| Laser texturing of Kapton HN RTM polyimide was performed by low-fluence ablation using a pulsed frequency tripled (349 nm) Nd:YLF laser. Laser pulses were scanned in two dimensions such that the pulses spatially overlapped in each direction, generating texture over areas larger than the laser spot. The laser overlap percentage and laser fluence were varied to study the resulting feature height and density.;Both bump and cone structures formed on the samples, often with one type being dominant. Formation of features was attributed to Radition Hardening, originally explained by Krajnovich and Vazquez. Samples were inspected by optical and scanning electron microscopy. Surface chemistry was examined by X-ray Photoelectron Spectroscopy. It was found that during a laser scan debris from preceding laser pulses has an effect on subsequent pulses, causing more cone structures to form.;The wetting behavior of de-ionized water was analyzed by a contact angle goniometer to measure the static contact angle. Unprocessed smooth polyimide was measured to be slightly hydrophilic, with a contact angle of 76 degrees. After texturing, contact angle increased for almost all sites, resulting in a hydrophobic surface. The contact angle increased to as high as 118 degrees for the largest structures. Contact angle data is plotted as a function of surface feature spacing over size, exhibiting a trend that follows Wenzel's model for homogeneous wetting. |
