Electrical Characterization of Membranes

Characterization of membranes used in filtration processes (microfiltration, ultrafiltration, nanofiltration, reverse osmosis) is usually carried out by hydro-dynamic measurements (hydraulic permeability, retention) [5-10], but electrical measurements such as streaming potential (SP or electroosmotic flow) and membrane potential (MP) are used for characterizing, respectively, the mem-brane/solution interface (zeta potential, surface charge density) and the effective membrane fixed charge and ion transport numbers in the membrane [11-27]. Moreover, great and rapid development of membranes for fuel cells 

This chapter presents a general description of the three kinds of measurements (SP, MP, IS) used for electrical characterization of membrane in working conditions , that is, with the membranes in contact with dectrolyte solutions and the information achieved from them is briefly indicated. The main attention focuses on the characterization of those membranes commonly used in traditional separation processes (from diverse materials and with different structures), and IS measurements are considered in more detail. Membrane and matrix material electrical parameters are obtained, but the measurements also provide thermodynamics and geometrical/structural information. 

As previously indicated, the most common measurements for membrane electrical characterisation are  

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Bijani S, Fortunato R, de Yuso MVM, Heredia-Guerrero FA, Rodriguez-Castellon E, Coehloso 1, Crespo J, Benavente J (2009) Physical-chemical and electrical characterizations of membranes modified with room temperature ionic liquids age effect. Vacuum 83 1283-1286... 

The influence of membrane effective fixed charge, Xf, on the transport of ions is estimated by determining the ion / transport number or fraction of the total electric current transported by ion i (TO, that is f = Ij/Ix since Zi h = 1, for single salts L + t. = 1. However, electrical characterization of membrane-surface/electrolyte interface is usually carried out by TSP measurements (A( ) gt), which allows the determination of zeta potential (Q, the electrical potential at the shear plane, by using the Helmholtz-Smoluchowski equation [33] ... 

Torras, C., Zhang, X., Garcia-Vails, R. and Benavente, J. 2007. Morphological, chemical surface and electrical characterizations of lignosulfonate-modified membranes. J. Memb. Sci. 297 13( 137. 

Bertolo JM, Bearzotti A, Generosi A, Palummo L, Albertini VR (2005) X-Rays and electrical characterizations of ordered mesostructured sdicathin films used as sensing membranes. Sens Actuators B Chem 111-112 145-149 Brinker CJ, Scherer GW (1990) Sol-gel science the physics and chemistry of sol-gel processing. Academic, San Diego... 

Impedance Spectroscopy (IS) is an a.c. technique for electrical characterization of materials and interfaces based on impedance measurements carried out for a wide range of frequencies (10 < f(Hz) < 10 ), which can be used for the determination of the electrical properties of homogeneous (solids and liquids) or heterogeneous systems formed by a series array of layers with different electrical and/or structural properties (for example membrane/electrolyte systems), since it permits us a separate evaluation of the electrical contribution of each layer by using the impedance plots and equivalent circuits as models, where the different circuit elements are related to the structural/transport properties of the systems [40, 41). 

Theoretical and experimental descriptions of three different types of electrical measurements commonly used for membrane characterization have been presented. Streaming potential, membrane potential, and impedance spectroscopy are nondestructive techniques and they can be carried out with the membranes in contact with electrolyte solutions, which allows characterization of membranes in working conditions , but they also permit us to established changes in the membrane characteristic parameters related to solution chemistry (ion size, charge, concentration, pH) and/or membrane structure. 

Impedance spectroscopy allows the determination of electrical parameters related to the flow or adsorption of charge (electrical resistance or capacitance, respectively) for simple and heterogeneous systems consisting of a series array of layers with different electrical/structural characteristics (such as membrane/elec-trolyte systems), and it can be used for a separate characterization of membrane and electrolyte solution. Moreover, if composite membranes are studied, electrical parameters for each layer could also be determined as well as other structural/ material information obtained from the estimated electrical parameters. 

Kim, K.-J., Fane, A. G., Nystrom, M., and Pihlajamaki, A. (1997). Chemical and electrical characterization of virgin and protein-fouled polycarbonate track-etched membranes by FUR and streaming-potential measurements. J. Membr. Sci. 134, 199. 

Researchers at the MoneU Center (Philadelphia, Pennsylvania) are using a variety of electrophysical and biochemical techniques to characterize the ionic currents produced in taste and olfactory receptor cells by chemical stimuli. These studies are concerned with the identification and pharmacology of the active ion channels and mode of production. One of the techniques employed by the MoneU researchers is that of "patch clamp." This method aUows for the study of the electrical properties of smaU patches of the ceU membrane. The program at MoneU has determined that odors stimulate intraceUular enzymes to produce cycUc adenosine 3, 5 -monophosphate (cAMP). This production of cAMP promotes opening of the ion channel, aUowing cations to enter and excite the ceU. MoneU s future studies wiU focus on the connection of cAMP, and the production of the electrical response to the brain. The patch clamp technique also may be a method to study the specificity of receptor ceUs to different odors, as weU as the adaptation to prolonged stimulation (3). 

Finally, with regard to synaptic type, there is the well-characterized electrical synapse [20], where current can pass from cell to cell across regions of membrane... 

Sadoulet-Puccio, H. M., Khurana, T. S., Cohen, J. B., and Kundel, L. M. (1996). Cloning and characterization of the human homologue of a dystrophin related phosphopro-tein found at the Torpedo electric organ post-synaptic membrane. Hum. Mol. Genet. 4, 44489-44496. 

INTESTINE Characterization of a membrane potassium ion conductance in intestinal secretory cells using whole cell patch-clamp and calcium-sensitive dye techniques, 192, 309 isolation of intestinal epithelial cells and evaluation of transport functions, 192, 324 isolation of enterocyte membranes, 192, 341 established intestinal cell lines as model systems for electrolyte transport studies, 192, 354 sodium chloride transport pathways in intestinal membrane vesicles, 192, 389 advantages and limitations of vesicles for the characterization and the kinetic analysis of transport systems, 192, 409 isolation and reconstitution of the sodium-de-pendent glucose transporter, 192, 438 calcium transport by intestinal epithelial cell basolateral membrane, 192, 448 electrical measurements in large intestine (including cecum, colon, rectum), 192, 459... 

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