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Register a new userTowards the description of water adsorption in slit-like nanochannels with grafted molecular brushes. Density functional theory
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We have explored a model for adsorption of water into slit-like nanochannels with two walls chemically modified by grafted polymer layers forming brushes. A version of density functional method is used as theoretical tools. The water-like fluid model adopted from the work of Clark et al. [Mol. Phys., 2006, 104, 3561] adequately reproduces the bulk vapour-liquid coexistence envelope. The polymer layer consists of chain molecules in the framework of pearl-necklace model. Each chain molecule is chemically bonded to the pore walls by a single terminating segment. Our principal focus is in the study of the dependence of polymer layer height on grafting density and in the microscopic structure of the interface between adsorbed fluid and brushes. Thermal response of these properties upon adsorption is investigated in detail. The results are of importance to understand shrinking and swelling of the molecular brushes in the nanochannels.
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A coarse grained model for flexible polymers end-grafted to repulsive spherical nanoparticles is studied for various chain lengths and grafting densities under good solvent conditions, by Molecular Dynamics methods and density functional theory. With increasing chain length the monomer density profile exhibits a crossover to the star polymer limit. The distribution of polymer ends and the linear dimensions of individual polymer chains are obtained, while the inhomogeneous stretching of the chains is characterized by the local persistence lengths. The results on the structure factor of both single chain and full spherical brush as well as the range of applicability of the different theoretical tools are presented. Eventually an outlook on experiments is given.
A finite-temperature density functional approach to describe the properties of parahydrogen in the liquid-vapor coexistence region is presented. The first proposed functional is zero-range, where the density-gradient term is adjusted so as to reproduce the surface tension of the liquid-vapor interface at low temperature. The second functional is finite-range and, while it is fitted to reproduce bulk pH2 properties only, it is shown to yield surface properties in good agreement with experiments. These functionals are used to study the surface thickness of the liquid-vapor interface, the wetting transition of parahydrogen on a planar Rb model surface, and homogeneous cavitation in bulk liquid pH2.
Non-equilibrium Greens function techniques (NEGF) combined with Density Functional Theory (DFT) calculations have become a standard tool for the description of electron transport through single molecule nano-junctions in the coherent tunneling regime. However, the applicability of these methods for transport in the Coulomb blockade (CB) regime is still under debate. We present here NEGF-DFT calculations performed on simple model systems in the presence of an effective gate potential. The results show that: i) the CB addition energies can be predicted with such an approach with reasonable accuracy; ii) neither the magnitude of the Kohn-Sham gap nor the lack of a derivative discontinuity in the exchange-correlation functional represent a problem for this purpose.
We present a modification to our recently published SAFT-based classical density functional theory for water. We have recently developed and tested a functional for the averaged radial distribution function at contact of the hard-sphere fluid that is dramatically more accurate at interfaces than earlier approximations. We now incorporate this improved functional into the association term of our free energy functional for water, improving its description of hydrogen bonding. We examine the effect of this improvement by studying two hard solutes: a hard hydrophobic rod and a hard sphere. The improved functional leads to a moderate change in the density profile and a large decrease in the number of hydrogen bonds broken in the vicinity of the solutes.We present a modification to our recently published SAFT-based classical density functional theory for water. We have recently developed and tested a functional for the averaged radial distribution function at contact of the hard-sphere fluid that is dramatically more accurate at interfaces than earlier approximations. We now incorporate this improved functional into the association term of our free energy functional for water, improving its description of hydrogen bonding. We examine the effect of this improvement by studying two hard solutes: a hard hydrophobic rod and a hard sphere. The improved functional leads to a moderate change in the density profile and a large decrease in the number of hydrogen bonds broken in the vicinity of the solutes.
The temperature dependence of the dynamics of water inside microporous activated carbon fibers (ACF) is investigated by means of incoherent elastic and quasi- elastic neutron scattering techniques. The aim is to evaluate the effect of increasing pore size on the water dynamics in these primarily hydrophobic slit-shaped channels. Using two different micropore sizes (sim 12 and 18 {AA}, denoted respectively ACF-10 and ACF-20), a clear suppression of the mobility of the water molecules is observed as the pore gap or temperature decreases. This suppression is accompanied by a systematic dependence of the average translational diffusion coefficient Dr and relaxation time <{tau}_0> of the restricted water on pore size and temperature. The observed Dr values are tested against a proposed scaling law, in which the translational diffusion coefficient Dr of water within a nanoporous matrix was found to depend solely on two single parameters, a temperature independent translational diffusion coefficient Dc associated with the water bound to the pore walls and the ratio {theta} of this strictly confined water to the total water inside the pore, yielding unique characteristic parameters for water transport in these carbon channels across the investigated temperature range.
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