Small-angle X-ray diffraction study of the thermotropic and lyotropic phases of five alkyl cyclic and acyclic disaccharides: Influence of the linkagebetween the hydrophilic and hydrophobic moieties

We present a comparative study of the thermotropic and lyotropic phases of 5 surfactants with an aliphatic chain of 12 carbon atoms and a cyclic or ac yclic sugar head with different linkages between the two moieties. These li nkages can concern different chemical groups or different orientations betw een the head and the chain. The compounds included the alpha- and beta -N d odecyl-D-maltosides, N-dodecylamino-1-deoxylactitol, N-dodecyl lactobionami de and N-acetyl N-dodecyl lactosylamine. The influence of the polar head (w ith closed- and opened-type sugars) and the linkage with the hydrocarbon ch ain on the phases obtained by the heating of the anhydrous compounds and af ter addition of water was studied by X-ray diffraction and optical microsco py. In the anhydrous state, the surfactants were either crystalline or amor phous. On heating, they went through a liquid crystal smectic phase which, in some cases, was preceded by solid-to-solid transitions. On addition of w ater, the sequence of phases from the micellar phase to the lamellar phase was accounted for in terms of the geometric model of Sadoc and Charvolin. H owever, with certain surfactants this sequence was not complete, and the do mains of existence of phases were altered.