Nano-scale thin polymeric films supported on different substrates have been investigated by using positron annihilation spectroscopy (PAS). The object of this research was to characterize and to understand basic physical properties of thin films at different depths.

"This is a Ph.D. dissertation. The positron is the antiparticle of the electron. It has the same mass as the electron and its charge is numerically identical but of opposite sign. The positron was first predicted by Dirac in 1930 and observed by Anderson for the first time in 1932. Being an antiparticle, a positron annihilates with an electron converting mass into energy in the form of radiation. Contents include: Simulation of electron and positron track structures in ploymers and simple hydrocarbons, Experimental methods, Positron formation dynamics in radiolytic tracks: a computer simulation study, Positronium formation in low density polyethylene, Charge accumulation in Polyethylene, Degradation of poly(paraphenylene vinylene) monitored by positron annihilation spectroscopy, Summary."

This volume includes contributions to the 10th Dresden Polymer Discussion held in 2005. The meeting focused on the characterization of polymer surfaces and thin films. The contributions cover a representative spectrum of surface sensitive techniques and their application to polymer surface and thin film characterization, as well as recent examples of technologically relevant materials and process development.

Positron annihilation Lifetime and Doppler broadening measurements are reported for six polymer films as a function of carbon dioxide absolute pressure ranging from 0 to 45 psi. Since the polymer films were thin and did not absorb all positrons, corrections were made in the lifetime analysis for the absorption of positrons in the positron source and sample holder using the Monte Carlo transport code MCNP. Different polymers are found to behave differently. Some polymers studied form positronium and some, such as the polyimide structures, do not. For those samples that form positronium an interpretation in terms of free volume is possible; for those that don't form positronium, further work is needed to determine how best to describe the behavior in terms of the bulk positron annihilation parameters. Some polymers exhibit changes in positron lifetime and intensity under CO2 pressure which may be described by the Henry or Langmuir sorption models, while the positron response of other polymers is rather insensitive to the CO2 pressure. The results demonstrate the usefulness of positron annihilation spectroscopy in investigating the sorption of CO2 into various polymers at pressures up to about 3 atm.