The characterization of porous membranes

Two different types of characterization method for porous membranes can be distinguished from the above considerations: ¨

structure-related parameters: determination of pore size, pore size distribution, top layer thickness and surface porosity. ¨

Permeation-related parameters: determination of the actual separation parameters using solutes that are more or less retained by the membrane (cut-off measurements).

There are a number of characterization techniques available for porous media and although both microfiltration and ultrafiltration membranes are porous, they will be discussed separately, because different techniques must be used.

In general, the pores in a porous membrane do not have the same size but exist as a distribution of sizes.

A nominal rating indicates that a percentage (95%or98%) of the particles or molecules of that size or larger is retained.

With an absolute rating, every particle or molecule of that size or larger is retained.

Microfiltration membranes posses pores in the 0.1 - 10μm range and are readily characterized with various techniques. The following methods will be discussed here: ¨

-  scanning electron microscopy

-  bubble-point method

-  mercury intrusion porometry

-  permeation measurements

The first three methods listed involve the measurement of morphological or structural-related parameters whereas the last method is a typical permeation-related technique. The syringe filters we provide are all using the microfiltration membrane.