The adsorption kinetics of surfactants at the solid--liquid interface is of fundamental interest to a wide variety of process including detergency, wetting of solid surfaces, agricultural sprays and paper processing. Accordingly, a significant body of work has been carried out to understand this field. Much of this work has used the optical techniques of ellipsometry and optical reflectometry or mass measurements from the quartz crystal microbalance. These methods have the time resolution to measure surfactant adsorption kinetics but are insensitive to chemical composition and thus produce limited information on the adsorption of surfactant mixtures. The technique I adopt here, total internal reflection (TIR) Raman spectroscopy, provides detailed information about the chemical composition of the surface with a time resolution of 2\,s. The short penetration depth of the probe laser into solution (${\sim}100$\,nm) provides surface sensitivity. The different components of the adsorbed film are distinguished by their vibrational Raman spectra. The Raman signal from a component in the adsorbed layer is linearly proportional to the amount of that component present, allowing straightforward interpretation of the acquired data. I use principal component analysis to deconvolute the recorded spectra. First I look at the equilibrium and kinetic aspects of the adsorption of two model surfactants to a flat silica surface as single component systems: the cationic surfactant cetyltrimethylammonium bromide (CTAB) and the non-ionic surfactant Triton X-100. Use of the well-defined wall jet geometry provides known hydrodynamics allowing the mass transport to the surface to be modelled. The mass transport model is coupled with a kinetic model consistent with the Frumkin isotherm allowing the whole adsorption process to be captured. The fit between the model and the experimental results helps to understand interactions on the surface. Secondly I look at the two model surfactants adsorbing to silica as a mixed system. The adsorption isotherm shows strong synergistic behaviour with the addition of small amounts of CTAB (${\sim}2$\%\ of the 2\,mM total surfactant concentration) doubling the adsorbed amount of Triton X-100. This synergism has a marked influence on the kinetics: for example, when Triton X-100 replaces CTAB the Triton X-100 surface excess overshoots its equilibrium value and returns only very slowly to equilibrium. For systems above the cmc, the repartitioning of surfactant between micelles and monomers results a local increase in the monomer concentration of Triton X-100 resulting in a temporary spike in the Triton X-100 surface excess during the rinsing of a mixed layer. Finally I study alternative model surfaces to silica. The adsorption to CTAB and Triton X-100 to a cellulose surface is studied, and detailed equilibrium isotherms obtained by slow variation of the bulk concentration controlled with a continuous stirred tank mixer. The preparation of the model cellulose surface is also followed spectroscopically. Spectra are also acquired from mica surfaces in optical contact with silica hemispheres; it is unfortunately not yet possible to acquire useful data on adsorption at the mica--water interface.

This project is devoted to the study of solid-liquid interfaces in pure Fe and Fe-C alloys using molecular simulation. It consists of three parts: first, we use the coexisting phases approach to calculate melting phase diagrams of several recent Fe-C interaction potentials, such as Embedded Atom Method (EAM) potential of Lau et al., EAM potential of Hepburn and Ackland, and Analytic Bond Order (ABOP) potential of Henriksson and Nordlund. Melting of both bcc (ferrite) and fcc (austenite) crystal structures is investigated with C concentrations up to 5 wt%. The results are compared with the experimental data and suggest that the potential of Hepburn and Ackland is the most accurate in reproducing the melting phase diagram of the ferrite but the austenite cannot be stabilised at any C concentration for this potential. The potential of Lau et al. yields the best qualitative agreement with the real phase diagram in that the ferrite-liquid coexistence at low C concentrations is replaced by the austenite-liquid coexistence at higher C concentrations. However, the crossover C concentration is much larger and the ferrite melting temperature is much higher than in the real Fe-C alloy. The ABOP potential of Henriksson and Nordlund correctly predicts the relative stability of ferrite and austenite at melting, but significantly underestimates the solubility of C in the solid phases. Second, we develop a new direct method for calculating the solid-liquid interfacial free energy using deformation of the solid-liquid coexistence system. The deformation is designed to change the area of the interface, while preserving the volume of the system and crystal structure of the solid phase. The interfacial free energy is calculated as the deformation work divided by the change of the interfacial area. The method is applied to the bcc solid-liquid interface of pure Fe described by the Hepburn and Ackland potential. The obtained results are somewhat different from those calculated by the established methods so further development and analysis are required. Third, we investigate the dependence on C concentration of the bcc solid-liquid interfacial free energy of Fe-C alloy described by the Hepburn and Ackland potential. We use the method proposed by Frolov and Mishin which is analogous to the Gibbs-Duhem integration along the solid-liquid coexistence line. The calculations are performed for three different crystal orientations (100), (110) and (111), allowing us to determine the anisotropy of the interfacial free energy and its dependence on C concentration along the coexistence line. Although the precision is somewhat limited by the high computational cost of such calculations.

