|dc.description.abstract||The first study investigates the impact of surface texture parameters of natural surface specimens on the attachment of algae communities. The primary objective of this effort is to show feasibility in the approach of reverse engineering natural surfaces (developing surface features that are biomimetically inspired) to enhance the attachment and species selectivity of benthic algae used in water pollution recovery systems. A secondary objective seeks to elucidate which surface parameters appear to explain the attachment behavior of a selected species. Finally, a method of reverse engineering natural surfaces is proposed in this study that can be implemented in other real-world applications. This work seeks to reveal the surface topography parameters that were significant for algal attachment by manipulating surface topographies using additive manufacturing. In this study, a method for capturing and reversing natural substrata has been developed and proven feasible. Natural rocks and surfaces with attached biofilms were retrieved from streams, scanned with optical profilometry, and the surface characteristics were analyzed. The results show that certain texture parameters (e.g., Smr, Sa, and Sv) show promise in predicting surface colonization by algae. The Pearson distribution was utilized to generate pseudo-randomized surfaces with surface characteristics. A material jetting process was used to additively manufacture the surfaces followed by optical profilometry to validate the resultant topography. The results validated that the set of Sa, Sv, and Smr significantly predict the surface adhesion of benthic algal species.
The second study aims to demonstrate the effects of geometric parameters such as shape, length, height, and pitch size of custom-3-D printed microtextured surfaces on receding and advancing water contact angle. This study reveals that the wetting behavior is highly dependent on the texture design. In addition, the geometrical parameters of the design such as shape, length, height, and pitch size significantly affect the contact angle. Among the geometrical parameters, the shape parameter had the greatest effect on contact angle, and the results indicated that groove design is strongly more hydrophobic than circular protrusion textures.
In the third study, three different issues regarding surface topography that are induced in 3-D printed surfaces are studied. In this study, three objectives were pursued: a) analyzing the surface finish and dimensional accuracy of material jetting processes in different designs and sizes, b) analyzing the effects of build orientation and surface slope on the fidelity of different surface texture designs, and c) analyzing the effects of tile thickness and build orientation on surface distortion and warpage. The results show that protrusion features have fewer dimensional errors than debossed features, especially for sizes smaller than 500 μm. In sizes smaller than 500 μm, the designs of features are indistinguishable and all printed features appear spherical. Slipping of partially cured (solidified) materials deposited right at the edge of features results in rounded shape edges and dimensional errors in fabricated designs.
This work indicated that surface slope creates stair-stepping, which affects different aspects of surface characteristics. The height and volumetric functional parameters are significant among others and show a better surface finish for the 0° surface slope compared to the 45° surface slope. This study showed that if the build tray is orientable through the printing process, the build tray can be tilted to variable degrees to increase the dimensional accuracy and create sharper edges for some designs such as polygons (not curved features) and features with recess designs. Increased surface slope also brings disadvantages such as a stair-stepping effect, a rough surface, asymmetry, and remains of the traces of moved material along the slope.
Minimizing the dimensional distortion in material jetting processes requires consideration of both the part design and process conditions. The type of distortion generated by a high aspect ratio specimen is dependent on the part thickness of the specimen, while the build orientation becomes a significant process parameter only when in very thin sections. The development of design guidelines should incorporate the knowledge that most geometries will experience distortion along the longest axis and that increasing wall thicknesses will help minimize potential deformations. Also, whenever thin part sections (~1 mm) are fabricated, the YX build orientation appears to decrease the amplitude of the deformation wave, as expressed by the height of the highest peak.||en_US