Fluctuating Hydrodynamics for Liquid Spreading over Heterogeneous Surfaces

Lead Research Organisation: University of Warwick
Department Name: Physics

Abstract

Description: Understanding the spreading of liquids over heterogeneous solid surfaces is the key to numerous emerging technologies (e.g. capabilities to 3D print metallic structures), biological systems (retention of liquids by plant leaves) and even forensic science (analysis of blood splatters). The most remarkable feature of the wetting process is its strong multiscale nature, which ensures that nanoscale and microscale effects have a strong macroscopic influence on systems of interest. It is the fascinating multiscale nature of wetting that makes it such a theoretically challenging topic, as one must connect the microscale with the macroscale in a computationally tractable manner.

Aims: To develop a stochastic computational model capable of capturing the nanoscale fluctuations that drive macroscopic wetting flows over heterogeneous surfaces and validate this against molecular dynamics simulations, in collaboration with our partners in Mons.

Novelty & Methodology: Thermal fluctuations, which allow molecules to 'hop' over potential barriers in the solid, have long been considered as a potential driving mechanism for dynamic wetting flows. Owing to the small spatial and temporal scales on which this physics acts, molecular dynamics (MD) simulations are able to capture the local dynamics, and can be used as a benchmark. However, attempts to connect this mechanism to macroscopic dynamics, and thus experiments, have remained elusive due to the computational intractability of MD above the nanoscale. Furthermore, there is debate over the dominant forces for 'real' (i.e. heterogeneous) surfaces, where hopping over defects in the surface structure may be more important than the molecular jumps. These open problems can only be addressed by the development of a computational model based on the theory of fluctuating hydrodynamics, i.e. stochastic partial differential equation (SPDEs), which would give new, much-needed capabilities for understanding this system.

Alignment:

i) EPSRC Programme Grant 'Nano-Engineered Flow Technologies: Simulation for Design across Scale and Phase' (EP/N016602/1, PI: Lockerby)
ii) EPSRC CDT HetSys Core Training Objectives:
a) Interdisciplinarity - will be essential as the project cuts across physics (development of models), computational engineering and applied mathematics (e.g. SPDEs).
b) Robust Software Engineering - is required to develop both MD and SPDE computational models that will have lifetime and legacy beyond that of the project.
c) Uncertainty - will become important when attempting to quantify the influence of the random surface structure on macroscopic flow; a new direction of research in this field.

Collaborations:
i) The primary partner will be the Laboratory of Surface & Interfacial Physics in Mons (one of HetSys's partners) who have unrivalled expertise in the MD of wetting processes.
ii) This research should lead to collaborations with Professor Bruno Andreotti's group at Universite Paris-Diderot, where great experimental and theoretical progress has been achieved in the wetting of heterogeneous substrates, and the Centre for Smart Interfaces in Darmstadt.
iii) Any progress in understanding dynamic wetting could be translated to industrial partners who we have an existing relationship with, such as Bell Labs (HetSys partner), Schlumberger and Akzo Nobel.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/S022848/1 01/04/2019 30/09/2027
2236750 Studentship EP/S022848/1 30/09/2019 30/09/2023 Jingbang Liu