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Title: The role of surface properties on the electrostatic behaviour of powders
Author: Biegaj, Karolina Weronika
ISNI:       0000 0004 6496 9953
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2018
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Electrostatic charging is an important, yet underappreciated, phenomenon associated with handling and processing of powders. The ambiguous character of the process of charge generation as well as the complex nature of solid surfaces make powder electrostatics unclear and hard to comprehend or explain. The work carried out in this thesis aimed to provide a detailed investigation on the impact of surface characteristics of powders on their electrostatic behaviour. Here, the experimental design was intended to evaluate the effect of a single parameter at a time, independently of other variables, in order to establish direct correlations between the properties studied. This approach aims to understand why powders exhibit different electrostatic behaviour and how this behaviour changes upon altering material properties. In this work, the influence of surface chemistry on the electrostatic performance has been determined explicitly for the first time for a number of surface chemical groups. The material’s electrostatic behaviour was linked to the surface hydrophobicity resulting from different groups being exposed. Furthermore, the impact of changing humidity on the charge accumulation and dissipation was investigated and concluded to be surface chemistry dependant. This concept was related to the crystal habit and surface energy for mannitol crystals showing how changes in the crystal shape can impact the powder electrostatics. The effect of the material’s internal structure was investigated for amorphous and crystalline lactose and demonstrated that disordered structures significantly decrease charge dissipation kinetics and lead to greater charge being accumulated. The effect of water present in the amorphous/ crystalline phases was also anticipated and determined to be a secondary factor guiding the behaviour. In this work, the importance of surface coating occurring for the binary systems is emphasised and the electrostatic behaviour of binary mixture is studied in detail. Finally, the impact of mixture homogeneity on the electrostatic response was evaluated.
Supervisor: Heng, Jerry Sponsor: Engineering and Physical Sciences Research Council ; Pfizer (Firm)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral