Search

HYPOTHESIS: Among other functions, mucins hydrate and protect biological interfaces from mechanical challenges. Mucins also attract interest as biocompatible coatings with excellent lubrication performance. Therefore, it is of high interest to understand the structural response of mucin films to mechanical challenges. We hypothesized that this could be done with Neutron Reflectometry using a novel sample environment where mechanical confinement is achieved by inflating a membrane against the films. EXPERIMENTS: Oral MUC5B mucin films were investigated by Force Microscopy/Spectroscopy and Neutron Reflectometry both at solid-liquid interfaces and under mechanical confinement. FINDINGS: NR indicated that MUC5B films were almost completely compressed and dehydrated when confined at 1 bar. This was supported by Force Microscopy/Spectroscopy investigations. Force Spectroscopy also indicated that MUC5B films could withstand mechanical confinement by means of steric interactions for pressures lower than ∼ 0.5 bar i.e., mucins could protect interfaces from mechanical challenges of this magnitude while keeping them hydrated. To investigate mucin films under these pressures by means of the employed sample environment for NR, further technological developments are needed. The most critical would be identifying or developing more flexible membranes that would still meet certain requirements like chemical homogeneity and very low roughness.

Cataracts are responsible for almost half of worldwide blindness, making it one of the biggest health challenges in this era. Cataracts are irreversible because of their pathology, which is controlled by the aging and biochemical change of eye tissues. As a result cataract surgery is currently the only effective treatment. The general procedure of cataract surgery includes separation and removal of the failed lens tissue from the surrounding soft tissue in the eye, followed by artificial lens implantation. Lens removal requires successful separation of lens tissues as a critical step that determines surgical success. However key parts of cataract separation affected by fluid mechanics and rheology are uncharacterised. This project aims to explain the behaviors of such separation phenomena and connect fundamentals with possible explanations and enhancements.A multi-layer bio-polymer injection model is developed to mimic the separation process in cataract surgeries. The separation can be considered peeling of a soft elastic tissue by a pressure-driven fluid flow, whose performance is closely related to properties such as flow rate and velocity as well as fluid viscosity, normal stress and yield stress. In our project, the separation physics is studied as a hydraulic fracture problem. Theories are proposed to discuss the effectiveness and safety of hydraulic fracture with different flow and fluid parameters. It is found both higher flow rate and viscosity will cause tissue to be deformed more, which may increase the risks of tissue damage. Yield stress fluids with significant elasticity are not suitable as in most cases they rupture the tissue. Normal stress fluids have the potential to provide safe and effective separation. It is found that with a small scale separation, however, the separation effectiveness is mainly affected by the flow rate, and the fluid properties play a more minor role. General ideas and potential improvements according to our results and theori

Polymer brushes are arrays of densely surface-tethered polymer chains, and are of interest for two reasons.Firstly, they possess interfacial characteristics, such as antifouling and lubrication, that are desirable in many applications.Secondly, they are model systems that can provide additional insight into polymer behaviour due to their unique geometry.Observing the interfacial structure of these brush layers is critically important for understanding both their properties and the mechanisms driving the polymer behaviour.To date, neutron reflectometry (NR) is the only technique that can demonstrably resolve the nanoscale structure of polymer brushes.However, these diffuse interfaces produce subtle features in the reflectometry data that challenge interpretation, with typical analyses failing to quantify the derived structure's uncertainty.Furthermore, the experimental potential of this technique for the study of brushes is only just being realised. This Thesis advances NR as a tool for studying polymer brush systems by establishing a robust analysis methodology that overcomes previous hurdles and demonstrating novel experimental techniques.In both cases, poly(N-isopropylacrylamide) (PNIPAM) brushes are used as model systems.First, the polymer system is characterised through the novel observation of surface-initiated ARGET ATRP using time-resolved NR, and a study of the dry brush as a function of humidity and temperature.Second, methodologies are developed that allow for robust determination of both solvated and confined brush structures.Lastly, NR is used to elucidate the behaviour of PNIPAM brushes in complex environments.A novel confinement apparatus is used to investigate the structure of a PNIPAM brush under mechanical confinement and contrast-variation provides unparalleled insight into PNIPAM–surfactant systems.In each case, complementary techniques are essential in guiding reflectometry experiments and fully understanding the polymer system.This work develops

The work presented is focused on assessing the viability and impacts of using mixtures of ionic liquids and carbon dioxide for the purposes of carrying out reactions and subsequently extracting the products of those reactions from the mixture. The expansion profiles of series of ionic liquids based on the 1-butyl-3-methylimidazolium cation were examined under varying pressures of carbon dioxide. It was found that the expansion was greater with bis(trifluoromethanesulfonyl)imide- and trifluoromethanesulfonate-based ionic liquids than the other salts considered. An expansion plateau was noted in each ionic liquid case at the same pressure, with minimal change in expansion observed above that pressure. Temperature dependent studies of these expansion profiles using the bis(trifluoromethanesulfonyl)imide salt showed a change in the degree of expansion with temperature. The densities of expanded 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide / carbon dioxide mixtures were determined under the same conditions as used for the expansion studies. These combined data allowed determination of carbon dioxide solubility and hence the proportion of each component (by mole) in the expanded phase. The rate constant for the reaction between cyclopentadiene and dimethyl acetylenedicarboxylate was determined in a series of expanded 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide / carbon dioxide mixtures with a wide range of solvent compositions dependent on the carbon dioxide pressure used. The changes in rate constant with solvent composition were analysed and compared to other reaction types, noting that intermediate amounts of carbon dioxide gave the greatest rate constant. Extraction studies were carried out on the reaction mixtures described above. Temperature and pressure dependent studies were performed to evaluate the amount of material that could be extracted from the ionic liquid using carbon dioxide, with higher pressures and temperature bein