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Flexible metal-organic materials are of growing interest owing to their ability to undergo reversible structural transformations under external stimuli. Here, we report flexible metal-phenolic networks (MPNs) featuring stimuli-responsive behavior to diverse solute guests. The competitive coordination of metal ions to phenolic ligands of multiple coordination sites and solute guests (e.g., glucose) primarily determines the responsive behavior of the MPNs, as revealed experimentally and computationally. Glucose molecules can be embedded into the dynamic MPNs upon mixing, leading to the reconfiguration of the metal-organic networks and thus changes in their physicochemical properties for targeting applications. This study expands the library of stimuli-responsive flexible metal-organic materials and the understanding of intermolecular interactions between metal-organic materials and solute guests, which is essential for the rational design of responsive materials for various applications.

Coordination states of metal-organic materials are known to dictate their physicochemical properties and applications in various fields. However, understanding and controlling coordination sites in metal-organic systems is challenging. Herein, we report the synthesis of site-selective coordinated metal-phenolic networks (MPNs) using flavonoids as coordination modulators. The site-selective coordination was systematically investigated experimentally and computationally using ligands with one, two, and multiple different coordination sites. Tuning the multimodal Fe coordination with catechol, carbonyl, and hydroxyl groups within the MPNs enabled the facile engineering of diverse physicochemical properties including size, selective permeability (20-2000 kDa), and pH-dependent degradability. This study expands our understanding of metal-phenolic chemistry and provides new routes for the rational design of structurally tailorable coordination-based materials.

Surface chemistry is a major factor that determines the wettability of materials, and devising broadly applicable coating strategies that afford tunable and selective surface properties required for next-generation materials remains a challenge. Herein, we report fluorinated metal-organic coatings that display water-wetting and oil-repelling characteristics, a wetting phenomenon different from responsive wetting induced by external stimuli. We demonstrate this selective wettability with a library of metal-organic coatings using catechol-based coordination and silanization (both fluorinated and fluorine-free), enabling sensing through interfacial reconfigurations in both gaseous and liquid environments, and establish a correlation between the coating wettability and polarity of the liquids. This selective wetting performance is substrate-independent, spontaneous, durable, and reversible and occurs over a range of polar and nonpolar liquids (60 studied). These results provide insight into advanced liquid-solid interactions and a pathway toward tuning interfacial affinities and realizing robust, selective superwettability according to the surrounding conditions.

The orientation-specific immobilization of antibodies onto nanoparticles, to preserve antibody-antigen recognition, is a key challenge in developing targeted nanomedicines. Herein, we report the targeting ability of metal-phenolic network (MPN)-coated gold nanoparticles with surface-physisorbed antibodies against respective antigens. The MPN coatings were self-assembled from metal ions (FeIII, CoII, CuII, NiII, or ZnII) cross-linked with tannic acid. Upon physisorption of antibodies, all particle systems exhibited enhanced association with target antigens, with CoII systems demonstrating more than 2-fold greater association. These systems contained more metal atoms distributed in a way to specifically interact with antibodies, which were investigated by molecular dynamics simulations. A model antibody fragment crystallizable (Fc) region in solution with CoII-tannic acid complexes revealed that the solvent-exposed CoII can directly coordinate to the histidine-rich portion of the Fc region. This one-pot interaction suggests anchoring of the antibody Fc region to the MPN on nanoparticles, allowing for enhanced targeting.

Metal-phenolic networks (MPNs) have received widespread interest owing to their modular incorporation of functional metal ions and phenolic ligands. However, the interaction between MPNs and biomolecules is still relatively unexplored. Herein, we studied the effects of MPN-coated gold nanoparticles on amyloid fibril formation (which is associated with Alzheimer's disease) as a function of the metal ion in the MPN systems. All coated particles examined inhibited amyloid formation, with cobalt(ii) MPN-coated particles exhibiting the highest inhibition activity (90%). Molecular dynamics simulations and quantum mechanics calculations suggested that the geometry of the exposed cobalt coordination site in the cobalt-tannic acid networks facilitates its interactions with histidine and methionine residues in the amyloid beta peptides. Furthermore, the unique structure of cobalt MPNs may enable a wider variety of biomedical applications.

