Combination of silicon microstructures and porous cellulose nanofiber structures to improve liquid-infused-type self-cleaning function

Various fine structures and/or low surface energy material coatings have been designed to develop self-cleaning surfaces. These structures work by trapping air in their vacant spaces. Surfaces based on liquid-infused-type design exhibit better performance than those based on the traditional design; however, their life is limited because the special liquid covering the surface drops off easily. Cellulose nanofibers (CNFs) have amphiphilic characteristics in addition to their small size; thus, an aggregated structure consisting of CNFs will have an improved liquid holding performance. This study discusses the deposition of CNF on silicon microstructured surfaces and the etching of the CNF structure to extend its self-cleaning life. The effects of microstructure design, CNF concentration, and etching conditions on the morphology and porosity of the CNF structures are comprehensively studied. Long-term performance tests were carried out to measure the sliding angle (SA) of diethylene glycol after repeated water dash operations. It was confirmed that the combined structure of highly porous CNF and silicon microstructures exhibits a durable self-cleaning function.