Particle coating using foams and bubbles : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemical and Bioprocess Engineering at Massey University, Palmerston North, New Zealand

This thesis investigates powder coating using foams or bubbles. The work initially started on foams. Wettability studies first showed that foams can be used to coat powders. Research then focussed on the fundamental unit of foams, the bubble. An experimental apparatus was designed and built to perform particle-bubble impact studies in air. Bubble solutions comprised of water, hydroxypropyl methylcellulose (HPMC) and sodium dodecyl sulphate (SDS). Four distinct physical behaviours occur when a particle impacts a bubble: (i) particle capture, (ii) particle slide-off, (iii) bubble burst and (iv) bubble self-healing. The rate processes that occur during particle-bubble impact are; (i), surface area creation by bubble film stretching; (ii), delivery of surface active molecules to the newly created surface; and (iii), stress dissipation as the film is stretched. The ability of the solutions to do (ii) and (iii) are highly complex relying on the thermodynamic equilibrium of the solutions and the local perturbations in the near surface region. Therefore, establishing quantitative boundaries of behaviour is a difficult exercise. It is proposed that, for solutions above the cac or cmc, (critical aggregate concentration, critical micelle concentration) where self-healing occurs, the rate of (ii) > rate of (i) and the rate of (iii) > rate of (i). For solutions below the cac, where bursting occurs, the opposite is true, the rate of (ii) < rate of (i) and the rate of (iii) < rate of (i). Intermediate behaviours such as slide-off of capture are within the range of self-healing behaviours, but where the energy of the particle is insufficient to penetrate the bubble. These behaviours are explained by complexation theory. For SDS concentration ≥ cac and cmc, small aggregates of SDS and HPMC locally supply surfactant to the surface of the stretching bubble film. This maintains low surface tension stress and self-healing results. For SDS concentrations < cac, self-healing occurs because the complexation is a HPMC-SDS sea containing SDS islands. The HPMC-SDS sea structure is sufficiently interlinked to simply stretch with the film, while the SDS islands de-aggregate quickly in the near surface region to supply the newly created surface with surfactant. Here the supply rate is faster than the stretching and so the new surface area is populated with SDS molecules. In contrast bursting occurs when the complexation is HPMC-SDS islands in a SDS sea. Here, the rapid film extension is so fast that the islands of HPMC-SDS become isolated and the film loses structural homogeneity. Furthermore, the rate of new surface creation is too fast for diffusion of SDS molecules from the bulk ‘sea’ to the newly created surface. This results in both an inhomogeneous structure and local increases in surface tension, causing both stress concentration in the film and the Marangoni effect. Extensional viscosity measurements, conducted in collaboration with Monash University, Australia, produced three behaviours as solutions were thinned: bead-on-string, blob and long-lived filaments. Solutions which produced long lived filaments here correspond to those that self-healed during particle impact (when the impact velocity was sufficient). It is proposed that this long-lived filament behaviour is due to the SDS concentration being > cmc, where the SDS micelles act like ‘ball-bearings’ between the extending HPMC chains. Coatings were characterised by SEM and gravimetric measurement. Cross-sectional imaging of the soft particle that penetrated self-healing bubbles were found to have a continuous coating layer around the particle. Surface topography of bubble coated particles were compared with classical droplet coated single particles from the literature. Bubble coated particles were found to be smoother than the droplet coated particle. The knowledge gained here was used to suggest how an industrial-scale particle coater using bubbles may be designed

Diabetes Management

Diabetes is a long-term metabolic condition characterized by high blood sugar levels (hyperglycaemia). It is a primary cause of illness and mortality around the world, and its incidence is increasing at an alarming rate. Diabetes affected an estimated 463 million persons in 2019, with the number expected to rise to 783 million by 2045. The increasing prevalence of diabetes is a major public health concern, and it is essential to implement effective strategies for prevention and management. Diabetes management is a complex task that requires a multidisciplinary approach involving healthcare professionals, patients, and their families

