(162b) Scalable Meniscus-Directed Fabrication of Assemblies from Microspheres and Nanoparticles on Hydrophobic and Superhydrophobic Surfaces

The controlled drying of liquid suspension droplets deposited on surfaces or confined in thin menisci is one of the simplest and most efficient ways to assemble particles and shape them in two and three dimensions. The organization of the particles is a result of a complex combination of convective transport and capillary forces at the liquid/air interface. We will demonstrate how the process can be engineered for controlled assembly of self-contained supraparticles in drying sessile suspension droplets on surfaces with intermediate or very high hydrophobicity. The dynamic shape of the liquid surface guiding the particle assembly changes as a function of the contact angle on the substrate, liquid interfacial tension, droplet volume, particle size and volume fraction. Depending on the combination of these parameters, the droplet drying process can result in the formation of particle crystals in the form of disks, hemispheres, spheres, "doughnuts", or ellipsoids. The supraparticle assemblies formed can also be made anisotropic, layered, magnetic or biologically active and in these roles they may find applications in various technologies. The method is very simple, inexpensive and scalable.