Research Progress on the Effect of Surface Micro-nano Structure and Chemical Modification on Wettability

Wettability is an important characteristic of a material surface and significantly contributes toward the service behavior of
functional parts. Thus, the wetting behavior of droplets on solid surfaces can effectively guide the design and application of functional surfaces, as well as further improve the surface properties and service capabilities of functional parts, providing broad application prospects in national defense, daily life, and other industries. In addition, the main factors affecting surface wettability include the material surface energy, surface roughness, and surface micro / nanostructure. However, few scholars have quantitatively studied the relationship between these parameters, and there is no clear description of how the surface wettability can be regulated through the interface. Therefore, the effects of the surface micro-nano structure and chemical modification on wettability are examined in this work, and three classical theoretical models of surface wettability and new progress in wetting theory are introduced. Then, the research status of the influence of surface micro / nanostructures and chemical modification on surface wettability is reviewed in detail. The internal mechanism and causes of the change in contact angle with roughness are discussed and analyzed. Furthermore, the influence of surface microtexture on wettability and the role of chemical modification in different fields are described. Finally, the main problems and future development directions are summarized. With the gradual improvement of the wetting theory, relevant
theoretical research has gradually changed from idealization to more suitable outcomes for actual working conditions. Many
researchers have attempted to extend and modify the classical wetting model based on the corresponding theory combined with a
large amount of experimental data. Subsequently, the resulting modified physical and mathematical models produced
experimental data more compatible with the theoretical model, thus establishing a more applicable theoretical model. Similarly,
the wettability surface textures have gradually developed from the single pattern of circular, square, and groove microstructure to
the current micro-nano multiscale, multilayer composite micro-texture and bionic functional surface. Laser processing combined
with other technologies to achieve multiresponsive and multifunctional surface wettability is an important future research
direction. More specifically, many factors affect the wettability of a material surface, which will react with the substrate material
and surrounding environment, besides the influence of the surface micro / nanostructure and chemical modification. Herein, the
preparation methods, principles, and applications of special wettability surfaces are summarized, which can provide a valuable
reference for scholars engaged in related research. In general, surface wettability technology remains in the preliminary
exploration stage, and existing research is only at the tip of the iceberg. Therefore, there is an urgent need to develop a surface
wettability test standard that considers surface microstructure, material, environment, and other factors. Unfortunately, the
current production method cannot efficiently prepare low-cost, multiscale, micro / nano functional surfaces. Regarding the
demand for green and sustainable development, there is an urgent need to meet the practical requirements of economic and
environmentally friendly low-surface-energy modification, high-strength wettability, functional surface stability, and excellent
service life for functional parts. Generally, there is room for improvement. In future, a database for the preparation of wettable
functional surfaces should be established. Then, based on collected experimental data and integration of the concept of green
environmental protection, a combination of numerical simulations and experiments should be used to obtain simple and fast
processing technology, as well as parameters to realize fine and complex or multiphase precise wetting. This will be significant
for specific applications such as military facilities, cell engineering, and intelligent sensing