Research Group of Molecular and Mesoscopic Modelling

There is compelling experimental evidence that modification of solid surfaces can dramatically alter the structure and phase behaviour of the surrounding fluid. It is well established that geometrical or chemical modification of solid surfaces can induce entirely new types of phase transitions and critical phenomena that are related to, but distinct from, wetting at planar (and ideally smooth) surfaces. 

Using methods of statistical mechanics, such as density functional theory, effective Hamiltonian models, and scaling theory, we endeavour to capture the essential physics of these phenomena and understand the subtle interplay between surface geometry, molecular interactions, interfacial fluctuations, and measurable system characteristics such as fluid adsorption. Our main focus is on surfaces whose heterogeneity is characterised by a nanoscopically small length scale. This research area is still in its infancy and continues to reveal a number of counter-intuitive phenomena that cannot be captured using standard theoretical tools. 

Besides its theoretical importance, this research also has close connections with modern nanotechnologies, including the fabrication of functional (e.g., superhydrophobic) materials and the development of devices for controlling flows of extremely small volumes of liquid (e.g., lab-on-achip devices).

Active matter has emerged as a fundamentally new class of many-body systems operating far from equilibrium. On the one hand, active matter systems differ fundamentally from equilibrium fluids (passive systems), as their intrinsic energy consumption and conversion mechanisms give rise to unique collective dynamics, structure formation, and emergent properties that have no counterparts in equilibrium fluids. On the other hand, despite the absence of detailed balance, a conventional chemical potential, or a well-defined surface tension, active-particle systems exhibit phase separation, interfacial structures, and confinement-induced ordering reminiscent of those observed in equilibrium fluids. 

Owing to these unique properties, synthetic active particles have recently attracted considerable practical interest. Their inherent ability to move autonomously, interact with their surroundings, and respond to complex environments offers potential applications in environmental management, biotechnology, and materials engineering. Representative applications include enhanced mixing, microfluidic pumping, and improved biosensing and diagnostics. 

Under confinement, geometry remains an effective control parameter, although particle activity may qualitatively transform and, in some cases, reverse mechanisms established for equilibrium fluids. A particularly striking example is provided by the antagonistic effects of particle activity: whereas repulsive walls promote drying and suppress condensation in equilibrium fluids, active particles tend to accumulate even at purely repulsive boundaries. Such inversions suggest that particle activity can fundamentally alter, and potentially reverse, geometry-controlled ordering mechanisms. We combine complementary modelling approaches, including particle-based simulations and molecularly based dynamical density functional theory, to determine the extent to which geometryinduced interfacial phenomena can be generalised to inherently non-equilibrium systems such as active matter and to identify the precise limits of such generalisations.