Despite the significant research being conducted on the mechanical reliability of additively manufactured parts, comparatively little focus has been paid to the property of thermal conductivity. Additively manufactured thermally conductive parts have the potential to benefit thermal management technologies that are currently a bottleneck of many classes of advanced electronic devices. Creating parts with high thermal conductivities remains a major challenge for the most prevalent form of material extrusion additive manufacturing, fused filament fabrication, which creates parts by extruding multiple layers of molten polymeric extrudate using an automated gantry system. The low thermal conductivity of these parts stems from several types of interfaces and voids inherent to the fused filament fabrication additive process, which create significant internal resistance to the flow of heat through a part. To increase thermal conductivity, many researchers and companies have added thermally conductive particles into the polymeric filaments. Still the achievable properties are largely constrained by the printing defects inherent to the printing process, especially when compared to injection molded parts. In this work, we investigate the role of thermal post-processing to both anneal the printed part and to tune the crystallization state of the polymer. We find that careful thermal post-processing of parts made with commercial filaments can improve thermal conductivity values to 2.5 times the asprinted property values. Further, we detail several correlations between processing conditions and thermal conductivity outcomes that will improve the implementation of fused filament fabrication for addressing thermal management challenges in industry.

Daniel J. Braconnier, Ryan M. Dunn, Eric D. Wetzel, Randall M. Erb, “The Role of Crystallization and Annealing on the Thermal Conductivity of Material Extrusion Additively Manufactured Parts”, Additive Manufacturing, 2024, https://doi.org/10.1016/j.addma.2024.104265.

Superhydrophobic materials rely on both chemical apolarity and surface roughness to achieve the high contact angles and the low roll-off angles that lead to self-cleaning and antibacterial properties. Current superhydrophobic coatings tend to be delicate and lose their properties easily when subjected to droplet impact. Such impact quickly deteriorates these coatings through hydrodynamic wear; changing structure, eroding hydrophobic chemistry, and quickly leading to full wet out of the substrate. In fact, hydrodynamic wear is more detrimental to coatings than seemingly more aggressive mechanical wear including scratching with sandpaper - a common approach used to claim both self-similarity of a material and extreme robustness against wear. What makes certain coatings more robust against hydrodynamic wear? To understand this answer, we systematically study ten disparate self-similar superhydrophobic coating approaches from academia to industry by subjecting them to hydrodynamic wear with rapid droplet impacts. We find rapid droplet impact that simulates a medium rain can deteriorate most coatings within seconds or minutes. Meanwhile, the more resilient coatings share common attributes including robust apolar chemistry, hierarchal topography, and a slow loss of sacrificial material. In addition, we offer an analytical model that nicely characterizes the hydrophobic lifetimes of these systems. 

Daniel J. Braconnier, Terence Davidovits, Randall M. Erb, “Understanding Hydrodynamic Wear in Self-Similar Superhydrophobic Coatings Subjected to Rapid Droplet Impacts”, RSC Advances, 2023, 13, 11356-11367, https://doi.org/10.1039/D3RA00700F.

Processing-structure-property relationships in material extrusion additive manufacturing are complex, non-linear, and poorly understood. In this work, we designed an informatics workflow for the collection of high pedigree data from each stage of the fused filament fabrication (FFF) printing process. In conjunction with a design of experiments, we applied the workflow to investigate the influences of processing parameters on weld strength across three commercially available FFF printers. Environmental, material, and print conditions that may impact performance were monitored to ensure that relevant data were collected in a consistent manner. Acrylonitrile butadiene styrene (ABS) filament was used to print ASTM D638-14 Type V tensile bars. Data were analyzed using multivariate statistical techniques, including principal component analysis. The magnitude of the effects of extrusion temperature, layer thickness, print bed temperature, and print speed on the tensile properties of the final print were determined. The results demonstrated that printer selection is important and changes the impact of print parameters. 

Daniel J. Braconnier, Robert E. Jensen, Amy M. Peterson, “Processing parameter correlations in material extrusion additive manufacturing”, Additive Manufacturing, Volume 31, 2020, 100924, https://doi.org/10.1016/j.addma.2019.100924.