Numeričko modeliranje difuzije u kompozitnim medijumima

Recent technological advances enabled with use of nanoscale dimensions, opened a lot of room for various investigations, especially with mass transport through nanoporous media and nanochannels. One of the fields of research is reproducible fabrication of nanofluidic devices with characteristic size from several hundred down to few nanometers, where precise mass exchange and timing are essential. Accurate prediction of the diffusive transport is needed for rational control of physical phenomena. Another field, which is very important, is diffusion within biological system such as extracellular space, consisting of various fibers and particles, which all together affect diffusion process. Despite the increasing focus on nanofluidics in many of these applications, the laws governing molecular transport through nanoscale fluidic channels and porous media have not been fully understood. As the size of the channels and pores is reduced to the molecule size, classical continuum theories fail to predict even the basic characteristics of fluid transport. In chapter 2 we presented fundamentals of diffusion process and fields of application. As presented in this chapter, mass transport by diffusion is crucial process in biological systems. We have notified the basic nonlinear diffusion equations of mass balance, which are further used in finite element analysis. In chapter 3 we employed molecular dynamics simulations to study the effects of confinement and concentration on diffusive transport of glucose in silica nanochannels. It is found that glucose modifies the electrical properties of nanochannel walls and that, below 5 nm in channel height, glucose diffusion coefficient (diffusivity) is significantly reduced. With increasing concentration, the diffusivity is reduced linearly in the bulk, while it is reduced nonlinearly at the interface. The effective diffusivity reduction is related to the interface thickness, and has an unexpected reduction at low concentrations. Simulation results presented in chapter 3, consistent with the experimental observations, suggest that nanoconfinement is the essential cause of the observed altered fluid diffusive transport, not accounted for by classical theories, because of coupling of confinement and concentration effects. In chapter 4 we presented research of reproducible fabrication of nanofluidic devices with characteristic size from several hundred down to few nanometers, where emerging new material properties and transport p