphere. The spherical cap approximation (SCA) has been widely used in many wettability studies. Comparison of numerical and SCA results have determined this assumption is valid only for contact angles far from 90 degrees. The present results are determined all the drops on each surface can be described by only one equation if the contact angle is measured for the line (in the case of a 2D drop) or the passing plate (in the case of a 3D drop) from the drop edges. The substrate characteristics at the three-phase contact point (TPCP) and the three-phase contact line (TPCL) are the only factors determining the drop shape. The other points and areas away from TPCP and TPCL have not influenced the drop shape.

Microarrays play a determinant role in the detection and specification of biological molecules. The immobility of probe oligonucleotide with different sequences on the substrate surface is one of the main aims in designing of microarrays. In this regard, we select five different DNA single-strands to determine the best of probe single strand in the microarrays with a striped patterned double-layer graphene substrate. The results of the simulation illustrate that DNA single-strands on the substrate have distinct conformations related to each other. Thymine single strand has the maximum end to end distance and is more accessible for detecting target single strand in the microarrays. Also, the analysis of wettability results displays that the presence of a DNA single-strand in water drop decreases the amount of spreading of the droplets. Another important point is that the presence of a single strand increases the chance of water droplet pining on such surfaces.

Studying the structure and dynamics of nano-confined water inside carbon nanotubes has consistently attracted the wide-spread interest of researchers. In the present work, molecular dynamics simulations indicated internal nonwetting behavior for the central region of the long and narrow single-wall carbon nanotube (5,5) (SWNT) and showed that continuous single-file water molecules are not formed through it. Unlike the SWNT, by adding boron nitride nanotubes (6,6) as an outer wall to the SWNT, a continuously long single-file water chain is formed through the double-walled carbon and boron nitride hetero-nanotube (DWHNT) and thorough internal wetting of the DWHNT is observed. The position and the number of water molecules, electrostatic potential heatmap of the nanotube's wall, free energy profile of nano-confined water, and number of hydrogen bonds between them confirmed the aforementioned results and complete internal wetting of the DWHNT. After using the boron nitride nanotube (6,6) as the outer wall, an homogeneous electrostatic potential distribution in the DWHNT and increase in the hydrophilic characteristics of the nano-channel wall are observed, bringing about gradual trapping of more water molecules through it. Finally, water molecules occupied the central region of the DWHNT and a thorough single-file water chain is formed inside the nano-channel. Water dipole orientation inside the DWHNT and their radial distribution function asserted the occurrence of the liquid-solid quasi-phase transition of single-file water molecules confined inside the long and narrow carbon nanotube (5,5) under ambient conditions.

A new solvent stimuli-responsive metallogel (VGel) was synthesized through the introduction of vanadium ions into an adenine (Ade) and 1,3,5-benzene tricarboxylic acid (BTC) organogel, and its supramolecular self-assembly was investigated from a computational viewpoint. A relationship between the synthesized VGel integrity and the self-assembly of its components is demonstrated by a broad range of molecular dynamics (MD) simulations, an aspect that has not yet been explored for such a complex metallogel in particular. MD simulations and Voronoi tessellation assessments, both in agreement with experimental data, confirm the gel formation. Based on excellent water stability and the ethanol/methanol stimuli-responsive feature of the VGel an easy-to-use visualization assay for the detection of counterfeit liquor with a 6% (v/v) methanol limit of detection in 40% (v/v) ethanol is reported. These observations provide a cheap and technically simple method and are a step towards the immersible screening of similar molecules in methanol-spiked beverages.

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.

The current work investigates the separation of water–oil mixture on amorphous poly methyl methacrylate (PMMA) surface in the absence and presence of Anatase and Rutile titanium dioxide nanoparticles using molecular dynamics simulation. The presence of nano domains with positive and negative charges on PMMA surface causes the water molecules to form water clusters of various sizes. Water clusters can slide on the PMMA surface which leads to the formation of larger clusters and in continues formation of large clusters was the reason of separation water–oil mixture. In the presence of Anatase and Rutile nanoparticles, accumulation of water molecules around the particles leads to formation of larger water clusters and improves the separation of water–oil mixture. Anatase nanoparticle acts faster than Rutile nanoparticle in the adsorption of water molecules, while Rutile nanoparticle forms larger clusters and is more successful in adsorbing water molecules from the water–oil mixture. The orientation and the order parameter of water molecules in different layers from PMMA surface and around the Anatase and Rutile nanoparticles are investigated as well.

