Free volumes in nematic and smectic liquid-crystalline polymers probed by positron annihilation

✍ Scribed by R. Sadamoto; A. Uedono; T. Kawano; S. Tanigawa; Y. Kosaka; T. Uryu

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 477 KB
• Volume: 34
• Category: Article
• ISSN: 0887-6266
• DOI: 10.1002/(sici)1099-0488(19960715)34:9<1659::aid-polb15>3.0.co;2-6

✦ Synopsis

Free volumes in thermotropic side-chain liquid-crystalline polymers were probed by positron annihilation technique. Lifetime spectra of positrons were measured in the temperature range between 130 and -60°C in cooling. For a nematic liquid-crystalline polymer (polyacrylate), the lifetime of ortho-positronium ( T ~) was decreased with decreasing temperature above the glass transition temperature (T#, 21OC) with larger temperature coefficient than that below Tr The intensity of ortho-positronium (I3) was constant above Tr These facts mean that the size of the free-volume holes decreased with the decreasing the temperature but the concentration was almost constant in nematic phase. For a smectic liquid-crystalline polymer (poly(p-methylstyrene) derivative), a discontinuous decrease in the value of 7 3 and that of Z3 were observed a t 107OC, which was the transition temperature from smectic to crystalline phase. Such discontinuous changes were not observed for the polyacrylate specimen. This difference was considered to be attributed to the higher-ordered structure of the smectic phase.