Understanding the self-pinning driven jamming behavior of colloids in drying droplets

The jamming of the colloids in a dried droplet is influenced by various parameters, where substrate wettability is notably crucial. Evaporating a sessile droplet on a wettable surface advances the pinning of the contact line which leads to the enhancement in the velocity of colloidal particles during the drying of the droplet (Marin et al., 2011). Now, the question arises: will the jamming of the colloidal particles in the case of evaporation of a droplet on the superhydrophobic surface (SH) and air-suspended spray colloidal droplet exhibit the increase in velocity of colloidal particles during drying of the droplet? The drying arrangement of the colloidal particles has been probed using electron microscopy and small-angle X-ray scattering. The fast Fourier transform of the electron microscopy images has been established utilizing ImageJ software. The supraparticles resulting from the evaporation of the droplet on the SH surface as well as by spray drying demonstrated a localized ordered arrangement on the outer surface whereas the arrangement becomes random in the inner region. The transition from ordered to the random arrangement of colloidal particles from the outer region to the inner region is due to the increase in the velocity of the colloidal particles during evaporation. The increase in the velocity can be attributed to the self-pinning of the colloids at the water-air interface resulting in elastic shell formation due to the locking of the colloidal particles in Van der Waals minima. Due to the presence of the menisci between the colloids, the formed shell behaves as nanomembrane, and the evaporation of the solvent through these nanopores accelerates and results in an increase in the velocity of the colloidal particles. Further, increasing polydispersity in the size of colloids led to random disordered jamming even on the top surface of the dried supraparticles.