ИСТИНА

The model-free method for determination of orientation distribution function from EPR spectra of paramagnetic additives is presented. The method is based on joint numerical simulation of EPR spectra recorded at different orientations of LC director relative to magnetic field of spectrometer. The order parameters, which are coefficients of an expansion of orientation distribution function in a series of generalized spherical harmonics, are directly determined in course of spectra simulation. It is shown that the method is capable of obtaining the order parameters up to the eighth rank. The possibility of characterization of biaxial order parameters is discussed. The limitations as well as possibilities and advantages of the described method are considered. The application of the method to model liquid crystals 5CB, 8CB and LC polymers is presented. The structure of appropriate paramagnetic nitroxide probes is discussed. The possibility of unbiassed determination of main orientational molecular axes is demonstrated. The values of order parameters obtained by the described method are compared with the results of dichroism measurements.