Evaporation Kinetics and Dried Agglomerate Particles Morphology of Aqueous Aerosol Droplet Containing Nanoparticles
LUKESH K. MAHATO, Panagiotis Georgiou, Barnaby Miles, Sorrel K. Haughton, Rachael E.H. Miles, Steven P. Armes, Jonathan P. Reid, University of Bristol
Abstract Number: 153
Working Group: Aerosol Physics
Abstract
Understanding the agglomeration of nanoparticles through evaporation-induced assembly is a key process, highly desirable for manufacturers in powder technology, such as those in pharmaceuticals, food products, cosmetics, and fine chemicals. Controlling the dried agglomerate particles can also facilitate understanding of the dried particles' optical and mechanical properties. Typically, morphology is influenced by the drying conditions and the diffusional properties of nanoparticles. In this study, we evaporate aerosol droplets of monodisperse size containing monodisperse, bi-disperse, tri-disperse or polydisperse copolymer nanoparticles of total concentration 2% v/v, at a relative humidity between 0 and 45% and a temperature of 21ºC. We obtained the dried particle using the falling droplet column (FDC) technique. Additionally, we use the electrodynamic balance (EDB) to measure the evaporation rate of the drying colloidal aqueous aerosol droplet. To prepare the sterically stabilized deblock copolymer nanoparticles of desired sizes (30 to 228 nm), we used the polymerization-induced self-assembly (PISA) technique. We observe that as the evaporation rate (K) increases, the degree of buckling increases (i.e. the shape transitions from spherical to donut shapes), consistent with changes in the commonly used Peclet number (Pe) for explaining the dried particle morphology. Moreover, the degree of buckling of dried particles increases with an increase in the nanoparticle initial diffusional coefficient (D) while keeping K constant. D increases as the nanoparticle’s size decreases. We estimate the average diffusion coefficient (Davg) using the weighted harmonic mean diameter of nanoparticles for bi-disperse, tri-disperse, or polydisperse nanoparticles. The harmonic mean diameter varies by varying the relative concentration of smaller to larger nanoparticles. Interestingly, we observed similar morphology of dried particles for a given average diffusional coefficient for monodisperse, bi-disperse, tri-disperse or polydisperse nanoparticles for a given K. Further, we varied the dried particle morphology from spherical to buckled by varying the Davg for a given K.