Wetting failure of hydrophilic surfaces promoted by surface roughness

Abstract

Wetting failure is of vital importance to many physical phenomena, such as industrial coating and drop emission. Here we show when and how the surface roughness promotes the destabilization of a moving contact line on a hydrophilic surface. Beyond the balance of the driving force and viscous resistance where a stable wetting interface is sustained, wetting failure occurs and is modified by the roughness of the surface. The promoting effect arises only when the wetting velocity is high enough to create a gas-liquid-solid composite interface in the vicinity of the moving contact line, and it is a function of the intrinsic contact angle and proportion of solid tops. We propose a model to explain splashes of rough solid spheres impacting into liquids. It reveals a novel concept that dynamic wetting on hydrophilic rough surfaces can be similar to that on hydrophobic surfaces, and brings a new way to design surfaces with specific wetting properties.

Polydopamine-induced hydroxyapatite coating facilitates hydroxyapatite/polyamide 66 implant osteogenesis: an in vitro and in vivo evaluation

“…It has been found that improvement in surface hydrophilicity could promote cell attachment and spreading. 29,30 Surface roughness increased cell attachment owing to its increased protein absorption. 31 In addition, research has shown that HA has good biocompatibility and bioactivity, 32 and PDA improves the bioactive behavior of materials owing to its catecholamine structure.…”

Capillary Dynamics of Water/Ethanol Mixtures

“…Later on, researchers further studied by finely controlling the micro/nanostructure or chemical composition of a surface, the contact angle of water on this surface can be manipulated between hydrophilic and hydrophobic [25][26][27][28] .…”

Stable-streamlined cavities following the impact of non-superhydrophobic spheres on water

“…The formation of an air cavity upon the sphere impact on water occurs above a critical impact velocity, which is a function of the sphere-water contact angle, as well as the sphere surface micro-roughness. [1][2][3][4][5][6][7] For smooth hydrophilic spheres the threshold velocity is about 7.5 m s À1 , corresponding to a drop height of more than 3 m. For rough 7 or hydrophobic sphere impacts the critical impact velocity decreases, with superhydrophobic spheres making an air cavity practically at any impact velocity. 4 For the smooth unmodified sphere used in most of the experiments here (Y E 901) we were able to form a cavity using an impact velocity of about 6.0 m s À1 , which corresponds to a sphere release height of about 2 meters above the water surface.…”

“…If the steel spheres were washed with ethanol and water before use (Y E 601), the release height needed to be increased to above 3 m, and for plasma cleaned spheres (Y o 301) to above 4 m above the water surface, in good agreement with prior experimental and theoretical studies. [4][5][6][7][8][9][10] All results presented in this section are for sphere impact on pure water, however we notice that when a surfactant is added the critical cavity velocity can be affected due to dynamic surface tension effects. 11 When the impact velocity of the sphere is below the threshold the sphere will cross the air-water interface without forming a cavity as in the example shown in Fig.…”

“…Formation of an air cavity upon sphere impact on a water surface is a classical fluid dynamics problem with relevance to a wide range of industrial, military and sport applications. [1][2][3][4][5][6][7][8][9][10][11] A remarkable difference is observed between the impact of a smooth hydrophilic sphere and the impact of water-repellent superhydrophobic sphere on a water surface. [4][5][6][7][8][9][10] A superhydrophobic sphere forms a cavity at a very low impact velocity, well below the threshold impact velocities for cavity formation by smooth hydrophilic spheres.…”