1,721,040 research outputs found
BslA-stabilised emulsion droplets with designed microstructure
No full textOriginal microscope images of BslA-stabilised emulsion droplets and two time-lapse confocal microscope sequences (available to view using ImageJ imaging software) of BslA-stabilised partially coalesced droplets melting in the absence and presence of free BslA in the medium.Bromley, Keith Matthew; MacPhee, Cait. (2016). BslA-stabilised emulsion droplets with designed microstructure, 2015-2016 [image]. University of Edinburgh. https://doi.org/10.7488/ds/1590
Structure and mechanical properties of model colloids at liquid interfaces
Get PDFColloidal particles adsorbed to liquid interfaces appear in a broad range of industries such as foods, mining and oil recovery. Yet our understanding of such systems remains incomplete. This thesis aims to characterise a model sterically-stabilised colloid system. We will explore their structure, stress-strain relationship, and the theoretical models used to describe them. Since the high barrier to adsorption and high desorption energy of particles are influenced strongly by size, we focus on the effects of varying particle size. This also allows us to begin connecting our micron-sized colloids to smaller surface active species such as proteins. We focus on the mechanical properties of the particle-laden interface, which are crucial to applications such as emulsion stabilisation, and complement this investigation with microscopic imaging. For simplicity, we focus on the less frequently investigated sterically-stabilised particles, as opposed to chargestabilised particles. The imaging reveals that for unsonicated samples, the characteristic structure changes with particle size: while large ( 1 µm radius) particles are relatively ordered in a two-dimensional crystal, as particle size decreases aggregates start to appear. This apparent difference persists in their stress response - which we measure using a Langmuir-Pockels trough - where the largest and most ordered particles can withstand the most stress before buckling the interface. However, once the number and size of aggregates are reduced by sonication, the variation in mechanical properties with particle size disappears and all sizes (from 1 µm radius down to 0.2 µm radius) show a comparable response, consistent with the behaviour of charge-stabilised particles. With particle size shown to be unimportant in our range, we focus on the smallest particles and use another technique - oscillating pendant drop tensiometry: first, to further explore the interfacial rheology, and second to verify our Langmuir-Pockels trough measurements by another method. The second point is particularly important because literature reports of pendant drop and trough measurements seem to show a surprising inconsistency: drop measurements often only model the effect of colloid adsorption while trough measurements often only include colloid interactions, and each model is consistent with their own data. We demonstrate a pendant drop experiment which can be modelled with interactions, and use this to develop the theoretical understanding of how colloidal particles affect the interfacial rheology, thereby offering an explanation for this apparent inconsistency. We also quantitatively characterise the scaling of our interactions with the surface density of particles, and find that it is not inconsistent with interfacial electrostatic interactions, as with charge-stabilised particles. This result agrees with an independent report which more directly measured interparticle interactions. Directly comparing the results of our pendant drop and trough measurements, we find consistency at low surface pressures and deviation at higher surface pressures. This is attributed to the limitations of the trough and our modelling at high surface pressures. In chapter 7 we present the first observations in particle-laden interfaces of a new mechanism of particle expulsion we call collective particle detachment, which was predicted to occur for particle-laden interfaces in earlier works on elastic sheets at liquid interfaces. In this process, thousands of particles collectively detach from the interface after wrinkling, producing long tubular structures, much like those produced by the highly elastic BslA protein in similar conditions. This provides a clear and novel link between particle and protein behaviour. Finally, having investigated particles as a model system for proteins, we perform oscillating pendant drop measurements on a model particle-like protein - ferritin - to explore the applicability of our colloidal understanding to proteins. We find that its dilational elastic modulus is linear with surface pressure, as it was for particles. By applying our particle-based model to ferritin, we find that its interactions are short-ranged, consistent with previous studies. We conclude with a discussion of particle-protein similarities - such as their high desorption energy - and differences, such as the compressibility and unfolding potential of proteins.
