Characterization of free volume and density gradients of polystyrene surfaces by low-energy positron lifetime measurements
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Free volume and density gradient widths of the free surface of high molecular mass polystyrene was characterized by use of a pulsed low-energy positron lifetime beam. A density gradient in terms of mass density (g/cm(3)) versus depth (nm) was obtained from the experimental beam data using a novel approach, yielding a width of the density gradient of approximately 3.5 nm. The procedure accounted for the broadening of the positron implantation probe as a function of energy as well as correcting for the increase in positron implantation depths due to the presence of a lower density at the surface region. Moreover, the spectra in the low implantation energy range were found to contain a long-lived lifetime that yielded very large estimates of the free volume effects at the surface. Accounting for this lifetime in the evaluation procedure, resulted in a much improved agreement with the results of other experimental and theoretical investigations in the literature. (C) 2004 Elsevier Ltd. All rights reserved.
|Research areas and keywords||
Subject classification (UKÄ) – MANDATORY
|Publication status||Published - 2004|
The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Polymer and Materials Chemistry (LTH) (011001041)