Nanostructured materials have potential as platforms for analytical assays and catalytic reactions. Herein, we report the synthesis of electrocatalytically active cobalt phosphate nanostructures (CPNs) using a simple, low-cost, and scalable preparation method. The electrocatalytic properties of CPNs toward the electrooxidation of glucose (Glu) were studied by cyclic voltammetry and chronoamperometry in relevant biological electrolytes, such as phosphate-buffered saline (PBS), at physiological pH (7.4). Using CPNs, Glu detection could be achieved over a wide range of biologically relevant concentrations, from 1 to 30 mM Glu in PBS, with a sensitivity of 7.90 nA/mM cm2 and a limit of detection of 0.3 mM, thus fulfilling the necessary requirements for human blood Glu detection. In addition, CPNs showed a high structural and functional stability over time at physiological pH. The CPN-coated electrodes could also be used for Glu detection in the presence of interfering agents (e.g., ascorbic acid and dopamine) and in human serum. Density functional theory calculations were performed to evaluate the interaction of Glu with different faceted cobalt phosphate surfaces; the results revealed that specific surface presentations of under-coordinated cobalt led to the strongest interaction with Glu, suggesting that enhanced detection of Glu by CPNs can be achieved by lowering the surface coordination of cobalt. Our results highlight the potential use of phosphate-based nanostructures as catalysts for electrochemical sensing of biochemical analytes.

Metal-phenolic networks (MPNs) are a versatile class of self-assembled materials that are able to form functional thin films on various substrates with potential applications in areas including drug delivery and catalysis. Different metal ions (e.g., FeIII, CuII) and phenols (e.g., tannic acid, gallic acid) have been investigated for MPN film assembly; however, a mechanistic understanding of the thermodynamics governing MPN formation remains largely unexplored. To date, MPNs have been deposited at low ionic strengths (<5 mM), resulting in films with typical thicknesses of ∼10 nm, and it is still unclear how a bulk complexation reaction results in homogeneous thin films when a substrate is present. Herein we explore the influence of ionic strength (0-2 M NaCl) on the conformation of MPN precursors in solution and how this determines the final thickness and morphology of MPN films. Specifically, the film thickness increases from 10 nm in 0 M NaCl to 12 nm in 0.5 M NaCl and 15 nm in 1 M NaCl, after which the films grow rougher rather than thicker. For example, the root-mean-square roughness values of the films are constant below 1 M NaCl at 1.5 nm; in contrast, the roughness is 3 nm at 1 M NaCl and increases to 5 nm at 2 M NaCl. Small-angle X-ray scattering and molecular dynamics simulations allow for comparisons to be made with chelated metals and polyelectrolyte thin films. For example, at a higher ionic strength (2 M NaCl), sodium ions shield the galloyl groups of tannic acid, allowing them to extend away from the FeIII center and interact with other MPN complexes in solution to form thicker and rougher films. As the properties of films determine their final performance and application, the ability to tune both thickness and roughness using salts may allow for new applications of MPNs.

© 2016 by the authors; licensee MDPI, Basel, Switzerland. Mobile phone subscriptions continue to increase across the world, with the electromagnetic fields (EMF) emitted by these devices, as well as by related technologies such as Wi-Fi and smart meters, now ubiquitous. This increase in use and consequent exposure to mobile communication (MC)-related EMF has led to concern about possible health effects that could arise from this exposure. Although much research has been conducted since the introduction of these technologies, uncertainty about the impact on health remains. The Australian Centre for Electromagnetic Bioeffects Research (ACEBR) is a National Health and Medical Research Council Centre of Research Excellence that is undertaking research addressing the most important aspects of the MC-EMF health debate, with a strong focus on mechanisms, neurodegenerative diseases, cancer, and exposure dosimetry. This research takes as its starting point the current scientific status quo, but also addresses the adequacy of the evidence for the status quo. Risk communication research complements the above, and aims to ensure that whatever is found, it is communicated effectively and appropriately. This paper provides a summary of this ACEBR research (both completed and ongoing), and discusses the rationale for conducting it in light of the prevailing science.

