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Membrane Material Sourcing For Environmental, Particle Analyses – Sourcebook
Membranes can be separated into categories based on their pore sizes. Reverse osmosis (RO) membranes contain pores that are typically
There are two types of basic membrane structures: anisotropic and isotropic. Anisotropic (or asymmetric) membranes do not contain a uniform and homogeneous structure and pore sizes and distribution vary throughout the membrane. Anisotropic membranes are composed of a thin surface layer on top of a thicker, more permeable sublayer. Isotropic (or symmetric membranes) have a uniform structure and composition. Permeability characteristics can be controlled by altering the thickness of the overall membrane structure; the thicker the isotropic membrane, the less permeable it is.
Another common membrane manufacturing method is track etching and producing membranes by track etching allows for accurate, uniform pore size and distribution. During track etching, thin films are exposed to radioactive, charged particles that create “tracks” in the film. The film is then treated with a solution that dissolves the membrane material along the tracks created, forming pores. Thus, the pore size and distribution can be regulated by controlling both the initial intensity of the charged particles and the contact time and concentration of the solution to the membrane surface.