Temperature-dependent slip length for water and electrolyte solution.

Area of Science:

• Fluid mechanics
• Surface science
• Nanotechnology

Background:

• Boundary slip at liquid-solid interfaces is crucial for micro/nanoscale fluid mechanics.
• Its temperature dependence is debated, lacking experimental validation.
• Understanding this is key for applications like sustainable electronic cooling.

Purpose of the Study:

• To experimentally resolve the controversy surrounding the temperature dependence of boundary slip.
• To investigate how interfacial energy barriers influence slip length.
• To provide a basis for thermal-hydrodynamic design in micro/nanofluidic devices.

Main Methods:

• Colloidal probe Atomic Force Microscopy (AFM) was used to measure slip length (l_s) versus temperature (T).
• Experiments were conducted with water and NaCl solutions on a Perfluorodecyltrichlorosilane (FDTS) surface.
• Molecular dynamics simulations and an analytical rate theory model were employed for quantitative explanation.

Main Results:

• A transition in the slip length-temperature (l_s - T) monotonicity was observed.
• For water and 0.1 M NaCl, slip length decreased with increasing temperature (negative correlation).
• For 1 M NaCl, slip length increased with increasing temperature (positive correlation).

Conclusions:

• The study provides the first experimental evidence for boundary slip being a rate process.
• The observed temperature dependence is explained by the interplay between liquid-solid and liquid internal energy barriers.
• Findings offer a foundation for optimizing thermal-hydrodynamic designs in microfluidic and nanofluidic systems.