Many
animals and plants have evolved wonderful hydrophobic abilities
to adapt to the complex climate environment. The microstructure design
of a superhydrophobic surface focuses on bionics and will be restricted
by processing technology. Although certain functions can be achieved,
there is a lack of unified conclusion on the wetting mechanism and
a few quantitative analyses of the continuity of the three-phase contact
line. Therefore, the relationship between the surface microstructure
of the lattice pattern and the critical sliding angle of the water
droplet in the Cassie state was investigated in this paper, and we
proposed a method to quantitatively analyze the continuity of the
three-phase contact line by a dimensionless length f. The results showed that the three-phase contact line was an important
factor to determine the sliding performance of the droplet. The upward
traction force generated by the surface tension through the force
analysis on the three-phase contact line can enhance the sliding ability
of the droplet on the solid surface. There was a good negative linear
correlation between the critical sliding angle and dimensionless length,
which provided a guiding basis for the optimal design of superhydrophobic
surfaces.
It
is confirmed that surfaces with specific microstructures could
exhibit good superhydrophobic properties, and there are also a lot
of conclusions about droplet hysteresis behavior. However, most of
the research methods are based on two-dimensional ideal model and
experimental observation at the macroscale. Further research needs
to be conducted about the hysteresis behavior of droplets on the microstructure
surface under three-dimensional conditions. In this paper, the influence
of curvature variation of the liquid surface between pillars on the
contact angle hysteresis (CAH) has been investigated. The simulation
results were in good agreement with the experimental measurements.
Analyses were conducted on the morphology change and force of the
liquid surface between pillars, and an index was proposed to describe
the degree of difficulty of liquid surface movement. It was revealed
that a change in the direction of the surface tension at the three-phase
interface caused by curvature variation of the liquid surface between
pillars played an important role in the movement of the liquid surface.
The greater the surface tension component in the normal direction
of the liquid surface, the more likely it was for the liquid surface
to advance or recede. The local curvature of the liquid surface increased
or the angles between the pillars increased, and the effect of the
CAH would be weakened.
Abstract:In order to improve the tribological properties of an engine piston ring and enhance its service life, magnetron sputtering technology and low temperature ion sulphurizing treatment technology were used to prepare CrMoN/MoS 2 solid lubricant coating on the surface of an engine piston ring. The morphologies and compositions of the surface and cross-section of the sulfuration layer were analyzed by field emission scanning electron microscopy (FESEM), and wear property under high load, high speed and high temperature conditions were tested by a SRV ® 4 friction and wear testing machine. The results show that the CrMoN/MoS 2 composite coatings appear as a dense grain structure, and the coating is an ideal solid lubrication layer that possesses an excellent high temperature wear resistance, reducing the engine operating temperature abrasion effectively and prolonging the service life of the engine.
In recent research, a method for manufacturing superhydrophobic metal surfaces using pulse laser texturing has been developed. After laser texturing, a sample can be converted into a superhydrophobic surface by aging the sample for several weeks in ambient air. Research on this method is currently focused on metal surfaces, such as aluminium, copper and so on. There are few studies of iron and steel materials, and the process and principle of wetting conversion is not sufficiently clear, and thus, further research is needed. In this study, a stainless steel surface with a large number of Gaussian pits was prepared using a nanosecond fibre laser, which was then naturally converted into a superhydrophobic surface in air. The effect of the roughness, lattice arrangement and chemical composition of a surface on its hydrophobic properties was studied to realize controllable hydrophobic properties. A hexagonal lattice surface prepared using 10 processing cycles showed the best hydrophobic performance, with contact and rolling angles of 161.3 and 3.2°, respectively.
Due to the complicated structure and serving environments, thermal barrier coatings (TBCs) usually encounter failure in the form of surface coating cracking and interface spalling without warning. At present, although many experimental techniques and equipment were developed to predict their service life, the transfer process of stress between different layers and the strain characteristics of ceramic surface are not clearly explained. In this paper, the nondestructive digital image correlation method was used to observe the character of surface strains of supersonic plasma‐sprayed TBCs systems in tensile failure processes. Also, mathematical model was established basing on the principle of minimum function to calculate interface stress and coating strain expressions. The results show the characteristics of strain change in the whole tensile stage can be divided into four stages. At first, strain concentration occurs in the range of 9%‐27% of the effective distance between one end of the tensile specimen, second, a certain number of strain fringes are formed and distributed at a certain distance, and then the first crack appears in the initial strain concentration area; as the load continues, more and more cracks on the coating surface reach saturation and finally fail. In the microlinear elasticity stage, the shear strain in the coating and the interface shear stress are in a linear relationship. As the thickness of the single‐layer coating increasing, the strain value of the surface strain of the coating decreases, the surface strain value of the single‐layer coating is about six times larger than that of the double‐layer coating.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.