Atomic force microscopy (AFM) has been used to determine the interaction forces between a spherical silica probe and immobilised colloidal droplets of polydimethylsiloxane (PDMS) in aqueous solution. Between pH 4.5 and 9.5 where PDMS droplets and the silica probe are both negatively charged, a repulsive force is evident that increases less rapidly on surface approach than expected for electrical double layer interaction of rigid particles. The departure from hard-sphere behaviour, i.e. the deformation, has been determined and by varying the extent of internal cross-linking within the PDMS droplets, the influence of bulk rheology and interfacial properties on droplet deformation and nano-rheology has been isolated. For highly cross-linked droplets, the extent of deformation is controlled by the bulk rheology rather than the droplet's interfacial properties. Upon retraction of the surfaces, force curve hysteresis is observed and is due to the viscoelastic response of the PDMS. The extent of hysteresis is dependent on the rate of approach/retraction anf the loading force, and has been theretically fitted to obtain nano-rheological paraameters, which describe the droplet relaxation process. For liquid-like droplets, with a low level of cross-linking, no force curve hysteresis is observed and the elastic deformation may be described by a single spring constant. The spring constant is proportional to the surface tension (as controlled by surfactant adsortion) and the reciprocal of the droplet radius, i.e. deformation is controlled by the Laplace pressure. Furthermore, droplet deformation is altered by the presence of adsorbed nano-particles. These colloid probe AFM studies offer due insight into the deformation and interaction of emulsion droplets and have implications when considering the stability, adhesion and processing of emulsions. / Thesis (PhD)--University of South Australia, 2003.
| Identifer | oai:union.ndltd.org:ADTP/281297 |
| Creators | Gillies, Graeme |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | copyright under review |
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