POROLUX™ - the standard in porometry

A porometer measures the through pores inside a sample. Through pores are open on both sides of a  filter or a membrane and therefore determine the functionality. Important parameters are the largest pores, the mean flow pore size and smallest pores. The smallest pores determine the diameter of the smallest particles that will pass through the filter, the mean flow pore size or MFP represent average pore size. The largest pores, historically  called the first bubble point or FBP, determine the size of the largest through pores in the filter. Besides these characteristics also the pore size distribution – showing the spread of the different pore diameters – and the gas permeability can be calculated.

Already in 1921, Washburn considered the existing relationship between pressure and pore size, whether a liquid is pushed into the pores as in mercury porosimetry or a liquid is pushed out of the pores as is the case in porometry. The following relationship is valid for these methods:

Pressure = 4 * g * cos q * (shape factor) / diameter

With the pressure in bar, the diameter in mm, g the surface tension of the wetting liquid, q the contact angle of the liquid on the solid. The shape factor is a parameter depending on the shape and the path of the pore inside the material.

The surface tension g is a measurable physical property and is available for many liquids. The contact angle q however depends on the interaction between the material and the wetting liquid. Typical wetting fluids used in porometry are perfluoroethers. They have a low surface tension and a contact angle of 0° with nearly all materials.

A standard analysis consists of the measurement of two curves: a wet curve measured after impregnating the sample in the wetting liquid and the dry curve measured on the same not impregnated filter. The pressure is increased in the desired pressure range. A full porometry measurement typically generates the graph above from which all pore characteristics are calculated.

Porometer.com offers two different types of porometers: the pressure scan porometer (POROLUX 100 series) and the pressure step/stability porometer (POROLUX 1000 series).

Porometer.com also allows you to determine the first bubble point with the calculated bubble point and/or the “true” measured bubble point method.