The saddle-splay modulus K¯ of a surfactant monolayer determines the stability of a spherical droplet microemulsion phase. Negative values of K¯ increase the droplet-size polydispersity, but inhibit shape fluctuations. Large values of the observed polydispersity may therefore not be indicative of small values of the bending modulus K, but of a ratio of K¯/K∼-2.

• Received 8 June 1990

DOI:https://doi.org/10.1103/PhysRevA.43.2903