Showing papers by "Johann Fischer published in 2008"
TL;DR: A density functional theory to describe adsorption of a simple fluid from a gas phase on a surface modified with pre-adsorbed chains is proposed and shows that new layering phase transitions can occur because of a chemical modification of the substrate under certain conditions, in comparison with nonmodified surfaces.
Abstract: A density functional theory to describe adsorption of a simple fluid from a gas phase on a surface modified with pre-adsorbed chains is proposed. The chains are bonded to the surface by one of their ends, so they can form a brush-like structure. Two models are investigated. According to the first model all but the terminating segment of a chain can change the configuration during the adsorption of fluid species. The second model assumes that the chains remain "frozen", and the system is considered as a nonuniform quenched-annealed mixture. We apply simple form of interactions to study adsorption phenomena, microscopic structure, and layering transitions. Our principal findings show that new layering phase transitions can occur because of a chemical modification of the substrate under certain conditions, in comparison with nonmodified surfaces. However, opposite trends, that is, smoothing the adsorption isotherms, can also be observed, depending on the surface density of the grafted chains.
16 citations
TL;DR: In this paper, the authors considered the squeeze out of benzene from an aqueous solution to a planar graphite wall by molecular simulations and obtained local density profiles from the mean force method with a particle balance.
Abstract: The squeeze out of benzene from an aqueous solution to a planar graphite wall is considered by molecular simulations. The system contains 1–10 benzene molecules in water at T = 300 K and p = 1 bar corresponding to an oversaturation from 10 to 100. Local density profiles are obtained from the mean force method with a particle balance. For improving the accuracy, standard simulations results are incorporated into the mean force method. The resulting density profiles of benzene show a first peak at the wall with parallel and a second with perpendicular orientation of the molecules. For larger distances from the wall the structure levels out and for up to 40-fold oversaturation a limiting density of 25.8 ± 3.6 mmol/l is obtained. This value is in surprisingly good agreement with the experimental solubility limit of 22.8 mmol/l. The method may also be used for obtaining liquid–liquid equilibria. © 2008 American Institute of Chemical Engineers AIChE J, 2008
3 citations