This work presents a molecular dynamics simulation study on the interfacial characterization of graphene/epoxy nanocomposites. In polymeric nanocomposites, the thermo-mechanical properties of a system strongly depend on the characteristics of the interphase region between the matrix and the inclusions. The first step in the characterization of this interphase is to distinguish its border limit (i.e., the interphase thickness). Here, we present a methodology to systematically quantify the interphase thickness based on analyzing the variation of the local mass density profile. To this end, three functions (average accumulated mass density, accumulated standard deviation (ASD) and its first derivative) are successively applied on the local mass density profile. Using this procedure, the interphase limit can be easily detected regardless of the oscillatory nature of the local mass density. The effect of the epoxy crosslinking density and number of graphene layers on the interphase thickness is then investigated, and the results are analyzed by studying the interaction energies, polymer dynamics and distribution quality of reacted and unreacted components, as well as conformational changes of the polymer chains in the interphase region. The results reveal that the crosslinking density is the most influential parameter on the interphase thickness: the higher the crosslinking degree, the thicker the interphase region. To a lower extent, the interaction energy has also an effect on the interphase thickness since there is an inverse relationship between the interaction energy and the crosslinking density in our case study. Overall, the reported findings highlight useful insights into the detection and properties of the interphase region in thermoset composites.

In this work, we investigate the effect of silicon substrate and temperature on the ice formation through molecular dynamics simulations. It was found that silicon substrate accelerates the ice formation rate. Depending on the temperatures of the systems, the formation rate can be accelerate or decelerated. The obtained results showed that, as the temperature increased from the lowest temperature 100K to the highest temperature 220K, the number of water molecules transformed into ice decreased. We found that the hydrophobic property of silicon is not a barrier for approaching ice formation. The high correlation between Si and the hydrogen atoms of water molecules stimulated the ice formation on the surface of silicon and allowed the formation of amorphous ice directly on the surface of silicon. The temperature effect on ice formation was in distinguishing two different behaviors one from 100K to 180K and the second above 180K. These behaviors were related to the temperature of which amorphous ice is stable. The results of the average number of hydrogen bonds and their lifetime are in parallel with the results of the number density profiles that can best explain how silicon affects the ice formation. The coordination number of water molecules increased with the decrease of the temperature for silicon substrate which means that bigger ice clusters were found. The ice molecules, which were formed near the silicon substrate, are more recognized than that of the bulk. To better understand these effects, bulk systems were used as comparative systems.

Increasing the hydrophobicity of polymeric surfaces, particularly polydimethylsiloxane (PDMS), has recently been the focus of research. In the present work, the wettability of smooth and rough PDMS surface was investigated. Surfaces with different chemical heterogeneity were examined for hydrophobicity using molecular dynamics simulation. In order to simulate surfaces with different heterogeneities, several distributions for the placement of polymer-forming atoms were taken into account. In addition, roughnesses with different distributions of the constituent atoms were applied to the polymer surfaces to increase hydrophobicity. As an indicator of the hydrophobicity, the contact angle was calculated using two approaches. Regarding the chemical heterogeneity of the polymeric surface, the simulation results showed that the contact angle and the radius of water droplets on the surface depended on the constituent atoms and their number, so that surfaces with more carbon atoms offered larger contact angles and smaller droplet radius, and thus more hydrophobicity. Furthermore, roughnesses rich in carbon also increased the surface hydrophobicity. It was concluded that the distribution of the constituent atoms of the polymeric surfaces played an essential role in water dispersion in that the number of carbon atoms at the pinning points of water droplets was higher than that of others.

