Harms S, Rätzke K, Faupel F, Egger W, Ravello L, Laschewsky A, Wang W, Müller-Buschbaum P
Institute for Materials Sience - Multicomponent Materials, Christian-Albrechts-University at Kiel, Kaiserstraße 2, 24143 Kiel, Germany.
Macromol Rapid Commun. 2010 Aug 3;31(15):1364-7. doi: 10.1002/marc.201000067. Epub 2010 May 18.
The free volume in thin films of poly(N-isopropylacrylamid) end-capped with n-butyltriocarbonate (nbc-PNIPAM) is probed with positron annihilation lifetime spectroscopy (PALS). The PALS measurements are performed as function of energy to obtain depth profiles of the free volume of nbc-PNIPAM films. The range of nbc-PNIPAM films with thicknesses from 40 to 200 nm is focused. With decreasing film thickness the free volume increases in good agreement with an increase in the maximum swelling capability of the nbc-PNIPAM films. Thus in thin hydrogel films the sorption and swelling behavior is governed by free volume.
