which corresponds to the Langevin chain model that accounts for finite extensibility of the chains. Here, R max = bN is the chain contour length. For practical implementation, we need to express Eqs. ( ) and ( ) in terms of the linear deformation factor α, and to stablish a relationship between R e and both the gel volume v and α. For a diamond-lattice unit cell with lattice parameter a d , 16 chains produce a total volume V = a 3 d . Then, the total volume of a network is approximately