Regensburg 2013 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 81: Post-Deadline Session
O 81.3: Vortrag
Donnerstag, 14. März 2013, 20:30–20:45, H36
Pressure Dependent and H2O Loaded Void Size Distribution in Bio-Polymers Studied by Positronium Lifetime Measurements — •Christoph Hugenschmidt and Hubert Ceeh — Physik Department E21 und FRM II, Technische Universität München, 85747 Garching, Germany
We present first experiments on glucose bio-polymers using the annihilation of Positronium (Ps) in the free volume in order to characterize the amorphous nano-structure in the near surface region. The behavior of the free volume dependent on uniaxial pressure, H2O loading and various dyes has been investigated. A semi-empirical quantum mechanical model was applied in order to correlate the lifetime of Ps in nano-scaled voids to the void size. This allowed us to determine the absolute value of the mean void radius. The variation of the total free volume as function of uniaxial pressure is modelled and illustrated by a log-normal distribution. Most interesting results have been obtained after saturation loading with H2O that lead to an increase of the free volume by a factor of six, whereas the mass density decreased only by 23%. This astonishing observation is explained by swelling and a formation of an interconnected network of large voids with a mean void size of 0.096 nm3. Very recent experiments on this class of bio-polymers including various dyes showed no significant change of the free volume. In summary, we could demonstrate that the measurement of the Ps lifetime is an ideal tool to investigate non-destructively the void size distribution in amorphous (bio-)polymers.