  Hypothesis: Lateral accumulation and film defects during drying of hard
particle coatings is a common problem, typically solved using polymeric
additives and surface active ingredients, which require further processing of
the dried film. Capillary suspensions with their tunable physical properties,
devoid of polymers, offer new pathways in producing uniform and defect free
particulate coatings.
  Experiments: We investigated the effect of small amounts of secondary liquid
on the coating's drying behavior. Stress build-up and weight loss in a
temperature and humidity controlled drying chamber were simultaneously
measured. Changes in the coating's reflectance and height profile over time
were related with the weight loss and stress curve.
  Findings: Capillary suspensions dry uniformly without defects. Lateral drying
is inhibited by the high yield stress, causing the coating to shrink to an even
height. The bridges between particles prevent air invasion and extend the
constant drying period. The liquid in the lower layers is transported to the
interface via corner flow within surface pores, leading to a partially dry
layer near the substrate while the pores above are still saturated. Using
capillary suspensions for hard particle coatings results in more uniform,
defect free films with better printing characteristics, rendering high additive
content obsolete.
