As an inherently unstable dispersed system, liquid foam requires surfactant for effective formation and stabilisation. However, the performance of conventional hydrocarbon-based small-molecule urfactants has now reached its design limit. Amphiphilic copolymers have emerged as promising alternatives, offering both superior foamability and a broader range of tuneable structural parameters. Nevertheless, their fundamental macromolecular nature poses significant challenges for their rigorous characterisation and the underlying structure-performance relationships remain unclear.
Copolymer compositions with optimal surface activity were identified through Design of Experiment (DoE) analysis of published data. In particular, statistical copolymers containing the 3,5,5-trimethylhexyl substituent as the hydrophobic unit and oligo(ethylene glycol) as the hydrophilic segment exhibited exceptional foamability. A series of statistical copolymers with various backbone structures, molecular weights, and comonomer ratios were synthesised via free radical copolymerisation to explore performance optimisation. Foam studies revealed that the (meth)acrylic backbone structure significantly affected foamability. Small-angle X-ray scattering (SAXS) was employed to characterise copolymer micelles in aqueous solution, revealing a strong correlation between comonomer composition, copolymer architecture, and foaming activity. Copolymers exhibiting superior foamability formed loosely packed micelles, which facilitates rapid surface adsorption. Synthesis of the analogous vinyl ether-based copolymers was also attempted for comparison with the best-performing acrylic statistical copolymers.
Furthermore, eight tertiary amine-based dihydrophilic statistical copolymers were prepared to investigate the influence of polyelectrolyte charge on chain flexibility. The conformations of both charged and uncharged chains were analysed using SAXS combined with the polymer reference interaction site model (PRISM) to evaluate the role of electrostatic interactions in modulating chain stiffness. The degree of protonation significantly influences the chain conformation and hence governs the aqueous solution behaviour.
In summary, this thesis provides new insights regarding the design of interfacially-active copolymer surfactants. In particular, tailoring the copolymer structure leads to optimal interfacial stabilisation efficiency.
