Highly organised structures have been well-known to be part of the complex neuronal network presented in the nervous system, where thousands of neuronal connections are arranged to give rise to critical physiological functions. Conventional in vitro culture methods are useful to represent simplistic neuronal behaviour, however, the lack of such organisation results in random and uncontrolled neurite spreading, leading to a lack of cell directionality and in turn, resulting in inaccurate neuronal in vitro models. Neurons are highly specialised cells, known to be greatly dependent on interactions with their surroundings. Therefore, when surface material is modified, drastic changes in neuronal behaviour can be achieved. The use of chemically modified surfaces in vitro has opened new avenues in cell culture, where the chaotic environment found in conventional culture methods can be controlled by the combination of surface modification methods with surface engineering techniques. Polymer brushes and self-assembled monolayers (SAMs) display a wide range of advantages as a surface modification tool for cell culture applications, since their properties can be finely tuned to promote or inhibit cellular adhesion, differentiation and proliferation. Therefore, when precisely combined with patterning techniques, a control over neuronal behaviour can be achieved. Neuronal patterning presents a system with instructive cues that can be used to study neuron-neuron communication by directing single neurites in specific locations to initiate synapses. Furthermore, although this area has not been much explored, the use of these patterned brushes could also be used in co-culture systems as a platform to closely monitor cell heterotypical communication. This research demonstrates the behaviour of SH-SY5Y neurons on a variety of SAMs and polymer brushes, both in isolation and combination to promote cellular spatial control. APTES and BIBB coatings promoted the highest cell viability, proliferation, metabolic activity and neuronal maturation, whilst low cell adhesion was seen on PKSPMA and PMETAC surfaces. Thereafter, PKSPMA brushes were used as a potential cell repulsive coating and its combination with micro- patterning techniques (photolithography and soft lithography) resulted in a system with instructive cues for neuronal guidance, where neuronal directionality was obtained. In the final chapter of this thesis, a chimeric co-culture system was developed where the patterned SH-SY5Y cells were co-cultured with C2C12 myoblasts in an attempt to obtain an organised neuronal-muscle co-culture system. Whilst preliminary observations showed first stages of a patterned neuronal-muscle co-culture, future work is necessary to refine and improve the patterned co-culture process.

Polymer applications have become more demanding as industry continuously turns to more microscopic parts. Due to the interactions of the polymer chains with the supporting surface and the air interface, the thinner films required for such applications have distinctly different properties than those of the well-defined bulk systems. The goal of the current research is to elucidate the behavior of ultrathin films. Two separate studies were performed on thin films supported on silicon wafer substrates: the first focuses on the viscoelastic cooperativity of thin films, and the second concentrates on the morphological behavior of polymer brush films. For the first study, polymethyl methacrylate films were spin coated onto silicon wafers, and the film thickness was determined using ellipsometry. A series of thin films were examined using techniques such as dielectric analysis and thermal mechanical analysis. The theory of cooperativity, which explains polymeric behavior using the intermolecular and intramolecular forces among polymer chains, was employed to understand the behavior of these thin films. Another type of thin film, a polymer brush, was investigated in the second study. Polymer brushes are formed by chemically bonding one end of many polymer chains to a substrate. The other ends of the chains can interact with the surrounding environment creating a brush-like structure. Constraining one end of a polymer chain alters the behavior of such a thin film. Polymer brushes of the di-block copolymer poly(t-butyl methacrylate) and polystyrene were produced on silicon wafers using spin coating techniques. The effects of both grafting density and solvent washes were analyzed using contact angle analysis and atomic force microscopy. In addition, hydrolysis was successfully performed on existing polymer brush samples to produce polymer brushes of the di-block copolymer polymethyl acrylic acid and polystyrene. / Master of Science