The inhibition of water permeation through aquaporins by ligands of pharmaceutical compounds is considered as a method to control the cell lifetime. The inhibition of aquaporin 1 (AQP1) by bacopaside-I and torsemide, was explored and its atomistic nature was elucidated by molecular docking and molecular dynamics (MD) simulation collectively along with Poisson-Boltzmann surface area (PBSA) method. Docking results revealed that torsemide has a lower level of docking energy in comparison with bacopaside-I at the cytoplasmic side. Furthermore, the effect of steric constraints on water permeation was accentuated. Bacopaside-I inhibits the channel properly due to the strong interaction with the channel and larger spatial volume, whereas torsemide blocks the cytoplasmic side of the channel imperfectly. The most probable active sites of AQP1 for the formation of hydrogen bonds between the inhibitor and the channel were identified by numerical analysis of the bonds. Eventually, free energy assessments indicate that binding of both inhibitors is favorable in complex with AQP1, and van der Waals interaction has an important contribution in stabilizing the complexes.

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.

Evaporation of water nanodroplets on a hydrophilically adjusted graphene sheet was studied based on a molecular dynamics approach. Suspended graphene was used as a physically heterogeneous surface, and fixed graphene was considered as an ideally flat surface. State of the triple-phase contact line (TPCL) and shape evolution were addressed at four different temperatures on both substrates. Additionally, contact angle (CA) was studied during 3 and 22.5 ns simulations in both closed and opened conditions. The observed constant contact angle regime was predictable for the fixed graphene. However, it was not expected for the suspended system and was attributed to the oscillations of the substrate atoms. The size of the nanodroplet also affects the constant-contact-angle mode in both systems, when the number of water molecules decreases to less than 500. The oscillations created a surface on which physical heterogeneities were varying through time. Examination of the evaporation and condensation processes revealed higher rates for the fixed systems. Local mass fluxes were calculated to reveal the contribution of TPCL and meridian surface (MS) of the nanodroplet to evaporation and condensation. The obtained results indicate similar values for the mass flux ratio at the TPCL, which remains twice as large as the MS for both suspended and fixed graphene. The results confirm the assumption that a surface with varying heterogeneities can overwhelm the droplet and act as an ideally flat surface.

Recently, graphene oxide has been widely used for the extraction of hydrocarbon compounds. In the present work, the separation of water from a water-oil mixture by two-layer graphene oxide has been studied using molecular dynamics simulation. Several interlayer spacing of graphene oxide layers was considered, and for each gap in each layer of graphene oxide, several sizes were considered and it was determined the efficient interlayer distance as well as gap size which gives highest water-oil separation. The simulation results unveil that as the interlayer spacing and the size of the gap is reduced, the flux and permeability of the water molecules decrease, but the amount of water molecules separating from the oil increases. To study the number of layers’ impact for higher separation efficiency, a system containing a graphene oxide layer was also studied and the importance of the number of graphene layers was highlighted. Also, for the analysis of graphene oxide functional groups’ effect on separation, a system containing graphene layers was also investigated and the role of functional groups was revealed in hydrogen bond formation between graphene oxide and water molecules. By calculating PMF, the effect of functional groups on the repelling oil molecules from the graphene oxide’s gaps was investigated.

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.

In this work, desalination by multilayer graphene membranes with a rippled structure has been considered by molecular dynamics simulation. The (6, 7.5 and 9) A distances between the graphene sheets in a layer (gap wide) are selected. Also, these mentioned distances are applied as an interlayer space (channel height). Results of simulation demonstrate that multilayer graphene membranes with a rippled structure are more efficient in water flux than multilayer graphene membranes with an unrippled structure. These differences are more significant for membranes with 9 A interlayer space. In this work, it is shown that water flux in 9 A rippled membrane is 20% more than 9 A unrippled one. According to the simulation results, multilayer membranes with a rippled and unrippled structure are different significantly in the case of water flux, but they do not show many differences with each other in rejection. Also, it is shown that the effect of channel is more important than gap; because ions lose more number of water molecules when flow through the channel as compared to flow through gap or pores. From calculation of density, the water flux, ions rejection and coordination number of ions, the results of investigation are obtained.

