Diffusion and sorption in cellulose. Part 2

Abstract

Equilibrium absorption-desorption isotherms and steady-state diffusion-rate data are reported for the leuco forms of three position isomers of dibenzamido-16H-dinaphtho(2,3-a : 2′,3′-i)-carbazole-5,10,15,17-tetrone, viz., the 4,9(II), the 4,11(III) and the 6,9(IV) dibenzamidos, and are compared to previously reported data for the leuco form of 16,17-dimethoxy-violanthrone (I). The distribution coefficients and steady-state diffusion rates for the carbazoles are lower than those found for (I), and carbazole (II) showed a unique absorption-desorption hysteresis effect while the other carbazoles and (I) were essentially reversible. The diffusion rates of the carbazoles are correlated with the extent of interaction of the sorbate with the cellulose as deduced from the slopes of the sorption isotherms, steeper slopes indicating more interaction and leading to lower diffusion co-efficients. The greater diffusion of (I) can be due to its lower interaction with the cellulose at the higher concentration where comparison is made. Explanations for the differences in sorption and diffusion properties among the carbazoles are explored in terms of the spacing of the benzamido groups in the three isomers. The hysteresis appears to be associated with the dipole moment of (II) arising from the dissymmetry of positioning of the benzamido groups.