Non-Newtonian Slippery Liquid Infused Porous Surfaces: NN-SLIPS

When a liquid comes into contact with a solid surface, its interface can be pinned by surface texture, giving rise to the ubiquitous phenomenon of the contact angle hysteresis. The presence of Contact Angle Hysteresis is a challenge for liquid manipulation and affects many practical applications ranging from self-cleaning coatings to microfluidics and oil recovery.

Inspired by the Nepenthes pitcher plant, SLIPS (Slippery Liquid-Infused Porous Surfaces) have been recently introduced. Their enhanced liquid mobility relies on the presence of a lubricating fluid between the liquid and solid, reducing the contact to the solid surface, and therefore the driving force required for liquid manipulation. Besides impacting the static friction, lubricating fluids impact liquid motion also through the presence of an additional fluid layer and the creation of a wetting ridge, where viscous dissipation mostly takes place.

The growing interest in SLIPS, lead to applications in areas such as food packaging and biomedical devices, which involve fluids with complex (non-Newtonian) rheological properties. Despite that, to date most studies of SLIPS address mainly equilibrium properties or dynamics of simple (Newtonian) liquids. In contrast, it is expected that the combination of solid texture, shape of liquid interfaces and complex fluid rheology will play a dominant role in liquid motion.

This project aims at exploring the impact of non-Newtonian liquid rheology on the Physics of SLIPS. With the aid of computational fluid dynamics simulations, based on a recently developed ternary lattice Boltzmann method, this project will elucidate the dynamics of complex liquids (both flowing and infusing) on SLIPS and develop new key principles combining the geometry of solid textures and complex liquid properties in the design of new smart materials.

Industrial Pathways

The study of non-Newtonian mechanics is a challenging problem, where theory and computer modelling are developing fast. The impact of non-Newtonian rheology is of paramount importance for controlling flow properties in complex microfluidic environments in multiphase systems. This project will identify a number of key ideas for leading innovation in a vast field of applications. I have identified the physics of food and cell biology research as two specific target industries in the UK landscape.

Physics of food
Food manufacturing is the UK's largest manufacturing sector, and is facing a number of significant challenges: population growth, globalisation, improving food security, minimising environmental impact, and health and nutrition concerns. Improving the manufacturing process is therefore essential to increase efficiencies and optimise food-processing systems, thereby reducing waste. In this proposal I will work with the National Centre of Excellence for Food Engineering at the Sheffield Hallam University, and explore how applications of SLIPS can lead to innovative packaging solutions that prolong shelf-life, reduce waste and decrease environmental impact. The main outcome of this collaboration will be a set of proof-of-principle results that can be developed in a follow up project.

Biological Microfluidics
The application of microfluidic techniques to cell biology is a step change in medicine and drug delivery, for example allowing high-throughput testing of single cells in specific microenvironments and development of novel tissue engineering approaches for more realistic in vitro models. In this context SLIPS coatings of microfluidic devices for cell biology has the potential for exploring new ways of controlling cell motion, as an alternative to chemotaxis and durotaxis. In this project, in collaboration with the UK innovative company Stemnovate, developing microfluidic devices for drug delivery, I will model the rheological properties of biological fluids, and numerically probe specific SLIPS surface geometries and operational conditions for achieving better flow control in microfluidic devices. The results of this collaboration will represent a first set of proof-of-principle simulations which can be developed as a follow-up project targeting the design of specific devices for biological/medical application.

Public Engagement

Non-Newtonian fluids are present in every-day life, and their properties are key for the correct mechanical functionality of natural (i.e. human body) and artificial (i.e. car engines) devices. The awareness of their properties however is not intuitive in young children. As part of this proposal, I and the PDRA will work with NUSTEM, the outreach and research group based at Northumbria University, to develop a classroom workshop which will be based on the research and its wider applications, and linked to the appropriate national curriculum topics. As part of each workshop a 'postcard home' will be produced and handed out to participants. This will allow children and parents to access more information and further activities linked to the research, and the researchers, via the NUSTEM website. In addition, two research and outreach demonstrators will be supported in the summer of Y2 and Y3 (one per year) to work on a research project related to the funding bid, and to deliver outreach with NUSTEM (including the research workshop).


People Development

This project will employ a Post Doctoral Research Associate, whose expertise will add to the UK's academic skills-base in theoretical and computational Soft Matter Physics. The PDRA will also benefit from training in project management, scientific reporting and networking through attendance to conferences, and in public engagement training.