Self-Assembly On Dual Wettable Surface

A droplet of nanoparticle suspension is deposited on a specially designed dual wettable surface. Half diagonal of SiO2 substrate was oil coated and other half stayed unchanged. The droplet forms contact angle of 35∘ on the unchanged dry portion whereas it reaches to 60∘ on the oil coated region. Nanoparticle dried in stick–slip fashion where such effect was more pronounced on the oil-wet region. Scanning electron microscope (SEM) images revealed large ribbon-like nanorod assembly on the dry-region and short monolayer ribbons on the oil-wet part of the substrate. On both surfaces, shape-separation effect produced rod-rich and sphere-rich regions. The assemblies formed over the dry portion were dense whereas significantly small number of nanoparticles were observed on the oil-wet region. The droplet contact-line remained partially dynamic owing to the dual wettable design of the surface. Such contact-line dynamics facilitated the shape-separation effect induced by the surfactant molecules and dictated the deposition process over the surface. This work will be helpful to study shape-separation effect of small biological entities and multisystem of nanoparticles.