Permeability membrane characterization

Membrane Characterization The two important characteristics of a UF membrane are its permeability and its retention characteristics. Ultrafiltration membranes contain pores too small to be tested by bubble point. Direc t microscopic observation of the surface is difficult and unreliable. The pores, especially the smaller ones, usually close when samples are dried for the electron microscope. Critical-point drying of a membrane (replacing the water with a flmd which can be removed at its critical point) is utihzed even though this procedure has complications of its own it has been used to produce a Few good pictures. 

In ultrafiltration, water and other low molar mass molecules are forced through a semi-permeable membrane by the application of high pressures (1-7 bar) or of a centrifugal field. This technique involves membranes with pore diameters in the range of 1.0-20 nm, which are most commonly characterized and selected based on their nominal molar mass cut-off... 

The membrane characterization data reported in this section have been obtained by means of a home-made apparatus which is made of stainless steel and can operate from high vacuum up to 70 bars [17], It is characterized by the unique capability of performing a broad range of porous membrane characterization and evaluation measurements, namely equilibrium isotherms, absolute (integral and differential) and relative gas and condensed vapor permeabilities and selectivities. 

This chapter aims to keep these challenges in mind as we review the defect chemistry, transport theory and aspects of characterization of hydrogen permeation in dense ceramics. We will first look at some applications and simple schemes of operation of hydrogen-permeable membranes and then, briefly, at the literature and status of hydrogen-permeable dense ceramics. 

Bowen et al. [40] used sulfonated poly(ether ether ketone) (SPEEK) as an additive in the polysulfone (PSf)/SPEEK/N-methyl-2-pyrrolidone (NMP) system. Membrane characterization was carried out using filtration studies and AEM. Membranes prepared from solutions in the region of polyelectrolyte behavior [41] showed more pronounced and systematic improvement of membrane permeability and salt rejection. A small decrease in pore size and surface roughness was also followed by an increase in SPEEK content. Compared with a - 28.5 mN m adhesion force of a 4 pm silica particle for a SPEEK free PSf membrane, a SPEEK modified membrane showed greatly reduced adhesion of - 0.75 mNm h This, together with the surface smoothening effect, leads to the reduction of membrane fouling when the surface is modified by the addition of SPEEK. 

A new series of studies [84] has focused on bilayers composed of unsaturated lipids. This was motivated in part by the fact that (1) bilayer permeability to glycerol was previously found to increase with lipid unsaturation [8] and (2) the solubility of water in alkenes is slightly greater than in alkanes. Transport of various molecules across the bilayer occurs by diffusion down a concentration gradient. The permeability, that characterizes this mass transfer is a property of the membrane composition, the solute, and the temperature,... 

There are several kinds of membrane characterization, depending on the information and knowledge required (morphological structure, chemical properties, permeability, selectivity, etc.). In this case, we focused on the morphological characterization of polysulfone membranes by using the SEM technique. 

Such water permeable membranes are characterized by pore structures in which the total porosity is greater than about 50%. Further, the average pore size may be from about 0.025 pm to about 0.1 pm. Such a humidifier is particularly suitable for use in humidifying a reactant gas supply stream for a solid pol5nner fuel cell. The fuel cell has a reactant gas inlet port and a reactant gas exhaust port (156). 

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