Determination of the molecular mobility and the free volume of thin polymeric films with fluorescence probes

Triphenylmethane (TPM) dyes were used as fluorescence probes for the characterization of thin polymeric layers. Glass transition temperature, mobility and free volume can be determined by this method. A correlation was found between the dye fluorescence and the free volume of the polymer. Above the glass transition temperature of the polymer the activation energies for the rotation of the dye phenyl groups were found at ca. 25–35 kJ/mol, at temperatures below the glass point these energies are in the range of 5–12 kJ/mol. Nearly all probes describe the free volume equally well. A relation was found between the dye mobility and gas diffusion constants (ammonia and oxygen).