The organized assembly of particles into superstructures is typically governed by specific molecular interactions or external directing factors associated with the particle building blocks, both of which are particle-dependent. These superstructures are of interest to a variety of fields because of their distinct mechanical, electronic, magnetic and optical properties. Here, we establish a facile route to a diverse range of superstructures based on the polyphenol surface-functionalization of micro- and nanoparticles, nanowires, nanosheets, nanocubes and even cells. This strategy can be used to access a large number of modularly assembled superstructures, including core-satellite, hollow and hierarchically organized supraparticles. Colloidal-probe atomic force microscopy and molecular dynamics simulations provide detailed insights into the role of surface functionalization and how this facilitates superstructure construction. Our work provides a platform for the rapid generation of superstructured assemblies across a wide range of length scales, from nanometres to centimetres.

In this study, by using X-ray powder diffraction profiles as blueprints, we successfully mapped the most probable molecular-level structural arrangement of the PMMA super-helix stereocomplexes through molecular dynamic simulations. Molecular-level resolution of the PMMA triple-helix supramolecule was not previously achievable by experimental methods. After constructing molecular models of stereo-regular complexes composed of linear it- and st-PMMAs, our all-atom molecular dynamics simulations identified the stereocomplex structure that best reproduces experimental diffraction profiles and thermodynamic properties as a double helix of isotactic (it-)PMMA with a helical pitch of 1.8 nm and 9 units per turn surrounded by a single helix of syndiotactic (st-)PMMA with an average helical pitch of 0.9 nm and 20 units per turn. The it-/st- complexing stoichiometry in the PMMA triple-helix is therefore 9 : 20. This presents the first all-atom model of the it-/st-PMMA triple-helix stereocomplex that accurately fits experimental X-ray diffraction profiles. In addition, the simulation results revealed the outer st-PMMA helix of the PMMA stereocomplex has a fiber diameter of at least 1.85 nm and adopts a non-ideal helical geometry. Furthermore, through dynamic simulations, surprising new sights into the effect of the structural configuration of the PMMA stereocomplex (i.e., helical pitch and direction, and tilt angle) on the physical properties of their crystal structures were obtained. Those crystal properties include X-ray diffraction profile, packing density, chain-chain spacing, chain width and cohesive energy density.

The novel duolayer system, comprising a monolayer of ethylene glycol monooctadecyl ether (C18E1) and the water-soluble polymer poly(vinylpyrrolidone) (PVP), has been shown to resist forces such as wind stress to a greater degree than the C18E1 monolayer alone. This paper reports all-atom molecular dynamics simulations comparing the monolayer (C18E1 alone) and duolayer systems under an applied force parallel to the air/water interface. The simulations show that, due to the presence of PVP at the interface, the duolayer film exhibits an increase in chain tilt, ordering, and density, as well as a lower lateral velocity compared to the monolayer. These results provide a molecular rationale for the improved performance of the duolayer system under wind conditions, as well as an atomic-level explanation for the observed efficacy of the duolayer system as an evaporation suppressant, which may serve as a useful guide for future development for thin films where resistance to external perturbation is desirable.

Understanding, and improving, the behavior of thin surface films under exposure to externally applied forces is important for applications such as mimicking biological membranes, water evaporation mitigation, and recovery of oil spills. This paper demonstrates that the incorporation of a water-soluble polymer into the surface film composition, i.e., formation of a three-duolayer system, shows improved performance under an applied dynamic stress, with an evaporation saving of 84% observed after 16 h, compared to 74% for the insoluble three-monolayer alone. Canal viscometry and spreading rate experiments, performed using the same conditions, demonstrated an increased surface viscosity and faster spreading rate for the three-duolayer system, likely contributing to the observed improvement in dynamic performance. Brewster angle microscopy and dye-tagged polymers were used to visualize the system and demonstrated that the duolayer and monolayer system both form a homogeneous film of uniform, single-molecule thickness, with the excess material compacting into small floating reservoirs on the surface. It was also observed that both components have to be applied to the water surface together in order to achieve improved performance under dynamic conditions. These findings have important implications for the use of surface films in various applications where resistance to external disturbance is required.

