Methodical developments for X-ray diffraction measurements and data analysis on lyotropic liquid crystals applied to K-soap/glycerol systems

 X-ray diffraction (XRD) data acquisition and processing software measurements on long-spacing binary systems, including adapted noise reduction algorithms, has been developed. The computation of XRD patterns has been summarized and the origin of the distinct patterns of long-spacing compounds has been illustrated with the aid of such simulations. This also provided the possibility to evaluate the retrievable amount of information used for graphical or numerical indexing programs. Numerical indexing programs were applied and limits of indexing method have been discussed. Differential scanning calorimetry (DSC) measurements and temperature-dependent XRD measurements have been carried out for the concentrations x _{KC 12} = 0.50 and 0.30 of the K-laurate/glycerol system. The analysis of the small- and wide-angle diffractograms in the various phase regions of the binary system as well as the DSC measurements provided the following results: – The creation of the lamellar phase extends over a temperature range of ΔT≈ 20 K at a concentration of x _{KC 12} = 0.50. The lamellas show a reduced degree of order. – The crystalline-to-gel phase transition is accompanied by a leap in the d values corresponding to the small-angle reflexes. Also a distinct splitting of the small-angle reflexes is observed within the gel phase. Simultaneously a rearrangement and intensity decay of the wide-angle reflexes occurs. Since some wide-angle reflexes are still present, the structure can be considered to have a partially reduced three-dimensional order. – During the creation of lamellar phases the d value decreases sharply with rising temperature. This decrease of d can be interpreted as a further decay of molecular order in the hydrocarbon chains of the K-laurate within the bilayers. – The XRD measurements correlate with the DSC data. According to our measurements a revision of the phase diagram with respect to the actual extension of the gel-phase region was necessary. Received: 3 March 1999 Accepted in revised form: 29 March 1999