Effect of film formers and drying methodology on liquid marble shape, structure and stability
thesisposted on 02.03.2017 by Yue, Sally Sang
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This thesis presents a study of liquid marbles and an overview of their applications. It covers the fundamental properties of liquid marbles in cosmetic and hair styling products; the effect of film former on the longevity and drying structure of liquid marbles; and investigates how different drying methodologies influence marble shape, structure and overall stability. Liquid marbles are made from droplets of fluid coated by a hydrophobic powder. Their distinctive properties such as low friction rolling, gas permeability, isolation from external environment, and the potential to contain up to 98% by weight liquid have made them of interest to researchers. Commercially, cosmetic companies have also found use for these remarkable particles in foundation and hair care products. Despite the many potential applications, our understanding of liquid marbles is limited. To date the longevity and shelf life of commercial products containing liquid marbles cannot be replicated in the laboratory. In conjunction, the lifetime and stability of liquid marble produced in the laboratory vary significantly between research groups even when similar liquid and powder combinations are used. These discrepancies underpin the motivations behind the need to explore the factors which contribute to the long term stability of liquid marbles. Commercial products containing liquid marbles were analysed for their formulation, particle size, moisture content and general appearance to gain clues into their significantly longer shelf-life. Based on the results reported in Chapter 4, film former (VP/VA copolymer) was added to a basic water and aerosil formulation to identify the effect of film former on liquid marble stability and longevity. The presence of film former significantly increased drying time and an optimal concentration of 2% (w/v) VP/VA copolymer is ideal, after which the drying time becomes independent of film former concentration and in some cases destabilises the liquid marble and decreases drying time. A unique drying pattern where a ‘rebound’ phenomenon was identified and a potential drying hypothesis is established in Chapter 5. The effect of other drying methodologies on liquid marble longevity, shape and structure were investigated in Chapter 6. Variations of temperature on the morphology of drying liquid marble were investigated for oven drying. Single droplet drying and freeze drying of liquid marbles and the resultant dried marbles were also investigated to further understand how different drying methods impact the shape and structure of liquid marbles. The ‘rebound’ phenomenon observed in Chapter 5 became less common as temperature increased. Single droplet drying showed little difference between drying of a pure water droplet and a liquid marble. In Chapter 6, a novel method of freeze drying a liquid marble to produce a resultant spherical structure consisting of a shell and porous center was produced. The results of this research will enhance the understanding of some of the fundamental aspects of liquid marbles and the factors which contribute to their stability and structure in the long term. In conjunction, it will provide some insight into how different drying methods affect the final size and shape of the final product.