We have applied a theoretical modelling approach to aid in the rational design of contamination resistant coatings. Using in silico nano-indentation we have characterised the adhesion between a contaminant particle and engineered polymer surfaces that include functionalised-surface-crosslinked and functionalised non-surface-crosslinked polyesters. The roughness, density and morphology of the surfaces were dynamically monitored as the coatings responded to the approaching particle. Our results suggest that surface crosslinking provides a stable platform for incorporation of functional groups that would otherwise migrate into the bulk substrate upon aging. However surface crosslinking with rigid cyclic curing agents renders the coatings far too stiff, which can result in slip whereby surface crosslinkers shift to the side of the incoming contaminant particle, leading to both the exposure of the flexible substrate and the envelopment of the contaminant. This type of deformation negates steric repulsions of the functional groups, crucial for preventing undesirable adhesion. In contrast, functionalisation combined with flexible acyclic surface crosslinks results in superior contamination resistance.

Responsive surfaces show potential for many applications; however, the molecular mechanisms of their responsive behavior are often dependent on the nature and properties of the substrate and this dependence is not fully understood. We present a molecular dynamics study on the mechanical response of poly(ethylene glycol) (PEG) grafted on substrates of varying flexibility in "dry" conditions. Our in silico surface loading tests show that when PEG is grafted onto a hard substrate (silica), there is a significant reduction in adhesion to a solid surface, owing to augmented steric repulsions at the interface. However, when the same chains are tethered onto a soft substrate (polyester), interfacial adhesion is strengthened. We find that the deformable substrate allows significant rearrangement of the subsurface and grafted segments during loading. Asperities along the rough soft surface also provide free volume for the tethered chains to occupy, enabling them to carpet the surface and increasing the density at the interface. Our results explain the molecular basis of the mechanical response of PEG when grafted onto hard and soft substrates and provide a rationale for surface protection using PEG.

The misfolding and aggregation of proteins to form amyloid fibrils is a characteristic feature of several common age-related diseases. Agents that directly inhibit formation of amyloid fibrils represent one approach to combating these diseases. We have investigated the potential of a cyclic peptide to inhibit fibril formation by fibrillogenic peptides from human apolipoprotein C-II (apoC-II). Cyc[60-70] was formed by disulfide cross-linking of cysteine residues added to the termini of the fibrillogenic peptide comprising apoC-II residues 60-70. This cyclic peptide did not self-associate into fibrils. However, substoichiometric concentrations of cyc[60-70] significantly delayed fibril formation by the fibrillogenic, linear peptides apoC-II[60-70] and apoC-II[56-76]. Reduction of the disulfide bond or scrambling the amino acid sequence within cyc[60-70] significantly impaired its inhibitory activity. The solution structure of cyc[60-70] was solved using NMR spectroscopy, revealing a well-defined structure comprising a hydrophilic face and a more hydrophobic face containing the Met60, Tyr63, Ile66 and Phe67 side chains. Molecular dynamics (MD) studies identified a flexible central region within cyc[60-70], while MD simulations of "scrambled" cyc[60-70] indicated an increased formation of intramolecular hydrogen bonds and a reduction in the overall flexibility of the peptide. Our structural studies suggest that the inhibitory activity of cyc[60-70] is mediated by an elongated structure with inherent flexibility and distinct hydrophobic and hydrophilic faces, enabling cyc[60-70] to interact transiently with fibrillogenic peptides and inhibit fibril assembly. These results suggest that cyclic peptides based on amyloidogenic core peptides could be useful as specific inhibitors of amyloid fibril formation.

