Membranes bubble-point procedure

The bubble point measurement is recognized as an ASTM procedure (F316-80 [26] and E128-61 [27]). This technique allows the determination of pore diameters and the presence of defects in the membrane. Bubble point is based on Jurin s law. If a porous membrane is impregnated with a liquid (e.g., water, alcohol) each pore has a meniscus of condensate at the gas-liquid interface which opposes the flux of gas. To unblock the pores a pressure Ap must be applied. According to the Jurin s law, the smaller the pores, the higher the pressure required... 

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. 

The bubble point test is simple, quick and reliable and is by far the most widely used method of characterizing microfiltration membranes. The membrane is first wetted with a suitable liquid, usually water for hydrophilic membranes and methanol for hydrophobic membranes. The membrane is then placed in a holder with a layer of liquid on the top surface. Air is fed to the bottom of the membrane, and the pressure is slowly increased until the first continuous string of air bubbles at the membrane surface is observed. This pressure is called the bubble point pressure and is a characteristic measure of the diameter of the largest pore in the membrane. Obtaining reliable and consistent results with the bubble point test requires care. It is essential, for example, that the membrane be completely wetted with the test liquid this may be difficult to determine. Because this test is so widely used by microfiltration membrane manufacturers, a great deal of work has been devoted to developing a reliable test procedure to address this and other issues. The use of this test is reviewed in Meltzer s book [3],... 

Bubble Point tests are usually carried out to characterize a membrane or porous material consistency or quality they are also a common procedure to determine the maximum pore size. 

Most of the research was done with 0.2 micrometer rated porous polypropylene (Accurel ) membrane, and the concentration of polyacetylene in the composite could be varied from 4 to 43 percent. Larger percentages should be possible. The membranes did not lose their flexibility, and membrane properties such as flux rates and bubble point pressure were not altered (see Experimental Procedure 1). As is the case for polyacetylene alone, the conductivity of these membranes could be varied depending upon the type and amount of dopant. Iodine doped laminates were the most stable of the two doped laminates investigated in this study. 

The pressure required to force water to enter the pore is called the breakthrough pressure. Bubble point as measured and reported in the literature is the air pressure needed to push out liquid imbibed in the pore of the membrane. The procedure for a bubble point test is described in ASTM Method F-316. The relationship between pore size and bubble point pressure is based on the application of the Young-Laplace equation. The smaller the... 

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