Optimisation of nanomaterial dispersion using acoustic cavitation for high strength nanocomposites

Ultrasonication is the most widely used technique for the dispersion of a range of nanomaterials, but the intrinsic mechanism which leads to stable dispersed solutions is poorly understood, with procedures quoted in the literature typically specifying only extrinsic parameters such as nominal electrical input power and exposure time. In this project we aim to study, identify and characterise the basic physics underpinning dispersion, creating the metrological tools essential in the large volume production of nanomaterial dispersions for high strength nanocomposite applications. This will be carried out by developing enhanced sensors, signal analysis tools and reference cavitation facilities, leveraging previous successful collaboration between NPL and Surrey. In a previous collaboration, we demonstrated that careful measurement and control of acoustic cavitation, rather than blind application of input power, is critical in the ultrasonic dispersion of single-walled carbon nanotubes. For the first time we highlighted the impact of the different types of cavitation on the efficiency of the dispersion process: a crucial step in the application to novel and more exciting nanomaterials (nanoparticles, nanowires, graphene, MoS2 and other 2D layered materials) where intermolecular/interlayer van der Waals interactions play an important role.

Project Aims:
(i) Critically evaluate existing methods of dispersing nanomaterials, looking at the combined effect of ultrasound and surfactants/solvents
(ii) Investigate the effects of different frequencies on dispersion quality in the newly established multi-frequency reference vessel for cavitation at NPL (RV-Multi)
(iii) Develop online cavitation detection methods with feedback control to characterise the applied dose and optimise the dispersion process
(iv) Critically evaluate the correlations between dispersion characteristics in a range of samples with different classifications of cavitation (i.e. non-inertial oscillations, inertial collapse), measured using acoustic emission and chemical techniques, and potentially allowing material selection
(v) Investigate the interactions of nanomaterials with single cavitating bubbles in the microfluidics-based NPL sono-optical tweezers and of small clouds of bubbles (<100) in the unique facilities at NPL
(vi) Establish guidelines for efficient dispersion of 2D layered nanomaterials, such as graphene, using cavitation dose as key measurement.
(vii) Fabricate and physically characterize liquid processed polymer composites using optimized mono-dispersed fillers of different aspect ratio.