From Microdroplets to Microcrystals: Tunable Caffeine Particles by Spray Flash Evaporation

Abstract

In this work, tunable caffeine crystals are formulated through a promising aerosol-based technology called spray flash evaporation (SFE). In this process, the vacuum atomization of a superheated and pressurized solution allows for the continuous flow and mass production of organic particles with tunable sizes and morphologies depending on the process parameters. Despite its versatility, the widespread application of SFE technology is still mainly hindered by the lack of systematic experimental works showing the correlation among the aerosol properties, such as the droplet size and solvent evaporation rate, the filtering method, and the final product morphology. Here, we characterize pure solvent aerosols, ethanol and dichloromethane, by in situ phase Doppler particle analysis and apply these solvents to grow caffeine rods with lengths ranging from submicron to 30 μm and different agglomeration states depending on the specific process and collection conditions. The nucleation and growth mechanisms are derived from accurate investigations on scanning electron micrographs. Results show the high potential and versatility of SFE for processing micron and submicron organic particles for many applications in biomaterials and pharmaceutics.

Synthesis of submicron‐sized silver azide by multi‐nozzle spray flash synthesis**

“…This means that the growth of AgN 3 particles happens by surface aggregation of elementary crystallites. The continuous washing of the filter by the condensation of water vapour, leads to propose two hypotheses to explain the increase in size of the particles: (i) The reaction of silver nitrate and sodium azide coming from the droplets which did not collide in the atomization chamber, that is activated by the condensation of water vapour on the filter; (ii) The superficial dissolution/recrystallization of pre‐existing AgN 3 crystallites trapped in the filter, as this was previously observed with caffeine crystals processed by Spray Flash Evaporation [23]. Further experiments were also performed with solutions of AgNO 3 and NaN 3 ten times more concentrated (7.5×10 −2 mol.…”