Light-Directed Particle Patterning by Evaporative Optical Marangoni Assembly

Controlled particle deposition on
surfaces is crucial for both exploiting collective properties of particles
and their integration into devices. Most available methods depend
on intrinsic properties of either the substrate or the particles to
be deposited making them difficult to apply to complex, naturally
occurring or industrial formulations. Here we describe a new strategy
to pattern particles from an evaporating drop, regardless of inherent
particle characteristics and suspension composition. We use light
to generate Marangoni surface stresses resulting in flow patterns
that accumulate particles at predefined positions. Using projected
images, we generate a broad variety of complex patterns, including
multiple spots, lines and letters. Strikingly, this method, which
we call evaporative optical Marangoni assembly (eOMA), allows us to
pattern particles regardless of their size or surface properties,
in model suspensions as well as in complex, real-world formulations
such as commercial coffee.