  Droplet motion on surfaces influences phenomena as diverse as microfluidic
liquid handling, printing technology and micro-organism migration. Typically,
droplet motion is achieved by inducing energy gradients on a substrate or flow
on the droplet's free surface. Current configurations for droplet manipulation
have, however, limited applicability as they rely on carefully tailored
wettability gradients and/or bespoke substrates. Here we demonstrate the
contactless long-range manipulation of binary droplets on pristine substrates
due to the sensing of localized water vapor sources. We show with analytical
considerations that the dissipative nature of the driving forces at play,
induced by tiny asymmetries in surface tension gradients, is essential to
capture the droplet's manipulation mechanism. We then demonstrate its
versatility by printing, aligning and reacting materials controllably in space
and time.

Soft Condensed Matter