Small Angle Neutron Scattering on Nematic Lyotropic Liquid Crystals

Abstract

Abstract A solution of 30% by weight of the tetramethylammonium salt of the perfluorononanoic acid (TMPFN = C 8 F 17 COON(CH 3 ) 4 ) in D 2 O forms a nematic phase in the temperature range between 32 and 37°C. The nematic phase was aligned and cooled down to 25°C in a magnetic field of 1.63 and 1.26 T. The structure of the aligned sample was studied with small angle neutron scattering (SANS) at different temperatures. In the liquid crystalline phase first and second order Bragg‐peaks were observed. This phase consists mainly of liquid crystals build by sheets of disk‐like TMPFN micelles alternating with layers of D 2 O. The lattice parameter is around 75 Å at 25°C. An order parameter S near 1 was determined by a thorough analysis of a rocking experiment. Besides the Bragg‐peaks further scattering features were observed: A Debye‐Scherrer like ring probably related to disclike micelles and a ridge related to a unknown aligned structure. The SANS‐pattern was examined in an temperature range between 25 and 45°C.