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Adhesion is a well-studied phenomenon, mainly for its industrial importance. We consider a smart water-based adhesive that is switchable, i.e. the adhesion may be turned on and off by an environmental trigger, in this case the pH. The interaction investigated is between a weak polyacid hydrogel of poly(methacrylic acid) (PMAA) and poly [2-( dimethyl amino )ethyl methacrylate] (PDMAEMA, a weak polybase) chemically grafted to planar silicon substrates (brushes) by atom transfer radical polymerisation. The interaction between PDMAEMA and PMAA is of great interest because it represents a situation where a surface adhesive (a polybase in contact with a polyacid) can be turned on and off simply by changing the external environment. In particular we observe that at pH less than 2, there is no significant interaction between the brush and hydrogel, whereas above pH 3, there is strong adhesion comparable to epoxy glue. The interaction between the brush and the gel is pressure sensitive so that the adhesion energy is a function of the applied load. To understand the mechanism involved in the pressure sensitive behaviour we performed neutron reflectivity experiments of the brush in contact with the hydrogel after known pressures were applied. Comparison of the conformations of brushes of different thicknesses but with the same applied pressure shows that the interaction between the brush and hydrogel takes place at the interface and is mainly due to electrostatic interactions between the carboxylic group of the hydrogel and the amino group into the brush. Viscoelastic dissipation in the hydrogel also contributes to the total work of adhesion.

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Controlling the behaviour of atmospheric pressure plasmas and their interaction with polymeric materials is of major interest for surface modification applications across multidisciplinary fields intersecting biomedical engineering, bio-nanoengineering, clinical/medical science, material science and microelectronics. The aim of the present work is to investigate the behaviour of atmospheric pressure dielectric barrier discharges in closed systems (microfluidic devices) and open systems (glass capillary devices) and their polymer-surface interactions. Atmospheric pressure microplasma jets operating in helium gas have been used to modify locally the surface energy of polystyrene (PS) and to interact directly with the surface of analytes using a novel plasma assisted desorption ionisation (PADI) method causing desorption and ionization to occur. Although atmospheric pressure micro-jets are now widely studied for the treatment of materials there is still a lack of understanding of the fundamental plasma-surface processes. A number of recent studies using plasma micro-jets for the surface modification of polymerics have used systems in which the emerging plume impinges directly the substrate head-on. Here, by placing the micro-jet side-on to the substrate we can observe how different flow regions of the jet affect the sample, allowing individual effects to be seen. In addition, this configuration may prove an efficient way of treating samples with reduced or no surface damage. These conclusions are considered to be an important contribution to the study of complex mechanisms underpinning the behaviour of radicals and reactive species in surface modification processes of polymeric materials. The study of the behavioural mechanism involved in the plasma was done using various diagnostic techniques such as electrical measurements, optical emission spectroscopy (OES), Time-averaged and time-resolved ICCD Optical Imaging and Schlieren Photography. The filamentary discharge mode was observed in bonded microchannels using metallic and liquid-patterned electrodes. The treated surfaces were characterised using various techniques such as X-ray photoelectron spectroscopy (XPS), Atomic Force Microscopy (AFM), Optical profiling measurements and Water Contact Angle (WCA) measurements. Schlieren photography has been used to indentify regions of laminar (pre-onset of visual instability) and turbulent flows (post-onset of visual instability) in the exiting gas stream and the nature of their interaction with the substrate surface. The length of both regions varies depending on operating parameters such as frequency, applied voltage and flow rate. WCA results from treated polystyrene (PS) samples exposed directly facing the microjet reveals a change from hydrophobic (high contact angle) to a hydrophilic (low contact angle) surface with substantial reductions in WCA (~ 50 to 60 °) occurring in downstream regions where the turbulent gas mixed with air impinges the substrate surface. In contrast, only small changes in WCA (~ 10 to 20 °) occur in regions where the gas flow is laminar. AFM imaging of treated PS samples reveal holes and ripple like effect with a much larger area than that of the capillary seen on treated samples positioned “head-on” and directly facing the sample but this was not seen using the side-on configuration. The results indicate that excited air species (either mixed or entrained in the He gas flow) which exist only in regions of turbulence are the main agents causing surface covalent bond breaking leading to surface modification. This thesis reports on atmospheric pressure microdischarges and their applications, a brief summary of work done so far including major results, using new and existing technologies including those under development in terms of design, properties and working conditions.

The primary aim of this thesis was to study the physical effect of energetic deposition on metal thin films. The secondary aim is to enhance the quality of the films produced to a desired quality. Grazing incidence X-ray reflectivity (GIXR) measurements from a high-energy synchrotron radiation source were carried out to study and characterise the samples. Optical Profilers Interferometry, Atomic Force Microscope (AFM), Auger electron spectroscopy (AES), Medium energy ion spectroscopy (MEIS), and the Electron microscope studies were the other main structural characterisation tools used.