Language
Country/Area
No result found
The secret intersection of liquids and solids: How do contact angles reveal their interactions?
In the world of physics and chemistry, the interaction of liquids and solids is a key research topic. Especially in the field of surface science, contact angle serves as an important parameter to help scientists understand the compatibility between different surfaces and how liquids spread out on different solid surfaces.
Contact angle is an important indicator that describes the behavior of a liquid on a solid surface. Its size can effectively quantify the wettability relative to the contact interface.
The contact angle (θC) is defined as the angle formed by the intersection of the liquid surface and the solid surface. Specifically, it is the angle formed by the tangent to the liquid-vapor interface and the tangent to the solid-liquid interface at their intersection. This angle not only tells us whether the liquid will completely wet the solid surface, but also involves the interaction between molecules.
Under static conditions, each specific system of solids, liquids and vapors will have a unique equilibrium contact angle, and the calculation of this contact angle is related to the surface tension, temperature and purity of the liquid. Its change depends not only on the properties of the liquid, but also on the material properties and interface state of the solid.
Equilibrium contact angle reflects the relative strength of molecular interactions between liquids, solids and vapors.
Dynamic changes in contact angle are a common phenomenon in daily life, such as raindrops on car windows or the reaction of cosmetics on the skin. These changes are called contact angle hysteresis, which is the difference between a surface's maximum contact angle (advancing contact angle) and minimum contact angle (receding contact angle).
The advancing contact angle is generally regarded as the maximum angle that a liquid can reach when sliding on a solid surface, while the receding contact angle is the minimum angle at which a liquid recedes across a solid interface. This phenomenon allows scientists to gain a deeper understanding of the behavior of liquids on solid surfaces and has important implications for a variety of applications such as coatings, medical devices and microfluidics.
The change in contact angle affects the flow behavior of liquids on solid surfaces, which has a crucial impact in many scientific and engineering applications.
In the context of thermodynamics, the theoretical description of contact angle is derived from the thermodynamic equilibrium between the three phases of liquid, solid and gas. This equilibrium can be characterized by Young's equation, which includes solid-vapor interface energy, solid-liquid interface energy and liquid-vapor interface energy. Further, Gibbs modified Young's equation to take into account the volume dependence of the contact angle, which is crucial for understanding wetting behavior at the micro- and nanoscale.
As advances in scientific instrumentation, such as atomic force microscopy and scanning electron microscopy, enable researchers to observe and measure the behavior of droplets at smaller scales, nonlinear changes in contact angles at such small scales have been discovered. These observations prompted the revision of traditional contact angle models and the development of new mathematical expressions to explain contact angle behavior.
At the micro-nano scale, the behavior of contact angles shows more complex phenomena, which require more accurate models to describe.
In addition, the phenomenon of contact angle hysteresis is also affected by factors such as functional groups, surface roughness, and external forces. Therefore, the surface in reality often does not have ideal uniformity. This requires scientists to consider multiple factors, including the motion state of the droplet, applied pressure and temperature, to accurately predict contact angle behavior.
In summary, contact angle is not only an important indicator of liquid-solid interaction, but also a window that allows us to glimpse the complex relationship between macroscopic substances and microscopic interfaces. This in-depth exploration of knowledge has not only improved our understanding of the behavior of liquids and solids, but has also catalyzed improvements in many practical applications. For example, in materials science, understanding contact angles can help design more functional surfaces, which has considerable implications for both everyday products and technology.
As we continue to explore more and more interactions between liquids and solids, will contact angles reveal more undiscovered physical phenomena?
