The purpose of this study was to characterize the micromechanical properties of various structural components in asphalt using Atomic Force Microscopy (AFM). The focus of the study was based on nano-indentation experiments performed within a micro-grid of asphalt phases in order to determine micromechanical properties such as stiffness, adhesion and elastic/plastic behavior. The change in microstructure and micromechanical behavior due to oxidative aging of the asphalt was also a primary focus of the study. The experiment was performed with careful consideration of AFM artifacts, which can occur due to factors such as geometry of the cantilever tip, hysteresis, filtering methods and acoustic vibrations. The materials used in this study included asphalts AAB, AAD and ABD from the Materials Reference Library (MRL) of the Strategic Highway Research Program (SHRP), chosen due to variations in crude source, chemical composition and elemental analysis for each asphalt type. The analysis of nano-indentation creep measurements corresponding to phase-separated regions ultimately revealed heterogeneous domains in asphalt with different mechanical properties, and oxidative aging was found to induce substantial microstructural change within these domains, including variations in phase structure, phase properties and phase distribution. The form and extent of these changes, however, were different for each asphalt studied. Data analysis and information collected during this study were used for comparisons to existing models and asphalt data, which validated results and established correlations to earlier, related studies. From these comparisons, it was found that data parallels followed expected trends; furthermore, analogous interpretations and distinctions were made between results from this study and the micellar and microstructural models of asphalt. This study of micromechanical properties that govern asphalt behavior has yielded information essential to the advancement of hot mix asphalt (HMA) performance, including a new asphalt “weak zone” hypothesis and a foundation of data for implementation into new and existing asphalt models.

In this thesis, atomic force microscopy (AFM), transmission electron microscopy (TEM) and optical microscopy techniques were used to investigate systematically the self-assembled nanostructure behaviour of two different types of spin-cast polymer thin films: poly(isoprene-b-ethylene oxide), PI-b-PEO diblock copolymers and [poly(9,9-dioctylfluorene-co-benzothiadiazole)]:poly[9,9- dioctyfluorene-co-N-(4-butylphenyl)-diphenylamine], F8BT:TFB conjugated polymer blends. In the particular case of the polymer blend thin films, the morphology of their composites with cadmium selenide (CdSe) quantum dot (QD) nanoparticles was also investigated. For the diblock copolymer thin films, the behaviour of the nanostructures formed and the wetting behaviour on mica, varying the volume fraction of the PEO block (fPEO) and the average film thickness was explored. For the polymer blend films, the effect of the F8BT/TFB blend ratio (per weight), spin-coating parameters and solution concentration on the phase-separated nanodomains was investigated. The influence of the quantum dots on the phase separation when these were embedded in the F8BT:TFB thin films was also examined. It was found that in the case of PI-b-PEO copolymer thin films, robust nanostructures, which remained unchanged after heating/annealing and/or ageing, were obtained immediately after spin coating on hydrophilic mica substrates from aqueous solutions. The competition and coupling of the PEO crystallisation and the phase separation between the PEO and PI blocks determined the ultimate morphology of the thin films. Due to the great biocompatible properties of the PEO block (protein resistance), robust PEO-based nanostructures find important applications in the development of micro/nano patterns for biological and biomedical applications. It was also found that sub-micrometre length-scale phase-separated domains were formed in F8BT:TFB spin cast thin films. The nanophase-separated domains of F8BT-rich and TFB-rich areas were close to one order of magnitude smaller (in the lateral direction) than those reported in the literature. When the quantum dot nanoparticles were added to the blend thin films, it was found that the QDs prefer to lie in the F8BT areas alone. Furthermore, adding quantum dots to the system, purer F8BT and TFB nano-phase separated domains were obtained. Conjugated polymer blend thin films are excellent candidates for alternatives to the inorganic semiconductor materials for use in applications such as light emitting diodes and photovoltaic cells, mainly due to the ease of processing, low-cost fabrication and mechanical flexibility. The rather limited optoelectronic efficiency of the organic thin films can be significantly improved by adding inorganic semiconducting nanoparticles.

No description available.

Yes / Tattooing has long been practised in various societies all around the world and is becoming increasingly common and widespread in the West. Tattoo ink suspensions unquestionably contain pigments composed of nanoparticles, i.e., particles of sub-100 nm dimensions. It is widely acknowledged that nanoparticles have higher levels of chemical activity than their larger particle equivalents. However, assessment of the toxicity of tattoo inks has been the subject of little research and ink manufacturers are not obliged to disclose the exact composition of their products. This study examines tattoo ink particles in two fundamental skin components at the nanometre level. We use atomic force microscopy and light microscopy to examine cryosections of tattooed skin, exploring the collagen fibril networks in the dermis that contain ink nanoparticles. Further, we culture fibroblasts in diluted tattoo ink to explore both the immediate impact of ink pigment on cell viability and also to observe the interaction between particles and the cells.

