In this talk I will discuss our recent work on two problems. The first problem concerns with capillary rise between rough structures, a fundamental wetting phenomenon that is functionalised in biological organisms and prevalent in geological or man-made materials. Predicting the liquid rise height is more complex than currently considered in the literature because it is necessary to couple two wetting phenomena: capillary rise and hemiwicking. Experiments, simulations and analytic theory demonstrate how this coupling challenges our conventional understanding and intuitions of wetting and roughness. For example, the critical contact angle for hemiwicking becomes separation-dependent so that hemiwicking can vanish for even highly wetting liquids. The rise heights for perfectly wetting liquids can also be different in smooth and rough systems. The second problem concerns with droplets (or condensates) formed via a liquid-liquid phase separation process in biological cells. Despite the widespread importance of surface tension for the interactions between these droplets and other cellular components, there is currently no reliable technique for their measurement in live cells. To address this, we develop a high-throughput flicker spectroscopy technique. Applying it to a class of cellular droplets known as stress granules, we find their interface fluctuations cannot be described by surface tension alone. It is necessary to consider elastic bending deformation and a non-spherical base shape, suggesting that stress granules are viscoelastic droplets with a structured interface, rather than simple Newtonian liquids. Moreover, given the broad distributions of surface tension and bending rigidity observed, different types of stress granules can only be differentiated via large-scale surveys, which was not possible previously and our technique now enables.
Further Information
Prof Halim Kusumaatmaja is currently a Professor of Physics at Durham University and he also holds an EPSRC Fellowship in Engineering. Prof Kusumaatmaja graduated with a Master of Physics from the University of Leicester in 2004 and a PhD in Physics from the University of Oxford in 2008. He worked as a Postdoctoral Research Associate at the Max Planck Institute of Colloids and Interfaces (2008-2011) and at the University of Cambridge (2011-2013), before moving to Durham University and rising through the ranks from Assistant Professor (2013-2017) to Associate Professor (2017-2020) and Full Professor (2020-now). Prof Kusumaatmaja leads an interdisciplinary research group in the area of Soft Matter and Biophysics. Current research interests include wetting and interfacial phenomena, bio-inspired materials, liquid-liquid phase separation in biology, multistable elastic structures, colloidal and molecular self-assembly, and high performance computing.