Cure Terms Glossary
The crosslink density can be defined in various ways. One way is as the number of chain segments (between crosslinks) per unit volume - designated ν.
Another way of expressing this is in terms of the average molecular weight between crosslinks - designated as Mc. These two conventions can be related numerically, since the average segment weight (in grams) is Mc / N (where N is the Avogadro number) and the average segment volume is therefore Mc / Nρ (where ρ is the material density). Thus the average number of chains per unit volume is given by,
Hence crosslink density
is inversely proportional to Mc. Increasing crosslink density
increases material stiffness, and various expressions have been derived
linking modulus to ν or Mc.
The basis of any direct correlation relies on the crosslink providing
the only restriction on segmental mobility (i.e. the hypothetical freely-jointed
chain) and the closest approximation is for crosslinked materials in their
rubbery state, especially when swollen.