Bipolar charge distribution of dry powder aerosols using an optical technique

Electrostatic properties of dry powder aerosols has emerged as a crucial element in various research areas ranging from medical applications, environmental pollution, volcanic plumes, stratospheric geo-engineering and space exploration. Characterization of size and bipolar charge distributions of dry particles with an instrument capable of in-situ and non-contact measurements is often necessary for the above mentioned applications. This paper reports an experimental study carried out employing the modified Phase Doppler Anemometry (PDA) system to evaluate the bipolar charge distributions of dry powders. The PDA technique was used to track the motion of charged particles in the presence of an DC electric field. The magnitude as well as the polarity of the particle charge was obtained by solving the equation of particle motion combined with the simultaneous measurement of its size and velocity. An innovative signal processing model was proposed to analyse the Doppler bust signals generated by the PDA system in order to trace the changes in the instantaneous frequency and improve the particle validation criteria. The material selected for the experimental work was lactose which is widely used in pharmaceutical industry especially as a Dry Powder Inhaler excipient. The feasibility of the PDA system in determining correctly solid non-spherical particles was investigated in conjunction with the measurements obtained using Sympatec Helos and Malvern Mastersizer optical systems. This work has the potential to further enhance the understanding of fundamental physical inter-particle mechanisms involved in acquisition of electrostatic charge, retention and neutralization; which will help pharmaceutical industry to develop more efficient treatments for various health conditions and better drug delivery devices.