The behaviour of polymer colloids in freshwater flow environment

The monitoring of the presence of microplastics in the environment (water, soil, organisms) has gained considerable traction, with a plethora of excellent initiatives. A recent example is that Californian state water resources control board has approved procedures for testing drinking water. The presence of plastic particles can enter the food chain for all living species, and potentially have a negative impact.

In this project we will look at particles in the diameter range of 20 nm - 5 micrometer, so considerably smaller than the 5 mm upper threshold, in other words a focus on the sub-micron range, plastic nanoparticles. In nature these exist in the form of a natural polymer latex (rubber trees, dandelions). Manmade polymer nanoparticles, in the form of polymer dispersions are produced in vast quantities since the 1930s for coatings/adhesives, paper production, medical diagnostic tests, to name but a few. These are often too small to be tracked with brightfield light microscopy.

We aim to fabricate a collection of model polymer dispersions in which the particles have varied characteristics in size, shape, molecular weight and chemical composition, and colloidal stability. A secondary focus is to make particles that will not degrade easily, and particles that are compostable/hydrolysable. For this we will use the latest polymer dispersion production techniques, such as (mini-) emulsion polymerization, and catastrophic phase inversion emulsification to prepare artificial latexes.

We then will study the underlying physical mechanisms that govern the particles' motility behavior (flow hydrodynamics, dispersion and diffusion), residence and accumulation behavior (adhesion, crowding, coagulation, film formation, disintegration/decomposition) in model aquatic systems including stagnant pond, river, and wetland.

This project, for the first time, will provide a better understanding of how such small particles will behave across aquatic domains, where they will reside, and how they potentially can be degraded into harmless substituents.

The new insights offered by this project will enable understanding the dynamics of micro- and nanoplastics transport and fate in challenging turbulent flow systems. Hence, this project will provide a step change in environmental protection and integrated catchment management by understanding and quantifying the transport and fate of plastic nanoparticles.

The project will combine heterogeneous polymer chemistry, colloid science, and fluid dynamics.

Polymer nanoplastics will be prepared by heterogeneous radical polymerization techniques, where (mini-) emulsion polymerization is combined with reversible deactivation radical polymerization developments, to tune molar mass distribution, chemical composition, colloidal stability, and particle shape and architecture.

Tracking methods of the particles in water and model soils will be developed through combination of darkfield and fluorescence microscopy (Cyclops sensors), Raman spectroscopy, and off-line analysis methods, such as hydrodynamic fractionation, and elemental analysis techniques (atomic absorption, XRF, ICP-MS). Model development of particle motility behavior across different aquatic flow domains will be studied using open-source computational fluid dynamic modelling packages (OpenFOAM). The algorithms which will be developed within this project will be coupled with existing multi-phase flow models in order to simulate pollutant transport under various hydrologic conditions. Particle degradation will be studied by kinetic modelling (ODEs and Monte Carlo approaches).