Optically controlled assembly of suspended particles from evaporating sessile droplets is an emerging method to realize on-demand patterning of particles over solid substrates. Most of the reported strategies rely either on additives or surface texturing to modulate particle deposition. Though dynamic control over the assembly of microparticles is possible, limited success has been achieved in nanoparticle patterning, especially in the case of metallic nanoparticles. This work demonstrates a simple light-directed patterning of gold (Au) nanoparticles based on the thermoplasmonically controlled liquid flow. Excitation at the plasmonic wavelength (532 nm) generates the required temperature gradient, resulting in the particle assembly at the irradiation zone in response to the thermocapillary flow created inside the droplet. Particle streak velocimetry experiments and analysis confirm the existence of a strong thermocapillary flow, which counteracts the naturally occurring evaporative convection flows. By modulating the illumination conditions, we could achieve patterns with various morphologies, including center deposit, off-center deposit, multi-spot deposit, and lines. We successfully applied the developed strategy for realizing closely packed hybrid particle assembly containing different particles: Au and polystyrene particles (PS). We performed optical microscopy, 3D profilometry, and SEM analysis to characterize the particle deposit. We analyzed the periodicity of Au-PS hybrid assembly using fast Fourier transform and radial distribution function analysis. PS particles formed a hexagonal close-packed arrangement at the irradiation zone, with Au NPs residing inside the voids. We believe that the presented strategy could significantly enhance the applicability of the evaporative lithography from sessile droplets for the programmable patterning of metallic nanoparticles.

A water/chloroform interface-assisted one-pot synthesis of ultra-thin PPy/MnO2 sheets enriched with ∼6 nm MnO2 NPs. The decrease in the dynamic interfacial tension (γ) of the L/L interface proved the adsorption of MnO2 attached PPy oligomers.

We report a thermoplasmonically actuated optical modulator based on a liquid–liquid interface decorated with self-assembled Au nanoparticles (Au NPs). The system comprises heptane (top layer) and water (bottom layer), and an Au NPs array at their interfaces. Focused excitation with the plasmonic wavelength (532 nm) generates a localized temperature rise at the interface ( Δ T = 3.2 ± 0.7 ∘ C ), resulting in a thermocapillary flow. We optimized the temperature gradient and the heptane layer thickness so that the resulting thermocapillary flow leads to the formation of a “self-healing hole” at the irradiating zone, which we exploited as an all-optical modulator. A signal beam (655 nm) positioned through the top layer, parallel to the interface, gives a maximum output when the layer is intact (no-hole situation, ON state) and a minimum output when the hole is present (OFF state). Nearly 100% optical modulation is achieved in a reversible manner, highlighting the potential of responsive and reconfigurable fluid–fluid interfaces for optical applications.

The generation and control of microscale flows are crucial for fundamental as well as applied aspects of microfluidics. Commonly employed strategies for creating microflows are based on the electric field,...

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