These are insightful and intricate questions related to fluid dynamics, wetting phenomena, and experimental validation techniques. I'll address each point with the most relevant concepts and experimental techniques:

1. Validation of Measured Macroscopic Contact Angle

The macroscopic contact angle, which is often measured at the millimeter or micrometer scale, may not always reflect the behavior at the molecular scale. Here’s why:

• Macroscopic vs. Nanoscopic Contact Angles: The macroscopic contact angle is influenced by the roughness and heterogeneity of the surface, as well as the underlying molecular interactions at the contact line. On the molecular scale, the contact angle can be much more variable due to factors like molecular orientation and interfacial forces that are averaged out in macroscopic measurements. Therefore, it's unlikely that the macroscopic contact angle would exactly match the nanoscopic contact angles.
• Moving Speed and Microscopic Contact Angle: The microscopic contact angle, especially at the contact line, is often influenced by the speed of motion (in dynamic conditions), which can lead to hysteresis or changes in the angle due to kinetic effects. These effects become particularly relevant for high-speed spreading or moving droplets.
• Measuring Thin Films and Interface Profiles (less than 100 nm): Techniques like Environmental-SEM (eSEM), wet-STEM, and TEM can indeed be used to observe the interface profiles at very small scales. These techniques allow for visualization of thin films, but capturing the dynamic nature of the fluid interface, especially under high-speed conditions or when molecular-scale interactions are involved, remains challenging. The resolution and imaging capabilities, especially under dynamic fluid conditions, are limited, but they are improving. Additionally, controlling environmental conditions (e.g., maintaining liquid films or wetting conditions in a vacuum or controlled atmosphere) is critical.

2. Capturing the Contact Line Movement in Oil-Brine-Gas Phases

The behavior at the contact line, especially when dealing with complex multi-phase systems like oil-brine-gas interfaces in a mixed or fractional wet reservoir, is indeed complex. Here are some challenges and opportunities:

• Molecular Jumping and Interfacial Rolling: These mechanisms, which are linked to the motion of the contact line, can be influenced by the interfacial tension between the phases and the heterogeneity of the surface. In such systems, capturing these phenomena at the molecular scale can be difficult due to the roughness and the dynamic nature of the phases involved. However, with molecular dynamics simulations (MD) and high-resolution imaging techniques like atomic force microscopy (AFM) or high-speed video microscopy, it’s possible to observe and capture contact line movement mechanisms.
• Control over Experimental Conditions: At the laboratory scale, controlling and capturing the contact line dynamics in oil-brine-gas systems may be feasible but requires specialized equipment. For instance, ensuring stable phase separation and controlling the interface under dynamic conditions (e.g., changing flow rates, applying external forces) would be necessary.

3. Regulation of Hydrodynamic Singularity (Slip, Diffusion, and Disjoining Pressure)

At the laboratory scale, capturing and controlling hydrodynamic singularities, such as slip lengths, diffusion, and disjoining pressures, is an advanced task that requires a deep understanding of interfacial physics and precise experimental techniques:

• Slip and Diffusion: Slip at solid-liquid interfaces is often related to molecular interactions near the contact line and can be influenced by surface roughness and fluid properties. Experimental methods like rheometry, microfluidics, and AFM can be used to measure slip lengths and diffusion coefficients. However, capturing these phenomena at the molecular scale (especially in complex multi-phase systems) can be difficult.
• Disjoining Pressure: Disjoining pressure refers to the pressure that arises between layers of a thin liquid film due to molecular interactions. It is particularly important in systems with thin films (e.g., less than 100 nm thick). This pressure can be influenced by surface forces and could potentially be measured using optical interferometry or atomic force microscopy (AFM), though measuring it under dynamic conditions remains a significant challenge.

In conclusion, while controlling and measuring these phenomena in complex, dynamic, multi-phase systems is challenging, it is not beyond the reach of current experimental techniques. Advances in imaging and molecular dynamics simulations, as well as specialized laboratory equipment, are making it increasingly possible to study such systems with higher precision. However, significant effort in controlling experimental conditions, resolution, and environmental constraints will be needed to extract meaningful data.