Direct experimental evidence of slip in hexadecane: solid interfaces

Prior research has shown that fluid flow near solid surfaces often assumes no-slip boundary conditions. However, this assumption may not always hold, especially for non-polar fluids or surfaces with specific chemical properties. Theoretical models have suggested that slip can occur, but direct experimental evidence has remained limited. Earlier studies have inferred slip indirectly through macroscopic flow measurements or simulations. This paper addresses a gap in the field by providing direct experimental observation of slip at fluid-solid interfaces. The study focuses on hexadecane, a model Newtonian fluid, and its interaction with hydrocarbon/lyophobic smooth surfaces. The novelty lies in using a high-resolution technique to measure flow behavior within 80 nm of the wall. This approach allows for a more precise understanding of how surface properties influence fluid behavior at the interface.

The aim of this work is to experimentally investigate the flow behavior of hexadecane near a solid surface and to determine whether slip occurs at the interface. The study seeks to provide direct evidence of slip, which has been theorized but rarely observed experimentally. The researchers are motivated by the need to understand how surface roughness and fluid-surface interactions influence slip. By using a novel setup involving total internal reflection-fluorescence recovery after photobleaching, they aim to achieve sub-100 nm resolution near the wall. This setup enables them to probe the velocity profile of the fluid in unprecedented detail. The study also aims to clarify the relationship between surface characteristics and slip magnitude. By combining experimental data with theoretical predictions, the authors hope to shed light on the mechanisms governing fluid-solid interactions.

The experimental setup uses total internal reflection-fluorescence recovery after photobleaching to measure fluid flow near a solid surface. This technique allows for high spatial resolution, capturing data within 80 nm of the wall. Hexadecane is chosen as the model fluid due to its Newtonian properties and low viscosity. The fluid is flowed over a hydrocarbon/lyophobic smooth surface, which is designed to minimize adhesion. The researchers track the recovery of fluorescence after photobleaching to infer velocity profiles. Surface roughness is controlled using smooth substrates, while fluid-surface interactions are studied by varying surface chemistry. The setup enables direct observation of slip at the interface. The data collected is analyzed to determine how surface roughness and fluid-surface interactions influence slip behavior.

The study provides direct experimental evidence of slip at the hexadecane-solid interface. Slip is observed within 80 nm of the wall, suggesting that the no-slip assumption may not always apply. The results indicate that surface roughness and fluid-surface interactions have opposing effects on slip. Surface roughness tends to increase slip, while stronger fluid-surface interactions reduce it. The magnitude of slip is quantified using fluorescence recovery measurements. The observed slip is consistent with theoretical predictions for non-polar fluids on lyophobic surfaces. The findings suggest that both surface roughness and interaction strength play significant roles in determining slip behavior. The results also highlight the importance of surface chemistry in controlling fluid flow at the interface.

The authors conclude that slip occurs at the hexadecane-solid interface, as evidenced by their experimental setup. They propose that surface roughness and fluid-surface interactions act in opposing ways to influence slip. The findings support the idea that slip is not solely dependent on surface roughness but also on the strength of fluid-surface interactions. The study confirms that the no-slip boundary condition may not always be valid for non-polar fluids on lyophobic surfaces. The results suggest that surface chemistry plays a critical role in determining slip behavior. The researchers emphasize the importance of considering both surface roughness and interaction strength when modeling fluid flow at interfaces. The study provides a foundation for further investigations into the mechanisms governing slip at fluid-solid interfaces.