Nonisothermal Spreading Dynamics of Self-Rewetting Droplets

Area of Science:

• Fluid dynamics
• Thermodynamics
• Materials science

Background:

• Understanding droplet spreading on heated surfaces is crucial for various industrial applications.
• Nonisothermal conditions and binary mixtures introduce complex behaviors like thermal and solutal instabilities.
• The Marangoni effect, driven by surface tension gradients, plays a significant role in fluid dynamics.

Purpose of the Study:

• To experimentally investigate the spreading dynamics of binary alcohol mixtures on a heated substrate.
• To analyze the influence of substrate temperature on droplet spreading exponents and thermal patterns.
• To elucidate the mechanisms behind thermal and solutal instabilities during evaporation.

Main Methods:

• Experimental study of binary alcohol mixtures and pure liquids on a heated substrate.
• Utilizing infrared thermography to capture temporal and spatial thermal dynamics.
• Analysis of droplet spreading exponents under nonisothermal conditions.

Main Results:

• Droplet spreading exhibits power-law growth in the early stage, with exponents dependent on substrate temperature.
• Unique thermal patterns were observed due to thermal/solutal instabilities and the Marangoni effect.
• Substrate temperature non-monotonically affects the inertial-capillary spreading regime for self-rewetting liquids.

Conclusions:

• Substrate temperature is a critical factor governing the early-stage spreading of evaporating binary alcohol droplets.
• The Marangoni effect significantly influences spreading dynamics through temperature-induced surface tension gradients.
• Later-stage spreading transitions to a viscous-capillary regime, similar to pure liquids.