This dissertation serves to study a protein's conformation-function relationship since immobilized proteins often behave differently from their solution-state counterparts. Therefore, this study is important to the application of protein-based biodevices. Another aim of this dissertation is to explore a new approach to realize low voltage electrowetting without the help of oil bath. Utilizing this approach, a protein micro-separation was realized. Additionally, the interfacial properties of ionic liquid (IL) solid-like layer, which played a key role in electrowetting, was studied for further developments of IL-based applications. Atomic Force Microscopy (AFM) was utilized in the study and played multiple roles in this dissertation. First, AFM was used as a fabrication tool. In the contact mode, conductive AFM tip was used to conduct the electrochemical oxidation to create a chemical pattern or to conduct an electrowetting experiment. Subsequently, AFM was used as a characterization tool in the tapping mode to characterize the surface structure, the thickness, and the surface potential. Furthermore, AFM in the contact mode was used as a measurement tool to measure the tribological force properties of sample. The results of the study concerning the conformational change in immobilized calmodulin showed that the immobilized CaM retained its activity. Additionally, the immobilization of CaM on a solid support did not interfere with the ability of the protein to bind calcium, as well as CaM kinase binding domain. For the electrowetting experiment, our data suggested that the ultra-high capacitance density of the IL dielectric layer leads to the low voltage electrowetting. We also successfully demonstrated the streptavidin and GFP proteins separation by Electrowetting-on-Dielectric (EWOD) force. The results of the surface properties study indicated that the charge and dipole of the substrate can influence the structures and properties of the IL interfacial layer. Our study would be beneficial in research and assay work involving engineered proteins, as well as the study and development of electrowetting applications.

Lipid bilayers form the basis of the membranes that serve as a barrier between a cell and its physiological environment. Their physical properties make them ideally suited for this role: they are extremely soft with respect to bending but essentially incompressible under lateral tension, and they are quite permeable to water but essentially impermeable to ions which allows the rapid establishment of the osmotic gradients. The function of membrane proteins, which are vital for tasks ranging from signal transduction to energy conversion, depends on their interactions with the lipid environment. Because of the complexity of natural membranes, model systems consisting of simpler lipid mixtures have become indispensable tools in the study of membrane biophysics. The objective of the work reported here is to develop a deeper understanding of the underlying physics of lipid bilayers through nanoscale measurements of the mechanical properties of mixed lipid systems including cholesterol, a key ingredient of cell membranes. Atomic force microscopy (AFM) has been used extensively to measure the topographical and elastic properties of supported lipid bilayers displaying complex phase behaviour and containing mixtures of important PC, PE lipids and cholesterol. Phase transformations have been investigated varying the membrane temperature, and the effects of cholesterol in controlling membrane fluidity, phase, and energetics have been studied. Elastic modulus measurements were correlated with phase behaviour observations. To aid in the nanoscale probing of lipid bilayers, AFM probes with a high aspect ratio and tip radii of $sim$4~nm were fabricated and characterised. These probes were used to investigate the phase boundary in binary and ternary lipid systems, leading to the discovery of a raised region at the boundary which has implications for the localisation of reconstituted proteins as well as the role of natural domains or lipid rafts. The electrical properties of the probes were examined to assess their potential application for combined structural and electrical measurements in liquid. A novel technique was developed to aid in the study of the physical properties of lipid bilayers. Membrane budding was induced above microfabricated substrates through osmotic pressure. Modification of the adhesion energy of the bilayer through biotin-avidin linking was successful in modulating budding behaviour of liquid disordered bilayers. The free energy of the system was modelled to allow quantitative information to be extracted from the data.

"Polyelectrolyte multilayer (PEM) thin films prepared via the Layer-by-Layer (LbL) deposition technique are of special interest in this research. The purpose of this study is to replace current mechanical closure systems, based on hook-and-loop type fasteners (i.e. Velcro), with PEM thin film systems. The technique is simple, cheap, versatile and environmental friendly; as a consequence a variety of thin films can be easily fabricated. By proposing PEMs as non-mechanical and nanoscopic molecular closures, we aim to obtain hermetic sealing, good adhesive strength, and peel off ease. Atomic force microscopy (AFM) and colloidal probe techniques were used to characterize the morphology, roughness and adhesive properties of PEMs. AFM measurements were conducted in air, necessarily requiring careful control of ambient humidity. PEMs were formed by consecutive deposition of polyanions and polycations on a charged polyethylene terephthalate (PET) solid surface, the result of which was stable nanostructured films. By systemically varying the parameters of PEM build-up process: different combinations of polyelectrolytes, different numbers of bilayers (polyanion/polycation pairs), and miscellaneous types and concentrations of salts (NaCl, NaBr and NaF salts at 0.5 M and 1.0 M concentrations), the adhesion and morphology of PEMs were thoroughly investigated. The PEM thin films specifically investigated include poly(ethyleneimine) (PEI), poly(styrene sulfonate) (PSS), poly(allylamine hydrochloride) (PAH), poly(acrylic acid) (PAA), and poly(diallydimethylammonium chloride) (PDADMAC). Silica colloidal probes were utilized in the investigation, some of which were functionalized with COOH and/or coated with PEI-PSS. Silica colloidal probes were used in order to quantify interaction forces on the PEMs. A functionalized silica colloidal probe (a probe with COOH surface chemistry) and a silica colloidal probe coated with PEI-PSS were used to simulate PEM-PEM interactions. The results suggest that adhesion in the PEMs depend on the number of layers, the salt concentration and the salt type used during the build-up process, the environmental conditions where the adhesion force measurements were made, and the choice of probe. "

