ORNL has developed a new method for quick assay of the durability of paints and other organic or polymer coatings, using positron annihilation spectroscopy. Beams of slow positrons having controlled energies are injected into surfaces of paint films. By measuring the lifetimes of the injected positrons and the Doppler broadening of the gamma spectra emitted by their annihilation, the degree of weather penetration into the paint films can be determined. The weathering of the films causes changes in the free volume and chemical alterations such as the production of hydroperoxide groups. These effects have been detected for specimens exposed for a little as two weeks. Studies of the interfaces of films and their substrates can be made. Useful measurements of paints in the liquid state can also be made with positron spectroscopy. In addition to paints, the method can be applied to rubbers (automobile tires), adhesives and other organic polymers; it should also be useful for the development of improved photoresist materials and thereby improve lithographic techniques. Positron spectroscopy has a proven record of accomplishment in the study of defects in inorganic films used in microelectronic devices. It is highly useful as a quality control method.
Les Hulett
Jun Xu, Bertram Somieski
Chemical and Analytical Sciences Division