Project description:Due to the high demand for clean, economic, and recyclable energy, phase change materials (PCMs) have received significant attention in recent years. To improve the performance of PCMs, they are confined in micro- and nano-capsules composed of organic or inorganic materials. In this study, encapsulated phase change material (EPCM) systems were constructed with paraffin molecules as the core material and capped carbon nanotubes (CNTs) as the shell. We investigated the effects of different parameters including CNT diameter, length, and chirality and the length of the alkane molecule chain. We also investigated metal nanocluster-enhanced PCM systems via the addition of Cu, Ag, and Al clusters to the EPCM systems. Different thermodynamic, dynamic, and structural properties including configurational energy, melting range, mean square displacement, self-diffusion coefficient, radial distribution function (RDF), and average end-to-end distance of the confined molecules were examined. We also investigated the effect of metal doping in CNT on the different properties of the confined PCM. The results indicated that a longer CNT has a lower melting point than the normal CNT system. It was also observed that the bigger (30,0) CNT, (14,14) armchair CNT, and icosane systems have higher melting ranges than the normal (25,0) system. The metal cluster systems also have a lower starting melting point than the normal system. Furthermore, it was found that the Al cluster system has the lowest starting melting point among the studied systems.
Project description:Mechanical properties of nanomaterials, such as nanowires and nanotubes, are an important feature for the design of novel electromechanical nano-architectures. Since grain boundary structures and surface modifications can be used as a route to modify nanostructured materials, it is of interest to understand how they affect material strength and plasticity. We report large-scale atomistic simulations to determine the mechanical response of nickel nanowires and nanotubes subject to uniaxial compression. Our results suggest that the incorporation of nanocrystalline structure allows completely flexible deformation, in sharp contrast with single crystals. While crystalline structures at high compression are dominated by dislocation pinning and the multiplication of highly localized shear regions, in nanocrystalline systems the dislocation distribution is significantly more homogeneous. Therefore, for large compressions (large strains) coiling instead of bulging is the dominant deformation mode. Additionally, it is observed that nanotubes with only 70% of the nanowire mass but of the same diameter, exhibit similar mechanical behavior up to 0.3 strain. Our results are useful for the design of new flexible and light-weight metamaterials, when highly deformable struts are required.
Project description:We report here on long-time all-atomistic molecular dynamics simulations of functional supramolecular nanotubes composed by the self-assembly of peptide-drug amphiphiles (DAs). These DAs have been shown to possess an inherently high drug loading of the hydrophobic anticancer drug camptothecin. We probe the self-assembly mechanism from random with ∼0.4 μs molecular dynamics simulations. Furthermore, we also computationally characterize the interfacial structure, directionality of π-π stacking, and water dynamics within several peptide-drug nanotubes with diameters consistent with the reported experimental nanotube diameter. Insight gained should inform the future design of these novel anticancer drug delivery systems.
Project description:In this study, we construct novel RNA nanoclusters, RNA nanotubes made of several nanorings up to the size of 20 nm, utilizing the molecular dynamics simulation, and study their structural properties [i.e., the root mean square deviation, the radius of gyration and the radial distribution function (RDF)] in physiological solutions that can be used for drug delivery into the human body. The patterns of energy and temperature variations of the systems are also discussed. Furthermore, we study the concentration of ions around the tube as a function of time at a particular temperature. We have found that when the temperature increases, the number of ions increases within a certain distance of the tube. We report that the number of ions within this distance around the tubes decreases in quenched runs. This indicates that some ions evaporate with decrease in temperature, as has been observed in the case of the nanoring. RDF plots also demonstrate a similar trend with temperature, as was found in the case of RNA nanorings.
Project description:Nafion nanocomposites for energy-related applications are being used extensively because of the attractive properties such as enhanced water retention, low unwanted crossover of electrolytes, and high proton conductivity. We present the results of the molecular dynamics modeling of Nafion films confined between two walls (substrates) of different polymer-wall interaction strengths and of different separation distances to model Nafion nanocomposites. Our goal is to provide insights into the effects of varying hydrophilicity and volume fraction of fillers/nanoparticles on the internal structure and water transport inside the Nafion membrane. The sulfur-sulfur radial distribution function first peak distance and the sulfur-oxygen (water) coordination number in the first hydration shell were negligibly affected by the wall (substrate) hydrophilicity or the film thickness. The Nafion side chains were found to bend toward the substrates with high hydrophilicity which is in qualitative agreement with existing experiments. The amount of bending was observed to reduce with increasing film thickness. However, the side-chain length did not show any noticeable variation with wall (substrate) hydrophilicity or film thickness. The water clusters became smaller and more isolated clusters emerged for highly hydrophilic substrates. In addition, the water cluster sizes showed a decreasing trend with decreasing film thickness in the case of hydrophilic substrates, which has also been observed in experiments of supported Nafion films. The in-plane water diffusion was enhanced considerably for hydrophilic substrates, and this mechanism has also been proposed previously in experiments. The in-plane water diffusion was also found to be a strong function of the substrate selectivity toward the hydrophilic phase. Our simulations can help provide more insights to experimentalists for choosing or modifying nanoparticles for Nafion nanocomposites.
