Abstract:
This work investigates the role of surface parameters such
as the nanoscale roughness, topography, and skewness of smooth and
rough Si surfaces in the shape of patterns left by evaporating colloidal
droplets of spherical polystyrene particles. The droplet contact angle,
colloidal deposition pattern, crack density, and rim growth velocities are
experimentally evaluated for varying roughness. The contact angle and
rim growth rate are found to be more for rough surfaces in comparison to
smooth ones. Roughness also helps in reducing stress in the drying
droplets, thereby impeding the process of crack formation as exemplified
by the experimental results. The altered Derjaguin−Landau−Verwey−
Overbeek (DLVO) interactions emerging from the contribution of
nanoscale roughness are theoretically evaluated for each differently rough
substrate−particle combination. The forces have been calculated by
considering large- and small-scale roughness parameters of the experimental surfaces. The experimental findings have been duly
corroborated by theoretical estimates. Finally, it is observed that the skewness of the surface and the small-scale asperity radius
bear a correlation with the DLVO forces and subsequently with the ring deposit pattern. The present understanding of the
influence of surface fluctuations on evaporative self-assembly would enable one to choose the right topographic surface for
particular applications.
