Selectivity and permeability are key properties to characterise a membrane. The selectivity indicates how well a membrane can separate. Comparing the composition of a mixture before the membrane and after it has passed the membrane gives an impression of the selectivity of the membrane for that mixture. If one component of the mixture does pass […]
Polystyrene foam, filters, porous asphalt, aerogel … They all have one thing in common: besides ‘real material’ they also consist of empty space: small cavities or continuous channels – sometimes even from one side of the material to the other. In other words: they are porous. The presence of pores influences the materials properties to […]
The Swedish mineralog Axel Fredrik Cronstedt was rather surprised in the middle of the 18th century when he heated a piece of stone with a burner. What happened? The stone started to bubble and hiss. Water adsorbed inside these stones was released as steam. He called these stones zeolites, after the ancient Greek words zeos […]
A membrane is a selectively permeable separation wall. Some substances can pass and others cannot, allowing to separate the ‘some’ from the ‘others’. Its simplicity, and therefore its versatility, is the great strength of this type of filter. Today, they are widely used to convert salt water into fresh water and in kidney dialysis. But […]
Exhaust gases from diesel cars contain soot particles, which are the result of combustion (pyrolysis) in the diesel engine. Soot particles in the (sub)micron range appear to have such a detrimental effect on human health that the European Commission decided to restrict their emission. For example, the Euro V standard came into effect as of […]
It becomes more and more common: rain or sportswear that is waterproof and breathable at the same time. Porous materials that allow water vapour (perspiration) to pass while rejecting liquid (rain) water form the basis. The secret lies in the combination of the open structure and the water repellence of tissues. In fact, any tissue […]
The porosity of a material indicates what is the volume of empty space with respect to the total volume. So if you know that a material is 25% porous, then it consists for 75% of ‘real material’, and the remaining quarter is ‘nothing’ or air. But in addition to this absolute value for the porosity, […]
