Effects of Surface Energy Reducing Agents on Adhesion Force in Liquid Bridge Microstereolithography

Projection microstereolithography (MSL) is a layer-by-layer manufacturing process used to fabricate three-dimensional (3D) microstructures. In this process, each layer of a photoreactive liquid resin is crosslinked by modulated ultraviolet (UV) light through a digital micromirror device (DMD). Despite the capabilities of MSL, there are some drawbacks such as incompatibility with highly viscous materials, long manufacturing time, large material consumption, and oxygen inhibition. To address these issues, liquid bridge microstereolithography (LBMSL) has been proposed as a vat-free process, which involves using a liquid resin supported by a capillary bridge between two substrates. One of the most important manufacturing steps in the LBMSL process is to detach the cured layers from the upper transparent substrate, without causing any damage to the structure during the 3D printing process. This paper has investigated the use of a small molecule additive, a surface energy reducing agent (SERA) that tends to migrate toward the transparent substrate and reduces adhesion at this interface. This has been proven through a series of adhesion force measurements and material characterization methods. The migration of SERA molecules has been studied using contact angle measurements and x-ray photoelectron spectroscopy (XPS). In addition, tensile measurements reveal that there are no detrimental effects on the mechanical properties of the resin due to adding SERA in the formulation. Multiple 3D microstructures have been fabricated to illustrate the advantage of adding SERA to reduce the adhesion of the resin to the transparent substrate in LBMSL.