The depolarised Rayleigh scattering temperature dependence of the seventh, eighth, ninth and tenth homologues of 4,n-alkyloxybenzoic acid was investigated. A sharp increase of the scattered light intensity upon cooling was observed in the middle of the nematic phase. Polarised microscopic investigations confirmed the textural difference between the high- and low-temperature nematic regions (N1 and N2). The observed anomaly as well as the transition between classical (N1) and smectic C-like (N2) regions are discussed.
First de Vries /1/ assumed a differentiation of the nematic liquid crystalline phase in a classical one and a nematic phase with smectic C-like order. On the base of X-ray investigations the authors in /2/ showed that in the nematic phase (N) so-called cybotactic groups can exista kind of smectic C (Sc) pretransitional effect. The molecules in the so formed molecular complexes are arranged in layers. The temperature dependence of the elastic constants /3, 4/, electrical conductivity anisotropy 15 to 8/, and dielectric anisotropy /9/ in the nematic phase with smectic C ordering displays anomalies. Their existence can be explained with the forniation of smectic-like molecular complexes.In the present communication we report results on the electrical conductivity dl of 4-n-heptyl-, 4-n-octyl-, and 4-n-nonyloxybenzoic acids (HOBA, OOBA, and NOBA).The phase transition temperatures are as follows: HOBA-C-SC: 365 K, The liquid crystals were oriented planar in a sandwich cell (d = 2 0 p m ) .The semitransparent glass electrodes have a conducting Sn02 layer evaporated with SiO. The sample was placed inside a temperature regulated Mettler hot stage. An ac bridge (f = 1000 Hz) for the electrical conductivity measurements was used. The electric field was smaller than the threshol'd one for electrohydrodynamic instabilities, Fig: 1 represents the experiment'al dl= f(T) curves for HOBA on cooling from an isotropic liquid (curve 1 ) as well as on heating back to the isotropic phase (curve 2 ) with 0.2 K/min rate. A sharp decrease in the electrical conductivity was observed on curve 1 at 390.6 K. A few degrees below this tem-1)boul. Lenin 72,
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