| Popis: |
We present intrinsic excimer fluorescence data from the polystyrene block of a polystyrene-b-poly(ethylene propylene) block copolymer micelle system to interrogate the state of the micelle core. The excimer bandwidth and bandposition as well as the ratio of the excimer to monomer emission intensities prove to be sensitive measures of the environment around the excimer forming sites. As the bulk concentration is increased, the fluorescence data indicate a decrease in the volume fraction of solvent within the micelle core. As the temperature is increased, a T g like phenomenon is observed in the micelle core around 60-80 °C without an apparent increase in the solvent content in the core. The excimer bandwidth proves to be an especially sensitive measure of the critical micelle temperature, and the thermodynamic parameters associated with the micellization process can be calculated. Finally, a proposal is made to explain the changes in the excimer spectral parameters as the local environment around the excimer forming sites is changed. |
