Mechanochemistry at the Molecular Scale

About the Project

The aim of this project is to combine nanomechanical methods with modelling (i) to develop quantitative, predictive models for the behaviour of molecules in sliding contacts, and (ii) to understand how mechanical pressure can be used to change chemical reaction pathways.

(i) Billions of people wash their clothes and their hair regularly; thus, improvements in the sustainability of haircare and laundry products have the potential to yield substantial global environmental benefits. Conditioners are an important component of these products, improving the feel and appearance of fibres, for example reducing friction as they slide against each other. Established surface-active agents deliver outstanding performance, but there are concerns about their environmental impact. Manufacturers are now anxious to replace them with sustainable alternatives. However, the mechanisms by which established conditioners improve surface properties are poorly understood. These mechanisms must be understood before sustainable replacements can be developed. Our aim is to solve this challenge. Using the atomic force microscope (AFM), you will investigate the organisation of surface-active agents at the molecular scale, and measure their mechanical, adhesive and frictional properties. By combining these data with classical molecular dynamics simulations and a molecular-scale approach to the thermodynamics of molecular interactions at interfaces, you will develop a comprehensive predictive model describing the strength of binding, conformations and behaviour of surface-active agents at interfaces that will enable the de novo design of new, sustainable surface-active agents.

(ii) Recent years have seen an explosion of interest in mechanochemistry, driven by hopes that it will facilitate a transition to green manufacturing of chemicals, through the development of mechanical methods to drive solventless chemical processes. Recently it has become clear that mechanical pressure is not simply a means to put energy into reaction systems; it can change the chemical reaction pathway too. Our aim is to develop an integrated approach to understanding how mechanical pressure can modify chemical reactivity. Using an AFM probe you will apply pressure to films of molecules in a highly controlled fashion. These films will be molecular monolayers formed at the surface of the AFM probe and on a counter-surface. By combining this with spectroscopic characterisation and quantum chemical modelling, you will explore the dependence of reactivity on pressure. Your goal will be to lay the foundations for an enhanced understanding of how to leverage the vast potential of mechanochemistry for green manufacturing through the development of a unified approach to the characterisation of molecular behaviour in sliding contacts, integrating nanomechanical methods with theory.

Funding Notes

This project is for Self-funded students or students with external funding.

References

https://sites.google.com/sheffield.ac.uk/nanoscalechemistrygroup/home
"Transcending Lifshitz Theory: Reliable Prediction of Adhesion Forces between Hydrocarbon Surfaces in Condensed Phases using Molecular Contact Thermodynamics", O. Siles-Brugge, C. A. Hunter and G. J. Leggett, Langmuir 2024, 40, 13753–13762.
"Tribochemical nanolithography: selective mechanochemical removal of photocleavable nitrophenyl protecting groups with 23 nm resolution at speeds of up to 1 mm s−1", R. E. Ducker, O. Siles-Brugge, A. J. H. M. Meijer and G. J. Leggett, Chem. Sci., 2023, 14, 1752.