An experimental assessment of the size effects on the strength and ductility of freestanding Cu films under macroscopically homogenous deformation

Metallic interconnects and circuitry has been experiencing excessive deformation beyond their elastic limits in many applications, ranging from micro-electro-mechanical systems (MEMS) to flexible electronics. These applications are creating needs to understand the extent of strength and ductility of free standing metallic films at scales approaching the micron and sub micron range. This work aims to elucidate the effects of microstructural constraint as well as geometric dimensional constraint on the strength and ductility of free-standing Cu films under uniaxial tension. Two types of films are tested, (i) high purity rolled films of 12.5-100μm thickness and average grain sizes of 11-47μm and (ii) electroplated films of 2-50μm thickness and average grain sizes of 1.8-5μm. Several experimental tools including residual electrical resistivity measurements, surface strain measurements and surface roughness measurements are employed to highlight the underlying deformation mechanisms leading to the observed size effects. The results show that thickness effects on the strength (yield and flow stress) of freestanding films are primarily an outcome of the competing contributions from two distinct dislocation mechanisms i.e. intragranular Frank-Read (IG) type dislocations and grain boundary (GB) dislocations. At large grain sizes, typically ~O(10μm) or larger, in bulk materials and foil/plate type specimen, IG dislocations dominate the overall response. In this regime, reducing the film thickness leads to a reduction of the effective microstructural constraint. Consequently, prominent thickness dependent weakening is observed. On the other hand, for small grain sizes, ~O(1μm) or smaller, GB dislocations play an increasingly prominent role. In such cases, reducing grain boundary area per unit specimen volume, with reducing thickness, results in a reduction of the available GB dislocation source density. As a result, plasticity commences under source-limited conditions leading to thickness dependent, source starvation strengthening. The role of film thickness on macroscopic ductility was more prominent for dg = 3.5μm and larger for the examined set of film microstructures. Generally, reducing ductility with reducing film thickness was observed. Surface scans showed that in specimens with many grains across the thickness, plastic deformation remains relatively uniform to higher level of macroscopic plastic deformation. On the other hand, for specimens with just one grain across the thickness, plastic deformation evolves into highly localized deformation bands at an early stage of deformation, leading to premature failure. It is speculated that local accommodation of deformation incompatibilities between neighboring grains are the primary driving mechanism for the observed trends. For films with the lowest dg = 1.8μm, the apparent ductility is inherently limited by the loss of strain hardening capability. These films show a limited ductility with maximum uniform strain of ~2%, irrespective of the thickness

A new tensile testing methodology for stable mechanical characterization of free-standing films

The advent of new technologies and applications employing structural components at the micron scale and their future development depends on the understanding of the fundamental behavior of materials at such small scale. The defining characteristic of these materials is the overlap and interaction between the structural length scales of the components and the intrinsic micro-structural length scale of the material. The objective of this work is to develop a new stable testing fixture that will facilitate quantitative understanding of the size-dependent material response and the heterogeneous deformation field at these length scales. The testing fixture utilizes compliant mechanisms which arrests deformation instabilities and premature failure. Detailed fixture stability analysis is performed to optimize the final fixture dimensions. The device design and performance is then calibrated with finite simulation and verified experimentally. The test methodology was implemented to test copper films with thickness between 10 -100[Mu].m. The copper microstructure was altered via heat treatment at different temperature to change the grain size to film thickness ratio at the same film thickness. Within the experimental window, the yield stress and strain to fracture showed strong dependence on the grain size i.e. the Hall-Petch effect. The experimental observations showed that the film ductility is a strong function of the testing methodology. For the same film microstructure and macroscopic dimensions, different level of ductility can be attained based on the relative stiffness of the test fixture and the specimen. The fundamental operative mechanism that has been identified is by consecutively stabilizing the longer wavelengths of shear band localization within the film and pushing them to shorter wavelengths. Thus, the film may attain higher levels of final strain to fracture. Detailed measurements of the in-plan finite strain field wilhin the film have revealed the structure of the shear bands and their interactions. The developed testing fixture was promising in the initial runs at the macro-scale. A micro-scale version is being developed for further analysis of plasticity and fracture at the microstructure length scale of the material

