Blind pores

Blind pores are the pores accessible from the surface but do not travel completely from the upstream to the downstream surface

Bubble point

This term has several definitions. It can refer to the maximum pore diameter as well as to the pressure at which the first flow of air occurs through a porous material saturated with the wetting liquid. It is a measure of the largest pore-throat in a porous sample.

Capillary Flow Porometry (CFP)

Capillary Flow Porometry (CFP) is a characterization technique based on the displacement of an inert and nontoxic wetting liquid embedded in a porous network by applying an inert pressurized gas. In this technique, only through pores are measured. CFP is widely used to measure minimum, maximum (or bubble point) and mean flow pore sizes, and pore size distribution of the through pores in membranes, nonwovens, paper, filtration and ultrafiltration media, hollow fibres, ceramics, etc.

Closed pores

are pores inaccessible to their surfaces.

Contact angle

Contact angle or ɵ (theta) is used in the Young-Laplace equation to calculate the pore diameter. It is a quantitative measure of the wetting of a solid by a wetting liquid. To ensure the complete wetting of a porous material with the wetting liquid, the contact angle should be zero.

Cumulative filter flow [SUM]

This shows which percentage of the flow (at the Y-axis) has passed through pores with a size larger than the value at the corresponding point at the X-axis. It is also known as filter efficiency.

Differential filter flow [DIF]

This shows the percentage of flow (at the Y-axis) which has passed the pores with a corresponding size at the X-axis and the following size value at the same axis. According to ASTM, this graph shows the so-called “pore size frequency”.

Dry curve

Dry curve is when the gas flow against the applied pressure on a dry sample is measured, the plot “gas flow rate against pressure” is built. This plot is called a dry curve.

Gas permeability

means the property of a porous material to allow the gas to pass through the body in the presence of a pressure differential. Our porometers measure the gas flow rate. If the material area and thickness are known, the gas permeability can be calculated.

Gas-liquid porometry

Gas-liquid porometry is also known as Capillary Flow Porometry (CFP), measures pore size and pore size distribution of through pores in materials. The technique is based on the displacement of an inert and nontoxic wetting liquid embedded in a porous network by applying an inert pressurised gas. Therefore, only through pores are measured.

Half-dry curve

This is the plot which is obtained by dividing the flow values of the dry curve by 2.

Liquid-liquid porometry

Liquid-liquid porometry is an alternative to CFP for the characterisation of micro and nanopores. The measurement consists of the impregnation of the porous sample with a wetting liquid, but unlike CFP, the displacement of the wetting liquid is carried out by using a second liquid immiscible with the first one (called displacement liquid) at increasing pressure.

Liquid permeability

Liquid permeability is the ability of a porous material to pass the fluid flow through its body. Different liquids can be used to measure liquid permeability, such as water, ethanol, oils, etc.

Mean flow pore diameter

Mean flow pore diameter is the pore size at which 50% of the total gas flow can be accounted (half the flow is through pores larger than this diameter).

Pore throat

The pore throat is the most constricted part of a pore. In other words, it is the most challenging part for the gas to displace the liquid along the entire pore path. The diameter measured in CFP is the pore throat, regardless of where exactly in the pore path it is.

Pore size distribution [CDIF]

Pore size distribution [CDIF] shows the flow distribution normalised per unit of change in size (flow changes are divided by size changes).

Shape factor

is a calculation correction method which includes the assumed shape of the pores in the calculation. Factor 1 – mostly used in Europe – assumes that all pores have an exact cylindrical shape. This assumption is, in many cases, not correct. In the USA, a value of 0,715 is prevalently used. This value assumes, that pores are asymmetric.

Smallest pore size

Smallest pore size is the pore size calculated at the pressure at which the dry curve meets the wet curve.

Through pores

This a type of pores which are opened from the upstream surface to the downstream surface of a material.

Wet curve

this curve represents the measured gas flow against the applied pressure measured on a sample impregnated with a wetting liquid.

Wetting liquid

A wetting liquid is a type of liquid which can easily penetrate inside the pores of a material. A good wetting liquid for capillary flow porometry should have a zero contact angle, low surface tension and low vapour pressure. In addition, it has to be chemically inert and should not cause swelling of the sample.

Young-Laplace formula

The young-Laplace equation is the basis for porometry measurements, as it explains the link between pore size and pressure: P = 4 γ cos θ / D

Where

P = pressure required to displace the wetting liquid from the pore

D= diameter of the capillary (or pore) γ= surface tension of liquid θ= contact angle between the liquid and capillary wall