Spontaneous spreading of a droplet on a solid surface is poorly understood from a macroscopic down to a molecular level. In our new publication entitled “Spontaneous Spreading of a Droplet: The Role of Solid Continuity and Advancing Contact Angle” and published in Langmuir, in collaboration with the Stevens Institute of Technology, we investigated the effect of surface topography and wettability on spontaneous spreading of a water droplet. Spreading force was measured for a suspended droplet that minimized interference of kinetic energy in the spontaneous spreading during its contact with solid surfaces of discontinuous (pillar) and continuous (pore) patterns with various shapes and dimensions. Results show that a droplet cannot spread spontaneously on pillared surfaces regardless of their shapes or dimensions due to the solid discontinuity. On the contrary, a droplet on pored surfaces can undergo spontaneous spreading whose force increases with a decrease in the advancing contact angle. Theoretical models based on both the system free energy and capillary force along the contact line validate the direct and universal dependency of the spontaneous spreading force on the advancing contact angle.
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