This thesis explores a model colloidal system and adds to the literature a new approach where we use the adaptability of colloidal particles (at the synthesis stage) to explore key variables for fundamental interfacial properties. In the process we develop an improved model for the effect of adsorbed particles on the interfacial rheology, which allows us to measure interparticle interactions at the interface. We find the novel phenomenon of collective particle detachment, and show that our sterically-stabilised particles behave as charge-stabilised particles at the interface. Future work might explore other crucial variables for interfacial properties such as the contact angle or anisotropy
Economic significance of biofilms: a multidisciplinary and cross-sectoral challenge
Get PDFThe increasing awareness of the significance of microbial biofilms across different sectors is continuously revealing new areas of opportunity in the development of innovative technologies in translational research, which can address their detrimental effects, as well as exploit their benefits. Due to the extent of sectors affected by microbial biofilms, capturing their real financial impact has been difficult. This perspective highlights this impact globally, based on figures identified in a recent in-depth market analysis commissioned by the UK’s National Biofilms Innovation Centre (NBIC). The outputs from this analysis and the workshops organised by NBIC on its research strategic themes have revealed the breath of opportunities for translational research in microbial biofilms. However, there are still many outstanding scientific and technological challenges which must be addressed in order to catalyse these opportunities. This perspective discusses some of these challenges
Exploring the Mechanisms of Fibrillar Protein Aggregation
Get PDFThis thesis has been submitted in fulfilment of the requirements for a postgraduate degree (e.g. PhD, MPhil, DClinPsychol) at the University of Edinburgh. Please note the following terms and conditions of use: • This work is protected by copyright and other intellectual property rights, which are retained by the thesis author, unless otherwise stated. • A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. • This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the author. • The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the author. • When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given
Self-assembly of rod-like colloids at the air-water interface
Get PDFTwo-dimensional (2D) colloidal materials and their assembly are of scientific
significance and industrial importance. The development of 2D colloidal structures is
a key stepping stone towards three-dimensional (3D) structures in relation to
controlled chemical composition, morphology, assembly and so on. Nowadays,
uniform colloidal structures with complexity in both shape and interactions have
become a popular topic in fundamental colloid science and applications.
Being motivated by this, in this thesis, micro-scale colloidal rods and self-assembled
dipeptides have been studied experimentally at the air-water interface. Monolayers
containing these colloidal materials were created in a Langmuir trough. Surface
pressure measurements, microscopic observations and many other techniques were
combined for the investigation. The aim of this work is to understand the phase
behaviours in complex monolayers, including the phase transitions during
compression, the flipping dynamics of micro-rods, the contribution of dipole-dipole
interactions between magnetic rods, and the interfacial self-assembly process of
dipeptide molecules.
Iron oxide micro-rods (β-FeOOH @silica) with different aspect ratios have been
synthesized to create the monolayers at an air-water interface. Microscopic
observations reveal a sequence of phase transitions by compressing the monolayers. It
has been proved that the aspect ratio of the rods plays an important role in the phase
transitions, —short rods flip into a perpendicular position relative to the interface to
relieve the compressional stress, while longer rods form multilayers under
compression. Magnetic rods (Fe3O4) were converted from the synthesized FeOOH
rods. They can be aligned in an external field, which further induces the reorganization
at the interface. To study these magnetic rods, differential dynamic microscopy (DDM)
was carried out to measure the magnetic moment. Their interfacial properties were
investigated in an external field applied perpendicular and parallel to the interface,
respectively. A magnetic field-induced flipping process has been observed, which
proves the theoretical prediction.
Besides rod-like particles, naphthalene dipeptides have been successfully trapped at
the interface of a low pH subphase, self-assembling into a hydrogel film. The
mechanism of interfacial self-assembly has been studied. Both FTIR spectra and AFM
images are used to investigate the fibrous structures of the film. The film has elastic
properties and buckles under compression. Moreover, dipeptide hydrogel induced by
metal ions has been used to create a wet foam system, which owns the advantages of
long-term stability (more than two weeks), low cost, and easy preparation
Density and temperature controlled fluid extraction in a bacterial biofilm is determined by poly-gamma-glutamic acid production
No full textA hallmark of microbial biofilms is the self-production of extracellular matrix that encases the cells resident within the community. The matrix provides protection from the environment, while spatial heterogeneity of expression influences the structural morphology and colony spreading dynamics. Bacillus subtilis is a model bacterial system used to uncover the regulatory pathways and key building blocks required for biofilm growth and development. Previous reports have suggested that poly-gamma-glutamic acid (PGA) production is suppressed during biofilm formation and does not play a major role in biofilm morphology of the undomesticated isolate NCIB 3610. In this work we report on the observation of multiple travelling fronts that develop during the early stage of B. subtilis colony biofilm formation. We find the emergence of a highly motile population of bacteria that is facilitated by the extraction of fluid from the underlying agar substrate. Motility develops behind a moving front of fluid that propagates from the boundary of the biofilm towards the interior. The extent of proliferation is strongly modulated by the presence of extracellular polysaccharides (EPS). We trace the origin of this moving front of fluid to the production of PGA. We find that PGA production is correlated with higher temperatures, resulting in a mature biofilm morphology that is distinct from the biofilm architecture typically associated with B. subtilis. Our results suggest that B. subtilis NCIB 3610 produces distinct biofilm matrices in response to environmental conditions.Morris, Ryan; MacPhee, Cait; Stevenson, David; Stanley-Wall, Nicola; Sukhodub, Tanya. (2022). Density and temperature controlled fluid extraction in a bacterial biofilm is determined by poly-gamma-glutamic acid production, [dataset]. University of Edinburgh, School of Physics and Astronomy. https://doi.org/10.7488/ds/3473
