Micromechanics of complex interfaces: deformation from quasi-static to sub-millisecond timescales

Macromolecules, surfactants or particles adsorbed at fluid interfaces can self-assemble to form hierarchical structures owing to their lateral interactions. This forms the basis of functional soft materials exhibiting specific catalytic, optical or viscoelastic properties. For the rational design, synthesis and application of such materials, the viscoelastic properties must be tuned such that the hierarchical length-scale and timescale features that give rise to the functionalities are preserved whilst not restricting the very degrees of freedom necessary to confer the features.
Conventional methods are often inadequate to characterise the interfacial rheology of complex interfaces to mimic realistic scenarios, where areal strain rates can typically vary between 10^-3 to 103 s^-1, especially since the bulk effects are not negligible. To address this, I have devised an experimental protocol and analysis framework to develop an acoustically-driven oscillating bubble as a probe to access interfacial deformation rates exceeding 103 s^-1. Further, by observing the dissolution of bubbles with complex interfaces, the quasi-static response of an interfacial layer can be characterised. Thus, utilising these developed techniques, bubbles can be used as interfacial rheological platforms to interrogate the broad-spectrum deformation timescales of complex interfaces ranging from quasi-static to sub-millisecond timescales. Next,
I will briefly describe my recent work in devising a microfluidic interfacial rheometer to characterise interfacial properties for picolitre-volume droplets, which is practical for biological applications where quantities are minute, expensive and precious. Finally, I will give an overview of my ongoing work towards developing genetically-encoded soft materials.