The research project aimed to synthesise semiconducting polymer brushes (polymer chains densely grafted to a surface) utilising simple and efficient organic chemistry methods, with a view to use in molecular-level electronic applications. Conjugated polymers were initially chosen for their ability to conduct electrical charge along a polymer chain by facilitating electron transfer between π-bonds. Polymers also aimed to be living , which could allow for further chain growth at a later point in time. This could lead to the production of various useful brush block co-polymers, with different blocks (or layers) of polymers having different chemical, structural and electronic properties. Initially, several syntheses towards monomers for poly(phenyl isocyanide) and poly(quinoxaline-2,3-diyl) were undertaken with limited success. Attention was turned to the synthesis of poly(thiophene)s by Kumada catalyst-transfer polymerisation (KCTP), again with varying success. After this, ring-opening metathesis polymerisation (ROMP) was explored as a possible avenue. The successful synthesis of several cyclopropenes for use as monomers was carried out. However, the ROMP of these monomers failed. ROMP of unsubstituted norbornene was successful. XPS studies suggested that vapour deposition of SAMs (Self Assembled Monolayers) gave homogenous monolayers. Solution-phase depositions appeared prone to inhomogeneous multilayer deposition. Vapour deposited SAMs gave better grafting densities at lower deposition pressures, leading to thicker polymer brushes. Finally, atom transfer radical polymerisation (ATRP) methods have been investigated. ARGET-ATRP was determined as the favoured method as it uses lower quantities of copper. Functionalised monomers for ATRP were synthesised, but homopolymers of these polyaromatic monomers have been difficult to synthesise by both copper-mediated ATRP and AIBN initiation. Polymer brushes and polymer brush diblocks of post-polymerisation modified PHEMA and PDMAEMA have been successfully grown on silicon wafers and glass slides, with a view to using the diblocks of these polymers as effective bulk heterojunction photovoltaic devices. The kinetics of the growth of both polymers by the ARGET and ATRP methods were studied to determine the degree to which each polymerisation is living; to determine if diblock growth would be possible. PHEMA brushes were successfully modified with a range of polyaromatic acid chlorides. Focussing on anthracene (which has excellent fluorescence properties, displaying a clear ability to move electrons between energy levels), this attachment was further confirmed by a range of techniques, before successfully growing a brush diblock of the unfunctionalised and functionalised polymers.

No description available.

Polymer brushes provide the responsive smart surfaces which can be used for fabrication of various devices. In this thesis work, adhesion, friction, and wear of polystyrene (PS) - poly(2-vinyl pyridine) (P2VP) and polystyrene - poly(acrylic acid) (PAA) binary brushes and corresponding monobrushes were investigated in dried state under controlled environment. Spin-coated films were also investigated for comparison. The aim was to explore possibilities to control/tune adhesion, friction, and wear between inorganic or polymeric surfaces by use of polymer brushes. Atomic force microscopy (AFM) with sharp silicon nitride tip and colloidal probes was employed to investigate the nanoscale adhesion and friction forces between different inorganic and polymeric surfaces. Adhesion and friction on the polymer brushes were comparable to that on the spin-coated films. Adhesion and friction force values were correlated, and were in accordance with the wettability of the brush surfaces for most of the samples. Switching in the adhesion and friction forces was observed for the PS+P2VP and PS+PAA binary brushes on treatment with selective solvents. Maximum switching in adhesion force and friction coefficient was by a factor of 2.7 and 5.4, respectively. Furthermore, switching of friction for mixed brush surface was observed during macroscale friction measurements using nanoindenter. Friction coefficients at macroscale were higher than those at the nanoscale. Moreover, adhesion and friction forces between the surfaces were significantly influenced by the humidity, grafting density of polymer brushes, chemical composition of top of the binary brush surface, and tip scan velocity. Nanowear studies were carried out with AFM using sharp silicon nitride tip while macrowear studies were carried out using nanoindenter. Nanowear on the surfaces was affected by molecular entanglements, adhesion and friction forces as well as shape and status of the tip. It was observed that the typical wear mode for PS brushes (treated with toluene) was ripple formation. In case of P2VP brushes (treated with ethanol) and PAA brushes (treated with pH 10 water), wear occurred via removal of the polymeric material. Wear mechanism observed for the monobrushes was similar to that observed for the spin-coated thick films of the same polymeric material. However, extent of the wear on the brush surfaces significantly differed from that on the spin-coated films. In case of PS+P2VP and PS+PAA binary brush samples, change in the wear mode was observed on treatment with the different selective solvents. On treatment with toluene (PS on the top), both of these binary brushes showed the wear by formation of the ripples. On the other hand, when these binary brushes were treated with selective solvent for P2VP or PAA, wear occurred mainly via removal of the polymeric material. The amount of wear increased with the number of scans for all the polymer brush samples. Moreover, wear on the polymer brush surfaces was also increased on increase in the applied load and decrease in the scan speed. Wear behavior on macroscale was averaged due to contact between surfaces at large number of asperities. Our results show that adhesion, friction, and wear of polymer surfaces can be controlled/tuned by the use of binary polymer brushes.

