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<p>The overall aim of this thesis was to prepare nanostructured more processable heteronuclear sulphonated polyanyline nanocomposites with electroconductive properties suitable for applications in biosensors. The sulphonated self-assembled polyaniline and derivatised polyaniline nanocomposites (SPAHs) were prepared by chemical oxidative polymerisation or electrical decomposition. The SPAHs prepared include those of polyaniline (PANi), poly-o-methoxyaniline (POMA) and poly-2.5 dimethoxyaniline (PDMA). Two types of sulphonic acids of heteronuclear aromatic hydrocarbons were used in the production of sulphonated SPAH composites. These were anthracene sulphonic acid (ASA) and naphthalene sulphonic acids (NSA) wich played both doping and surfactant roles.</p>

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The four-electrode method modified for laboratory use was employed for electrical conductivity measurements of eight Scottish and two Greek Ca-saturated soils (< 2 mm fraction) over a range of soil solution conductivities (0.5 - 10 dS m^-1 as CaCℓ2) and for a range of tensions (saturation to 8 bars). Soil bulk conductivity, κb(dS m^-1), was linearly related with the soil solution conductivity κw (dS m^-1) for the tensions used, the relationship being of the form, κb = 1/F_f κw + κs, where κs (dS m^-1) is the adsorbed Ca conductivity and 1/F_f accounts for tortuosity and available pore volume fraction for conductance. For each soil, 1/F_f was linearly related with the volumetric moisture content θ. It was found that for the type of the soils used, non-montmorillonitic soils and mean organic matter content 5% for the Scottish soils, the adsorbed Ca molar conductivity is only a small fraction (1 - 4%) of its infinite dilution value. Also κs was related to soil properties like clay content, total surface area, CEC and organic matter. Diffusion coefficients for Ca and Cℓ for the soil solution and for adsorbed Ca were calculated by the Nernst-Einstein relationship from the measured solution conductivities and from the κs values. For θ= 0.57 to 0.15 and soil solution concentration of 0.0025 - 0.0045M as CaCℓ2, Ca diffusion coefficients ranged from 2.67 to 0.062 x 10^-10m²s^-1 and Cℓ diffusion coefficients from 6.9 to 0.16 x 10^-10m^2s^-1. A concentration correction was applied. Adsorbed Ca diffusion coefficients ranged from 11.8 to 0.045 x 10^-12m^2s^-1 for θ= 0.52 tp 0.14. A bulk density effect was introduced by consolidating and compacting four of the soils with a static load of 0.45 kg cm^-2. Soil bulk conductivities were measured at the same range of soil solution conductivities and for a tension range of 40 cm to 2 bars. Diffusion coefficients for Ca and Cℓ in the soil solution calculated using the Nernst-Einstein relationship were higher than the non-compressed soils on a tension basis, while for each soil on a common θ basis diffusion coefficients for Ca and Cℓ tended to increase slightly as bulk density was increased.

The effects of air trapped in soils at zero or small negative values of matric potential were studied in relation to saturated and unsaturated hydraulic conductivity, the water release characteristic, and root growth. A reliable method was developed for measuring the trapped air porosity of 'saturated' soils. Using this method, the surface layer of three soils of contrasting texture, in a relatively undisturbed state, was found to have similar amounts of trapped air (5 to 7% of total soil volulme). After digging, the amount of air trapped by ponding water on the surface increased to a value of about 10%. Values of trapped air porosity below a stationary water-table were very low (1%) and this can be attributed to opportunity which the trapped air has to go into solution and diffuse to the water-table. The effects of trapped air on the water release characteristic were investigated in both field and laboratory studies using the neutron-probe and both the neutron-probe and the gamma-probe to measure the water content in the field soil and in a tank packed with sand in the laboratory, respectively. The presence of trapped air had an effect on the field water release characteristic. This effect was more pronounced in dug soil than in undisturbed soil. In the laboratory, the amount of trapped air differed according to the method of wetting, less trapped air occurred when wetting was from the bottom upwards compared to wetting by ponding water from the top. Amounts of trapped air decreased with increasing depth of sand. The water release characteristic was found to depend not only on the method of wetting but also on the previous history of wetting. In a comparison between a tension-table water release and the water release characteristic measured in a sand tank, they were found to be closely similar except at zero and small negative values of matric potential, where effects due to varying amounts of trapped air with depth and wetting history caused differences. Unsaturated hydraulic conductivity measured in the field was affected by the presence of trapped air but only at potentials close to zero. In the laboratory, the values of saturated hydraulic conductivity measured in the sand tank and the values calculated from the water release characteristic using Marshall's theory agreed to within the limits of experimental accuracy. Unsaturated hydraulic conductivity values were found to be not only dependent on the method of wetting but also on the previous history of wetting. The results suggested that once dry sand has been wetted and allowed to drain, that rewetting leads to trapping of air in large pores which reduces the flow during the next drainage period. There was an agreement between unsaturated hydraulic conductivity variation with matric potential obtained from the instantaneous profile method in the sand tank and that using Marshall's theory, however, it is not to be expected that such an agreement will be found for most soils which are not comparable to the relatively homogenous sand used here. In a laboratory experiment with winter barley, the relationship between the presence of trapped air, soil aeration and root growth was studied at 9 and 15°C. The techniques of measuring redox potential with bare platinum electrodes, measuring exygen flux with the same platinum electrodes, and measuring the concentrations of O₂, CO₂ and N₂O in samples extracted through a hypodermic needle gave results which were consistent with one another and with observed root growth rates. Root extension rate was much slower in the saturated soil than in the freely-drained soil. At both temperatures, root growth during 'daytime' (the time of illumination) was about 3 times greater than at night. At 15°C, there was a greater rate of root growth in soil cores which had been flooded rather than vacuum saturated which was related to a slightly greater measured rate of oxygen flux from air trapped by the flooding procedure.

