(18f) Modeling and in-Situ Observation of Mesomorphological Structure Formation of Colloids in Drying Droplets

Colloidal suspensions are ideal model systems to study crystallization, gelation, and porosity development and to create novel materials structured at the mesoscale. When colloidal particles are confined to micron-sized droplets, novel phenomena, such as segregation, shell formation, and shell buckling are prevalent. Reproducing mesomorphological structure formation in drying droplets is challenging, both for modeling and computer simulation due to the requirement to model across multiple length scales from particle interactions via confinement geometries to fluid-particle hydrodynamic effects and for experiment because it requires precise thermodynamic control and in-situ observation for complete resolution of the underlying processes. This presentation reports joint computational-experimental advances in understanding colloidal self-assembly during drying of colloids in water-in-old droplets created by microfluidics. We fully resolve the individual stages of structure formation in supraparticles from shell formation near the confinement interface, to crystal nucleation and growth, and the consolidation of defects. In droplets with monodisperse colloids and under rapid evaporation, magic number colloidal clusters are observed, as can be confirmed by high-precision free-energy calculations [1]. Structure formation is affected by the interplay of thermodynamic and kinetic effects [2]. We demonstrate supraparticle applications for structural color in form of photonic balls [3]. The curved surface of the droplet has pronounced influence on both kinetics and thermodynamics of the resulting mesomorphologies. Our findings have importance for slow colloidal crystallization but can also provide insights into related processes relevant for rapid consolidation during spray drying for the synthesis of nanomaterials.

[1] J. Wang, C.F. Mbah, T. Przybilla, B. Apeleo Zubiri, E. Spiecker, M. Engel, N. Vogel, Nat. Commun. 2018, 9, 5259.
[2] C.F. Mbah, J. Wang, S. Englisch, P. Bommineni, N.R. Varela-Rosales, E. Spiecker, N. Vogel, M. Engel, Nat. Commun. 2023, 14, 5299.
[3] J. Wang, U. Sultan, E.S.A. Görlitzer, C.F. Mbah, M. Engel, N. Vogel, Adv. Funct. Mater. 2020, 30, 1907730.