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PALS Investigation of Aged Epoxy Films

ps reduction is sometimes interpreted in terms of a reduction of the density of free-volume voids in a polymer [10, 20]. However, the influence of the free volume on Iq-ps should be less pronounced than on the ortho-positronium lifetime ro-Ps, which depends directly on the average free-volume void size [Ij. We will see later that Tq-ps varies much less than lo.ps during aging. Therefore, the T.ps reduction should not be interpreted in terms of a free-volume change. [Pg.469]

2 atom% of Cu ions dissolve in the epoxy under the given preparation conditions. This metal ion dissolving effect is negligible for Al and Au. The efficiency of Cu ions in trapping free electrons easily explains the T-Ps reduction in the case of a Cu substrate (22% for the unaged state instead of 28% on Al and Au). For average positron implantation depths less than approx. 50 nm, T-Ps decreases in all cases. [Pg.470]

Whereas Tq-ps is in the range 1710 10 ps inside the unaged epoxy films on Al and Au, it is only 1695 10 ps on the Cu substrate. As described below, these films on Cu contain fewer residual oxirane groups than on Al and Au. This could be the reason for the lower size of the free-volume voids in the epoxy network on Cu. [Pg.470]

Additionally, both aging mechanisms have less effect on in the volume of the epoxy films on a Cu substrate than on Au and A1 substrates for hygro-thermal aging there is an increase of 15 ps instead of approximately 30 ps, and for thermal aging the decrease is 20 ps instead of approximately 25 ps. [Pg.471]


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