Oxygen diffusion into polystyrene-bentonite films

Abstract

A simple fluorescence technique is proposed for the measurement of the diffusion coefficient of oxygen into polystyrene-clay composite films. The composite films were prepared from the mixture of surfactant-free pyrene (P)-labeled polystyrene latexes (PS) and modified bentonite (MNaLB) at various compositions at room temperature. These films were annealed at 200 degrees C above the glass transition (T-g) temperature of polystyrene for 10 min. Oxygen diffusion into the films was monitored with steady state fluorescence (SSF) measurements. Measurements were performed at room temperature for different film compositions (0 510 2030 50 and 60 mass% modified bentonite) films to evaluate the effect of MNaLB content on oxygen diffusion. The diffusion coefficient D of oxygen was determined by the fluorescence quenching method by assuming Fickian transport and increased from 7.4 x 10(-10) to 26.9 x 10(-10) cm(2) s(-1) with increasing MNaLB content. This increase in D value was explained by formation of microvoids in the film. These voids are large enough to contribute to the penetration of oxygen molecules through the films. The montmorillonite content did not affect the quenching rate constant k(q) and mutual diffusion coefficient D-m values. (C) 2008 Elsevier B.V. All rights reserved