Controlling the Morphology of Microparticles Formed by Evaporation of Aerosol Droplets Containing Polymer Nanoparticles

SORREL K. HAUGHTON, Panagiotis Georgiou, Lukesh K. Mahato, Steven P. Armes, Jonathan P. Reid, University of Bristol

     Abstract Number: 183
     Working Group: Aerosol Chemistry

Abstract
Final morphology of spray-dried microparticles is an important factor in determining the particle’s chemical and physical properties, which in turn is important for applications such as spray-dried pharmaceuticals, cosmetics and food products. The morphology of the dried particle governs its surface area and density, which in turn affects the suitability for application; for example, low density particles are useful for inhaled drug formulations. It has previously been shown that the drying kinetics and the composition of the feed solution of the evaporating droplets affects the dried particle’s morphology. Here, aqueous, nanoparticle-laden droplets, prepared via polymerization-induced self-assembly, are used to investigate the effect of polymer glass transition temperature on the dried particle morphology. Four aqueous samples of the monodisperse nanoparticles were tested, with hydrodynamic diameters of 72.8 to 86.2 nm and glass transition temperatures of -30.4 to 93.3 °C, to allow a comprehensive investigation of the effect of glass transition temperature on the evaporation kinetics and dried particle morphology of the aerosol droplets (28 – 36 μm radii). To study levitated single droplets, a comparative kinetics electrodynamic balance was used to record the evaporation profiles of the droplets at relative humidities (RH) of 0 to 55%. A falling droplet column paired with scanning electron microscopy was used to dry and collect the droplets under the same external conditions and visualize how the evaporation kinetics and glass transition temperature of the nanoparticles impacted their final morphology. Decreasing the RH led to an increased evaporation rate and increased buckling in the final nanoparticles. At dilute concentrations the nanoparticles’ properties had no impact on the evaporation kinetics, but decreasing the glass transition temperature of the nanoparticles did lead to softer dried microparticles which exhibited a greater degree of buckling. These results signify a move towards increased control over a microparticle’s final morphology.