No / The growth in Micro Electro-Mechanical Systems (MEMS) and demand for functional devices at smaller and smaller length scales has placed increasing demands on industry for product miniaturisation. Consequently, the micro-injection moulding (micromoulding) technology has evolved for the mass production of minute, intricate, polymer and composite components. Although there has been significant growth in the technology, there is little understanding of the effects of the process dynamics on product properties. This paper presents details of a programme of work conducted within these laboratories with the objectives of enhancing the understanding of polymer processing-property interaction. More particularly, the effects of microscale processing on the rheological, mechanical and tribological properties of engineering and commodity polymers, nanocomposites, metal and ceramic injection moulded feedstock and biomaterials are being explored. Simple analysis reveals that process conditions are potentially more severe on melts than those encountered during conventional moulding. High shear and rapid cooling rates combined with a large surface area to volume ratio may have a much greater influence over the resultant properties of a micromoulded product. A Battenfeld Microsystem50 micromoulding machine has been instrumented with a variety of sensors and data acquisition equipment, producing process data for a number of different cavity geometries. A novel microinjection compounding (MIC) machine has also been developed minimising the process stages and reducing material exposure to excessive residence times. This paper gives details of the effects of micromoulding process conditions on component surface morphology and mechanical properties measured using SEM, atomic force microscopy and nano-indentation techniques.

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Within a colloidal dispersion, the presence of negatively adsorbing material can produce a variety of effects on the dispersion properties and interactions. With increasing concentration, the negatively adsorbing material induces both depletion and structural forces on the dispersion, which can dramatically affect both colloidal stability and near-contact hydrodynamics. This project focused on expanding our understanding of the effects of such negatively adsorbing materials on both equilibrium and dynamic interactions between particles. The effects of charged, hard spheres (silica nanoparticle) on the hydrodynamic drag force a particle experiences as it approaches a flat plate were measured experimentally using colloid probe atomic force microscopy (CP-AFM). Deviation was found between the measured drag force and predictions for the drag force in a simple, Newtonian fluid. The measured drag force was always smaller than the predicted drag force as the particle approached contact with the plate. An effective viscosity, that approached the dispersing fluid viscosity at contact and the bulk viscosity at large separations, was determined for the system. This effective viscosity displayed similar characteristics to those predicted theoretically by Bhattacharya and Blawzdziewicz (J. Chem. Phys. 2008, 128, 214704.). The effects of both anionic and cationic micelles on the depletion and structural forces in a colloidal dispersion were studied both experimentally (with CP-AFM) and theoretically. The depletion and structural forces between a microparticle and a flat plate were measured and compared with the depletion force predicted by the force-balance model of Walz and Sharma (J. Colloid Interface Sci. 1994, 168, 485-496.). Consistent with previous work, the measured depletion force for both micelles was smaller in magnitude than that predicted by the Walz and Sharma model for hard, charged spheres. It is theorized that rearrangement of the micelle surfaces charges or physical deformation of the micelles may be responsible for the observed result. An effective surface potential for the micelles is proposed as a correction to the Walz and Sharma model. Finally, the stability of colloidal dispersions was studied macroscopically in solutions of ionic micelles. The colloidal dispersions displayed clear flocculation behavior in both cationic and anionic micelles. This flocculation behavior was compared with energy profiles determined from CP-AFM experiments between a single particle and a flat plate. A simple phase diagram was proposed for predicting the stability of colloidal dispersions based solely on the depth of the depletion energy well and the height of the repulsive energy barrier. / Ph. D.

This study describes the covalent and the electrostatic attachment of molecules, nano-particles, and proteins to patterned self-assembled monolayers. A scanning probe nanografting technique was employed to produce patterns of various sizes, down to 10 nm. Thus, we are able to demonstrate a degree of surface patterning which is an order of magnitude smaller than that used in the semiconductor industry. One efficient strategy for creating chemically specific nanostructures is to use the extraordinary catalytic properties of enzymes. However, as the dimension of a catalyst patch is reduced down to nanometer scale, it is difficult to detect the very low concentration of product. This study resolves the problem by developing a new strategy: the surface trapping of a product generated by a nanometer-scale patch of surface-bound enzyme. An array of proteins finds use when the array contains a number of different proteins. Toward this end, a new and convenient method for immobilizing enzymes is developed, which will allow the preparation of thin films containing several different catalytically-active enzymes on the nanoscale. The disadvantage of scanning probe nanografting technique is that the AFM tip loses resolution through wear during the patterning procedure. This study examines the possibility of developing a new AFM lithographic method to avoid wear: the use of enzymes covalently attached to a tip as a site-specific catalyst. / Ph. D.

This thesis addresses development of a new force spectroscopy tool, correlation force spectroscopy (CFS), for the measurement of the mechanical properties of very small volumes of material (molecular to µm³) at kHz-MHz time-scales. CFS is based on atomic force microscopy (AFM) and the principles of CFS resemble those of dual-trap optical tweezers. CFS consists of two closely-spaced micro-cantilevers that undergo thermal fluctuations. Measurement of the correlation in thermal fluctuations of the two cantilevers can be used to determine the mechanical properties of the soft matter, e.g. a polymeric molecule, that connects the gap between the two cantilevers. Modeling of the correlations yields the effective stiffness and damping of the molecule. The resolution in stiffness is limited by the stiffness of the cantilever and the frequency by the natural frequency of the cantilevers, but, importantly, the damping resolution is not limited by the damping of the cantilever, which has enabled high-resolution measurements of the internal friction of a polymer. The concept of CFS was originally presented by Roukes' group in Caltech [Arlett et al., Lecture Notes in Physics, 2007]; I developed the first practical versions of CFS for experimentation, and have used it in two applications (1) microrheology of Newtonian fluids and (2) single molecule force spectroscopy. To understand the correlation in thermal fluctuations of two cantilevers I initially validated the theoretical approach for analyzing correlation in terms of deterministic model using the fluctuation-dissipation theorem [Paul and Cross, PRL, 2004]. I have shown that the main advantages of such correlation measurements are a large improvement in the ability to resolve stiffness and damping. Use of CFS as a rheometer was validated by comparison between experimental data and finite element modeling of the deterministic vibrations of the cantilevers using the known viscosity and density of fluids. Work in this thesis shows that the data can also be accurately fitted using a simple harmonic oscillator model, which can be used for rapid rheometric measurements, after calibration. The mechanical properties of biomolecules such as dextran and single stranded DNA (ssDNA) are also described. CFS measurements of single molecule properties of ssDNA reveal the internal friction of the molecule in solution. / Ph. D.

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 work describes two closed-loop atomic force microscopy methods that utilize the heated silicon probe to interrogate surfaces. The first method identifies the softening temperatures of a selected polymer and organic substrate as a function of contact force and surface hardness. Motivation partly stems from nanosampling, which requires knowledge of phase-specific transitions to identify and extract mass from multicomponent systems for chemical analysis. In the second method, the cantilever is implemented as a Kelvin probe to study the effect of temperature on the measured contact potential. The objective is to ascertain whether the probe functions as a capable electrode for scanning Kelvin probe microscopy (SKPM) applications. This was achieved by performing heated force-distance experiments on a biased gold film with the tip operating at various potentials. Both experiments examine the interaction between the tip and substrate and analyze sample effects both induced and sensed by the cantilever.