IR SPECTROSCOPIC INVESTIGATIONS OF PECULIAR BEHAVIOR OF 4,N-ALKOXYBENZOIC ACIDS IN THEIR MESOMORPHIC STATE .1. NONALIGNED SAMPLES

The equilibrium concentration of cyclic dimers, open dimers and monome rs in 4,n-heptyloxybenzoic acid (HOBA) has been determined by IR spect roscopic investigations. It was found that the evolution of correlatio n between these molecular forms upon temperature variation provokes a strong textural transition in the nematic phase at temperature T. The decisive role of local orientational order in the process of formatio n and destruction of hydrogen bonds is discussed. In addition, the shi ft of T caused by bulk deformation of the nematic phase of HOBA on th e basis of temperature variation of dimer-monomer concentration is con sidered as well. A new peculiar temperature (T(f)) was found in the ne matic phase where maximal dispersion in the temperature dependence of the cyclic and open dimer concentration is established. Strong textura l oscillation is observed at that temperature.