International Conference on Laser Ablation (COLA)
Polydimethylsiloxane (PDMS) is a widely well-known elastic material due to its physical elasticity, chemical inertness, bio-compatibility and non-toxicity as well as optical transparency. In the applications of PDMS, a thin layer coating of PDMS onto free-form surface is required. However, in the conventional way a thin layer of PDMS with a thickness of less than 5 µm, coated by spin-coating, takes longer than half an hour or must be diluted with a solvent to decrease its viscosity. In addition, the principles of spin-coating limit the usage to only flat surfaces. To overcome this problem, we have developed the hybrid technique of aerosol jet printing followed by UV laser direct writing, and enabled successful 2D patterning of thin film UV curable PDMS. The UV curable PDMS is recently developed as a commercially available new material (KER-4690 A/B, Shin-Etsu Silicones Europe B.V.), and could be applied into 2D/3D large-scale structures using a combination of UV laser direct writing. The aerosol jet printing technique generates aerosol and enables spray coatings of the UV curable PDMS. Figure 1 shows the fluid flow schematic of the Aerosol Jet System (Optomec Inc.) with a dual atomizer module. In the experiment, the UV curable PDMS material which is comprised of two components (Materials A and B) were individually atomized in each atomizer and the dual-aerosol jet streams of the UV curable PDMS material were mixed together in the Aerosol Jet System. A homogeneously mixed aerosol jet stream was ejected from a wide nozzle head (3.0 x 0.5 mm2) with nitrogen Sheath gas surrounding it to focus and collimate the stream into a tight beam and prevent clogging. The gap distance between the nozzle head aperture and the substrate was kept at 3 mm. The combination of a computer-controlled stage and a mechanical shutter enabled a uniform coating of UV curable PDMS layer, 3 mm in line width, on a glass substrate. After coating, the UV curable PDMS underwent photo-initiated polymerization by UV laser irradiation (CW, λ= 355 nm). The focused UV laser beam directly scans a 2D pattern in the X-Y plane using a galvanometer scanner. When the aerosol jet system generated constant amount of aerosol jet stream of UV curable PDMS, the printed layer thickness of UV curable PDMS depends on the moving speed of the nozzle head. The minimum layer thickness of 1.6 µm was obtained at a nozzle-moving speed of 900 µm/s. Figure 2 shows the 3.00 x 8.07 mm² LZH logo printed onto a cylindrical glass bottle. The aerosol jet printing system coated a uniform PDMS layer at a nozzle-moving speed of 200 µm/s on a glass cylinder with an outer diameter of 14.8 mm. The coated PDMS was cured with a 1.5 mW of laser beam at a scan speed of 500 mm/s. After the laser irradiation, the sample was placed in an oven at 70 °C for 20 min to help the polymerization reaction at the irradiated areas. Finally, unpolymerized area of the PDMS layer was washed away in the development process. The resulting pattern showed good adhesion to the curved substrate and clearly displayed the LZH logo. Thus, this new thin-film coating technique of PDMS can be promised for a wide variety of applications.