New silver gallium thiophosphate glasses in the Ag<SUB>2</SUB>S-Ga<SUB>2</SUB>S<SUB>3</SUB>-'P<SUB>4</SUB>S<SUB>8</SUB>' system were studied employing a.c. impedance, Raman and IR spectroscopy. 'P<SUB>4</SUB>S<SUB>8</SUB>' does not exist and is used so that the compositions can be conventionally expressed in terms of network modifier and network formers. The glasses were in fact prepared from the elements. The trends in conductivity of other series of glasses were also studied including glasses with added AgI and mixed Ag-Na glasses. These glasses are interesting in that the phosphorus is formally in a IV+ oxidation state whereas other thiophosphate glasses previously reported in the literature contain phosphorus in a V+ oxidation state. Also, Raman spectroscopy has shown that these glasses contain hypothiodiphosphate units (P<SUB>2</SUB>S<SUB>6<SUP>4-</SUB></SUP>) which could be described as octahedral (the P-P occupies the place of the central atom). The phosphate and thiophosphate glasses studied thus far, have had structures based on meta(thio)phosphate chains of corner-sharing tetrahedra. Therefore these hypothiodiphosphate glasses are different in several respects to other thiophosphate glasses. Raman and IR studies of the 0.33Ag<SUB>2</SUB>S-0.33Ga<SUB>2</SUB>S<SUB>3</SUB>-0.33'P<SUB>4</SUB>S<SUB>8</SUB>' glass (or AgGaP<SUB>2</SUB>S<SUB>6</SUB> as it is more usually referred to in this thesis) suggest that the glass is composed of linear chains of -(Ga<SUB>1/2</SUB>P<SUB>2</SUB>S<SUB>6</SUB>Ga<SUB>1/2</SUB>)- units as proposed by Wibbelmann. Studies on the Ag<SUB>(1+x)</SUB>Ga<SUB>(1-x/3)</SUB>P<SUB>2</SUB>S<SUB>6</SUB> series lend weight to this model of the structure. The partial depolymerisation as Ga was replaced by Ag along the series could be followed by Raman spectroscopy. It was possible to relate the increase in conductivity (decrease in activation energy) along the series of changes in local structure. It was found that the compositional trends in activation energy can be explained in terms of the modified Anderson-Stuart model of Martin and Angell and in particular in terms of changes in the jump distance.

The theory of conductivity in organic metals and a review of organic π-electron donors is introduced in Chapter One, outlining some of die many variations that have been made to the tetrathiafulvalene (TTF) molecule, the donor component in the first true organic metal. A range of new' alkylseleno-substituted ethanediylidene-2,2’-bis(l,3-dithiole) donors have been efficiently synthesised. These compounds form semi-conducting charge- transfer complexes with 7,7,8,8-tetracyano-p-quinodimethane (TCNQ). The synthesis, electrochemistry. X-ray crystal structure and magnetic properties are presented (Chapter Two). Various 1,3-dithiolium cations and 1,3-dithiole anions have been used in the synthesis of compounds targeted as high-spin systems (Chapter Three). The theory of organic ferromagnetism is discussed, and various compounds with interesting magnetic and redox properties have been prepared. Chapter Four deals with the synthesis of a series of conjugated, multi-1,3-dithiole, multi-chalcogen, π-electron donors. These compounds are members of the dendralene family of hydrocarbons and the crystal structure of a tricyclic [3]-dendralene is presented. The formation of semi-conducting charge-transfer salts is also discussed. Multistage redox behaviour of a new anthraquinodimethane derivative of TTF has been observed (Chapter Five), and cyclic voltammetic data and X-ray crystal structures of such systems are presented.

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