POSITRON-ANNIHILATION STUDIES OF CHROMOPHORE-DOPED POLYMERS

Positron annihilation lifetime experiments have been performed in two chromophores, Disperse Red I (DRL) and Disperse Orange 3 (DO3), doped in a poly(methyl methacrylate) polymer (PMMA;IA) as a function of temp erature. Significant chemical quenching and inhibition effects on posi tronium annihilation due to doping are observed. These effects are int erpreted in terms of a chemical reaction between positronium and chrom ophore molecules and a change of free volume and hole properties in po lymers. Diffusion coefficients of positronium in polymers are found to be on the order of 10(-6) cm(2)/s and to increase with temperature. T he activation energy for the reaction between positronium and chromoph ores is found to be 4 and 8 +/- 1 for DO3 and 10 and 15 +/- 1 kJ/mol f or DR1, at the glassy and the rubbery states, respectively. Both ortho positronium lifetime and differential scanning calorimetry analyses sh ow that doping polymers results in a significant decrease to glass tra nsition temperature. Applications of positron annihilation spectroscop y to study the effect of free volume and holes in nonlinear optical po lymeric materials are discussed.