Hot embossing of multifunctional transparent polymers from Cr stamps structured by direct laser interference patterning

In this contribution, Cr stamps were structured with periodic hole-like arrays using Direct Laser Interference Patterning. Using optimized laser processing parameters, homogeneous textures with different spatial periods and aspect ratios were produced, as observed with confocal microscopy. Then, these stamps were used as molds for patterning transparent polymers, namely polyethylene terephthalate (PET), poly(methyl methacrylate) (PMMA) and polycarbonate (PC) by plate-to-plate hot embossing. Adjusting the imprint time and temperature, replicas of the Cr stamps were fabricated reproducing faithfully the mold shape. Static water contact angle (WCA) measurements were done to study the wettability properties of these structured polymers. The results show that the produced topographies increase the WCA compared to the flat references up to an absolute maximum of 55° in the three polymers. For instance, a PET foil structured with a spatial period of 4.7 mm and a structured depth of 3 mm showed a WCA of 139° representing an increase of about 70% compared to a flat sample. The diffraction intensity of the patterned polymers was measured with an imaging optics and a spectrometer coupled to a goniometer in order to characterize their optical properties. It was found that for those samples processed with 80 or less applied laser pulses the diffraction peaks are clearly identified, whereas for large number of pulses there is more diffuse light travelling along random directions and the diffraction peaks become less defined. In conclusion, enhanced wettability and optical functionalities were achieved in transparent polymers imprinted with periodic microstructures.