The development of ultrasound contrast agents, or microbubbles, over the past 40 years has increased the possibilities for diagnostic imaging, although, more recently they have been proposed as a new vehicle for delivery of drugs and genes. However, there yet remains a considerable lack of fundamental understanding of microbubble behaviour under ultrasound excitation which has restricted their translation to therapeutic use. This project focussed on three key areas relating to the generation, observation, and bioeffects of microbubbles and the ultrasound used in their excitation. The experimental endeavour involved first, a full characterisation of the performance of a rotating mirror high-speed camera (Cordin 550-62) that was previously used by our group [and others] to investigate microbubble dynamics. Specifically, the investigation begins with an assessment of the frame-rate reporting accuracy of the system, a key aspect to the robustness of quantitative measurements extracted from recorded image sequences. This is then followed by the demonstration of a novel method of analysis for examining the image formation process in this type of camera, which facilitates a sensor-by-sensor assessment of performance that was not previously realised. Consolidating with previous work from within the group, this new analysis method was used to clarify previous data, and in the process suggested the presence of a temporal anomaly embedded within recorded images. In addition, the analysis also revealed empirical evidence for the mechanisms leading to this anomaly. Following on, a holographic optical tweezer system was developed for the purpose of exercising precise spatial control over microbubbles within their experimental environment. By positioning microbubbles in specific arrangements, interesting behaviours that were not previously achieved experimentally in the context of shelled microbubbles, were observed. Furthermore, by careful positioning of microbubbles within the imaging plane, it was possible to exploit the temporal anomaly present in the camera to greatly improve the integrity of data recorded, and to also operate in an enhanced imaging mode. Group aspirations to accelerate the development of therapeutic microbubbles had previously generated some early work on the in-house generation of bespoke bubble populations using microfluidic lab-on-a-chip techniques. In order to facilitate further development in this area, a finite-element computational model was herein developed to aid next generation chip design. Finally, in a slightly different context, considering not only the mechanical effect a microbubble may effect in a therapeutic treatment, a single biological cell assay was developed in order to probe any mechanical effects that were induced by the excitation ultrasound itself. Capitalising on the precise force control possible with atomic force spectroscopy, the elastic moduli of cells pre- and post-ultrasound insonation (sans microbubbles) were recorded. These new developments have extended the group capability and expertise in the areas of high-speed imaging, experimental observations of microbubble dynamics and with microfluidic generation of microbubbles. Additionally, the insights garnered have both served to consolidate the group's previous and as yet unpublished data, opening the way for circulation with absolute confidence in the integrity of that data.

The aim of this work is to better understand the factors and mechanisms leading to the supramolecular organization of collagen layers adsorbed on polymers. Native collagen adsorption on polystyrene (PS) and plasma-oxidized polystyrene (PSox) substrates revealed that the adsorbed layer consists in two parts: a dense and thin sheet (~ 10 nm) in which fibrils are formed, as revealed by atomic force microscopy, and an overlying thick layer (~ 200 nm) which contains protruding molecules, as revealed by quartz crystal microbalance with dissipation monitoring. The protruding molecules are in low density but modify noticeably the local viscosity. Faster and enhanced fibril formation takes place on hydrophobic compared to hydrophilic substrate. As a result of drastic thermal denaturation, the ability of collagen to assemble into fibrils is lost and the number of protruding molecules responsible for higher viscosity is reduced. Radiochemical measurements showed that collagen molecules are more easily displaced when adsorbed on a hydrophobic substrate compared to a hydrophilic substrate. This may explain why fibril formation occurs more readily on the more hydrophobic substrate, but is in contrast with higher surface affinity. The possible explanation of this paradox by the quick formation of a dense layer of collagen molecules having a smaller number of contact points with a very hydrophobic surface could not be demonstrated by a comparison of adsorption procedures. Comparing different collagen sources revealed various modes of aggregation with different characteristics regarding size and order (large fibers in solution, smaller fibrils to featureless underneath layer in the adsorbed phase). Moreover, collagen aggregation in the solution is a process competing with adsorption: more aggregated solutions behave like less concentrated solutions regarding the adsorbed amount and fibril formation in the adsorbed phase. It must be emphasized that interpretation of the QCM-D data, which is based on fitting physical quantities according to a model, has to be performed very carefully, and requires the examination of the sensitivity of the fitted data to the fitting parameters.

No description available.