Search

Responsive surfaces have been suggested to enhance longevity and antifouling performance of materials in many applications from industrial coatings to tissue engineering and drug delivery. We present a molecular dynamics study investigating de-swelling and swelling of some of the most commonly used responsive materials – PEG-functionalised silica and polymer surfaces – as a function of hydration and temperature. We show that PEG chains grafted onto the hard silica substrates exhibit a dehydration-induced collapse that is far more pronounced compared to chains grafted onto the soft polyester surface. The difference between the hard and soft substrates is particularly notable at low coverage densities where the chains are sufficiently separated from one another. We also show that inter-molecular hydrogen bonding responsible for the conformational state of the tethered chains in water can be temperature controlled. It can be suggested that the hard substrates with the intermediate-to-high coverage densities of low molecular weight hydrophilic grafts may be more appropriate for anti-fouling applications due to their ability to trap greater amount of water molecules. Soft substrates may be detrimental for the efficient response of the functionalised surfaces to changes in hydration and enhancement of the surface hardness must be considered when designing responsive surfaces for solution-based applications, such as antimicrobial coatings for industry and biomedicine. [ABSTRACT FROM AUTHOR]

In this work, adsorption of hydrogen on Al13 clusters has been investigated theoretically using the density functional theory (DFT) approach. We have performed geometry optimization of atomic and molecular hydrogen in the proximity of Al13 and calculated the binding energy and electronic properties of the stable Al13+Hn assemblies. We have also calculated the energy barrier for the hydrogen atom transition between different adsorption sites on Al13 cluster as well as the activation energy for the dissociation and adsorption of molecular hydrogen. We found that the hydrogen atom adsorbs on the surface of Al13 cluster, without an energy barrier onto atop, bridge and hollow sites. A small barrier for H atom transition from one adsorption site to another together with the minor energy difference between the most stable isomers points towards high mobility of the hydrogen atom on the surface. The calculated dissociation–adsorption barrier for the hydrogen molecule of ~14?kcal/mol and a desorption barrier of ~19?kcal/mol together with a high theoretical storage capacity of Al13 clusters suggest further investigations of Al nanostructures for application in hydrogen storage. [ABSTRACT FROM AUTHOR]

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 ( W sep) and equilibrium interfacial separation ( d 0). 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. [ABSTRACT FROM AUTHOR]

We have used the density-functional theory (DFT) method with a plane wave-pseudopotential basis to compute the structure and properties of a model xanthate molecule ( ) and its adsorption characteristics on the (100) surface of pyrite (FeS 2 ). Results from DFT calculations suggest that by itself does not readily adsorb on the (100) surface. However, adsorption of a xanthate-Fe-hydroxide complex species on the surface Fe site is energetically favourable, and this is consistent with experimental results which indicate that adsorption of such a molecular complex is likely to be one mechanism responsible for collector-induced surface hydrophobation of real FeS 2 surfaces. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations have been performed for precursor molecules used for organic/inorganic polymer hybrid preparation. The initial stage of the sol-gel process was simulated with the components at various water concentrations. Analyses of structural properties of the equilibrium configurations were performed via radial distribution functions. It was concluded that water concentration plays an important role in the agglomeration of the clusters due to the hydrophobic effect. Low water concentration leads to less pronounced hydrophobic interactions between the components resulting in structural instability. [ABSTRACT FROM AUTHOR]