In the ordinary-sized world, you need some kind of adhesive to stick things together.
When they become very small, however, things often don't need adhesives to bind them together. There are various
forces that cause things to bind, including magnetism and Coulomb forces mentioned previously, but magnetism
and Coulomb forces work both ways, causing repulsion as well as attraction. Van der Waals (intermolecular)
forces, on the other hand, serve only to bind molecules together.
Intermolecular forces work their effect between atoms or molecules. Individually, they are very weak, but even
in the ordinary-sized world, when they are combined, they are capable of bringing things together. The picture
shows how such intermolecular forces join two lead sinkers whose polished surfaces are pressed together.
Intermolecular force is created by the balance of forces that come into play as the result of the electrical
properties of adjacent molecules or atoms. Such force is at its maximum at a set distance (less than about one-tenth
of a nanometer), which is called the Van der Waals' radius. Intermolecular force suddenly diminishes when the
separation of these molecules or atoms increases beyond this distance.
Because intermolecular forces arise between any substances, they are often used to bind substances at the nano
level.
