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A membrane unbinding transition sends the equilibrium layer spacing to infinity. In a dilute lamellar stack, competition between a quadratic virial attraction and cubic Helfrich repulsion gives a continuous transition with spacing exponent one.

Write the free energy asWhen $A_H<A_H^{\ast }$, $B_2>0$ and the global minimum on $\varphi \ge 0$ is ${\varphi }_{\ast }=0$, corresponding to an unbound stack. When $A_H>A_H^{\ast }$, $B_2<0$, and minimization givesUsing $B_2\sim -r(A_H-A_H^{\ast })$ yieldsSince $d_{\ast }=\delta /{\varphi }_{\ast }$,so the continuous membrane unbinding transition has exponent