Ridge-Texturing for Wettability Modification by Using Angled Fine Particle Peening

The industrial demand for wettability control has been increasing because wettability is a key factor for achieving novel anti-contaminant surfaces and related products. In this paper, the potential of angled fine particle peening (angled-FPP) was explored as a method of surface modification to control wettability. Angled-FPP, which is an abrasive jet machining process conducted using a peening nozzle set at an angle inclined to the material surface, is a potential texturing technique. With it, it is possible to create periodically aligned peaks and valleys (“ridges”) on the peened surface. Because control of wettability could possibly be achieved by varying the geometric characteristics of the texture, an attempt was made to vary ridge texture by conducting angled-FPP using three kinds of shot particles: steel, glass, and alumina grit. Thereafter, changes in the wettability owing to creation of a ridge texture on the surfaces were evaluated, with focus on the geometric and morphological features of the ridge texture. The results indicate that the size of the ridges depends on the size and shape of the shot particles, and the angled-FPP conducted using finer angular particles created densely concentrated ridges. The superficial appearance of the ridge texture differed depending on the shot particles used for angled-FPP. The topographies created by angled-FPP using steel particles and alumina grit were “hierarchical” (i.e., the ridge structure was overlapped by finer-scale roughness). In contrast, angled-FPP conducted using glass particles created ridge structure with a quite plain surface. Measurement of the water drop contact angle revealed that the surface became less hydrophilic after creation of the hierarchical topography. It was concluded that the predominant influence on the wettability of the angled-FPP surfaces came from the superficial morphology of the ridge texture.