Heats of reaction of trapped intermediates in ggr;hyphen;irradiated organic glasses and relaxation processes in unirradiated glasses measured by low temperature differential thermal analysis

摘要

Differential thermal analysis (DTA) has been used to determine the following: (1) the heat of photobleaching of trapped electrons in ggr;hyphen;irradiated 3hyphen;methylpentane (3MP) glass as a function of ggr; dose; (2) the heats of combination of radicals and of ions in ggr;hyphen;irradiated 3MP and methyltetrahydrofuran (MTHF) glasses; (3) the glass transition temperatures and the rates of enthalpy loss during 77 K annealing of 3MPhyphen;h14, 3MPhyphen;d14, 3hyphen;ethylpentane, and MTHF; (4) the effect of cooling rate and annealing time on crystallization ofnhyphen;hexane in 3MP cooled to 77 K. The Dgr;Hof neutralization of photobleached electrons in ggr;hyphen;irradiated 3MP at 72 K is sim;minus;150 kcalthinsp;moleminus;1at low dose, implying an upper limit of 80 kcalthinsp;moleminus;1for the solvation energy of the combining charges, and decreases to sim;80 kcalthinsp;moleminus;1for a dose of 1.2times;1020eVthinsp;gminus;1implying an increasing ratio of reaction with radicals to reaction with cations as the dose is increased. When ggr;hyphen;irradiated MTHF is warmed from 77 K, a large fraction of the trapped electrons appear to react with radicals to form carbanions, which then react with cations, the total Dgr;Hbeing sim;80 kcalthinsp;moleminus;1. The Dgr;Hof ion pair solvation is estimated to be minus;120 to minus;150 kcalthinsp;moleminus;1. The decrease in the enthalpy of the matrix due to relaxation during annealing in 3MP at 77 K parallels the decrease in the decay rate of trapped electrons for similar samples. Seemingly anomolous effects of sample size and shape on trapped electron decay rates in 3MP glass as a function of time of annealing at 77 K can now be rationalized in terms of the restrictions on viscous flow in different types of sample tubes.