We have used density functional theory to investigate how Al13 cluster dimers can be formed with or without a bridging hydrogen. We have identified several stable dimers in which 0, 1, or 2 hydrogen atoms link two bare clusters together. Each of these structures can adsorb further H atoms in atop sites on the surface of the dimer. Additional dimers were identified with 3 and 4 H atoms linking the clusters but these are only stable in the multihydrogenated form. Reaction profiles for the formation of these dimers from a range of cluster and H atom combinations indicate that the dimer structures are energetically favored over the isolated clusters. This observation may have significant implications for the design of cluster-assembled materials.

Molecular monolayers reduce the amount of water lost to evaporation due to their ability to form closely packed films at the air-water interface. However, they are susceptible to loss from the water surface and poor performance on exposure to wind. This study combines experimental and theoretical techniques to investigate the properties of a small molecule monolayer mixed with comb polymers. The study reveals that at high concentrations of polymer the monolayer exhibits increased mechanical stability which improves the resistance to disruption by wind. Inclusion of hydrophilic functional groups along the backbone of the polymer leads to further improvements in wind stability. However, the improved wind stability observed in the composites comes at the expense of poorer water evaporation resistance.

The leaf of the lotus plant provides an elegant example of how a natural surface can remain clean even in the dirtiest of environments. The leaf’s fine-scale surface structure combined with its hydrophobic chemistry ensures that water droplets bead off its surface, carrying away contaminant particles [1]. An alternative dirt-shedding surface, also found in nature, is based on hydrophilic surface chemistry. Water droplets that come into contact with hydrophilic surfaces spread, forming a thin film of water and lifting contaminant from the surface. There is significant motivation to pursue both of these types of behaviour for artificial systems because of the wide range of possible applications ranging from self-cleaning paints to dirt-resistant clothing. However, for some applications, pertinent to the system in question, the synthesis of a self-cleaning surface is indeed a difficult task to achieve, and one needs to first elucidate the precise properties required to generate a certain level of resistance to the adhering contaminant. Atomistic simulations provide a useful tool to gain such insight and add value to surfaces where stay-clean properties are highly desirable. Here, using force-field-based molecular mechanics and dynamics, we explore the properties of polymer surfaces in order to develop design aspects for self-cleaning industrial paint-coatings. A polyester surface model is constructed, on the basis of a realistic cured paint coating [2] while various carbon models are selected [3–6], to emulate commonly encountered atmospheric dirt particulates [7–10]. The purpose of this work is to gain a fundamental understanding of the nature of interactions between contaminant and polymer coating in various environments, including aqueous conditions [11], and explore nanoscale modifications of the coating that help reduce the strength of the adhering contaminant. The modifications are based on hydrophobic or alternatively hydrophilic surface treatments. Here we demo

This study compares the performance of the all-atom molecular dynamics force fields OPLS-AA and COMPASS, and the united-atom GROMOS96 ff53a6 force field, for organic monolayers at aqueous interfaces, as a function of surface density, temperature, and system size. Where possible, comparison with experimental data was undertaken and used to scrutinize the performance of each force field. We find close agreement between the all-atom force fields (OPLS and COMPASS) and experiment for the description of organic monolayers on water. However, the united-atom force field 53a6 tends to exhibit poorer agreement than the all-atom force fields

The structure and bonding in charged and doped aluminum clusters have been investigated using Regional Density Functional Theory (RDFT). The RDFT method provides a measure of the electronic stress tensor from which it is possible to determine bond indices and electronic chemical potential. We find that the distribution of bond indices on the surface of Al12X clusters provides not only an understanding of the internal bonding and stability but also some insight into the regioselectivity observed in reactions of the clusters.

This study examines intermolecular interactions of a monolayer of octadecanol (CH3(CH2)17OH) on water as a function of surface density and temperature, using classical molecular dynamics simulations. We observe increased interaction between the alkyl chains (van der Waals) and hydroxyl groups (H-bonding) with increased surface density, which leads to increased order and packing within the monolayer. We also identified clear trends in the intermolecular interactions, ordering and packing of the monolayer molecules as a function of temperature. The observed trends can be closely related to features of the current empirical theories of evaporation resistance.

