Radiothermoluminescence of n-eicosane mixtures with n-tetracosane: Effect of mixture composition

Abstract

Radiothermoluminescence (RTL) curves of mixtures of C20 and C24 n-alkanes have been deconvoluted into the curves of crystalline and disordered regions, and their change depending on the mixture composition has been analyzed. The shape of the total RTL curve of the mixture regardless of the its composition is fundamentally different from that shape of the sum of the curves of the individual components taken in the relevant ratios. The difference becomes noticeable at as low a C20 amount in the mixture as 2% and is manifested in the disappearance of the intense RTL peaks of the individual components and appearance of new intense peaks in temperature intervals other than those of the RTL peaks of the components. It has been shown that these changes correlate with changes of the crystalline structure of the mixture: a new crystalline structure other than the structure of any of the individual components emerges and the mixture becomes amorphous. High selectivity of charge trapping in disordered regions of the mixture has been revealed: the contribution of RTL of the disordered regions to the total curve is many times higher than their volume fraction in the mixture. This selectivity might be due to an increase in concentration of defects in the unordered regions of the mixture in comparison with their concentration in the pure alkanes. These defects are traps for electrons that are accessible to acceptors introduced into the mixture.