Spontaneous spreading of nanodroplets on partially wetting surfaces with continuous grooves: Synergy of imbibition and capillary condensation

The wetting behavior of nanodroplets deposited on hydrophilic textured surfaces with discontinuous and continuous grooves was investigated by many-body dissipative particle dynamics. For surfaces with discontinuous grooves, the apparent contact angle (θ_a) can be described by the Wenzel model with an effective area ratio. However, for surfaces with continuous grooves, θ_a of nanodroplets depends on roughness topology, and spontaneous spreading of nanodroplets can take place even for partially wetting surfaces (θ_Y > 0). That is, the partial-to-total wetting transition can occur on hydrophilic surfaces as surface textures change from discontinuous to continuous grooves. The dynamics of the spreading can be characterized by the apparent radius and groove radius (R_g). While the former is time-invariant at early stage, the latter follows the power law R_g ~ t^1/4. This spreading of nanodroplets along continuous grooves can be explained from the synergy of spontaneous imbibition into continuous grooves, arrest by sharp edges, and capillary condensation for resuming the flow.