Polymer brushes generated via "grafting-from" approach emerged as an attractive surface modification tool offering chemical stability, synthetic flexibility and unprecedented control over the polymer grafting density, thickness, chemical composition and functionality. They display interesting features to many applications in regenerative medicine including cell culture, tissue engineering and as delivery systems due to exquisite control of physicochemical and biological properties. Cationic polymer brushes are particularly attractive in the field of designing effective vectors for gene delivery as polymer brush allows the design and coating of a variety of particles with well-defined core-shell architecture and chemistry to efficiently condense and deliver nucleic acids. This thesis concentrates on designing safe and efficient gene delivery vectors based on 'graft from' cationic polymer brush and understanding the interaction of nucleic acids with polymer brush. Chapter one presented fundamental knowledge of polymer brush and its biomedical application. The first part of this chapter describes the definition of polymer brush, the preparation strategies, mechanism of atom transfer radical polymerisation and the responsiveness of polymer brush including solvent, pH and ionic strength. The second part discusses the state-of-art applications of polymer brush in regenerative medicine including protein resistant polymer brush for tissue engineering and as drug/gene delivery systems.

There is an increasing demand for materials that are physically robust, easily recovered, and able to perform a wide variety of chemical functions. By combining hard and soft matter synergistically, organic-inorganic hybrid materials are potentially useful for a number of applications (e.g. catalysis, separations, sensing). In this respect, organic/ordered mesoporous silica (OMS) hybrids have attracted considerable attention, with an increasing emphasis on complex organic moieties achieved through multi-step reactions and polymerizations. It is on this front that we have focused our work, specifically in regard to polypeptides. Polypeptides are well suited organic components for hybrids as they provide a wide range of possible side chain chemistries (NH2, -SH, -COOH, -OH, etc.), chirality, and have conformations that are known to be responsive to external stimuli (pH, electrolytes, solvents, etc.). Our work has shown that N-carboxyanhydride chemistry offers a facile single step approach to the incorporation of dense polypeptide brushes in OMS. Modifying the initiator loading, pore size, pore topology, and monomer identity significantly impacted the properties of the obtained composites and peptide brush layers. Extending this work, a synthesis paradigm for preferentially grafting poly-L-lysine to the external and internal surfaces of SBA-15, a widely used OMS material, was developed. We observed that the pores of these hybrids could be opened and closed by the reversible swelling of the polypeptide layer. Similarly, novel bifunctional hybrids were synthesized by grafting polypeptides to the external surface of monodisperse OMS spheres that contain a thiol-functionalized core. The accessibility of the internal thiols to a fluorescent dye shows the potential of these hybrids for applications such as controlled uptake/release.

This research focuses on the modeling of surfaces decorated by grafted polymers in order to understand their structure, energetics, and phase behavior. The systems studied include flat and curved surfaces, grafted homopolymers and random copolymers, and in the presence of solvent conditions, homopolymer melt conditions, and diblock copolymer melt conditions. We use self-consistent field theory to study these systems, thereby furthering the development of new tools especially applicable in describing curved particle systems and systems with chemical polydispersity. We study a polymer-grafted spherical particle interacting with a bare particle in a good solvent as a model system for a polymer-grafted drug interacting with a blood protein in vivo. We calculate the energy of interaction between the two particles as a function of grafting density, particle sizes, and particle curvature by solving the self-consistent field equations in bispherical coordinates. Also, we compare our results to those predicted by the Derjaguin approximation. We extend the previous study to describe the case of two grafted particles interacting in a polymer melt composed of chains that are chemically the same as the grafts, especially in the regime where the particle curvature is significant. This is expected to have ramifications for the dispersion of particles in a polymer nanocomposite. We quantify the interfacial width between the grafted and free polymers and explore its correlation to the interactions between the particles, and use simple scaling theories to justify our results. In collaboration with experimentalists, we study the behavior of the glass transition of polystyrene (PS) films on grafted PS substrates. Using the self consistent field theory methods described above as well as a percolation model, we rationalize the behavior of the glass transition as a function of film thickness, chain lengths, and grafting density. Grafting chemically heterogeneous polymers to surfaces in melt and thin film conditions is also relevant for both particle dispersion and semiconductor applications. To study such systems, we model a random copolymer brush in a melt of homopolymer that is chemically identical to one of the blocks. We modify the self-consistent field theory to take into account the chemical polydispersity of random copolymer systems and use it to calculate interfacial widths and energies as well as to make predictions about the window in which perpendicular morphologies of diblock copolymer are likely to form. We also explore the effect of the rearrangement of the chain ends on the surface energy and use this concept to create a simple modified strong stretching theory that qualitatively agrees with our numerical self-consistent field theory results. We explicitly study the system that is most relevant to semiconductor applications - that of a diblock copolymer melt on top of a substrate modified by a random copolymer brush. We explore the morphologies formed as a function of film thickness, grafting density, chain length, and chain blockiness, and make predictions about the effect of these on the neutral window, that is, the range of brush volume fractions over which perpendicular lamellae are expected to occur. / text

