In-situ imaging to investigate the concentration profile and morphology formation of single droplets during convective drying

• Applicant: Professorin Dr.-Ing. Petra Först
• Subject Area: Mechanical Process Engineering
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 538902239

Spray drying is a widespread drying technology in food and pharmaceutical production due to its fast and gentle drying characteristics. In recent years, research aims at using spray drying as tool to produce particles with defined morphology. The final particle morphology depends both on the composition of the solution to be dried, the particle size and the drying conditions. Particle morphology influence the spray drying process and the final powder properties. Droplet-to-particle transition is usually investigated with single droplet drying methods in defined setups. The decisive parameter for the formation of the particle morphology is the local crust formation and the mechanical properties of the crust that depend on the local concentration. Therefore, the knowledge of crust formation during drying is key for the understanding of particle morphology, as local concentration, demixing phenomena and local instabilities influence particle morphology. Therefore, it is essential to measure the local concentration during droplet drying. So far, no technologies exist to measure the concentration profile in a 3D droplet during drying with a sufficient resolution. In this project it is planned to measure the concentration profile and the formation of the crust with a 2D setup, where the droplet is dried in a confined geometry between two hydrophopic glass slides. The size of the droplet is measured by light microscopy whereas the concentration profile is measured with fluorescence microscopy. Next to binary systems, also ternary systems will be studied. At first, the 2D method will be validated by means of water drying in a temperature range between 20 and 120 °C and compared to theoretical values. In the second work package, the method will be applied to the drying of binary and ternary solutions with molecular and colloidal dissolved components. The crust formation will be studied in a broad temperature and concentration range. In the third work package, an image analysis algorithm will be developed to both quantify the droplet area for drying kinetics as well as the fluorescence intensity for local concentration. The last work package is dedicaded to the transfer of the results from the 2D setup to 3D. Here, CSLM and time resolved µ-Computertomography will be employed to in situ measure the crust formation during single droplet drying. This knowledge is key for the prediction of morphology formation.

• DFG Programme: Research Grants