We present a simulation methodology to chemically cross-link the surface of fully atomistic models of polymers. We simulated nanoindentation of the cross-linked model surfaces whereby nanoparticles (fullerene in this case) are used to probe different regions of the polymer surface enabling us to characterize the surface hardness of the polymer film and calculate the work of adhesion between polymer and nanoparticle. The cross-linked polyester surfaces are constructed using hexamethylene and isophorone di-isocyanate cross-linkers. Our results indicate that, despite surface cross-linking with hexamethylene di-isocyanate molecules, the polymer top surface still maintains significant softness. The hexamethylene cross-links that protrude from the surface are deformable, resulting in a strong adhesion between the surface and carbon particle. In contrast, isophorone surface crosslinking results in significantly weaker adhesion with carbon, due to the less deformable rigid structure formed at the top layer. In this case, while rigidity is imparted to the polymer top surface, the flexibility of the core region of the polymer is maintained.

In this study we use density functional theory (DFT) to investigate the properties and H adsorption characteristics of structural isomers of the magnesium-doped aluminum cluster, Al12Mg. Our results show that the exohedral structure (exo-Mg Al12) is significantly lower in energy (1.59 eV) than the endohedral structure (endo-Al12Mg); however, the exohedral structure shows significant structural distortion, Our calculations demonstrate that H binds favorably to both exohedral and endohedral structures. Generally, binding energies for II to both clusters range from ∼2.3 to 2.5 eV with atop positions slightly favored, except for addition directly to the exohedral Mg atom, where the binding energy drops to 1.92 eV. We include a DFT molecular dynamics study of the endo-Al12Mg and endo-AI 12MgH clusters which revealed the isomerization to the respective exostructures at finite temperatures (100-600 K). Interestingly, hydrogen adsorption appears to enhance the isomerization.

We have investigated axial interactions of H2 with Al 12X(X = Mg, Al, and Si) clusters and found that homolytic dissociation leading to Al12XH and H atom proceeds without a barrier but is an extremely endothermic process. The calculated difference in energy of the addition and abstraction reactions indicates that any Al12X-based hydrogen storage technology that involves predissociation of H2 will be limited by the competing processes. We have also discovered that while there is a modest barrier for dissociation of H2 on a single Al12Mg cluster to give the dihydride, the process occurs spontaneously between two closely spaced Al12Mg clusters, resulting in the formation of two Al12MgH species. Doping of the cluster with an electropositive atom (Mg) enables the transfer of electron density to the Al cage, which enhances H2 dissociation. The information gained can contribute to the design of novel solid-state materials made of doped Al clusters, which may ultimately be suitable for catalytic processes.

The dissociative chemisorption of molecular hydrogen on charged and neutral aluminum clusters A112X (X = Mg, Al, Si) was investigated using DFT and a modified G3(MP2)-RAD procedure. Reaction barriers and enthalpies were determined for both neutral and singly charged clusters. The lowest barrier for dissociative adsorption of H2 on a neutral cluster was found for the Al12Mg cluster, whereas the highest barrier was found to be on the closed-shell Al12Si. The interaction of H2 with Al13+ is found to proceed via an association complex that is 0.07 eV lower in energy than the isolated species and from which the barrier to H2 dissociative adsorption is only 0.16 eV. The most exothermic reaction of H2 with A112X occurs for the Al13+/H2 system. In comparison, reactions with the closed-shell Al13~ and Al12Si clusters are found to be endothermic. The barriers for H2 desorption from the dihydrogenated clusters are generally quite substantial.