- / -

The issue of skin friction related injuries has been one of the problems challenging the artificial sports turf industry. It has been identified by users as a major factor impeding acceptance of artificial turf at the professional level. However, information explaining the mechanisms for skin-turf abrasion is limited and little progress has been made, it appears, to derive an appropriate testing method for product approval or in evidence of improvement of the skin-friendliness of these products in sport surface surfaces. This research project focused on exploring the potential for improving the skin-friendliness of artificial turfs through a multi-faceted approach: identifying the contribution of the abrasive-components in modern artificial turf surfaces through mechanical testing; while critically evaluating currently available skin friction standards , evaluating strategies for polymer material modifications to reduce the skin-surface friction; and the designing of an appropriate bench-top set-up for the lab-based assessment of material skin-friendliness. The lack of understanding of skin-turf interaction was addressed by identifying the turf-component that has the greatest influence on the skin-turf friction with the mechanical device used in the current industry standard. The skin -turf frictional profiles of a series of third generation (3G) turf surfaces were examined, in combination with independent measurements of the silicone skin surface roughness pre- and post-friction testing. Results indicated that turf carpets without any infill material exhibited the highest frictional values while surfaces completely filled with either sand or rubber displayed similarly low frictional values, independent of infill type. Morphological measurements also showed the largest decrease in surface roughness for skin samples tested on carpet-only surfaces, indicating a smoothening effect via abrasion. This abrading effect is alleviated with the addition of infill to the surface, with fully-filled surfaces having the least damage to the skin s. This unprecedented study suggests that the carpet may have the largest influence on the overall frictional behaviour of an artificial turf surface narrowing down the turf component to be targeted when applying product improvements to address skin-friendly properties. The strategy of material surface modification was then employed, to study the effect of polyzwitterionic brushes on improving the skin-friendliness of the identified polypropylene substrate. To address the intended application for artificial turfs, a bench-top test was developed to investigate the frictional properties of the hydrated samples outside of commonly used aqueous environments, where an excess of lubricating water molecules is absent. Photo-grafted poly(sulfobetaine methacrylate) (pSBMA) brushes of various irradiation durations were prepared and the improvement in frictional properties was studied. Frictional measurements using silicone skin tips, under both dry and hydrated surface conditions, showed that the applied modification was capable of forming a stable lubrication layer in the absence of excess water, significantly reducing the coefficient of friction by up to 78.8 %. The pSBMA brushes also provided the additional advantage of antifouling exhibiting resistance towards pathogenic Staphylococcus aureus with almost zero surface colonization for well-grafted samples. The low skin -sample friction under ambient conditions and desirable fouling-resistance highlights the potential of pSBMA brushes as a modification strategy for achieving skin-friendly surfaces targeted at reducing the risk of skin abrasions. The tribological implications of counter-surface selection were investigated. Frictional assessments of the pSBMA-modified samples were carried out using standard steel tribo-tips, in addition to the skin tips used. Measurements with the skin tips showed that the hydrated pSBMA brushes were successful in reducing initial skin -sample friction though the effect diminishes with extended testing, attributed to the drying of the interfacial water. The standard steel tribo-tips were unable to reciprocate these results, returning consistently low frictional values regardless of extent of surface modification or hydration. These observations draw attention to the importance of counter-surface selection in frictional assessments, highlighting how appropriate test materials can identify characteristic surface properties while providing an interaction that simulates that of the intended application. The simple experimental set-up used may potentially be enhanced as an intermediate product qualification method in the manufacturing of skin-friendly artificial turf yarns.