Two explanations can be put forward: either the corresponding acids with an average formula of C12(EO)10OCH2COOH are highly water-soluble and therefore do not act as a second surfactant to form acid–carboxylate pairs, or the head groups of these surfactants are too big in average so that never a packing parameter close to one can be achieved.In any case, it seems that in order to spontaneously form vesicles, a compromise is necessary between a sufficient hydrophily of the surfactant (i. e. a sufficiently low Krafft point) and a sufficiently small hydrophilic headgroup that allows lamellar structures to be formed.