Abstract

Drops are often used to produce particles of a defined size, shape, and composition. For example, pharmaceutical and food industries often employ airborne drops to produce particles through spray drying. In this case, spray-dried particles are usually spherical and their size scales with that of the drops. Drops can also be employed to tune the structure of these particles, which influences their properties. This can be achieved by controlling the evaporation rate of the solvent. If drops are made sufficiently small, such that they have a high surface-to-volume ratio and therefore dry very quickly, they can even produce amorphous particles from materials that have a high propensity to crystallize. In the first part of this talk, I will present a microfluidic spray-dryer that produces µm-sized drops, which are surrounded by fast-flowing air. These drops dry so quickly that crystallization of solutes, contained in the drops, is kinetically suppressed. Hence, the resulting spray-dried particles are amorphous even in the absence of any crystallization inhibiting additives. This is particularly beneficial for the formulation of hydrophobic substances, such as many newly developed drugs, whose bioavailability is limited by their slow dissolution rates and low solubility. A possibility to produce much larger particles of controlled sizes and compositions is the use of emulsion drops as templates. These drops can be converted into particles that are dispersed in a liquid by solidifying their content. The liquid-liquid interfaces of these emulsion drops offer possibilities to tune the surface chemistry of particles that are produced from them. In the second part of the talk, I will show how we use these liquid-liquid interfaces to tune the surface chemistry of particles and capsules, thereby making them responsive to external stimuli or making them mechanically very stable. However, these particles and capsules are only truly useful, if they can be produced in sufficient quantities. In the last part of my talk, I will present a parallelized device that produces monodisperse drops at sufficiently high throughputs to use them as building blocks for macroscopic materials whose structure can be tuned with the size and arrangement of drops.