An experimental study about the imbibition of aqueous solutions of low concentration of a non-adsorbable surfactant in a hydrophilic porous medium
ABSTRACT The imbibition of aqueous solutions of Triton X-100 in calcium fluoride columns has been studied in order to determine the influence of the interfacial adsorption of the surfactant in the capillary rise of the solutions. This system has been chosen because this surfactant behaves as non-adsorbable at the surface of this solid when it is in aqueous solution. The experiments have consisted of the measurement of the increase in the weight of the porous columns caused by the capillary rise of the solutions. The analysis of the results has been made through a modified expression of Washburn's equation that takes into account that the experimental increase in the weight is caused by the imbibition as well as by the development of a liquid meniscus around the bottom base of the columns. From this analysis, it has been deduced that the surfactant concentration does not influence on the imbibition rate, it being equal to the observed for water. However, it has been also proved that the contact angle depends on the surfactant concentration, taking decreasing values as the surface tension of the solutions decreases. In order to justify these findings, a study about the influence of the interfacial adsorption on the imbibition has been carried out. By means of them, it has been proved that the absence of adsorption at the solid-liquid interface is the reason that explains both the independence of the imbibition rate from the surfactant concentration and the decrease of the contact angle. Moreover, this fact indicates that the depletion of the surfactant molecules from the advancing meniscus, which has been normally adduced as the phenomenon causing the observed behaviour, has to be ruled out as the physical cause that justifies the behaviour found from the analysis of the imbibition experiments. As a corollary, it has been also stated that only if the adsorption at the solid interfaces happened, the imbibition of aqueous solution of surfactant in hydrophilic media could be influenced by the surfactant concentration.
- [Show abstract] [Hide abstract]
ABSTRACT: We report on dye deposition patterns obtained when printing dye-labeled protein solutions onto a macroporous membrane. A typical area of application would be the manufacturing of immunochromatographic tests, but the results bear significance for a wide range of printing processes. As the liquid is taken up by the membrane, the protein adsorbs non-specifically to the wetted membrane surface. The transport of protein to the pore surface involves spreading of a drop on top of the membrane, imbibition of liquid into the membrane, adsorption of protein at the pore surface, liquid redistribution from large to small pores, and liquid redistribution from the center of the wetted area to the rim.Two techniques were employed to monitor the transport of protein, which are, firstly, conventional optical imaging of the wet membrane, and, secondly, fluorescence microscopy on vertical cuts through dried samples. The latter technique visualizes protein deposition. It is conceptually related to the acquisition of breakthrough curves in chromatography. Comparison of the deposition patterns obtained with different amounts of proteins allows to reconstruct the flow pattern.We frequently find a brightening of the rim, which can be traced back to redistribution of liquid from the center to the edge during drying and to a preferential uptake of liquid across the rim of the drop. Small pores and slow drying are beneficial for the achievement of sharp printing patterns.Journal of Membrane Science 06/2008; 318(1-2-318):280-287. DOI:10.1016/j.memsci.2008.02.060 · 4.91 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Capillary analogical experiments have been designed to simulate the impregnation of surfactant-contained Nafion® solution in porous PTFE (ePTFE) matrix. It is found that the gas pressure in the capillary (initial Pinner) is the most important factor for the solution impregnation although the capillary force has slight influence on the capillary rise. The Nafion® solution can occupy 98.2% (4.91 cm vs. 5 cm) of the end-sealed capillary when the Pinner is lowered to 5 × 102 Pa. Hence, the decrease of the gas pressure in the porous PTFE matrix is very important to obtain compact Nafion®/ePTFE composite proton exchange membranes. The PFSA/ePTFE polymer electrolyte membranes (PEMs) prepared in the conditions of initial Pinner of 5 × 102 Pa and 5 vol.% surfactant concentration are well impregnated and show a high resistance to the hydrogen gas permeability over 4500 dry/wet cycles, indicating a better durability and stability. These thinner and highly conductive composite membranes are significant to improve the fuel cell output voltage. The single cell with the PEM prepared at optimized conditions gives the open circuit voltages of 0.954 V and current density of 1 A cm−2 @ 0.6 V at 60 °C.Journal of Membrane Science 12/2007; DOI:10.1016/j.memsci.2007.09.008 · 4.91 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Fluid displacement in porous media is of interest for environmental, petroleum and chemical engineering. Percolation theory and pore-scale models are useful in describing filling and emptying of pores and throats but fail to capture characteristics of the fast interfacial jumps and reconfigurations occurring during fluid displacement processes such as imbibitions and drainage. Energy release caused by these rapid events generates acoustic waves which propagate through the porous medium and can be detected at its surface using acoustic emission (AE) sensors. Through a series of experiment displacing various fluids through Hele-Shaw cells filled with glass beads of different sizes we investigate correlation between acoustic emission signals, fluid and pore space properties, and energy dissipation. Acoustic emission signals were quantified by considering number of hits (events) and amplitudes. The exponent of power law relating these characteristic values varied with the displacement process and pore size. The number of AE events and amplitudes dropped with decreasing liquid surface tension for displacement within the same porous medium (water, ethanol, silicon oil). Similar trends were observed with increasing liquid viscosity, only a few hits are recorded for silicon oil with 10 mPas. The results are interpreted considering air or liquid entry pressures into the pore spaces, with increasing pressure entries for small pores and liquid with higher surface tension. The viscosity plays an important role in restraining AE-producing jump events and dumping interfacial oscillations as could be shown theoretically for simple capillaries. The study establishes direct relationships between measured AE fluid and pore properties and offer potential for quantifying energy dissipation during fluid displacement in porous media as well as other transient flow characteristics using non invasive AE signals.Water Resources Research 12/2009; DOI:10.1029/2012WR012525 · 3.71 Impact Factor