The
deposition of particles on a surface by an evaporating sessile
droplet is important for phenomena as diverse as printing, thin-film
deposition, and self-assembly. The shape of the final deposit depends
on the flows within the droplet during evaporation. These flows are
typically determined at the onset of the process by the intrinsic
physical, chemical, and geometrical properties of the droplet and
its environment. Here, we demonstrate deterministic emergence and
real-time control of Marangoni flows within the evaporating droplet
by an external point source of vapor. By varying the source location,
we can modulate these flows in space and time to pattern colloids
on surfaces in a controllable manner.
The oligomerization of ethylene produces α-olefin distributions ranging from Schulz−Flory distributions to alternating and selective oligomer distributions that can be mathematically analyzed and characterized by recurrence relations.
Droplet motion on surfaces influences phenomena as diverse as microfluidic liquid handling, printing technology, and energy harvesting. Typically, droplets are set in motion by inducing energy gradients on a substrate or flow on their free surface. Current configurations for controllable droplet manipulation have limited applicability as they rely on carefully tailored wettability gradients and/or bespoke substrates. Here, we demonstrate the nonmonotonic contactless long-range manipulation of binary droplets on pristine substrates due to the sensing of localized water vapor sources. The droplet-source system presents an unexpected off-centered equilibrium position. We capture the underlying mechanism behind this symmetry breaking with a simplified model based on the full two-dimensional functional form of the surface tension gradient induced by the source on the droplet’s free surface. This insight on the transport mechanism enables us to demonstrate its versatility for applications by printing, aligning, and reacting materials controllably in space and time on pristine substrates.
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