Understanding and optimisation of non-conventional emulsions

Thompson, Michael Andrew

Abstract

This thesis is concerned with understanding the effect of diols on emulsion properties and to use knowledge gained to optimise emulsions containing them. The project was sponsored by GlaxoSmithKline, a world leading pharmaceutical company, whose interest is in using the knowledge to help in research and development of new products and optimising existing products during manufacture. For this reason pharmaceutical ingredients were used throughout unless additional knowledge could be gained from using non-pharmaceutical ingredients. Systems studied included emulsions with water, diols and paraffin liquid stabilised by surfactants and particles using various techniques from microscopy, conductivity, surface tension, rheology, light scattering, stability analysis, differential scanning calorimetry and nuclear magnetic resonance.

The thesis will examine three aspects of emulsion non-conventionality; addition of diol to both surfactant and particle-stabilised emulsions and the effect of crystallisation in diol containing emulsions stabilised solely by surfactant. Surfactant and particle-stabilised systems will be discussed in terms of phase inversion where it will be shown that inversion of emulsions can be controlled by addition of diol within both systems. For phase inversion in water, diol, paraffin liquid and non-ionic surfactant systems it will be argued that the phase inversion witnessed is due to the change in preferred surfactant monolayer curvature. This will be shown by examining the structurally and isomeric nature of the diols as well as their surface activity. Also considered and compared will be the well established experimental facts that occur in related systems at phase inversion including initial droplet diameter, emulsion stability, temperature variation and surfactant structure change. Results will show that for all traits examined at phase inversion diol addition follows all well known facts regarding a change of preferred surfactant monolayer curvature from negative to positive values.

Emulsions stabilised by particles will be shown to phase invert from w/o to o/w emulsions with the addition of diol and changing particle hydrophobicity at fixed hydrophobicity and fixed diol content respectively. This will be contributed to the surface energies of each system and therefore a decrease in contact angle θ with increasing diol addition and changing hydrophobicity. Included will be a comparison between calculated and measured phase inversion of a number of diol containing series which shows good correlation. Systematic studies will also include the effect of this phase inversion on droplet diameter, stability and emulsion type. These will be explained in terms of existing theory regarding particle stabilised emulsions. Diol effect on the in situ contact angle will also be shown in water/diol–air mixtures. Investigations will include the immersion times of fumed silica powders of varying wettability in water-propane-1,2-diol mixtures and from theory the contact angles of particles at the air-polar phase interface will be determined. The materials formed upon aerating these samples will also be described in terms of the wettability of the particles in situ. Again the result will indicate that diol increase the inherent hydrophilicity of the system and therefore change the materials formed upon aeration.

The final chapter of the thesis will discuss the effects of crystallisation in emulsions containing diol stabilised solely by surfactant. Crystallisation with surfactant stabilised systems will be discussed in terms of changing temperature and varying droplet diameter of emulsions. It will be shown that droplet diameter has an effect on the crystallisation of dispersed oil droplets and linked to stability. Systemic investigations using differential scanning calorimetry, rheology and nuclear magnetic resonance will show the crystallisation effect of a model system and attempts to link such findings to stability and the crystallisation mechanism. Microscopy of an additional model system containing high amounts of diol will show the ability of such systems to produce ‘dumbbell’ droplets when the systems temperature is decreased. Additional discussion on the formation of dumbbells and the effect on stability in diol containing emulsions will also be considered.

Citation

Thompson, M. A. (2012). Understanding and optimisation of non-conventional emulsions. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4213500

• Thesis Type: Thesis
• Deposit Date: Dec 4, 2012
• Publicly Available Date: Feb 22, 2023
• Keywords: Chemistry
• Public URL: https://hull-repository.worktribe.com/output/4213500
• Additional Information: Department of Chemistry, The University of Hull
• Award Date: Aug 1, 2012