Structure and flow of droplets on solid surfaces.

The structure and flow of droplets on solid surfaces is investigated with imaging and scattering techniques and compared to simulations. To access nanostructures at the liquid-solid interface advanced scattering techniques such as grazing incidence small-angle x-ray scattering (GISAXS) with micro- and nanometer-sized beams, GISAXS and in situ imaging ellipsometry and GISAXS tomography are used. Using gold nanoparticle suspensions, structures observed in the wetting area due to deposition are probed in situ during the drying of the droplets. After drying, nanostructures in the wetting area and inside the dried droplets are monitored. In addition to drying, a macroscopic movement of droplets is caused by body forces acting on an inclined substrate. The complexity of the solid surfaces is increased from simple silicon substrates to binary polymer brushes, which undergo a switching due to the liquid in the droplet. Nanostructures introduced in the polymer brush due to the movement of droplets are observed.

Polymer-template-assisted growth of gold nanowires using a novel flow-stream technique.

By utilizing a fluidic device, a gold nanoparticle dispersion is cast onto a nanostructured polymer template using solution subjected to hydrodynamic flow. With in situ grazing incidence small-angle X-ray scattering (GISAXS), the progressive gold deposition from a stream of gold solution onto the polymer template of a diblock copolymer with parallel cylinder morphology arranged into powder-like domains is investigated. The continuously flowing solution causes a systematic increase in the X-ray contrast between both of the microphase-separated blocks of the block copolymer film, indicating flow-induced selective gold immobilization on one block. Both in situ GISAXS data and atomic force microscopy of the metal-deposited polymer film prove the 1D coalescence of nanoparticles into continuous nanowires. With additional gold nanoparticle upload by the continuous flow-stream method, the selectivity of the nanoparticle deposition diminishes as a result of the formation of a pseudo uniform gold layer. Consequently, this flow-stream deposition technique introduces an easy alternative method to the vapor deposition technique for surface gold nanopatterning.