Topography, crystallinity and wettability of photoablated PET surfaces

Surface topography, crystallinity, and wettability of photoablated poly(ethylene terephthalate) (PET) resulting from various ablation conditions have been characterized by atomic force microscopy (AFM), microconfocal Raman spectroscopy, and wettability measurements. Two ablation modes have been considered 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 ablation process have been varied. The laser fluence has been observed to strongly affect the resulting surface roughness, which increased to a maximum value 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 remarkable effects could be attributed to the pulse frequency of the 23 ns laser pulses. Raman spectroscopy studies demonstrated that the polymer surface exhibits 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 homogeneous surface state than when the polymer is ablated in the dynamic mode. Experiments measuring channel filling velocities by capillary action showed that the surfaces of structures fabricated in static photoablation mode were much more hydrophobic than those fabricated under dynamic photoablation.