UV Laser Photo-Polymerization of Elastic 2D/3D Structures Using Photo-Curable PDMS (Polydimethylsiloxane)
International Symposium on Laser Precision Microfabrication (LPM)
2D/3D structuring with the UV curable Polydimethylsiloxane (PDMS) was developed using UV laser direct writing. In this technique, UV curable PDMS was locally polymerized to fabricate 1D and 2D single layer structures, as well as 3D multi-layer structures with good stability and repeatability. In this experiment, commercial available UV curable PDMS which is a pre-mixed condition of the two components of the PDMS (50/50 wt.\% mixture of A and B) was used. The focused UV laser beam (CW, 20 mW, 355 nm) was scanned by an x-y galvanometric mirror scanner on the UV curable PDMS layer coated on the glass substrate. The UV curable PDMS has an absorption range at wavelengths less than 455 nm. At the relevant wavelength of 355 nm, the absorbance was 0.131, which is enough absorption for a photo-chemical reaction and deep penetration depth. As an example of the 2D structuring, figure 1(a) shows 2D pattern of LZH logos with different size. The UV curable PDMS layer with uniform thickness was prepared by spin coating on glass substrate. The polymerization of UV curable PDMS using UV laser scanning had adequate resolution to produce very small gaps for the striped part of the LZH logo. The polymerized PDMS retained its transparency. The samples also had very smooth outer surfaces and good sharpness at all corners and edges. On all samples, there was no deformation due to shrinkage effects. In addition, the 3D structuring has been demonstrated with the creation of a spider web style net shown in figure 1 (b). Each layer of liquid UV curable PDMS was dropped into a frame (diameter of 15 mm and a height of 3 mm) on a glass substrate. The first dropped UV curable PDMS layer was polymerized to form a spider web pattern. A second layer was then dropped into the frame and irradiated to form the posts. Thus, the entirety of the structure was able to be built in a two layer process, demonstrating the high aspect ratio of the UV curable PDMS. The structure was again able to maintain its transparency and had smooth outer surfaces. Due to the deep absorption depth of the UV curable PDMS, a 3 mm thick layer can be polymerized without a layer by layer process. Thus, pillars on the web structure with an aspect ratio of 2 could be obtained. The polymerized PDMS was strong and flexible, even in the thinnest 0.39 mm section. The strength and elasticity of the polymerized UV curable PDMS enables to hold a 7mm diameter, 1.49 g steel ball in the netting of the structure. The netting was able to return to its original shape after the steel ball was removed. Thus, the UV curable PDMS can be expected for wider and more flexible applications in additive manufacturing techniques.