The temperature of Si master plays a vital role

Microtexture ENMD-2076 on polycarbonate was achieved thermally by sandwiching the laser microtextured Si master and the PC between two hot plates as shown in the Fig. 1. Preliminary experiments were devoted to study the thermal response of PC between two hot plates which further helped to optimize the temperatures of the hot plates such that PC becomes soft enough to create microtexture impression on its surface leaving the bulk unmodified. The temperature of the bottom hot plate was found to be optimum at 175 °C, which was much higher than the glass transition temperature of the PC (~ 147 °C). Relatively higher temperatures (> 175 °C) caused melting and bubbling of PC whereas at lower temperatures the PC remained unchanged as far as the replication was concerned. The use of hot plate on the top was indispensable to achieve uniform replication as it not only helped to keep the PC substrate always under positive pressure but also kept it warmer. This otherwise results in unwanted deformation of PC due to significant temperature difference between top and bottom surfaces. Fig. 3 shows SEM image of thermally replicated polycarbonate using microtextured Si master at 175 °C for 15 min. It is clearly seen that the microtexture of the Si master was uniformly replicated onto the PC surface. The morphology of the replicated PC essentially looks like a negative of Si master wherein voids present in the Si microtexture appear to be filled with PC resulting in formation of thicker micro-pillars with wider tips and the micro-pillars in the Si microtexture created similar sized voids in the replicated microtexture.