Viscometric investigations and molecular interactions of triphenodioxazine dyes in mixed organic solvents

Colloid chemical behaviour of 6,13-dichloro-3,10-dimethyl triphenodioxazine (TPDO-I) and 6,13-dibromo-3,10-dimethyl triphenodioxazine (TPDO-II) in non-aqueous solvent mixture benzene-methanol of varying composition has been investigated by viscometric measurements at 303 ± 0.1 K. The viscosity of the system increases with the increase in triphenodioxazine concentration. The Trend Change Point (TCP) values have been determined by intersection of two straight lines which are found to be dependent on the composition of solvent mixtures. The study confirms that the nature of triphenodioxazine agglomerate formed below and above 50% benzene concentration is quite different. The viscometric data have been analysed in terms of Einstein, Vand, Moulik and Jones-Dole equations. These well known equations have been successfully applied to explain the results of viscosity measurements and the viscometric parameters show that the behaviour of triphenodioxazine dyes changes in the proximity of 50% benzene concentration.