Developments for single molecule studies
Get PDFSingle molecule fluorescence spectroscopy has attracted considerable attention over the past two decades. Measurement on a single entity provides an opportunity to avoid ensemble averaging which is always present in conventional bulk fluorescence measurements. This makes single molecule spectroscopy particularly interesting for biophysics and biochemistry where heterogeneous systems are often encountered. The general interest of this thesis is in studies of single immobilised molecules carried out at room temperature. One of t.he major issues of single molecule spectroscopy is finding a suitable immobilising medium. Inorganic silica matrices prepared by the sol-gel method have a great potential to provide a close- to-natural immobilising environment even for sensitive biomolecules and thus allow investigation of their natural behaviour on the most fundamental level. In order to be able to tailor both physical and chemical properties of the final gel, it is of great importance to develop reliable methods to control each stage of polymerisation. In one part of this thesis, applications of fluorescent probes to investigation of sol-gels properties, as well as monitoring the gel assembly process, are discussed. The thesis further presents studies of the genetically engineered glucose binding protein labelled with the environmentally sensitive dye badan. This system was developed in a search for an appropriate recognition-reporter unit to serve as a part of fluorescence-based sensor for continuous blood glucose monitoring. This labelled biomolecule represents an interesting subject for a single molecule study. Due to technical reasons however, single molecule spectroscopy could not be applied in this case. Therefore, conventional ensemble fluorescence spectroscopy methods were used to characterise behaviour of the labelled protein at different glucose concentrations. The last part of the thesis deals with instrumental aspects of single molecule imaging and spectroscopy. The aim of the work was to assess the applicability of a freshly installed commercial microscope a-SNOM (WITec GmbH) in single molecule fluorescence studies and at the same time to adopt the technique for future experiments in our research group.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Quantifying Disorder through Conditional Entropy:An Application to Fluid Mixing
Get PDFIn this paper, we present a method to quantify the extent of disorder in a system by using conditional entropies. Our approach is especially useful when other global, or mean field, measures of disorder fail. The method is equally suited for both continuum and lattice models, and it can be made rigorous for the latter. We apply it to mixing and demixing in multicomponent fluid membranes, and show that it has advantages over previous measures based on Shannon entropies, such as a much diminished dependence on binning and the ability to capture local correlations. Further potential applications are very diverse, and could include the study of local and global order in fluid mixtures, liquid crystals, magnetic materials, and particularly biomolecular systems.</p
Gender differences in undergraduate students' performance, perception and participation in physics
Get PDFResearch has been undertaken to obtain a thorough understanding of
the existence and degree of gender disparity in students' participation and
performance in introductory university physics courses at the University of
Edinburgh. The research on this topic has focused on three main subject
areas: the proportion of male and female students enrolled in undergraduate
physics courses and their reasons for choosing to study this subject, gender
differences in student performance and, Finally, how students' attitudes and beliefs
towards studying physics change after a period of instruction. Gaining an insight
into students' attitudes towards studying and learning physics, as well as their
conceptual understanding of the topics being assessed, can draw attention to
potential areas of weakness which can be targeted in future teaching.
This thesis comprises a comprehensive review of the current situation
surrounding male and female participation in the undergraduate physics degree
programme at the University of Edinburgh in comparison to other STEM
subjects, as well as a description of factors potentially influencing the gender
performance in physics. With respect to student performance, conceptual understanding
tests have been used as evaluation tools to measure the effectiveness
of introducing interactive engagement, such as Peer Instruction, into teaching
environments in order to improve student performance, as well as a means by
which male and female learning gains could be compared. Results indicate that
female students show a lower level of conceptual understanding of Newtonian
Mechanics than male students when entering the degree programme, and that
this gender difference remains after a period of instruction. Qualitative interviews
highlight the preconceptions of first year undergraduate physics students with
regards to Newtonian concepts of force and motion and demonstrate the range
of misconceptions held by both male and female students.
The research presented here compares male and female performance on
different forms of assessment; coursework, laboratory assessments, examinations
and peer instruction in-lecture questions. Results indicate that while examination
scores show no distinct gender trends, female students show consistently higher
coursework scores compared to males across physics, chemistry and biology
first year courses. Analysis of Peer Instruction questions implemented in the
introductory physics lectures suggest that such teaching methodologies have had
an overall positive effect on class performance, although there is evidence that
differences exist between male and female performance on individual questions.
Students' attitudes towards learning physics have been measured at under-
graduate level in order to evaluate the level of 'expert-like' thinking of first
year undergraduate students. One notable finding of this study has been the
lack of decline in the `expert-like' thinking after a semester of teaching in recent
years, where previously a decline had been witnessed in this expert-like thinking.
This result coincides with a change in the format of lectures to a 'flipped-
classroom' approach and may have implications for the introduction of new
teaching methods. As well as focusing on the progression of undergraduate
students' attitudes, this study has evaluated UK academics' attitudes towards
physics. This has enabled a UK level of `expert-like' thinking to be established,
with gender differences between male and female academics identified. Students'
opinions of the transferable skills gained and their experiences during their degree
programme are discussed. Each of the gender topics discussed in this thesis
has provided a deeper insight into gender differences in student attainment at
undergraduate level which could have implications for the further improvement
of future courses
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