Fig. 4.

Evolution of $\mathrm{\Delta }\theta$ as a function of $u=h/R$ for different cholesteric mixtures of 5CB and CB15. Each point corresponds to a different experimental shell with a given geometry u, and each symbol/color corresponds to a different value of p (p = 9.3, 6, or 3.6 $\mu \text{m}$). The data for $p\to \infty$ (nematic) have been taken from ref. 9. The solid lines represent the theoretical curves, for different values of the minimal shell thickness $h_0$, obtained from solving $f=0$ in Eq. 1. The dashed lines containing down arrows indicate the critical values of u, denoted $u_{\text{bm}}\ast$, above which no bivalent shells are found. The dashed lines containing up arrows indicate the critical values of u, denoted $u_{\text{bm}}\ast$, below which no monovalent shells are found. To facilitate the reading of the image, we have plotted these lines only for the blue and red symbols. (Inset) Evolution of $u_{\text{bm}}\ast$ and $u_{\text{bm}}\ast$ as a function of $p/R$. The gray region corresponds to the zone where the two configurations coexist.