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 temperature. Significant chemical quenching and inhibition effects on positronium annihilation due to doping are observed. These effects are interpreted in terms of a chemical reaction between positronium and chromophore molecules and a change of free volume and hole properties in polymers. Diffusion coefficients of positronium in polymers are found to be on the order of 10(-6) cm(2)/s and to increase with temperature. The activation energy for the reaction between positronium and chromophores is found to be 4 and 8 +/- 1 for DO3 and 10 and 15 +/- 1 kJ/mol for DR1, at the glassy and the rubbery states, respectively. Both orthopositronium lifetime and differential scanning calorimetry analyses show that doping polymers results in a significant decrease to glass transition temperature. Applications of positron annihilation spectroscopy to study the effect of free volume and holes in nonlinear optical polymeric materials are discussed.