Beyer’s non-linearity parameter ( B/ A) in benzylidene aniline Schiff base liquid crystalline systems

The non-linearity parameter B/ A is estimated for a number of liquid crystal materials of the type N-(p-n-alkoxy benzylidene)-p-n-alkyl anilines, popularly known as nO. m, where n and m are the aliphatic chains on either side of the rigid core, which can be varied from 1 to 18 to realize a number of LC materials with a variety LC phase variants. The B/ A values are computed from both density and sound velocity data following standard relations reported in literature. This systematic study in a homologous series provides an opportunity to study how this parameter behaves with (1) either the alkoxy and/or alkyl chain number, (2) with the total chain number ( n+ m), (3) with increase in molecular weight and (4) whether the linear relations reported in literature either with αT [thermal expansion coefficient ( α) and temperature ( T)] and sound velocity ( u) will hold good or not and if so to what extent. The results are discussed with the body of data available in literature on liquids, liquid mixtures and other LC materials. ► The Bayer's non-linearity parameter ( B/A) is estimated for the first time for a number liquid crystal materials of the type N-(p-n-alkoxy benzylidene)-p-nalkyl anilines. ► The magnitude of B/A estimated from sound velocity data is higher compared to that estimated thermal expansion data. ► The B/A value decreases with increase in molecular weight with an even odd fashion and reaches a minimum value and saturates. ► These studies reveal that both the thermal expansion coefficient and sound velocity are the tools to estimate the non-linear parameter B/A in the case of liquid crystals.