| Summary: | Fluids containing nano-sized structures are being increasingly employed in modern technologies, ranging from lubrication fluids to drug delivery. However, despite their numerous applications, our fundamental understanding of the surface forces mediated by nanofluids is still relatively limited. In particular, due to their nanosize and related characteristics, the applicability of established surface force theories, such as the DLVO theory, remain unclear. With several tunable parameters such as the size, shape and surface chemistry, dendritic macromolecules (or dendrimers) offer a unique model nanofluid for investigating the effect of nanostructures on classic colloidal phenomena. Accordingly small-angle X-ray scattering (SAXS) and X-ray reflectivity (XRR) measurements have been performed to study the interactions between negatively charged poly(amidoamine) (PAMAM) dendrimers in the bulk and at the mica-water interface. In particular, how their interactions can be influenced by the presence of cationic surfactant dodecyl trimethyl ammonium bromide (DTAB) have been studied. Using a version of the surface force apparatus (SF A), the surface forces mediated by these dendrimer-surfactant mixtures under nano-confinement and shear have then also been directly measured. In further work the effect of the surface chemistry on the interactions in dendrimer nanofluids has been studied in two systems: i) as a comparison to the above system, the interactions between positively charged dendrimers with an anionic surfactant have been characterised both in the bulk and at the mica interface using SAXS and XRR, and ii) the interactions between three different surface chemistries of P AMAM dendrimers in an ionic surfactant mesophase have investigated using SAXS. Overall, the results presented demonstrate the tunability of inter-dendrimer interactions via their intramolecular architecture, which in turn may be harnessed to control and tailor the physical properties of dendrimer nanofluids. Such interactions bear fundamental importance to the application of dendrimers, as well as contribute to a better understanding of the surface forces mediated nanofluids.
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