There has been considerable interest in recent years in the effects of doping of light metal materials with transition metals to improve the thermodynamics and kinetics of hydrogen chemisorption and desorption. Foremost among these is the work of Bogdanovic and Schwickardi (1997) who demonstrated that doping alkali metal hydrides with a few mol% of Ti can lead to reversible decomposition at reasonable temperatures and pressures. Theoretical studies (Chaudhuri 2005, 2006) of Ti-doped NaAlH 4 indicate that the Ti dopant is responsible for catalysing H 2 chemisorption when the Ti atoms are in specific local arrangements. The reactivity, electrostatic fields and surface features of small metal clusters can differ significantly from that of bulk materials and is often dependant on not only the composition but the size of the cluster. While theoretical and experimental studies have shown that the interaction of hydrogen atom with aluminium clusters is thermodynamically favoured, experimental studies have suggested that the kinetics for chemisorption of hydrogen molecule on pure aluminium clusters are quite slow. Experimental studies of the interaction of molecular hydrogen with aluminium clusters have generally been carried out in the gas phase with charged clusters to enable isolation and detection of the products (Cox, 1988) (Jarrold, 1988). In this study we investigate the interaction of diatomic hydrogen with a series of neutral and charged X-centred aluminium clusters (Al 12X, X = Mg, Al, Si). We use the PBE/6-311G(d, p) and PBE/DNP levels, which have been found to give close agreement with CCSD/6-31G(d, p) for the ground state structures of Al 12X clusters and ions (Henry, 2008).

In this paper, we present a comparison of the performance of a series of embedded atom method potentials for the evaluation of bulk and small aluminium cluster geometries and relative energies, against benchmark density functional theory calculations. In general, the non-pairwise potential-B (NP-B), which was parametrized against Al cluster data, performs the best.

Nowadays, when technology has already been moved to the area of nano-devices, the description of properties at very microscopic level, within molecules, concerning interatomic interactions, had gained remarkable importance. Since these properties come to affect functionality and reliability of manufactured devices it is crucial to understand how to transfer practicality of macro-devices to nano (or subnano) level and what interferes with desirable features. The new materials for hydrogen storage devices might possibly be based on Al-nanostructures. We have modeled the structures and properties of Al-clusters and characterized atomic and molecular hydrogen adsorbed on its surface. The internal framework of clusters was studied using the Regional DFT method [1] and the insights into bond strengths and surface reactivity originating from the electronic stress tensor [2,3] has been given. The stress tensors are widely used to describe internal forces of matter. In molecules, the electronic stress tensor describes distortion of the charge density which has primary significance for physical and chemical properties being displayed by the system.

We have investigated and compared the ability of numerical and Gaussian-type basis sets combined with density functional theory (DFT) to accurately describe the geometries, binding energies, and electronic properties of aluminum clusters, Al12XHn (X = Al, Si; n = 0, 1, 2). DFT results are compared against high-level benchmark calculations and experimental data where available. Properties compared include geometries, binding energies, ionization potentials, electron affinities, and HOMO-LUMO gaps. Generally, the PBE functional with the double numerical basis set with polarization (DNP) performs very well against experiment and the analytical basis sets for considerably less computational expense.

We present a molecular dynamics study of the interaction of fullerene (C60) with polyester surfaces in water. Three different polyester surfaces are studied, including untreated polyester (Polyester), fluorine-modified polyester (Polyester75F), and hydroxyl-modified polyester (Polyester75OH). Results indicate that in the absence of any surface modification, the fullerene particle is drawn down onto the polyester, even for a significant initial depth of water separating the particle and the surface. However, the addition of hydroxyl or fluorine groups on the surface of the polymer leads to a stronger interaction between water and surface atoms and, when combined with structural features such as rigidity and surface roughness, can reduce adhesion of the C60 particle in water.

This theoretical study examines the adhesion of amorphous carbon to functionalized polyester surfaces. Several modifications to the polyester surface have been investigated including the addition of hydroxyl, carboxyl, or fluorine substituents at varying surface concentrations. Initially, the polyesters were artificially held rigid, and the surface modification not only imparted chemical changes to the polymer surface but also accentuated its atomic scale roughness. Under this rigid regime, low concentrations of surface modifiers have been shown to lead to the greatest reduction in adhesion with amorphous carbon, and increasing the level of modification does not provide further advantages in the reduction of adhesion, due to saturation. The effects of surface reorganization were also investigated and have been shown to be strongly dependent on the structure of the carbon surface, the chemical type, and surface density of modifiers. The surface modifiers reorganize during relaxation, which leads to significant differences in their effects on adhesion.

