A central draw$-$back of the $FH$ model is that the energy parameter $$ must depend on both

temperature and composition $=(T,{}_2)$ to represent most real solvent$/$polymer solutions.

Dobashi et al$.($J$.$ Chem. Phys$.72,6692-6697,1980)$ proposed the following functional form for

the PS$/$MCH system:

$=-0\mathrm{.}1091+\frac{b(T)}{1-0\mathrm{.}2481*{}_2}$

$B=-0\mathrm{.}5832+\frac{278\mathrm{.}6}{T}+1\mathrm{.}695e-3T$

$2$b$)$ The change in Gibbs energy due to mixing can be written $($per volume of mixture$)$ as

$g_{\text{m}\text{i}\text{x}}=\frac{G_{\text{m}\text{i}\text{x}}}{RT}={}_{1}ln{}_1+\frac{{}_2}{r}ln{}_2+{}_1{}_2$

Combine eqs. $2-3,2-4$ and $2-5$ and derive an expression that allows you to calculate points

on the spinodal curve $($recall that $\frac{de{l}^2{g}_{\text{m}\text{i}\text{x}}}{\text{d}\text{e}\text{l}{}_1^2}=0$ defines the spinodal curve$).$ Calculate and

report the spinodal compositions at $T=290K.$