Case Study: Hashimoto’s Thyroiditis and Increased HbA1C

Several metabolic problems and clinical symptoms are caused by hypothyroidism. According to some research, hypothyroidism may cause blood sugar levels to rise. It has been shown that people with diabetes who also have hypothyroidism may have higher Hemoglobin A1C values (HBA1C). This test is used to diagnose and monitor diabetes patients' blood &nbsp;&nbsp;sugar control. A high HBA1C typically implies poor diabetes management. Patient was suffering from Hashimoto’s Thyroiditis, which was diagnosed through blood investigations and was given treatment as per functional medicine approach. HbA1c was seen high in start, which reduced significantly after functional medicine treatment and therapies. Our study suggests that we should be cautious while interpreting HbA1c values in patients with hypothyroid and treating patients while observing all their symptoms and treating them by working on their root cause i.e., functional medicine approach

A case of methotrexate resistant gestational trophoblastic neoplasia

Gestational trophoblastic neoplasia (GTN) is a subset of gestational trophoblastic disease (GTD) which has a propensity to invade locally and metastasize. Patients with low risk GTN generally respond well to single agent chemotherapy (methotrexate (MTX) or actinomycin-D (ACT-D). However, high risk cases may develop resistance or may not respond to this first-line chemotherapy and are unlikely to be cured with single-agent therapy. Therefore, combination chemotherapy is used for treatment of these cases. Here we present a 25 years old P2 L2 A1 lady, who was initially treated at a peripheral hospital with multiple doses of Injection methotrexate with a working diagnosis of persistent trophoblastic disease. She didn’t respond to this treatment and reported to our centre for further management. On evaluation she was found to be a case of high risk GTN (invasive mole) (I:8) for which she was put on combination chemotherapy in the form of Etoposide-Methotrexate-Actinomycin-Cyclophosphamide-Oncovin (EMA-CO) regime. She responded to this treatment and is presently asymptomatic and is under regular follow up

A rare case of post-partum cerebral venous sinus thrombosis

Cerebral venous sinus thrombosis is a rare neurologic emergency during pregnancy. Life threatening complications can be prevented if it is detected and treated well in time. A 24 years P2L3A2 lady, who had undergone elective caesarean delivery developed sudden onset severe episodic parieto-occipital headache and bilateral diminution of vision on 4th post-partum day. She had no known risk factors for thrombosis. There was no history suggestive of sepsis or pre-eclampsia. On clinical examination her blood pressure was found to be very high (164-180/104-110 mm Hg). There was no sensory or motor deficit. Relevant haematological and biochemical investigations were within normal limits. Urinary protein was negative. With a provisional diagnosis of imminent eclampsia, she was put on antihypertensive and Magnesium Sulphate. However, in view of persistence of the symptoms even after 24 hours, contrast-enhanced computed tomography (CECT) was done, which revealed venous infarction in occipital cortex and subcortical white matter. Magnetic resonance (MR) venography confirmed thrombus in left transverse and sigmoid sinuses. Thus, definitive treatment in the form of heparin in therapeutic doses was started. Antihypertensive was continued and prophylactic anticonvulsant was added in view of presence of the infarction. Patient responded well. Vision improved, and headache resolved completely. The patient was discharged on antihypertensive, anticonvulsant and vitamin K antagonist (Warfarin sodium) with an advice of regular follow-up. Cerebral venous thrombosis (CVT) is an uncommon entity and a high index of suspicion is needed to diagnose it at an earlier stage for timely initiation of treatment and prevention of complications. Prognosis in pregnant cases is better than that during a non-pregnant state