Understanding the properties of the interface of water nano-droplet and rutile TiO2 (110) nanocrystal has attracted the attention of many surface scientists. In this research the interface of water nano-droplet and (110) plane of Rutile titanium dioxide nanocrystal along with the formation of water chains was studied based on a molecular dynamics approach. Density profiles of oxygen and hydrogen atoms of the water molecules show less movement in hydrogen atoms that reside closer to the TiO2 surface than the ones that are further away. The calculated results indicate that the average interlayer hydrogen bonds per water molecule is about 0.51 at the interface where water molecules form two different water-water hydrogen bonds with 28.55 and 670.24 ps lifetimes. The simulation data reveal the formation of one-dimensional chain structures of water on the TiO2 substrate. Certain values for the estimated angles among every three water molecules that participate in the formation of the chain structures is observed. The electrostatic energy contour map and the orientation of water molecules at the interface suggests that these molecules form ordered and periodic pair structures around the regions with high negative charge on titanium dioxide. The dynamical analysis of the water molecules indicates a dynamical independence from one another which results in their independent motion at the interface. Furthermore, the dynamical results also show that the water nano-droplet is pinned on the surface of titanium dioxide without any major movement.

Water adsorption and wetting of titanium dioxide surface along with its structure and dynamics of liquid water molecules has recently been studied as an important subject. In the current work, the interface of water and (110) surface of titanium dioxide is analyzed based on the formation and distribution of water molecules in the first and second layer from a molecular dynamics perspective. The simulation results illustrate that the water molecules form a linear chain in the interfacial layer, also known as the first layer. As the number of water molecules increases a second layer forms while the TiO 2 surface remains partially dry. Further increase results in the exchange of water molecules between first and second layers which facilitates the filling of the first layer. These results are extracted from density profiles, lifetime and number of hydrogen bonds in different layers, order parameter, mean squared displacement and, the orientation of water molecules at different distances from the surface all of which are in line with the reported quantum calculations and experimental data.

In the present work, wetting behavior of an ionic liquid droplet containing 1-methyl-3-butylimidazolium and fluorophosphate on the titanium dioxide (110) surface is studied using a molecular dynamics simulation. On the basis of the anisotropic characteristics of titanium dioxide surface, contact angles were calculated along different directions which are in agreement with experimental data. The obtained results show that a cation-rich layer is spread on the surface. Imidazolium rings of cations of ionic liquid are parallel to the titanium dioxide surface, but their orientation in the upper layer is almost vertical. Such positioning leads to the butyl-ring substituents locating at the top of the first layer to create a relatively empty space of cations while resulting in an anion-rich region. The cations and anions form a spherical shape on top of the first layer. Cross-sectional analysis of the ionic liquid reveals the circular configuration of cations and anions within the nanodroplet. The above observat...

In this paper the adsorption behavior of a water droplet on the molybdenum disulfide and graphene surfaces were examined and compared. Results obtained from the calculation of the average of interaction energy between the water and the molybdenum disulfide surface and the graphene surfaces indicated that the van der Waals interaction plays an important role in the adsorption of water on these surfaces. The contour maps of the interaction energy between the water and the surfaces have revealed some different behaviors of the water droplet on these surfaces. The results showed that water sliding on the molybdenum disulfide surface and water pinning on the graphene surface is due to the difference in structural patterns of the surfaces. Molecular investigations of the water on the surfaces showed that the water molecules occupy continues positions on the molybdenum disulfide surface while they occupy discrete positions on the graphene surface. Two mechanisms for orientation and displacement of the water molecules on the surfaces were proposed. In addition, the effects of temperature and external field on movement of the water molecules on the surface were investigated. It was observed that the water - graphene system is more sensitive to the applied electric field than water-molybdenum disulfide system. In addition, the simulation results in the presence of the electric field showed that it is possible to take control of the water droplet on the graphite surface, so that the displacement of the water droplet can take place in a particular direction.