This study examines the diffusion of small methylated and hydroxylated siloxanes through solutions of polymer and crosslinker molecules. The diffusivity of the siloxanes was calculated for bulk diffusion and for surface segregation. Our simulations demonstrate that there is significant interaction between 3,3-dimethylhexahydroxytrisiloxane (hexa-OH-TS) and the polar solvent components of the paint matrix at 298 K. The nature of these associations is largely due to hydrogen bonding between the siloxane and the polar solvent molecules. At 573 K the diffusivity of solvent molecules is sufficiently high to disrupt interactions. The smaller number of hydroxyl groups in 1,5-dihydroxyhexamethyltrisiloxane (hexa-Me-TS) results in a weaker interaction with the polar solvent. Surface segregation studies indicate that there is a slight increase in the concentration of hexa-OH-TS in the surface layer of the system as a result of curing and relaxation processes. However, for hexa-Me-TS there is in fact a decrease in the surface concentration of the siloxane relative to the bulk concentration.

This study uses classical molecular dynamics to examine how aging (relaxation) of functionalized polyester surfaces effects their adhesion to carbon particles. We show that relaxation leads to significantly increased adhesion compared to the rigid polymers. Functionalization of polyester surfaces followed by aging results in negligible reductions in adhesion to carbon compared to the unmodified polyester and, in some cases, leads to slight increases in interfacial adhesion. These results indicate that for surface modification to be effective, i.e., reduce interfacial adhesion with carbon, the polyester surfaces need to maintain both the rigidity and atomic roughness.

This study examines the interaction of neutral and charged fullerenes with model silica and polyester surfaces. Molecular dynamics simulations at 298 K indicate that van der Waals forces are sufficiently strong in most cases to cause physisorption of the neutral fullerene particle onto the surfaces. The fullerenes are unable to penetrate the rigid silica surface but are generally able to at least partially infiltrate the flexible polymer surface by opening surface cavities. The introduction of charge to the fullerene generally leads to an increase in both the separation distance and Work of Separation with silica. However, the charged fullerenes generally exhibit significantly closer and stronger interactions with polyester films, with a distinct tendency to absorb into the "bulk" of the polymer. The separation distance and Work of Separation of C60 with each of the surfaces also depend greatly on the sign, magnitude, and localization of the charge on the particle. Cross-linking of the polyester can improve resistance to the neutral fullerene. Functionalization of the polyester surface (F and OH substituents) has been shown to prevent the C60 from approaching as close to the polyester surface. Fluorination leads to improved resistance to positively charged fullerenes, compared to the unmodified polyester. However, hydroxylation generally enables greater adhesion of charged fullerenes to the surface due to H-bonding and electrostatic attraction.

A continual testing development program for Colorbond, a prepainted steel product carefully designed multilayer system that offers corrosion protection and theoretical studies of the material's performance at the nanoscale are conducted. Results suggest that increasing the hardness and atomic roughness of the polyester surface by crosslinking and/or carefully chosen nano-functionalisation can significantly decrease its interactions with the carbonaceous solids and nanoparticles.

This study examines the interaction between graphite and polyester-based polymers and silica in order to compare the adhesive properties of these surfaces. Surface interaction energies were calculated at different interfacial separations, and the resultant adhesion energy curves were used to determine the Work of Separation (Wsep) and equilibrium interfacial separation (d0). Adhesion between graphite and polyester was calculated to be significantly greater than between graphite and silica. Our calculations indicate that Van der Waals Forces lead to significant adhesion between graphite and polyester. However, the Van der Waals attraction is approximately 30% less between graphite and silica.