POSITRON LIFETIME STUDIES OF FREE-VOLUME HOLE SIZE DISTRIBUTION IN AMORPHOUS AND IN SEMICRYSTALLINE POLYMERS

Positron lifetime spectroscopy has been applied to estimate the free-v olume hole size distribution in glassy polycarbonate (PC) and polystyr ene (PS) as well as in plastically deformed and undeformed, semi-cryst alline polyethylene (HDPE). ?he hole radius density distribution is de termined from the ortho-positronium lifetime distribution which is obt ained via a Laplace-inversion of the positron lifetime spectrum. ?he h ole volume density distribution and the number density distribution of holes is estimated from the hole radius density distribution. In PC a nd in PS all of the distributions may be well approximated by a single Gaussian. The hole radius and the hole number density distributions h ave centres [r] and [v(n)] at 0.29 nm and 0.1 nm(3) in PC, and at 0.28 nm and 0.09 nm(3) in PS. The FWHM of the corresponding distributions are 0.042 nm and 0.040 nm(3) (PC), and 0.039 nn and 0.34 nm(3) (PS), r espectively. Both, the shape and the width of the distributions correl ate well with the free volume theory of BUECHE. In PE the lifetime spe ctra consist of four components. The o-Ps lifetime distribution is bim odal and may be attributed to o-Ps annihilation in the crystalline and in the amorphous phase of the polymer. The corresponding hole size di stributions show definite changes of their position and width followin g plastic deformation which we attribute to homogeneous crystal lattic e dilatation and/or a local disorder in the crystals and to an increas e in the eccentricity of holes in the amorphous phase.