Porous media mimicking and analysis through nanotechnology
Natural systems, as beach sand, rocks, soils and several biological tissues, as bones and wood, can be classified as porous media. A porous medium can be generally defined as any material consisting of a solid matrix with an interconnected void volume typically referred as pore volume. In many fields, as geosciences, the solid matrix is either rigid or slightly deformable. The interconnectedness of the pores allows the flow of one (single phase flow) or more (multi-phase flow) fluids, either a liquid or a gas, through the material. The analysis, characterization and understanding of fluid flow in porous media under a wide range of different thermodynamic, physical and chemical conditions is of common interest in many areas of science, from geosciences to petroleum and environmental engineering, from material science to biology and many others. Microfluidic models, or micromodels, are establishing as the ideal platform to tackle this class of problematics. Indeed, they provide several advantages such as flexible implementation of different channel geometries at micro and nano scale, modification and functionalization of surface properties, control of operating thermodynamic conditions and possibility for direct visual inspection and related analysis, integration of nanoporous materials to model even complex systems. Actually, micromodels to mimic and investigate transport in porous media were firstly introduced in the ‘50s, but it is only recently, thanks to the advancement of nanotechnology, that they overcame the technical limitations that hindered their diffusion. The current generation of microfluidic devices represent a valuable tool for the description, characterization and understanding of the physical phenomena governing fluid flow in porous media, such as fluid properties, solid-fluid and fluid-fluid interaction properties, phase trapping, wettability modification, solids deposition or emulsions, etc.. They show great potential in applications in several areas such as: reservoir engineering and underground gas storage, providing key information for the definition of the optimal reservoir management strategy, for processing and analysis of produced fluids as well as for the design and manipulation of injected fluids; food technology, as an example to design new strategies for food packaging; environmental engineering for filtration and separation; biomedical engineering to mimic biological tissues. Therefore, the design and fabrication of microfluidic micromodels to mimic the key features of porous media is emerging as a new fascinating area to enable the analysis of complex fluid flow, giving access to a more mature understanding of several natural and industrial processes.