Wetting properties of polymer additively manufactured surfaces – Multiscale and multi-technique study into the surface-measurement-function interactions

The functional features of 3D printing surfaces can be controlled by changing the parameters of additive processes. This study investigates the correlations between built-up angle, surface fractal complexity, and wettability in additively manufactured surfaces using Fused Deposition Modeling (FDM), Selective Laser Sintering (SLS), and Multi Jet Printing (MJT). Surface topography was measured using four optical techniques: focus variation, confocal microscopy, confocal fusion, and interferometry, across multiple scales. The study explored linear, logarithmic, and exponential regression models to identify the best correlations and scale of interactions between the built-up angle, surface complexity, and contact angle. It was found that the built-up angle significantly influences surface fractal complexity, with strong correlations (R² > 0.85) observed particularly at a scale of around 1100 µm². Confocal fusion offered the best reproducibility of measurements, especially at finer scales (< 100 µm²). Surface complexity was also found to correlate strongly with wettability, especially at scales around 1000 µm² and under 10 µm², where exponential regression models performed slightly better, particularly for MJT surfaces. Topographic measurement modes are reproducible with slightly better correlation indices for confocal fusion, between built-up angle and surface complexity. The best correlation of built-up angle, surface complexity and contact angle parameters was obtained for linear regression. The results suggest that surface wettability can be controlled by adjusting the built-up angle, with FDM and SLS surfaces transitioning from hydrophobic to hydrophilic as the angle increases beyond 70 degree, while MJT surfaces remained hydrophobic even at higher angles. The built-up angle parameter allows modeling wettability in the range of 80–120°. The study also indicates the superiority of multiscale parameters over conventional topographic characterization methods in describing additively manufactured surfaces.