Nowadays, the demand for surface functionalized plastics is constantly rising. To address this demand with an industry compatible solution, here a strategy is developed for producing hierarchical microstructures on polyethylene terephthalate (PET) by hot embossing using a stainless steel stamp. The master was structured using three laser-based processing steps. First, a nanosecond-Direct Laser Writing (DLW) system was used to pattern dimples with a depth of up to 8 µm. Next, the surface was smoothed by a remelting process with a high-speed laser scanning at low laser fluence. In the third step, Direct Laser Interference Patterning (DLIP) was utilized using four interfering sub-beams to texture a hole-like substructure with a spatial period of 3.1 µm and a depth up to 2 µm. The produced stamp was used to imprint PET foils under controlled temperature and pressure. Optical confocal microscopy and scanning electron microscopy imaging showed that the hierarchical textures could be accurately transferred to the polymer. Finally, the wettability of the single- and multi-scaled textured PET surfaces was characterized with a drop shape analyzer, revealing that the highest water contact angles were reached for the hierarchical patterns. Particularly, this angle was increased from 77° on the untreated PET up to 105° for a hierarchical structure processed with a DLW spot distance of 60 µm and with 10 pulses for the DLIP treatment.

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Hierarchical textures (combining 2D periodic large and small micro textures) as an external outcoupling solution for OLEDs have been researched, both experimentally and by optical simulations. For the case of a red bottom emitting OLED, different hierarchical textures were fabricated using laser-based methods and a replication step and applied to the OLED substrate, resulting in an increased light outcoupling. Laboratory-size OLED devices with applied textured foils show a smaller increase in efficiency compared to the final large area devices. The results show that the full exploitation of textured foils in laboratory-size samples is mainly limited by the lateral size of the thin film stack area and by limited light collection area of the measuring equipment. Modeling and simulations are used to further evaluate the full prospective of hierarchical textures in large area OLED devices. Optimization of hierarchical textures is done by simultaneously changing the aspect ratios of the small and large textures and a potential of 57% improvement in EQE compared to devices without applied textures is predicted by simulations. Optimized hierarchical textures show similar outcoupling efficiencies compared to optimized single textures, while on the other hand hierarchical textures require less pronounced features, lower aspect ratios, compared to single textures to achieve the same efficiencies. Hierarchical textures also help in eliminating flat parts that limit outcoupling efficiency. Finally, the limiting factors that prevent higher outcoupling are addressed. We show that the dominant factor is non-ideal reflection from the organic thin film stack due to parasitic absorption. In addition, possible ways to further increase the outcoupling from a thick substrate are indicated.

When used as lighting elements to illuminate surfaces and spaces, a homogeneous angular distribution of the light intensity is of particular importance. [5][6][7][8] This requires for instance the use of diffusing optics with a roughened surface, called diffusers. In particular, polymethylmethacrylate (PMMA), also known as acrylic glass or Plexiglass, has proven to be an outstanding material for this application, due to its high transparency, durability, processability, and resistance to scratches. [9][10][11] Relevant parameters for characterizing the optical properties of diffusers are for instance the total transmittance, the haze and the scattering, or diffusion angles. Total transmittance is defined

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In this study, the wetting behavior of microstructured polyethylene terephthalate (PET) foils for polar and nonpolar liquids produced by plate‐to‐plate hot embossing is investigated. For the embossing step, stainless steel plates are used as stamps, which are microstructured with single‐scaled and hierarchical textures using direct laser writing and two‐beam direct laser interference patterning. The imprinted microstructures, containing pillar‐ and line‐like textures, show increased water contact angles combined with a superoleophilic behavior. Time‐resolved measurements reveal that oil droplets spread rapidly on the hierarchical textures with velocities of up to 1.4 mm2 s−1. This functionalization of PET foils creates new opportunities for a wide range of industrial applications, such as the use of oil‐based instead of solvent‐based paints, an improved distribution of lubricants in mechanical components or for oil–water separation in maritime surroundings.