Fluorine-Free Superhydrophobic Surface by Single-Step-Synthesized Homogeneous Polymeric Raspberry Nanoparticle Coating

We introduce a superhydrophobic surface that is composed of homogeneous polystyrene (PS) raspberry nanoparticles of around 50 nm diameter, via a convenient single-step scalable synthesis method. The surface has multiple stabilization wetting points, which is caused by hierarchical roughness from the unique raspberry morphology. Raspberry morphology also enables PS (which has higher surface tension than fluorinated materials) to have superhydrophobicity with more than 120° of the receding contact angle as well as over 150° of the advancing contact angle. Embedded hierarchical topography in raspberry nanoparticles enables the enhancement of secure physical roughness for superhydrophobicity, which can be less affected by structures from the aggregations of nanoparticles during the coating process such as the spraying method. The nonfluorination-driven superhydrophobic surface composed of homogeneous polymers, which can wet step-by-step stabilization from the Cassie-Baxter state to the Wenzel state through multiple metastable states, opens avenue for practical applications requiring instant and cost-effective superhydrophobic surfaces.