Study on the turbulent shear controllable synthesis of functional Micro/nanoparticle materials and their interfacial behaviour related to anti corrosion and lubrication

Abstract

Controllable synthesis in micro‑ and meso‑scale environments has attracted considerable academic interest as a potential means of process enhancement to meet the increasing demands for sustainable production. For decades, researches on nanoparticle synthesis, however, have mainly focused on identifying suitable chemical reagents and methodologies to produce structure-function controlled nanomaterials. In this endeavour, it has been recognised that chemical reactors are fundamentally important as they provide the essential environment for chemical synthesis. Therefore, a comprehensive investigation of the hydrodynamic behaviour of turbulent shear flow within novel reactors with an analysis of the properties of the resulting synthesised products can provide a foundation for optimising reactor performance, designing efficient reactor structures, and broadening the scope of application for novel-designed reactors. In recent years, the synthesis of powders with controlled shape and narrow particle size distribution has remained a major challenge in the chemical industry. The fundamental relationship between advanced powders and novel reactors is established by the specific flow field generated within the reactor, which interacts directly with the particle synthesis process at the macro, meso and micro-mixing levels. To figure out the underlying correlation between powder properties and the characteristics of turbulent shear-flow field, both the experimental particle synthesis and the computational fluid dynamics (CFD) method are employed in this PhD project to investigate the effects of turbulence-induced shear stress on the morphology and size distribution of micro/nanoparticles, and to evaluate their potential for industrial applications, especially in the anti-corrosion and lubrication fields.
The current status of the controllable synthesis process of functional micro/nanoparticles across various areas, with particular emphasis on the turbulence shear controllable method, is comprehensively reviewed in Chapter 1. Conventional top-down and bottom-up synthesis approaches face significant practical limitations, particularly in controlling particle size distribution and achieving complex morphologies, which hinder their scalability and environmental sustainability. For decades, researchers have devoted considerable attention to this topic because the properties of the synthesised particles, including size and structure, have been confirmed to exert a significant influence on their practical performance. Compared with conventional methods, the turbulence-controllable synthesis method demonstrates significant potential for process intensification and regulatable particle formation. The reactor is considered critical to realise such precise, shear‑mediated control over particle nucleation, growth, and final properties. An effective reactor must facilitate intimate contact between reactants and catalytic sites, maintain appropriate pressure, temperature, and concentration conditions to ensure that the synthesised or formed nanoparticles have a sufficient residence time for mixing while allowing for efficient product removal.
A counter axial-swirling impinging jet flow vortex flow reactor (CASIJR) is proposed in Chapter 2. The reactor consists of two Rankine vortex chambers, each with two tangential inlets positioned at the ends of the reactor block, and a circular cylindrical impinging chamber. The top of the impinging chamber is connected to a small vertical pipe, allowing the ultrasound probe to be inserted for ultrasound irradiation. To evaluate the advantage of such features, the sol-gel method for the synthesis of silica nanoparticles is performed using the CASIJR reactor. Meanwhile, numerical simulations are employed to investigate the characteristics and evolution of turbulence‑induced shear stress within the system. Both the experimental and numerical results demonstrate that the intensified turbulence-induced shear with the axial swirling counter flow impingement has a significant impact on controlling the silica nanoparticle size and size distribution. Despite the effective and intensified mixing environment, the shear stress is considered a critical factor in the controllable synthesis process, which has been largely ignored in previous studies of reactor performance.
The investigation presented in Chapter 2 has revealed that an increase in Reynolds number enhances the turbulence intensity, producing a greater number of deformed eddies. These eddies amplify the mechanical shear stress acting on the nanoparticles, driving both aggregation and morphological changes. Chapter 3 further explores the mixing efficiency and turbulence-induced shear in the flow inside the CASIJR reactor, which are evaluated using Reynolds Average Navier-Stokes (RANS) modelling coupled with the Reynolds Stress Model (RSM) and species transport equation. Moreover, the orientation of shear stress influences the morphology of silver nanoparticles, resulting in the formation of nanorods. It can be speculated that the turbulent eddies participate in particle formation, interacting with the nucleation, growth, aggregation and breakage processes. This phenomenon, which directly links turbulence-induced shear orientation to nanoparticle morphology, has been observed for the first time in this reactor system and plays a supporting role in the subsequent research.
Previous chapters have demonstrated that the swirling vortex flow reactor is an effective reactor structure for the intensification process in functional particle synthesis. To further validate our findings, Chapter 4 presents a novel hybrid Rankine-Taylor-Couette vortex flow reactor (RTCVFR) that integrates the concept of a swirling vortex flow reactor with that of an annular cross-section-varying Taylor-Couette reactor. The synthesis of two‑dimensional manganese phosphate nanosheets (MnPNs) is employed to investigate the effects of turbulence‑induced shear within this system. The aggregation and growth of the MnPNs are estimated by employing the Population Balance Model (PBM) coupled with the use of the two-fluid model. As the annular gap narrows axially, the generated Taylor vortices give rise to strong trapping for those formed MnPNs while the embedded micro-scale turbulent eddies (down to the Kolmogorov scale or even smaller) can generate turbulence-induced shear acting on the nanoparticles, enabling the formation of MnPNs. The resulting rectangular morphology of the MnPNs demonstrates that the unique staged design of the combined vortex reactor enables precise control over particle properties.
Furthermore, this project investigates the effects of adding synthesised particles on metal protection, which is a foundational engineering discipline essential for safety, economic stability, and technological progress. The synthesised functional particles, characterised by their uniform size and well‑defined morphology, are engineered to optimise their performance in protective applications. The MnPNs exhibit outstanding tribological performance, high thermal conductivity, and piercing resistance, which are explored in Chapter 4 through the application of MnPNs as lubricant grease additives. The unique 2D rectangular nanostructure promotes the alignment of MnPNs in the grease, which are then deposited onto the wear scar, and thus separates the friction pair, reducing direct contact. In Chapter 5, mesoporous silicon oxide (SiO2) nanoparticles encapsulated with cetyltrimethylammonium bromide (CTAB) are used as anti-corrosion additives for simulated coolant to inhibit corrosion of aluminium alloy. The one‑step synthesis of silica nanoparticles is conducted as described in Chapter 2. The experimental results indicated that the uptake of CTAB becomes relatively high due to the high porosity of the synthesised SiO2 nanoparticles. The COMSOL Multiphysics simulation model is employed to provide a detailed analysis of the effects of variables such as temperature and inhibitor presence on the corrosion process. The weight loss tests and electrochemical measurements are carried out for the evaluation of anti-corrosion performance. Comparisons are made between metal substrates exposed to the cooling solutions with and without the addition of MSN-CTAB.
In summary, the controllable synthesis process of functional particles in a counter axial-swirling impinging jet flow vortex flow reactor and a hybrid Rankine-Taylor-Couette vortex flow reactor is investigated. The correlation between turbulence-induced shear stress and particle size and morphology is successfully emphasised and established using the CFD technique. The Reynolds Average Navier-Stokes (RANS) modelling coupled with the Reynolds Stress Model (RSM) is adopted, which primarily predicts the turbulent flow field with the macro‑ and micro‑mixing characteristics within the reactors, and explains the shape orientation of synthesised particles under the influence of turbulent eddies, especially those at small length scales. Additionally, to better align with industrial requirements, the metal‑protection performance of two different micro/nanoparticles is systematically investigated.

Date of Award	18 Jul 2026
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Xiaogang Yang (Supervisor), Jiusheng Li (Supervisor) & Sean P. Rigby (Supervisor)