Dynamic spreading of nanofluids on solids. Part I: experimental

Area of Science:

• Materials Science
• Fluid Dynamics
• Surface Science

Background:

• Nanofluids exhibit superior thermophysical properties due to nanoparticle inclusion.
• Previous studies indicate that nanoparticles enhance nanofluid spreading behavior.

Purpose of the Study:

• To experimentally investigate the spreading dynamics of silica nanofluids.
• To analyze the effect of nanoparticle concentration and oil drop volume on spreading.
• To observe the formation of a distinct inner contact line during nanofluid spreading.

Main Methods:

• Experiments were conducted using silica nanofluids (5, 10, 20 vol%) with 19 nm particles.
• A sessile drop on a glass surface was displaced by the nanofluid.
• Advanced optical techniques provided simultaneous top and side views of the contact line.
• The position of the contact line was monitored over time.

Main Results:

• Nanofluids formed a thin film between the oil drop and the surface, creating a bright inner contact line.
• This inner contact line, distinct from the outer three-phase contact line, was not observed in nanoparticle-free fluids.
• The spreading rate of the inner contact line increased with higher nanoparticle concentrations.
• Spreading speed decreased as oil drop volume decreased (i.e., capillary pressure increased).

Conclusions:

• Nanoparticle presence significantly alters fluid spreading dynamics, leading to the formation of an inner contact line.
• The concentration of nanoparticles is a key factor controlling the rate of nanofluid film spreading.
• These findings offer new insights into nanofluid behavior at interfaces, relevant for applications involving thin film formation.