Metolose-PEG interaction as seen by positron annihilation spectroscopy.

The plasticizing effects of poly(ethylene glycol) (PEG 400) on methylcellulose (Metolose) cast films were studied by conventional physicochemical methods and positron annihilation spectroscopy. The PEG concentrations relative to the total polymer content were varied within the range 0-75% (w/w). At low concentrations (below 33.3%, w/w), the plasticizer was found to build in into the methylcellulose structure. On the other hand, at higher concentrations (above 50%, w/w), it formed small separate phases in the films. Positron annihilation spectroscopy (PALS) was applied to track the Metolose-PEG interaction. Controlled ageing of Metolose-PEG films at room temperature and at 75% RH revealed a significant difference between the ageing processes of the monophase and those of the separate phase films. The ageing involves two steps in both cases: a fast and a slow one. The PALS measurements demonstrated that the slow process is hindered in the phase-separated samples.

Effect of plasticizer on the dynamic surface tension and the free volume of Eudragit systems.

The purpose of the present study was to determine the changes of dynamic surface tension of aqueous Eudragit dispersions quantitatively and compare these data with the free volume of the free films formed from several dispersions of different dibutyl sebacate (DBS) concentrations. Eudragit L 30D and Eudragit RL 30D aqueous colloidal polymer dispersions and their cast free films were examined. The concentration of DBS varied in the dispersions from 0 to 20%. The dynamic surface tension of the dispersions were measured by the Du Nouy ring method while the free volume of cast films were determined by positron annihilation spectroscopy. The obtained results show that dynamic surface tension measurements indicate the white point (WP) of Eudragit dispersions by a significant standard deviation increase. This may suggest the applicability of dynamic surface tension measurements for the determination of the WP of polymeric dispersions. A decrease in the WP temperature of Eudragit dispersions with an increasing plasticizer concentration was observed up to the DBS concentration of 10% w/w. Above this concentration neither the WP of the polymer dispersion nor the free volume of the free films of the polymer were changed remarkably.

[Positron lifetime studies of sodium- and zinc-hyaluronates]. / Nátrium- és cink-hialuronát vizsgálata pozitronélettartam-spektroszkópiával.

The aim of this work was to test the positron lifetime technique (PLT) as a tool of the structure study of sodium- and zinc-hyaluronates. The information based on the PLT measurements (outlined as follows) proved that this method can be useful in this field as well. The lifetime of ortho-positronium (o-Ps) significantly increased and its intensity decreased in the samples containing Zn2+, comparing to Na-hyaluronates. It showed that the electronic orbitals are more closed in the case of Zn2+ cation that means the overlapping between the wave functions of the positron and of the electrons decreased. (See equation No 1.) The study of the effect of water content suggested that the hydrogen-bridge-bonds "localised" the free electron pairs. The increasing pressure increased the lifetime and it is an evidence that the effect of the cations (Na+ and Zn2+) can be explained rather with the change of the electronic structure than with the altering of the free volumes of the samples.