الفهرس 
The effect of terminal alkoxy groups proportionation on the mesophase
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Abstract
Two series of newly prepared liquid crystalline compounds, each is formed from twenty four different homologues, were prepared and investigated for their mesophase behaviour. The first group has the formula 4-alkoxy phenylazo phenyl 4ʹ-(43-alkoxyphenylazo) benzoates (Im/n), while the second group possesses the formula 4-alkoxy phenylazo phenyl 4ʹ-(4{u2032}{u2032}-alkoxyphenylazo) benzoates (IIm/n). Within each series, the length of the terminal alkoxy group attached to the benzoate moiety (n) varies between 8 and 16 carbons, while the length of the other alkoxy group, attached to phenolic portion, varies between 6 and 12 carbons. Their mesophase characteristics were examined via differential scanning calorimetry (DSC) and the type of the phase is identified by polarized light microscopy (PLM). These newly prepared compounds were structurally characterized by infrared, ¹ H-NMR, mass spectroscopy, thermogravemetric and elemental analyses. Comparative study was first made between the two series (Im/n) and (IIm/n), aiming to investigate the effect of replacing the azo group with an azomethine one on their mesophase behaviour. A second comparative study was made between the prepared four-ring compounds, series Im/n, and their corresponding previously investigated threering azo/ester analogues namely, 4-alkoxyphenyl 4ʹ-(4{u2032}{u2032}-alkoxyphenylazo) benzoates (IIIm/n). The stabilities and mesomorphic ranges of the prepared fourring compounds (Im/n) were found to be significantly higher than those of their three rings analogues (IIIm/n)