, University of Southampton


Science Made Simple


The word 'mesoporous' simply means that a material is full of very narrow holes that are much longer than they are wide. Scientists call these holes 'pores'. In the material these holes are so tightly packed together that when you look at it from the top there is more empty space than there is material. Each hole is so small, just a few nanometres big, that the material looks like a solid block. The image below (click to expand) shows a top down view magnified through an electron microscope so that you can see the pores and a side view showing what the pores look-like inside the material.

Top-Down View of a Mesoporous MaterialSide View of a Mesoporous Material

A template is anything that is used to define the shape of something-else. As an example think of a cake tin which is really just an empty space with a solid edge to it. When you pour cake mixture into the tin it takes the shape of the tin, i.e. it has templated the cake. In SCFED we do the same, but instead of using the cake tin we use the tiny holes in the mesoporous material as the template. This is why in SCFED we call the material a 'mesoporous template'.

For Scientists... mesoporous materials are solids that have densely packed, small diameter (< 50 nm), high aspect ratio pores. They have proven themselves highly versatile with industrial uses including: catalysis, filtration, energy storage and sensors. A new application is their use as template materials for SCFED of aligned nanowires. The spacing, alignment, diameters and surface properties (e.g. do they repel contaminant molecules) are all important features for tailoring mesoporous materials for applications.

The animation above shows how a mesoporous template can be made. Molecules called 'surfactants' are dissolved in an aqueous (water based) bath. One end of the molecule is hydrophobic (repels water) and the other end is hydrophilic (attracts water). Because of this the molecules align themselves into rings called 'micelles' so that the hydrophobic ends are shielded from the solution by the hydrophilic ends. Under the correct conditions these rings can stack together to form closely aligned columns around which a material, such as silica, can be grown. After the growth process the surfactant molecules can be burnt or washed out to leave a mesoporous material, for our example mesoporous silica.