Surface Functionalization of 3D Printed Polymer Substrate for Enhanced Non-Wetting Behavior

Abstract

Amphiphobic surfaces are obtained by lowering the surface energy through changes in surface geometry. These changes can be designed on the surface, thereby altering its wettability, and in turn rendering it amphiphobic. The main geometrical entities behind this phenomenon are reentrant geometries which prevent the solid-liquid interface tension from breaking, thereby resulting in contact angles greater than 90° or sliding angles less than 15°. The science behind modelling and manufacturing of these reentrant geometries is well established apart from manufacturing them via extrusion-based 3-Dimensional (3D) printing processes. This research focuses on the creation of these reentrant geometries using Fused Deposition Modelling (FDM) 3D printing technique which despite being the most common has rarely been used to create reentrant edge structures. We discuss how layer-by-layer deposition leads to the creation of natural reentrant geometries which act as entrapment sites thereby preventing liquid imbibition. Having established this paradigm we go a step forward in identifying limitations in our process and formulate a methodology to convert our 3D printed structures into Slippery Liquid Infused Surfaces (SLIPS). SLIPS help in altering the wettability due to the distinctive properties of the interfacial liquid which in combination with our reentrant geometry forms the new surface. If the interfacial liquid is repellent towards polar (hydrophobic) and non-polar (oleophobic) liquids, the overall surface becomes slippery (amphiphobic) and prevents any new target liquids from adhering. A two-step facile method is presented to quickly transform a 3D printable polymeric material into robust SLIPS, which changes the wettability properties of the original polymer. 3D printing aids in the manufacturing of the complex geometrical porosity required for locking the interfacial liquid. Surface wettability characteristics of the 3D printed porous structure are then enhanced by increasing the liquid-adsorption sites where the locking of the infused interfacial (repellent) liquid takes place. The SLIPS demonstrate low rolling-off (sliding) angles with both polar and non-polar solvents of up to 2 degrees with high resistance to mechanical abrasion undergoing sliding frictional wear.