Self-Pinning by Colloids Confined at a Contact Line

Colloidal particles suspended in a fluid usually inhibit complete wetting of the fluid on a solid surfaceand cause pinning of the contact line, known as self-pinning.We show differences in spreading and dryingbehaviors of pure and colloidal droplets using optical and confocal imaging methods. These differencescome from spreading inhibition by colloids confined at a contact line. We propose a self-pinningmechanism based on spreading inhibition by colloids. We find a good agreement between the mechanismand the experimental result taken by directly tracking individual colloids near the contact lines ofevaporating colloidal droplets.