Nanotechnology Lect.3

Surface properties
Regardless of whether we consider a bulk material or a nanoscale material, its physical and chemical properties depend on many of its surface properties. Surfaces perform numerous functions: they keep things in or out; they allow the flow of a material or energy across an interface; they can initiate or terminate a chemical reaction, as in the case of catalysts. The branch of science that deals with the chemical, physical and biological properties of surfaces is called surface science. In this context, the term interface, rather than surface, is often used, to emphasise the fact that it is a boundary between two phases: the material and the surrounding environment (liquid, solid or gas).
If a bulk material is subdivided into an ensemble of individual nanomaterials, the total volume remains the same, but the collective surface area is greatly increased. This is shown schematically in Figure 4.
The consequence is that the surface-to-volume ratio of the material — compared to that of the parent bulk material is increased.
A very simple example is granular sugar and caster sugar. Caster sugar is finer, stickier (more surface absorption) and dissolves faster in water.
How would the total surface area increase if a cube of 1 m3 were progressively cut into smaller and smaller cubes, until it is composed of 1 nm3 cubes? Table 2 summarizes the results.