title: Investigation of free volume changes in the structure of the polymer bifocal contact lenses using positron lifetime spectroscopy PALS.
abstract: Positron annihilation lifetime spectroscopy PALS has been applied of free volume properties in bifocal contact lenses. The measurements have been made on new lenses and then after one, two, three and four weeks wear. The longest lifetime, obtained via three-component analyses of the spectra, was associated with the pick-off annihilation of ortho-positronium trapped in the free volume. After wear of the lenses changes in the ortho-positronium lifetimes and the relative intensity of the longest component were observed. These results are discussed on the basis of a free volume model.
authors.affiliation: Department of Structural Research and Medical Physics, Institute of Physics, Jan Dlugosz University, Czestochowa, Poland. j.filipecki@ajd.czest.pl
authors.forename: Jacek
authors.initials: J
authors.lastname: Filipecki
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Kocela
authors.forename: Piotr
authors.initials: P
authors.lastname: Korzekwa
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Filipecka
authors.forename: Edmund
authors.initials: E
authors.lastname: Golis
authors.forename: Witold
authors.initials: W
authors.lastname: Korzekwa
mesh_terms: D003261:Contact Lenses; D004583:Electrons; D004867:Equipment Design; D008422:Materials Testing; D008962:Models, Theoretical; D011108:Polymers / Q000737:chemistry*; D013057:Spectrum Analysis
chemical_list: D011108:Polymers