The effect of the triple-phase contact line (TPCL) on the wetting phenomenon has been extensively discussed during the past decade. Numerous attempts have also been made to quantify its characteristics based on thermodynamic or mechanical definitions. In this research, molecular dynamics simulation was used to define the term “vicinity of the TPCL” and its effect on the hydrophilic and hydrophobic behaviors of a water nanodroplet. A nanodroplet was placed on a substrate that was modified in a stepwise manner by growing a patch of heterogeneity from either the center of the substrate or from the sides. The relative direction of motion of the TPCL and the patch determined the pathway that the nanodroplet chooses in order to change its wetting regime from hydrophilic to hydrophobic and vice versa. A gradual change occurs when the TPCL and the heterogeneity move in the same direction, and an abrupt change takes place otherwise. In addition to the insights into the wetting phenomenon, the width of the TPCL is also discussed. The obtained data suggest that the effective width of the TPCL, δ, is different inside the perimeter of the nanodroplet from outside of it. Moreover, the value of δ for the abrupt pathway is twice as large as the gradual one. In conclusion, the width, or vicinity, of the TPCL depends on the type of the pathway and the configuration of the substrate-patch system and cannot be treated similarly in both cases.

Nanotubes have extraordinary properties, which have attracted the attention of many researchers from diverse fields. The interaction between carbon nanotube (CNT) or boron nitride nanotube (BNNT) and polymer/copolymer/surfactant has shown potential improvement in properties and performance. This paper reviews the recent studies in this field obtained from molecular dynamics simulation calculations, focusing on the interaction energies between nanostructure and polymer, radial distribution function, diffusion and radius of gyration and some other physical chemistry properties. Recent studies show that the intermolecular interaction in mentioned systems is strongly influenced by the specific monomer structure of polymers. The high values of intermolecular interaction energy of such composites offer that an efficient load transfer exists at the interface between nanotube and polymer, which is of a key role in the composite reinforcement practical applications. Our study reviewed the possibility of wrapping CNT/BNNT/CNT bundles by polymers and also the effects of CNTs/CNT bundles’ length on the conformational behavior of polymer adsorbed on these nanostructures.

In this work, the melting/freezing point of confined water between two graphene sheets was calculated from the direct coexistence of the solid-liquid interface. Also, molecular dynamics simulation of confined liquid water-ice between two graphene sheets was applied. The phase transition temperature of the confined ice-water mixture was calculated as 240 K that was 29 K less than the non-confined ice-water system. In order to study the behavior of water molecules at different distances from the graphene sheets, 5 regions were provided using some imaginary planes, located between two graphene sheets. The obtained simulation results showed that water molecules located in the region near each graphene sheet with the thickness of 2 nm had a different behavior from other water molecules located in other regions. The results demonstrated that water molecules in the vicinity of graphene sheets had more mean square displacements than those in the middle regions.

In this study, adsorption of water nanodroplets, oil nanodroplets and oil–water mixtures on a poly vinylidene fluoride (PVDF) surface is investigated computationally by a molecular dynamics (MD) approach and a mechanism for adsorption of the droplets is proposed. MD simulation results revealed that the PVDF surface is hydrophobic and oleophilic and can be used to separate oil from water. The acquired results are in good agreement with experimental results. As to investigate the origins for hydrophobicity of the PVDF surface, mobility of water molecules on the PVDF surface has been meticulously investigated. Investigations have proven that once the water molecules are organized singly or in small groups with two or three molecules, they exhibit very low levels of mobility, whereas water molecules in groups of four or more have high mobility. Some descriptive studies were performed based on MD simulation results to investigate the behavior observed in the systems including: (i) distribution of partial charges on the surface of PVDF. (ii) Dependence of the orientation of water molecules near the PVDF surface on the size of water cluster. (iii) Dependence of the distance of water molecules to the PVDF surface on the water cluster size. Manner of charge distribution on the PVDF demonstrated a formation of nano-domains with positive and negative charges on the surface. Dependence of the behavior of water molecules on the nano-domains on the water cluster size was investigated.

This study provides a comprehensive investigation on the effect of epoxy crosslinking density and number of graphene layers on the interfacial mechanical behavior of graphene/epoxy nanocomposites. In particular, the graphene layers are detached in the normal and sliding directions within the framework of steered molecular dynamics, and the traction-separation curves are extracted for the whole separation process. The damage mechanism is also studied by analyzing the evolution of the local number density during pull-out tests. For better results interpretation, the variation of the interaction and adhesion energies, the number of pulled-out epoxy chains, and the distribution of crosslinked and uncrosslinked species are also investigated and discussed. Based on the results obtained, the crosslinking density has a significant effect on the interfacial properties between graphene and epoxy, especially in the normal mode. The damage behavior is also determined as the function of the epoxy crosslinking density so that at low crosslinking densities, the damage occurs in the polymer near the graphene, while the failure takes place in the interphase for higher crosslinking degrees. Increasing the number of graphene layers leads to a weaker interfacial strength, except for the double-layered graphene systems which have the highest traction peak among all samples.

