Positron annihilation lifetime study of PTFE/silica composites

✍ Scribed by M. M. Madani; R. C. MacQueen; R. D. Granata

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 335 KB
• Volume: 34
• Category: Article
• ISSN: 0887-6266
• DOI: 10.1002/(sici)1099-0488(19961130)34:16<2767::aid-polb9>3.0.co;2-m

✦ Synopsis

Positron annihilation lifetime spectroscopy (PALS) was used to study the microstructure of PTFE/silica composites. The positron lifetimes (7,) and intensities (1,) of PTFE and the composites (30-62% silica) were measured at room temperature as a function of specimen thickness. Four lifetime components were found in PTFE and the composites. The longer lifetime components, 73 = 1.4 ns and 74 = 4.4 -4.1 ns, were interpreted to be due to the presence of two different sized free volume cavity distributions within the PTFE/silica composites. A strong silica concentration dependence was found in the bulk intensities (136 and &b). The 136 value increased from 13.0% in PTFE to 28.2% in the 62% composite, while the 1 4 6 value decreased from 17.5% in PTFE to 4.5% in the 62% composite. The smallervoid size, free volume fraction (7313b) values increased linearly between 0 and 100% silica concentration, while the larger void size, free volume fraction (74146) values decreased nonlinearly with silica concentration. Since silica has a long lifetime component ( T ~ = 1.6 ns), this behavior is ascribed to silica particles occupying the large free volume cavities (370 A3) in the PTFE/silica composites.