Multi-Scale 3D Printing Using Vat-free Photopolymerization

University Of Akron, Akron OH

Investigators

Abstract

3D printing has the potential to revitalize the manufacturing sector in the US. A widely used 3D printing process is stereolithography because of its ability to print complex objects with relatively high resolutions. This process works by scanning a focused laser or projecting a light pattern on the surface of a vat of liquid photopolymer to print series of layers. However, limitations of this process include its inability to print large structures with micron features. This award supports fundamental research on a new stereolithography process where the vat is replaced by a liquid bridge formed between two optically clear plates using surface tension. Research results can enable the development of low-cost, high-resolution 3D printers for manufacturing complex structures with micron resolutions on a large area. Examples of such structures are 3D fluidics, sensors, actuators, drug delivery devices, and tissue engineering scaffolds. The objectives of this research are: (1) to understand effects of the size (height and volume) of the liquid bridge and material properties (surface tension and density) of the photopolymer on the profile of the liquid bridge formed within two optically clear plates; (2) to understand effects of surface energy at interfaces (between bottom plate and fabricated structure, between layers within the fabricated structure, and between top plate and fabricated structure) on the stability of the fabricated structure; (3) to establish relationships between curing parameters (light intensity, scanning speeds, and light patterns) and accumulated energy over the polymer surface. To achieve the first objective, a modified equilibrium quasi-static liquid bridge model using Young-Laplace equations will be used to predict the profile of the liquid bridge with different values of liquid bridge size and polymer material properties. Some predicted results will be verified by experiments. Liquid bridges will be formed by supplying the polymer into two plates and their profiles will be measured by optical microscopy. The height of the liquid bridge will be varied from 1 to 5 mm by a motorized stage and its volume with a base area of 4 by 4 cm will be controlled by a syringe pump. Surface tension and density will be controlled by using different polymers with surface energy reducing agents (such as fluorinated alcohols and silicone polyether). For the second objective, various structures will be fabricated using different polymers containing surface energy reducing agents. Surface energy at three interfaces will be measured by a Zisman plotting technique and the conventional peel test. Stability of fabricated structures will be observed by optical and scanning electron microscopy. To achieve the third objective, a modified Beer-Lambert cure model and the energy accumulation equation will be used to predict accumulated energy on the polymer surface with different values of light intensity, scanning speed, and light pattern. Some predicted results will be verified by experiments. Accumulated energy will be measured by a beam profiling camera installed at a location so that it can measure the accumulated energy the polymer surface would get. A horizontal xy-stage, light source (mercury lamp), and digital micromirror device will be used to control scanning speed, light intensity, and light pattern.