Topography, crystallinity and wettability of photoablated PET surfaces

Surface topography, crystallinity, and wettability of photoablated poly(eth ylene terephthalate) (PET) resulting from various ablation conditions have been characterized by atomic force microscopy (AFM) microconfocal Raman spe ctroscopy, and wettability measurements. Two ablation modes have been consi dered here: (i) static ablation, where the samples are immobilized in front of the pulsed laser beam and (ii) dynamic ablation, where the samples are moved in order to write three-dimensional structures in the polymer. Laser fluence, repetition rate, and speed of the substrate motion during the abla tion process have been varied. The laser fluence has been observed to stron gly affect the resulting surface roughness, which increased to a maximum va lue at fluences between 70 and 600 mJ.cm(-2). For all fluences in the range of 1000-3000 mJ.cm(-2), the roughness was found to be similar. No remarkab le effects could be attributed to the pulse frequency of the 23 ns laser pu lses. Raman spectroscopy studies demonstrated that the polymer surface exhi bits a high degree of crystallinity when ablated in the static mode. Raman imaging of the surface indicated that these conditions also led to a more h omogeneous surface state than when the polymer is ablated in the dynamic mo de. Experiments measuring channel filling velocities by capillary action sh owed that the surfaces of structures fabricated in static photoablation mod e were much more hydrophobic than those fabricated under dynamic photoablat ion.