Catálogo de publicaciones - libros

Osmosis through a clay membrane, and osmotic swelling of a capsule formed from an HSA-alginate membrane, are compared. Compacted clay acts as an imperfect semipermeable membrane. When the clay membrane separates two salt solutions of different concentrations, osmotic effects are observed, and two relaxation processes control the rate at which the salt solutions come into equilibrium. Capsules, created with an HSA-alginate membrane, exhibit osmotic swelling when the salt concentration of the surrounding fluid is changed. Their return to a new equilibrium exhibits only a single relaxation rate. Analysis explains why two relaxation rates are observed in one case and not in the other.

The aim of this contribution is to derive macroscopic equations describing flow of two-ionic species electrolytes through porous piezoelectric media with random, not necessarily ergodic, distribution of pores. Under assumption of ergodicity the macroscopic equations simplify and are obtained by using the Birkhoff ergodic theorem.

This paper is concerned with the experimental identification of some chemoporoelastic parameters of a reactive shale from data obtained in pore pressure transmission - chemical potential tests. The parameter identification is done by matching the observed pressure response with a theoretical solution of the experiment. This solution is obtained within the framework of Biot theory of poroelasticity, extended to include physico-chemical interactions. Results of an experiment on a Pierre II shale performed in a pressure cell are reported and analyzed.

When a biological tissue is subjected to a mechanical load, an electrical potential gradient is generated. Such potential gradient is associated with the flow of charged particles through a matrix with fixed charges. A deformation of the matrix causes a fluid flow relatively to the solid matrix. This fluid flow tends to separate the freely moving ions in the fluid from the oppositely charged particles, that are attached to the matrix. In this way, an electrical field is created collinear to the fluid flow. This results in an electrical potential. A similar effect appears when charged particles start moving because of a chemical load.

In this study, uniaxial confid swelling and compression experiments were performed on a hydrogel that mimics the behaviour of biological tissues. The deformation of the sample and the electrical potential difference over the sample, caused by varying mechanical and chemical loads, were measured successfully.

A poromechanics formulation for transversely isotropic chemically active poroelastic media under non-isothermal conditions is presented. The formation pore fluid is modeled as a two-species constituent comprising of the solute and the solvent. The model is applied to study the thermo-chemical effects on the stress and pore pressure distributions in the vicinity of an inclined borehole drilled in a chemically active transversely isotropic formation under non-isothermal conditions.

Salt weathering is one of the major causes of deterioration of buildings and monuments. We have determined the underlying moisture and ion transport within a representative building material by measuring the time evolution of NaCl saturated samples during one-sided drying with Magnetic Resonance Imaging. The obtained NaCl concentration profiles reflect the competition between advection to the surface and redistribution by diffusion. By representing the measured moisture and NaCl profiles in a so-called efflorescence pathway diagram (EPD) also information about the crystallization process is obtained. The pathways followed in the EPDs indicate that for historical objects in general crystallization at the surface cannot be avoided, when evaporation cannot be prevented.

We use Nuclear Magnetic Resonance relaxometry ( the frequency variation of the NMR relaxation rates) of quadrupolar nucleus (Na) and H Pulsed Gradient Spin Echo NMR to determine the mobility of the counterions and the water molecules within aqueous dispersions of clays. The local ordering of isotropic dilute clay dispersions is investigated by NMR relaxometry. In contrast, the NMR spectra of the quadrupolar nucleus and the anisotropy of the water self-diffusion tensor clearly exhibit the occurrence of nematic ordering in dense aqueous dispersions. Multi-scale numerical models exploiting molecular orbital quantum calculations, Grand Canonical Monte Carlo simulations, Molecular and Brownian Dynamics are used to interpret the measured water mobility and the ionic quadrupolar relaxation measurements.

A three-phase multi-species electro-chemo-mechanical model of articular cartilage is developed that accounts for the effect of two water compartments, namely intrafibrillar water stored in between collagen fibrils and extrafibrillar water covering proteoglycans. The collagen fibers constitute the solid phase while intrafibrillar water and dissolved NaCl on one hand and extrafibrillar water, ions Na and Cl and proteoglycans on the other hand form the two fluid phases. Chemical equilibrium between the fluid phases is assumed and only the mechanical aspects of the behaviour are considered.

A three-scale model based on a modified convection-diffusion-reaction equation wherein the partition coefficient governing the instantaneous adsorption/desorption of the species in the micro-pores appears appears coupled with the local electric potential sastisfying a Poisson-Boltzmann equation, is proposed to describe contaminant transport in swelling clays characterized by two levels of porosity (micro and macro-pores). At the microscale the medium is composed of charged clay particles saturated by a binary monovalent aqueous electrolyte solution. At the intermediate (meso) scale the two-phase system is represented in a homogenized fashion with movement of the ionic charges governed by the Nernst-Planck relations. At the macroscale, the mesoscale mixture of clay clusters is homogenized with the bulk solution in the macro-pore system. A notable consequence of the approach proposed herein is the microscopic representation for the partition coefficient which can be exploited to derive the constitutive behavior for this quantity.

We formulate the balance principles for an immiscible mixture of continua with microstructure in the broadest sense for include, , phenomena of diffusion, adsorption and chemical reactions. After we consider the flow of a fluid/adsorbate mixture through big pores of an elastic solid skeleton and propose suitable constitutive equations to study the coupling of adsorption and diffusion under isothermal conditions.