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.

In the present study, a computational investigation on the effect of surface roughness on the wettability behavior of water nanodroplets has been performed via molecular dynamics simulation. To fabricate the roughness, several grooves with different depths and widths were considered on the top layer(s) of graphite. Free energy analysis indicates that surface roughness reduces the solid–liquid adhesion and the work done for the removal of the nanodroplet from the solid surface. This reduction increases with an increase in both the depth and width of the grooves. Furthermore, the adhesion in Wenzel state is greater than that in the Cassie–Baxter state. Results show that increasing the depth and decreasing the width of the grooves decrease the wettability and the nanodroplet locates in the Cassie–Baxter state. In addition, both the Cassie–Baxter and Wenzel models effectively predict the nanodroplet contact angle on the rough surfaces. Furthermore, the probability of successful interactions decreases in the solid–liquid interfaces due to the heterogeneity of the surface. Therefore, the density, the residence time and the hydrogen bond lifetime of the water molecules in the layer in the vicinity of the substrate decrease. In addition, surface roughness affects the orientation of the water molecules at the interface, the diffusion of water molecules as well as the movement of the water nanodroplet.

In this study, the water droplet behaviour of four different types of single-strand DNA with homogeneous base sequence on a graphene substrate during evaporation of the droplet was investigated using molecular dynamics (MD) simulation. The simulation results indicated that the evaporation depended on the DNA sequence. The observed changes can be divided into four parts: (i) vaporization mode, (ii) evaporation flux, (iii) mechanism of single-strand placement on the surface, and (iv) consideration of remaining single strands after evaporation. Our simulation observations indicated different evaporation modes for thymine biodroplets as compared to those for other biodroplets. The evaporation of the thymine biodroplets occurred with an increase in the contact angle, while that of the other biodroplets occur in a constant contact angle mode. Moreover, thymine biodroplets generate the lowest contact line compared to other single strands, and it is always placed far away from the centre of the droplets during evaporation. Investigating variations in the evaporation flux shows that thymine has the highest evaporation flux and guanine has the lowest. Moreover, during initial evaporation, the flux of evaporation increases at the triple point of the biodroplets containing thymine single strands, while it decreases in the other biodroplets. The following observation was obtained from the study of the placement of single strands on the substrate: guanine and thymine interacted slower than other single strands during evaporation with graphene, adenine single strand had a higher folding during evaporation, and guanine single strand showed the lowest end-to-end distance. The investigation of single-strand DNA after evaporation shows that adenine produces the most stable structure at the end of evaporation. In addition, cytosine is the most stretched single-strand DNA due to its lack of internal π–π stacking and hydrogen bonding. Therefore, cytosine single strand is more accessible for use in microarrays to detect target single strands.

Water and air pollutants have huge impacts on the entire living system. In addition, the newly emerging nanopollutants, increasing global warming, and consequent climate changes are posing major threats to the freshwater or fresh air availability. This has made it urgent to invent an appropriate water/air treatment technology that removes nanopollutants and also desalinates water to a significant extent. Carbon-based nanomaterials have generated marvelous interest in a wide range of research activities due to their high adsorption capacities. Carbon nanotubes, carbon nanotube bundles, and related materials have potential applications in gas/ion separation and water purification. Recently, gas/ion separation and water purification through carbon-based nanomaterials have received increasing attention. This review summarizes the properties of carbon nanotubes and carbon nanotube bundles related to gas separation, ion separation, and water purification using molecular dynamics simulations. Membranes-based carbon nanomaterials show promise of water purification and gas separation. These attractive properties of carbon nanotubes-based and carbon nanotube bundles-based nanomaterials make them proper candidates for gas separation, gas molecular-sieving processes, and desalination purposes in nanoscale dimensions.

