Molecular dynamics confinement effects

Chapter 15 gives an extensive and detailed review of theoretical and practical aspects of macromolecular transport in nanostructured media. Chapter 16 examines the change in transport properties of electrolytes confmed in nanostructures, such as pores of membranes. The confinment effect is also analyzed by molecular dynamic simulation. 

For ultrathin films, it should also be mentioned that Tg is strongly subjected to interface effects, thus it may be higher or lower than in the bulk material [3], This finding can be attributed to the interplay between surface and geometric confinement effects. Due to attractive interactions at interfaces, the molecular dynamics may be slowed down, resulting in an increase of Tg, whereas the confinement to a small layer may lead to an increase in the free volume, resulting in a decrease of Tg [4],... 

Lately, quantum-classical molecular-dynamics simulations of an excess electron in water performed for wide ranges of temperature and pressure suggest that the observed red shift of the optical absorption spectrum is a density effect rather than a temperature effect. Indeed, by increasing the temperature, the mean volume of the cavity occupied by the solvated electron increases due to weakening of bonds between solvent molecules the electron is less confined in the cavity, and the potential well becomes less deep. 

In the present article, molecular dynamics simulations of simple molecules physically adsorbed on surfaces or in pores will be reviewed. In most of these simulations, it is assumed that the solid adsorbent is rigid, providing a force field for particles in the fluid via their physical interactions with the solid. These cause the fluid in the vicinity of the solid to become inhomogeneous. The inhomogeneity is often sufficient to allow one to describe the fluid as a separate (adsorbed) phase on or near to the solid surface. Another point of view that is fi quently adopted is that the repulsive part of these interactions causes the fluid to be restricted to the volume outside the range of the strong repulsions. Evidently, this is relevant primarily when the fluid is contained in a void volume i.e., when it is sorbed in a pore. In such cases, experimental, theoretical and simulation studies of the effect of confinement upon fluid properties are of interest. 

IV. Confinement Effects on the Molecular Dynamics in Thin Films of Hyperbranched Polyester... 

Gas transport in nano-confinements can significantly deviate from the kinetic theory predictions due to surface force effects. Kinetic theory-based approaches based on the assumption of dynamic similarity between nanoscale confined and rarefied flows in low-pressure environments by simply matching the Knudsen and Mach numbers are incomplete. Molecular dynamics simulations of nanoscale gas flows in the early transition and free-molecular flow regimes reveal that the wall force field penetration depth should be considered as an important length scale in nano-confined gas flows, in addition to the channel dimensions and gas mean free path. 

The effects of constraints in general on the freezing temperature have been studied theoretically, specifically in an entanglement/frozen tube model, and by molecular dynamics simulations. Confinement of liquids also affects the glass transition temperature, which typically decreases as the pore size decreases. " ... 

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