Contributions of intermicellar distance, micelle volume and screw angle to the temperature dependence of helical pitch in the intrinsic lyotropic cholesteric phases

Two series of lyotropic quaternary liquid crystalline mixtures exhibiting intrinsic cholesteric phases were prepared from potassium N-dodecanoyl-l-alaninate (L-KDDA) and l-serinate (L-KDDS), having different amphiphile concentrations. The phase types and texture characterizations of the cholesteric phases were determined via polarizing light microscopy. The pitches of the cholesteric phases, depending on both concentration of the l-enantiomer and temperature, were measured by laser diffraction. The helical twisting power of the cholesteric phases was calculated from the pitch values in the temperature range of 25 and 45°C. The results showed that the L-KDDA system had higher helical twisting power than the L-KDDS system at all temperatures. Small-angle x-ray scattering (saxs) technique was performed for determination of some micellar level parameters, e.g. intermicellar distance (W⊥), micelle volumes (Vmic), etc, and their temperature dependences. In addition, we calculated the screw or twist angle (θ) along the helix axis of the cholesteric phases as a function of temperature, combining the saxs results with the pitch values. According to all our experimental results, it seems that θ, Vmic and W⊥ contribute differently to the temperature dependence of the helical pitch. It was observed that the less (the most) contribution was provided by the intermicellar distance (the screw angle).