Structure and local ordering of a lyotropic nematic phase and its intrinsic cholesteric counterpart

This study presents results of texture analysis and of small-angle X-ray scattering (SAXS) of a lyotropic liquid crystal nematic phase and the corresponding intrinsic cholesteric phase. An intrinsic cholesteric mesophase was obtained by the doping of a nematic mixture with an amphiphilic chiral molecule. The mixture of potassium laurate, 1-dodecanol, potassium sulphate and water exhibits the calamitic nematic phase (N_C). The calamitic cholesteric phase (Ch_C) was obtained from this mixture by the doping with the chiral compound potassium N-dodecanoyl-L-serinate. With this procedure, one obtains an <i>intrinsic</i> cholesteric calamitic mesophase since the chiral molecule is incorporated in the micelles. The SAXS analyses showed that the presence of the chiral amphiphilic molecule did not alter the shape, shape anisotropy and dimensions of the micelles. The pseudo-lamellar ordering, typical of lyotropic nematic, was also preserved. However, in this case, neither was it possible to determine the specific interactions and affinities between these molecules that drive the transition from the N_C to the Ch_C phase nor how they influence the shape and size of the micelles. The water and counterions present in the intermicellar medium may transfer information from one micelle to others to form the helical structure. Advanced SAXS modelling analysis was used to compare the nanostructure and local ordering of the nematic calamitic (N_C) and the respective cholesteric calamitic (Ch_C) phases.The results showed that the average micellar form factor is not modified by the addition of the chiral amphiphilic molecules. Advanced SAXS modelling analysis was used to compare the nanostructure and local ordering of the nematic calamitic (N_C) and the respective cholesteric calamitic (Ch_C) phases. The results showed that the average micellar form factor is not modified by the addition of the chiral amphiphilic molecules.