Project description:Although the properties of carbon nanotubes (CNTs) are very well-known and are still extensively studied, a thorough understanding of other carbon-based nanomaterials such as C3N nanotubes (C3NNTs) is still missing. In this article, we used molecular dynamics simulation to investigate the effects of parameters such as chirality, diameter, number of walls, and temperature on the mechanical properties of C3N nanotubes, C3N nanobuds, and C3NNTs with various kinds of defects. We also modeled and tested the corresponding CNTs to validate the results and understand how replacing one C atom of CNT by one N atom affects the properties. Our results demonstrate that the Young's modulus of single-walled C3NNTs (SWC3NNTs) increased with diameter, irrespective of the chirality, and was higher in armchair SWC3NNTs than in zigzag ones, unlike double-walled C3NNTs. Besides, adding a second and then a third wall to SWC3NNTs significantly improved their properties. In contrast, the properties of C3N nanobuds produced by attaching an increasing number of C60 fullerenes gradually decreased. Moreover, considering C3NNTs with different types of defects revealed that two-atom vacancies resulted in the greatest reduction of all the properties studied, while Stone-Wales defects had the lowest effect on them.
Project description:In this work, molecular dynamics (MD) simulation is used to study the adsorption of the anticancer drug, doxorubicin (DOX), on the wall or surface of pristine and functionalized carbon nanotubes (FCNTs) in an aqueous solution. Initially, the CNTs were functionalized by tryptophan (Trp) and folic acid (FA), and then the DOX molecules were added to the system. The simulation results showed that the drug molecules can intensely interact with the FCNTs at physiological pH. Furthermore, it was found that as a result of functionalization, the solubility of FCNTs in an aqueous solution increases significantly. The effect of pH variation on drug release from both pristine and FCNTs was also investigated. The obtained results indicated that in acidic environments due to protonation of functional groups (Trp) and as a result of repulsive interaction between the DOX molecule and functional groups, the release of DOX molecules from FCNT's surface is facilitated. The drug release is also strongly dependent on the pH and protonated state of DOX and FCNT.
Project description:Carbon nanotubes (CNTs) display exceptional properties that predispose them to wide use in technological or biomedical applications. To remove the toxicity of CNTs and to protect them against undesired protein adsorption, coverage of the CNT sidewall with poly(ethylene oxide) (PEO) is often considered. However, controversial results on the antifouling effectiveness of PEO layers have been reported so far. In this work, the interactions of pristine CNT and CNT covered with the PEO chains at different grafting densities with polyglycine, polyserine, and polyvaline are studied using molecular dynamics simulations in vacuum, water, and saline environments. The peptides are adsorbed on CNT in all investigated systems; however, the adsorption strength is reduced in aqueous environments. Save for one case, addition of NaCl at a physiological concentration to water does not appreciably influence the adsorption and structure of the peptides or the grafted PEO layer. It turns out that the flexibility of the peptide backbone allows the peptide to adopt more asymmetric conformations which may be inserted deeper into the grafted PEO layer. Water molecules disrupt the internal hydrogen bonds in the peptides, as well as the hydrogen bonds formed between the peptides and the PEO chains.
Project description:Recent advances in low-dimensional materials have enabled the synthesis of single-walled carbon nanotubes encapsulated in hexagonal boron nitride (BN) nanotubes (SWCNT@BNNT), creating one-dimensional van der Waals (vdW) heterostructures. However, controlling the quality and crystallinity of BNNT on the surface of SWCNTs using chemical vapor deposition (CVD) remains a challenge. To better understand the growth mechanism of the BNNT in SWCNT@BNNT, we conducted molecular dynamics (MD) simulations using empirical potentials. The simulation results suggest that spontaneous BN nucleation is unlikely to occur on the outer surface of the SWCNT when we assume only vdW interaction between the BN and SWCNT layers. However, we observe the elongation of the BNNT when a short BNNT is provided as a seed nucleus on the SWCNT. This grown BNNT structure, with its sharply cut edges, aligns with experimental observations made using transmission electron microscopy (TEM). Moreover, the edge-reconstruction process favors zigzag B edges, which exhibit low edge energy according to the ReaxFF potential. Our simulation successfully provides insights into the catalyst-free growth process of this one-dimensional vdW heterostructure.