No description available.

The effects of fundamental solution parameters including polymer molecular weight, concentration and solvent on electrospinning of polystyrene were investigated. Each parameter was found to play a vital role in determining the morphology of beads and fibers. For dilute to semi-dilute solutions, a wide range of bead structures including wrinkled beads, cups, dishes, and toroids were observed when a volatile solvent, tetrahydrofuran, was used. Various rheological regimes where these structures may be obtained were identified. The morphological transition from bead to fiber was characterized by two critical concentrations, Ci and Cf, at which incipient and complete fibers may be observed respectively. These values were determined as a function of molecular weight. A comparison with the models proposed in the literature indicated that solvent evaporation may play an important role in jet stabilization. The fiber diameter and distribution was found to decrease significantly with molecular weight at the critical concentration, Cf. The use of N,N-dimethylformamide, a solvent with relatively high dielectric constant, also resulted in an appreciable reduction in fiber diameter and improved uniformity. The observation of solution jet evolution during the process with high speed camera (2000 frames/s) indicated that solvents have a significant influence on the jet breakdown behavior. Two types of behavior were identified based on the extent of extensional flow, bending instability, and the number of secondary jets. Solvents with high dielectric constant were found to induce extensive bending instability, which resulted in extremely fine microstructures of electrospun polymer.

Caramel is a mixture of sugars, milk proteins, fat and water cooked at high temperatures to initiate Maillard reactions. We study caramels as ‘active emulsion-filled protein gels’, in which fat droplets are chemically-bonded to a background gel matrix of cross-linked proteins in a concentrated aqueous sugar solution. A ‘caramel region’ in composition space is delimited by the varying the four ingredients; sugar, milk protein, fat and water. The boundaries of the composition space define various modes of ‘failure’. Boundaries are determined for transitions to toffee and emulsification failure leaking out of the caramel, and protocol dependent failures, scum formation during the cooking step and subsequent boil over or the formation of a ‘creme Chantilly. Oscillatory rheology within the caramel region reveals that we can superpose the mechanical spectra of all caramels into a single pair of G'(ω),G''(ω) master curves using time-composition superposition (tCS) over 12 decades of frequency, so that all caramels are instances of an underlying ‘universal material’. The master curve is an example of a very lightly cross-linked amorphous polymer, a weak rubber. Utilising the cross-over point of G'(ω) and G''(ω) as a common point to compare caramel master curves the viscous and elastic dependency of caramel is determined and linked to the caramels ingredients. Viscosity is dependent on the aqueous sugar content and the elastic dependency on protein content. This insight constrains the molecular mechanisms for structure formation, and implies that measuring a couple of parameters suffices to predict the rheology of caramels over 12 orders of magnitude in frequency.

Complex interfaces stabilized with materials including surfactants, polymers, and particles have dilatational properties that are important in processing emulsions and foams. Dilatational rheology is difficult to measure on interfaces due to the coupling of dilatation and shear inherent in common measurement apparatuses. Compounding the problem is the lack of control over complex interface formation in emulsification, which can obscure relationships between interfacial rheology and bulk emulsion properties. This thesis provides tools to measure dilatational properties of interfaces and generate interfaces with controlled surface coverage. A small amplitude analysis of dilatational rheology on capillary pressure tensiometers is used to develop a method for separating intrinsic rheology from surface tension effects. This analysis is applied in dilatational measurements of insoluble interfaces at the microscale, and good agreement is observed between the microscale measurements and Langmuir trough measurements. The second half of the thesis focuses on the controlled generation of particle-stabilized interfaces. A two-lobed shape transition is observed for confined bubbles traveling in a surface active particle suspension, and a model is developed to predict the particle surface coverage on the bubble interface. This model is then applied to generate monodisperse bubbles with uniform nonspherical bubbles due to particle jamming at the interface. The tools developed in this thesis are crucial to future development of relationships between the dilatational rheology of interfaces and the bulk properties of emulsions and foams.

Thesis--Copenhagen. / Summary in Danish. Includes bibliographical references (p. 117-133) and index.

Thesis--Copenhagen. / Summary in Danish. Includes index. Bibliography: p. 117-133.

