Fabrication and Shadowgraph Imaging of a Zinc Sulfate Polyacrylamide Hydrogel Undergoing Blunt Impact

Shadowgraph imaging is an optical imaging technique that uses a density differential to show contrast in transparent mediums. It allows for the easy visualization of shockwaves and cavitation due to impact. The purpose of this project is to provide researchers who use shadowgraph imaging techniques with imaging mediums of different properties. Polyacrylamide was chosen because of its tunable properties. The material properties of the hydrogels were modified to have a higher density while maintaining the required transparency for shadowgraph imaging. A protocol was created to make these hydrogels using polyacrylamide and zinc sulfate. A desired density of about 1.4 g/cm3 was achieved with a molality of 3 m ZnSO4. The fabrication procedure for this hydrogel was iteratively optimized. A 3D-printed polylactic acid (PLA) box and a part ellipse part logarithmic spiral shape were used as the mold and insert for the hydrogels. Once removed from the gel, water could be placed in the empty space and a density differential could be achieved for imaging. Inertial cavitation is when a pressure differential causes a vapor bubble to form, grow, and finally collapse resulting in shockwaves. These shockwaves were captured in the media-filled box undergoing impact with shadowgraph imaging. Future work for this project involves optimizing the picture quality of the gel as it undergoes blunt impact to capture shockwaves and further study the effect of shockwaves on the gel. This should assist other researchers using shadowgraph imaging.