Swelling and shrinking of porous materials: from colloid science to poromechanics

Abstract

Electrochemical interaction between colloidal particles and an aqueous solution is a central subject in Colloid Science. Such interactions give rise to electrokinetic phenomena in electrically charged porous media, and have received considerable attention with a wide range of applications in different fields of science and engineering. Several porous materials composed of electrically charged macromolecules saturated by saline solutions may undergo swelling by fresh water uptake. Among this class of colloidal systems, we highlight 2-1 lattice clays, hydrophilic polymers, gels, shales, corneal endothelium and connective biological tissues. For example, the response of smectite 2:1 clay particles to changes in water content has been studied for decades. Such phenomenon plays a critical role in the quality of groundwater, in the effectiveness of some clean up technologies and in the distribution of plants and nutrients in the Earth's crust. Clay swelling (or collapse) is of widespread relevance in geotechnical and geoenvironmental fields. Upon inundation, it may have undesired consequences, as they heave upward upon hydration (or shrink upon desiccation) causing damage to the foundations of buildings ranging from minor cracking to irreversible displacements of footings. Moreover, swelling and deterioration of shales are the major contributors to drilling problems and are key factors in the wellbore stability management. Finally, due to their low hydraulic conductivity, plasticity, swelling and adsorptive capacity for contaminants, bentonitic based compacted clays have been used as sealing materials to inhibit the migration of contaminants to the environment, and have been also considered to investigate the disposal of high-level radioactive waste in various countries.Beyond applications in natural geomaterials, swelling polymers/biopolymers have numerous technological applications, such as size exclusion chromatography, gel electrophoresis in filtration processes, development of efficient drug delivery substrates, in contact lenses, in semiconductor manufacturing and in food stuffs. In biomedical technology, electrical interactions between ions and negatively charged proteoglycans rule the deformation of cartilaginous soft hydrated tissues as load-bearing structures. The swelling property is tied-up to the physiological states of soft connective tissues (articular cartilage and intervertebral disk) and plays an important role in articulating joint lubrication and damping of dynamic forces in the human body.The fundamental thermodynamic processes underlying electrokinetic phenomena involve several couplings, such as: transport of mobile ions near charged surfaces (electro-migration), flow and motion of charged particles driven by an electric field (electro-osmosis and electrophoresis), dissolution/precipitation reactions, electrolysis of water, sorption, desorption and protonation/deprotonation chemical reactions. Owing to their complexity, it is imperative that any macroscopic model describing these electro-chemo-me...

A palaeobiogeographic model for biotic diversification within Amazonia over the past three million years

“…At about approximately 1.0 -0.7 Ma, the lower Negro River was established as a barrier, resulting in the creation of the Negro area of endemism [19], as well as the separation of P. ochroptera and P. crepitans (figure 3e and table 1, node 5). The palaeogeographic mechanism for this vicariance event apparently involved the establishment of the current course of the lower Negro River in response to a series of neotectonic faulting events [10,47,48] (see electronic supplementary material). Supporting this molecular dating result, Soares et al [47] found evidence for an age of about 0.4 Ma for the initiation of sedimentation covering the Miocene Novo Remanso formation along the lower Negro River.…”

“…The palaeogeographic mechanism for this vicariance event apparently involved the establishment of the current course of the lower Negro River in response to a series of neotectonic faulting events [10,47,48] (see electronic supplementary material). Supporting this molecular dating result, Soares et al [47] found evidence for an age of about 0.4 Ma for the initiation of sedimentation covering the Miocene Novo Remanso formation along the lower Negro River.…”