copolymers and introduce an asymmetry parameter $\varepsilon$:[@Miln94b; @mmnote] $$\varepsilon^2 = 
{n_{\scriptscriptstyle B}^2\over n_{\scriptscriptstyle A}^2}
{\Omega_{\scriptscriptstyle B}\over R_{\scriptscriptstyle B}^2} { R_{\scriptscriptstyle A}^2\over\Omega_{\scriptscriptstyle A}}
= {n_{\scriptscriptstyle B}^2\over n_{\scriptscriptstyle A}^2}
\varepsilon_{\scriptscriptstyle F}.
\label{eq:asym}$$ The second equality relates $\varepsilon^2$ to Fredrickson’s asymmetry parameter $\varepsilon_{\scriptscriptstyle F}$ [*e.g.*]{} Ref. [@BateFred94]). The ratio $\ell_{\scriptscriptstyle A}
=\Omega_{\scriptscriptstyle A}/ R_{\scriptscriptstyle A}^2$ is a characteristic length which is independent of the length of an $A$-arm, and is larger for more flexible chains at a given volume. A smaller $\varepsilon$ indicates an enhanced tendency for the $B$ species to stretch. Table \[table2\] shows asymmetry parameters for several diblocks.

  ----------------------------------------------------------------------------------------------------------------------------
  A-B               $\varepsilon = \sqrt{{\Omega_{\scriptscriptstyle B}          $\varepsilon_F=\varepsilon^2$       ref
                            \over R_{\scriptscriptstyle B}^2}                                                   
             { R_{\scriptscriptstyle A}^2\over\Omega_{\scriptscriptstyle A}}}$                                  
  --------- ------------------------------------------------------------------- ------------------------------- --------------
  PE-PEP                                   1.22                                               1.5                 [@faraday]

  PE-PEE                                   1.58                                               2.5                 [@faraday]

  PEP-PEE                                  1.22                                               1.5                 [@faraday]

                                           1.27                                              1.61                [@fetters94]

  PI-PS                                    1.22                                               1.5                 [@faraday]

                                           1.11                                              1.23                [@fetters94]

  PB-PI                                    1.18                                              1.39                [@fetters94]

  PB-PS                                    1.31                                              1.72                [@fetters94]
  ----------------------------------------------------------------------------------------------------------------------------

  : Asymmetry parameters for diblock copolymers $(n_{\scriptscriptstyle A}=n_{\scriptscriptstyle B}=1)$ as defined by eq \[eq:asym\].

\[table2\]

Upon minimizing eq \[eq:ftot\] over the scale of the structure, [*i.e.*]{} the radius $R$, it is convenient to normalize all energies by a characteristic energy $f_0$ to obtain a compact form for the free energy: $$f = f_0 