AdvisorsThoroddsen, Sigurdur T
KAUST DepartmentPhysical Sciences and Engineering (PSE) Division
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AbstractGranulation, the process of formation of granules from a combination of base powders and binder liquids, has been a subject of research for almost 50 years, studied extensively for its vast applications, primarily to the pharmaceutical industry sector. The principal aim of granulation is to form granules comprised of the active pharmaceutical ingredients (API’s), which have more desirable handling and flowability properties than raw powders. It is also essential to ensure an even distribution of active ingredients within a tablet with the goal of achieving time‐controlled release of drugs. Due to the product‐specific nature of the industry, however, data is largely empirical . For example, the raw powders used can vary in size by two orders of magnitude with narrow or broad size distributions. The physical properties of the binder liquids can also vary significantly depending on the powder properties and required granule size. Some significant progress has been made to better our understanding of the overall granulation process  and it is widely accepted that the initial nucleation / wetting stage, when the binder liquid first wets the powders, is key to the whole process. As such, many experimental studies have been conducted in attempt to elucidate the physics of this first stage , with two main mechanisms being observed – classified by Ivenson  as the “Traditional description” and the “Modern Approach”. See Figure 1 for a graphical definition of these two mechanisms. Recent studies have focused on the latter approach  and a new, exciting development in this field is the Liquid Marble. This interesting formation occurs when a liquid droplet interacts with a hydrophobic (or superhydrophobic) powder. The droplet can become encased in the powder, which essentially provides a protective “shell” or “jacket” for the liquid inside . The liquid inside is then isolated from contact with other solids or liquids and has some fascinating physical properties, which will be described later on. The main potential use for these liquid marbles appears to be for the formation of novel, hollow granules , which may have desirable properties in specific pharmaceutical applications (e.g. respiratory devices). They have also been shown to be a highly effectively means of water recovery and potentially as micro‐transporters and micro‐reactors . However, many studies in the literature are essentially proof‐of‐concept approaches for applications and a systematic study of the dynamics of the marble formation and the first interactions of the liquid droplet with the powder is lacking. This is the motivation for this research project, where we aim to provide such information from an experimental study of drop impact onto hydrophobic powders with the use of high‐speed imaging.