The Influence of Sub Tg Annealing on the Properties of Polymers Above and Below Tg.
Abstract
One of the fundamental tenets of all kinetic treatments of the glass transitions is that changes in viscosity occur as glasses age or anneal below the glass transition temperature even under isothermal conditions. To explain these experimental results it is necessary to assume that these changes are large, i.e, orders of magnitude under ordinarily employed experimental conditions. However, since the viscosity of glasses is always so high, (these materials are solids) even such large changes in the viscosity can go undetected. To probe these predicted large viscosity variations, we investigated changes in the effective local or micro viscosity of polymeric glasses doped with fluorescent dye molecules at very low concentrations. We reasoned that changes in viscosity of the glass will influence the local environment of the dye molecules and will be reflected as changes in rotational relaxation times or tumbling rates of the dye. These can be measured by monitoring the polarization of fluorescence emission of the dye molecules. We have investigated changes in fluorescence depolarization associated with thermal aging of several polymer glasses. Our results are much different than what has been observed earlier where the optical experiments were done at room temperature. We have concluded that, in the previous work, macroscopic orientation of the samples was induced via the severe quenching conditions and that the unexpected extremes of time and temperature necessary to erase the influence of sub Tg annealing were, in fact, associated with relaxation of this macroscopic ordering.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 10, 1985
- Accession Number
- ADA165899
Entities
People
- John J. Aklonis
Organizations
- University of Southern California