Chronic in ammation and variations in blood flow have been implicated in the pathogenesis of cardiovascular disease. It is also possible that inflammatory and rheological processes are involved in the development of mild cognitive impairment and dementia, either through their association with vascular disease or via some other, more direct effect on the brain. Evidence is increasing for a causal relationship between Alzheimer's disease and inflammation, possibly related to inflammatory activation of microglia. Inflammatory processes may also be involved in the pathogenesis of cerebral small vessel disease, which in turn has been linked to cognitive impairment and dementia. There is also evidence showing that rheological factors affect cerebral blood flow. However, despite these findings, the associations between inflammatory and rheological markers and cognitive ability have not been extensively studied in large groups of ageing people. The primary aim of this thesis was to test for associations between late-life levels of inflammatory and rheological markers (C-reactive protein (CRP), fibrinogen, tumor necrosis factor (TNF)-α, interleukin (IL)-6, plasma viscosity, and haematocrit) and cognitive ability. A genetic analysis was then performed to model single nucleotide polymorphisms (SNPs) in the genes encoding the markers against cognition in an attempt to determine the weight of evidence for a causal inflammation-cognition association. Four studies were used to test these aims with the majority of the analysis being performed on the Aspirin for Asymptomatic Atherosclerosis (AAA) Trial (n = 3,350), and the Edinburgh Type 2 Diabetes Study (ET2DS) (n = 1,066). The Edinburgh Artery Study (n = 534), and the 1936 Lothian Birth Cohort (n = 1,091), were used as replication cohorts for the genetic analysis. All cohorts comprised community-dwelling, elderly citizens (aged around 70 years) living in central Scotland. With the exception of the ET2DS, all data used were for secondary analyses. Cognitive ability was assessed in all studies using comprehensive batteries of neuropsychological tests that included a measure of crystallised intelligence in the form of a vocabulary test. As performance on such tests varies little across a lifespan, adjusting for these scores in the late-life models enabled the determination of estimated lifetime cognitive change. In the case of the 1936 Lothian Birth Cohort an actual age-11 IQ measure was available in addition to the cognitive follow-up scores recorded at age-70. Linear regression showed small but significant associations between CRP, fibrinogen, and plasma viscosity, and cognition and estimated lifetime cognitive decline in the AAA Trial. Similar results were observed in the ET2DS for CRP, IL-6, and TNF-α. These associations tended to be of a magnitude whereby the markers explained 1% of the variance of the cognitive test scores. The cognitive domains most consistently associated with the markers were processing speed, and a data derived general intelligence factor. A novel genetic analysis was then undertaken to model SNPs against cognitive ability and decline. Most of the results generated were null findings. However, strongly significant associations were found between the rs2227412 fibrinogen beta gene SNP and the cognitive test scores in the ET2DS. Furthermore, the genotype associated with the lowest cognitive scores was also related to higher levels of plasma fibrinogen. Whilst replication of the association between the fibrinogen SNPs and cognition was not found across all cohorts, these results still indicate a potentially causal role for this haemostatic/inflammatory marker. To date, the majority of inflammation-cognition associations have focussed on the acute-phase protein CRP. The main outcomes from this thesis suggest that its close correlate, fibrinogen, is an equally, if not more important factor in the complex process of cognitive ageing.

The falling film flow of milk was studied both analytically and experimentally. Experiments were carried out for concentrations from 19.93% to 62.09% to obtain the rheological data of milk while analytical studies were done to derive the solutions of the problem. Studies which include calculations and simulations were carried out for a typical milk flow in a falling film evaporator. It was found that milk was non-Newtonian at high concentrations and Herschel-Bulkley model was able to model the milk flow. The typical falling film flow was able to be simulated as a two phase flow in COMSOL to gain a better understanding of the flow. It was found that there were counter-current flow between the film and air in the evaporator. A Matlab program was also used to study the analytical solutions of the film temperature change while it flows down the tube with results showing that heat transfer was not linear as would have believed. Results from several experiments also enabled the change of milk viscosity with time to be modeled. Milk viscosity increased steadily with time and higher at higher total solids from 35.47% to 49.25% for three hours. Calculations revealed that film thickness of milk was very thin, from 0.00116 m at the entrance of tube to 0.00146 m at the tube exit. From the use of models developed of the rheological parameters, results showed that these parameters have impacts on film flow except the yield stress. However, the viscosity and yield stress are factors that will limit the operating range available for falling film evaporator.

No description available.

No description available.