In this study, the dispersion mechanism of aggregated carbon nanotubes (CNTs) using Triton X-100 surfactant under various concentrations is investigated with and without water molecules via molecular dynamics simulation. The obtained results showed that because of interaction between water molecules and hydrophilic segments of surfactant, water molecules play a significant role in the manner of adsorption of the surfactant on the CNT surface. In the presence of water molecules, the surfactant molecules are not able to wrap the CNTs, and they are located in the neighborhood of the CNTs. The results suggested that the creation of space between two CNTs in the absence of the surfactant is performed slowly, while, in the presence of the surfactant molecules, the creation of space between two CNTs which leads to the dispersion of the CNTs is remarkably rapid. The surfactant molecules cause to introduce more numbers of water molecules in the vicinity of and between the CNTs, and with the increasing radial distances between two CNTs, the number of water molecules is rapidly increased. The interfacial angle between two CNTs, surfactant gyration radius, and diagrams of radial distribution function between water molecules, the CNTs, and the surfactant molecules were calculated for a better description of dispersion mechanism of the CNTs by the surfactant and water molecules.

We present an investigation on the permeability and selectivity of graphene sheets with designed sub nanometer pores using molecular dynamics simulations. We show that nanoporous graphene can be used to separate water from a gaseous mixture of nitrogen, oxygen and water. The obtained results show that the separation is performed based on the absorption of water molecules on the nanoporous graphene surface. Pore size plays an important role in the possible formation of water clusters on the nanoporous graphene surface. In graphene sheets with large pores, the space between the neighboring graphene becomes smaller and water molecules form a cluster on the graphene surface quickly. Because the size of the water clusters is larger than that of the nanopore, they cannot pass through it, whereas nitrogen and oxygen molecules are able to pass through the nanoporous graphene. In this study, we propose a mechanism for the formation of water clusters on the nanoporous graphene surface. To illustrate the different steps of the proposed mechanism, several investigations were performed such as calculation of the distribution and accumulation of water molecules on the graphene surface, angle between the dipolar moment vector of water molecules and the graphene surface and formation and movement of multi-layer clusters. Moreover, a specific method to pass N2 and O2 molecules through nanoporous graphene is presented.

In this work, we compared the structural and dynamical properties of water confined between two graphene oxide (GO) sheets with water confined between two graphene sheets through molecular dynamics simulations. Our results showed how the structure and dynamics of the water near the GO surfaces changes under confinement conditions. Different orientations of the water molecules to the GO sheets confirm the heterogeneous nature of the confined water. The density distribution of water near the GO sheets is different from the graphene surfaces due to the presence of hydrophilic functional groups of the GO sheets. Also, the hydrogen bonds between the water molecules are disturbed due to the presence of these groups on the GO surfaces. The results showed that as water molecules in areas which are close to the GO surfaces are isolated, and due to hydrogen bond formation between water molecules and the substituents of the GO, the water molecules have fewer hydrogen bonds with other water molecules around. In the middle region between two GO sheets, it has been seen that each water molecule is surrounded by more water molecules, and there are many more hydrogen bonds, so it is possible to consider a network structure of water in this region. There is a good quantitative agreement between experiments and the above mentioned results. These results were confirmed by the calculated coordination number, radial distribution functions and mean square displacements.

In this work, the liquid–solid phase transition temperature of water confined between two graphene oxide (GO) sheets is investigated using molecular dynamics simulations. The results demonstrate that, due to the presence of functional groups of the GO sheets, at temperatures below liquid–solid phase transition temperature, the water molecules near the confining sheets are not structured like ice and remained in the liquid form. The results also reveal the confinement effects on the melting and freezing rate of water molecules. The confining conditions delay the freezing process of the water molecules compared to the bulk water molecules. These results are confirmed by the calculated total energy, the density profile of water molecules confined between two GO sheets, the number of hydrogen bonding, radial distribution function, and mean square displacement. The liquid–solid phase transition temperature of water in the presence of GO sheets was calculated as 236 K, which was 34 K less than the temperature of the bulk water.