What uses do cycloalkanes have?

I can point to one signal use of cyclohexane. Cyclohexane has a melting point of #6.47# #""^@C#. Of course, when solutes are dissolved in this solvent, the freezing point is depressed proportional to the number of species in solution. If we use a known mass of solute, we can get an excellent estimate of the solution molecular weight of the solute simply by taking a melting point measurement.

Note that even these days, when structure determination by an X-ray crystallography experiment has become almost routine, there is always the possibility that the solution structure is different to the solid-state structure. Molecular weight in solution measurements, such as cyclohexane affords here, is one handle on the solution structure.

Cyclohexane is converted to cyclohexanol and cyclohexanone, which are used in the manufacture of adipic acid and caprolactam. These are used to produce nylon 6,6 and nylon 6 respectively.

Cyclopentane can be used as a blowing agent for polyurethanes, where it has replaced CFCs which fell out of favour due to their perceived reaction with atmospheric ozone.

Cyclopropane and cyclobutane are generally more used as building blocks for other molecules in synthetic organic chemistry.