Volatile propellant droplet evaporation measurements in metered dose inhaler sprays

Abstract

Many aerosol products rely on the rapid vaporization of volatile propellants to produce a fine spray. In the simplest case, these are binary mixtures of propellant and a delivered product which undergo a flash-evaporation process leaving only the less volatile product in the resultant droplet. In more complex applications, such as pressurized metered-dose inhalers, the non-propellant component may contain dissolved or suspended drug which precipitates or dries to form a matured particle. The size and morphology of the particles depend strongly on the time-history of the droplet as the propellant evaporates. However, measuring the dynamic evaporation processes that occur in dense sprays containing millions of droplets is challenging. In this paper, we demonstrate a novel application of Ultra Small Angle X-ray Scattering to measure the bulk composition of volatile HFC134a–ethanol sprays and compare the obtained results with simple evaporation models in a dry nitrogen environment. The data reveal that diffusion-limiting processes inside the droplet are equally important as external convection and mixing-limited factors in determining evaporative timescales.

Copyright © 2023 American Association for Aerosol Research

EDITOR:

• Jonathan P. Reid

Acknowledgments

Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. We gratefully acknowledge the computing resources provided on Bebop, a high-performance computing cluster operated by the Laboratory Computing Resource Center at Argonne National Laboratory. The authors also acknowledge the use of the National Computational Infrastructure (NCI), which is supported by the Australian Government. The author also wishes to acknowledge David Lewis (OZ-UK Limited), Matt Frith, Katarzyna Matusik, and Chris Powell (Argonne National Laboratory) for their support.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Australian Research Council under Grants LP190100938 and DP200102016, and by Kindeva Drug Delivery.