Laser irradiation of polyethylene oxide

The temperature profiles in polyethlene oxide (PEO) films on a soda lime glass substrate heated by scanning a continuous wave (cw) CO2 laser beam are calculated by finite element methods. The volumetric heating rate in the irradiated film depends on the total power of the laser, the radius of the illuminated spot and the scan rate, as well as film parameters such as absorption depth, density, heat capacity, and thermal conductivity. The absorption depth in PEO at a wavelength of 10.6 μm is less than, but comparable to the thickness of the the PEO film (40 μm). Therefore, heat loss from the bottom surface of the polymer film cannot be neglected. The thickness of the glass substrate is much greater than that of the PEO, so that heat loss from the bottom surface of the glass may be neglected. We use a coordinate system fixed in the material. The beam is parallel to the z axis and scans continuously along the x direction with velocity v. A time dependent temperature profile on the surface, along the trajectory of the beam center, is shown. Comparison of calculated temperature profiles and the shapes of PEO spherulites in the zone refined polymer enable us to elucidate melting, nucleation, and recrystallization under laser irradiation