We aim to understand and predict the nature of triboelectric charging by an electronic structure approach.  Molecular visualisation and ab-initio (electron level) studies [1] will be used to investigate molecular surface termination and electronic properties.  Recent research [2, 3] has suggested the link between the electronic structure of a material, in particular the effective work function, and the propensity for triboelectric charging.  The work will address facets of model crystals (to be chosen in consultation with the industrial partners) and surfaces of polymers (polypropylene, PP and polyethylene, PE, which are of interest to several Partners). The foundation has been laid by the current PhD student, James Middleton, supported by the EPSRC Centre for Doctoral Training in Complex Particulate Products and Processes (https://particulates.leeds.ac.uk/) with AZ as the industrial partner.  Specific surface facets from these crystalline materials as well as from amorphous solid-state structures will be generated.  The effects of adsorbed water (due to relative humidity), charge modifying/neutralising chemical agents, such as aluminium stearate (AlSt) and hydrophobic-hydrophilic contacts (known to generate greatest charge transfer [4]) will be modelled and compared with experimental results of WP2 and WP3.  This approach will enable the identification of functional groups accountable for maximum charge transfer. AlSt, having three forms (mono-, di- and tri-stearate) is an ideal chemical for developing a fundamental understanding of its charge transfer, and at the same time of great industrial interest. UoL has offered a PhD studentship, which will be allocated to this aspect of the work, together with other antistatic agents of industrial interest, such as ATMER 190 (Croda).  The electronic structure including the work functions will be determined using the density functional theory (DFT) method. The DFT will be performed using the established CASTEP code [1].  The Materials Studio modelling suite is necessary for the efficient building and visualisation of structures and surfaces.  This modelling suite will aid in the setting up of the DFT calculations and detailed interpretation and visualisation of the electronic structure output information.  Materials Studio also enables us to use molecular mechanics using the Compass III forcefield for computationally efficient and accurate molecular geometry optimisations prior to the more demanding DFT calculations.  An example of calculations is shown in the above Figure (viewed using BIOIVA Materials Studio Visualiser) for an [001] slab of aspirin together with the effective surface work function calculated by the DFT code CASTEP.  Excellent high performance computing (HPC) is provided through the UoL ARC3 and ARC4 supercomputers.

References:

1. Clark, S. J., Segall, M. D., Pickard, C. J., Hasnip, P. J., Probert, M. I. J., Refson, K., & Payne, M. C. (2005). First principles methods using CASTEP. Zeitschrift Fur Kristallographie, 220(5–6), 567–570.
2. Zou, H., Guo, L., Xue, H., Zhang, Y., Shen, X., Liu, X., Wang, P., He, X., Dai, G., Jiang, P., Zheng, H., Zhang, B., Xu, C., & Wang, Z. L. (2020). Quantifying and understanding the triboelectric series of inorganic non-metallic materials. Nature Communications, 11(1).
3. Brunsteiner, M., Zellnitz, S., Pinto, J. T., Karrer, J., & Paudel, A. (2019). Can we predict trends in tribo-charging of pharmaceutical materials from first principles? Powder Technology, 356, 892–898.
4. Lee, V., James, N. M., Waitukaitis, S. R., & Jaeger, H. M. (2018). Collisional charging of individual submillimeter particles: Using ultrasonic levitation to initiate and track charge transfer. Physical Review Materials, 2(3), 035602.