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No description available.

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There is a strong rationale for replacing traditional carbon fibre and glass fibre composites with nano-composites as smaller size and higher aspect ratio reinforcement can lead to improved mechanical properties, via improved load transfer from reinforcement to polymer matrix but also increased dissipation of mechanical energy within the material, an advantage for maximising toughness and fatigue resistance. This project focuses on using dynamic nanoindentation to characterise polymer nano-composites made with graphene and carbon nanotubes (CNT), namely, CNT-polymethylmethacrylate (PMMA) composites, CNT-polydymethylsiloxane (PDMS) and graphene-polyamide composites. Melt-processed PMMA nano-composites studied by optical microscopy show a gradual increase in aggregate size for the functionaLized CNT/PMMA composites, the results for the nonfu nctionalised CNT/PMMA composite showing a poorer dispersion of CNT. Thermogravimetric analysis (TGA) also indicates that the functionalized-CNT are better dispersed into the polymer. These results are consistent with those obtained by nanoindentation and Rockwell hardness testing; higher storage modulus, lower loss tangent and higher HR value for the composites made with functionalized-CNT, sign of a better interfacial load transfer. The addition of solvent, the use of tip sonication as well as the e NT aspect ratio were all found to have an influence on the CNT dispersion within in-situ cured CNTIPDMS nano-composites. TGA showed a lowering of the degradation temperature upon CNT addition, indicative of CNT inhibiting the cure process, in accordance with recently reported results. Nanoindentation resu lts indicate that the specimen made with the better dispersed CNT exhibit the larger storage modu lus. Generally, these stiffness values increase at low CNT content and then decrease, possibly because of the effect that CNT have upon the PDMS cross-linking. In these nanocomposites, the loss tangent is large, dominated by the elastomeric matrix and not sensitive to the interfacial energy dissipation. Finally. in situ-polymerised graphene-polyamide nano-composites were investigated. TGA showed that the graphene was oxidised in these composites. Optical microscopy indicates that the fine-dispersion of the reinforcement disappear at higher graphene content. Nanoindentation showed that the storage modulus peaked at low graphene content and then decreased at higher percentages, while tested at a larger scale (mm\ the mechanical properties of these composites only saturates with graphene content. This result may be due to the processing of the high graphene content specimen, made by solvent evaporation, during which aggregates may reform, as observed by optical microscopy. Overall, this investigation has shown that dynamic nanoindentation is a valuable tool for studying the dispersion of reinforcement in polymer nanocomposites.

Sherrington and co-workers have shown that branched vinyl polymers can be synthesized by the addition of a chain transfer agent to a conventional free radical statistical copolymerisation of a vinyl and a divinyl monomer. In the presence of the chain transfer agent, the molecular weight of the primary chains is reduced, gelation can be suppressed and soluble, branched polymers are obtained as the sole product. Living polymerisation techniques offer a way to control the primary chain length without the need for a transfer agent simply by adjusting the monomer/initiator molar ratio. It is suggested that a significant degree of intramolecular cyclisation is the most likely explanation for the remarkable delay in the onset of gelation.

Styryl-terminated polystyrene macromonomers have been synthesised by the anionic polymerisation of styrene. Initiation was by sec-butyl lithium; termination involved the addition of diphenylethylene prior to vinyl benzyl chloride. Characterisation of the macromonomers was performed using gel permeation chromatography (GPC) and proton nuclear magnetic resonance spectroscopy (nmr). Novel comb graft copolymers were synthesised by the copolymerisation of the macromonomer with a comonomer. The following comonomers were used: Z-vinylpyridine (Z-VP), 4- vinylpyridine (4-VP) and N-(vinylbenzyl)pyrrolidone (VBP). Graft copolymers were made with a range of compositions by varying the feed ratios of the comonomer to the macromonomer. Reactivity ratios were determined for the different graft copolymer systems and compared to the simple statistical copolymerisation of styrene with comonomer. Characterisation of the graft copolymers was performed using GPC, nmr and membrane osmometry. Micellar dispersions of the comb graft copolymers were prepared in cyclohexane, toluene and methanol. These were subsequently characterised by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Micellar behaviour was related to graft copolymer composition and structure. The graft copolymers were subsequently used as steric stabilisers in dispersion polymerisations of bis-hydroxyethyl terephthalate in high boiling aliphatic hydrocarbon, methyl methacrylate in cyclohexane, vinyl pyridine in toluene/cyclohexane and styrene in methanol. A number of parameters have been investigated including initiator, stabiliser and monomer concentrations. Graft copolymer composition and structure were shown to be important factors for the effective steric stabilisation of polymer particles in conjunction with information on surface coverage data.

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