  Liquid droplets usually wet smooth and homogeneous substrates isotropically.
Recent research works have revealed that droplets sit, slide and spread
anisotropically on uniaxially stretched soft substrates, showing an enhanced
wettability and contact line mobility along the stretching direction. This
phenomenon arises from the anisotropic deformation of the substrate below the
contact line. Here, we investigate how the stretching of soft substrates
affects droplets drying. We observe that water droplet evaporates with an
elongated non-circular contact line on the stretched substrates and switches
the elongation direction during evaporation. The contact line velocity and its
temporal evolution depend on the orientation of the contact line relative to
the stretching direction. On the substrate stretched by 250%, the contact line
recedes about 20% of the droplet lifetime earlier along the stretching
direction and faster than its perpendicular direction. When nanoparticles are
added into the liquid, the circular deposition pattern, i.e., the so-called
coffee-ring, becomes elongated along the direction perpendicular to the
stretching direction. Particularly, such non-circular deposition pattern
exhibits periodic height gradients along its rim. The finer structure of the
pattern can be controlled by applying different stretching ratios to the soft
substrate and thus are correlated to the anisotropic surface stresses near the
contact line.
