Liquid-Liquid Porometry for Characterising Ultrafiltration Membrane Pores

Liquid-Liquid Porometry (LLP) is a valuable technique for measuring the pore structure characteristics of ultrafiltration membranes without damaging the membranes themselves. These membranes can act as barriers to a whole range of particles, both organic and inorganic, including bacteria, pollens, spores, pathogens and pesticides and even high molecular weight solutes, colloidal suspensions, and viruses.

Pore characteristics such as pore distribution, liquid permeability, pore throat diameter, bubble point pore diameter and mean flowpore diameter all offer valuable insights into pore function. However, capillary flowporometry a technique that can provide the required information about such characteristics uses high test pressures not suited for measuring ultrafiltration membranes. Liquid-Liquid Porometry (LLP) by comparison can measure the required pore structure characteristics without distorting the pore structure or damaging the membranes. In addition LLP is faster, uses less energy and lower pore sizes can be characterised.poro fror blog

LLP is an elegant technique that works by initially filling the pores of a sample, such as the ultrafiltration membrane with a wetting agent. A second wetting agent is applied that is less wetting to the sample and immiscible with the first wetting liquid. This is then used to displace the first wetting liquid from the pores of the membrane under applied differential pressure. The flow rate of the second wetting liquid through the emptied pores of the sample is thereby measured as a function of differential pressure and also measured without the first wetting liquid in the membrane pores.

The pore structure characteristics can then be computed from the measured differential pressures and flow rates of the second wetting liquid through the dry sample and sample wetted by the first wetting liquid.