On the uniaxial stress‐strain dependence of highly swollen chemically crosslinked networks

Many experiments show that the second Mooney‐Rivlin coefficient disappears for highly swollen chemically cross‐linked gels. Hence we are led to a paradox: Highly swollen gels seem to behave phenomenologically like phantom networks. Due to the finite extensibility of network chains, entanglements and excluded volume effects, one should ‐on the contrary‐ expect non‐Gaussian behaviour. On the basis of the phenomenological van der Waals equation of state, we have concluded that the virtual ideality of highly swollen gels is the consequence of a compensation between global interactions and excluded volume effects.