Polymer self assembly on carbon nanotubes

This chapter analyses the poly(3-hexylthiophene) self-assembly on carbon nanotubes and the interaction between the two materials forming a new hybrid nanostructure. The chapter starts with a review of the several studies investigating polymers and biomolecules self-assembled on nanotubes. Then conducting polymers and polythiophenes are briefly introduced. Accordingly, carbon nanotube structure and properties are reported in Sect. 3. The experimental section starts with the bulk characterisation of polymer thin films with the inclusion of uniformly distributed carbon nanotubes. By using volume film analysis techniques (AFM, TEM, UV–Vis and Raman), we show how the polymer’s higher degree of order is a direct consequence of interaction with carbon nanotubes. Nevertheless, it is through the use of nanoscale analysis and molecular dynamic simulations that the self-assembly of the polymer on the nanotube surface can be clearly evidenced and characterised. In Sect. 6, the effect of the carbon templating structure on the P3HT organisation on the surface is investigated, showing the chirality-driven polymer assembly on the carbon nanotube surface. The interaction between P3HT and CNTs brings also to charge transfer, with the modification of physical properties for both species. In particular, the alteration of the polymer electronic properties and the modification of the nanotube mechanical structure are a direct consequence of the P3HT p-p stacking on the nanotube surface. Finally, some considerations based on molecular dynamics studies are reported in order to confirm and support the experimental results discussed.

Synthesis of one-dimensional nanocomposites based on alumina nanofibres and their catalytic applications

Materials with one-dimensional (1D) nanostructure are important for catalysis. They are the preferred building blocks for catalytic nanoarchitecture, and can be used to fabricate designer catalysts. In this thesis, one such material, alumina nanofibre, was used as a precursor to prepare a range of nanocomposite catalysts. Utilising the specific properties of alumina nanofibres, a novel approach was developed to prepare macro-mesoporous nanocomposites, which consist of a stacked, fibrous nanocomposite with a core-shell structure. Two kinds of fibrous ZrO2/Al2O3 and TiO2/Al2O3 nanocomposites were successfully synthesised using boehmite nanofibers as a hard temperate and followed by a simple calcination. The alumina nanofibres provide the resultant nanocomposites with good thermal stability and mechanical stability. A series of one-dimensional (1D) zirconia/alumina nanocomposites were prepared by the deposition of zirconium species onto the 3D framework of boehmite nanofibres formed by dispersing boehmite nanofibres into a butanol solution, followed by calcination at 773 K. The materials were characterised by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscope (TEM), N2 adsorption/desorption, Infrared Emission Spectroscopy (IES), and Fourier Transform Infrared spectroscopy (FT-IR). The results demonstrated that when the molar percentage, X, X=100*Zr/(Al+Zr), was > 30%, extremely long ZrO2/Al2O3 composite nanorods with evenly distributed ZrO2 nanocrystals formed on their surface. The stacking of such nanorods gave rise to a new kind of macroporous material without the use of any organic space filler\template or other specific drying techniques. The mechanism for the formation of these long ZrO2/Al2O3 composite nanorods is proposed in this work. A series of solid-superacid catalysts were synthesised from fibrous ZrO2/Al2O3 core and shell nanocomposites. In this series, the zirconium molar percentage was varied from 2 % to 50 %. The ZrO2/Al2O3 nanocomposites and their solid superacid counterparts were characterised by a variety of techniques including 27Al MAS-NMR, SEM, TEM, XPS, Nitrogen adsorption and Infrared Emission Spectroscopy. NMR results show that the interaction between zirconia species and alumina strongly correlates with pentacoordinated aluminium sites. This can also be detected by the change in binding energy of the 3d electrons of the zirconium. The acidity of the obtained superacids was tested by using them as catalysts for the benzolyation of toluene. It was found that a sample with a 50 % zirconium molar percentage possessed the highest surface acidity equalling that of pristine sulfated zirconia despite the reduced mass of zirconia. Preparation of hierarchically macro-mesoporous catalyst by loading nanocrystallites on the framework of alumina bundles can provide an alternative system to design advanced nanocomposite catalyst with enhanced performance. A series of macro-mesoporous TiO2/Al2O3 nanocomposites with different morphologies were synthesised. The materials were calcined at 723 K and were characterised by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscope (TEM), N2 adsorption/desorption, Infrared Emission Spectroscopy (IES), and UV-visible spectroscopy (UV-visible). A modified approach was proposed for the synthesis of 1D (fibrous) nanocomposite with higher Ti/Al molar ratio (2:1) at lower temperature (<100oC), which makes it possible to synthesize such materials on industrial scale. The performances of a series of resultant TiO2/Al2O3 nanocomposites with different morphologies were evaluated as a photocatalyst for the phenol degradation under UV irradiation. The photocatalyst (Ti/Al =2) with fibrous morphology exhibits higher activity than that of the photocatalyst with microspherical morphology which indeed has the highest Ti to Al molar ratio (Ti/Al =3) in the series of as-synthesised hierarchical TiO2/Al2O3 nanocomposites. Furthermore, the photocatalytic performances, for the fibrous nanocomposites with Ti/Al=2, were optimized by calcination at elevated temperatures. The nanocomposite prepared by calcination at 750oC exhibits the highest catalytic activity, and its performance per TiO2 unit is very close to that of the gold standard, Degussa P 25. This work also emphasizes two advantages of the nanocomposites with fibrous morphology: (1) the resistance to sintering, and (2) good catalyst recovery.

Hydrothermal synthesis of single crystallin strontium titanate nanocubes

Strontium titanate nanocubes with an average edge length of 150mm have been successfully synthesized from a simple hydrothermal system. Characterization techniques such as X-ray powder diffraction analysis, scanning electron microscopy and energy-dispersive analysis of X-rays were used to investigate the products. The results showed that as-prepared powders are pure SrTiO3 with cubic shape, which consists with the growth habit of its intrinsic crystal structure. These uniform nanocubes with high crystallinity will exhibit superior physical properties in the practical applications. Furthermore, during the experimental process, it has been found that the dilute acid washing process is very important to obtain high pure SrTiO3.

Fabrication of macro-mesoporous zirconia-alumina materials with a 1D hierarchical structure

A series of one dimensional (1D) zirconia/alumina nanocomposites were prepared by the deposition of zirconium species onto the 3D framework of boehmite nanofibres formed by dispersing boehmite nanofibres into butanol solution. The materials were calcined at 773K and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), N2 adsorption/desorption, infrared emission spectroscopy (IES). The results demonstrated that when the molar percentage X=100*Zr/(Al+Zr) was > 30 %, extremely long ZrO2/Al2O3 composite nanorods with evenly distributed ZrO2 nanocrystals on the surface were formed. The stacking of such nanorods gave rise to a new kind of macroporous material without the use of any organic space filler\template or other specific technologies. The mechanism for the formation of long ZrO2/Al2O3 composite nanorods was proposed in this work.

Characterisation of sugarcane juice particles that influence the clarification process

Problems associated with processing whole sugarcane crop can be minimised by removing impurities during the clarification stage. As a first step, it is important to understand the colloidal chemistry of juice particles on a molecular level to assist development strategies for effective clarification performance. This paper presents the composition and surface characteristics of colloidal particles originating from various juice types by using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray photoelectron spectroscopy (XPS) and zeta potential measurements. The composition and surface characteristics of colloidal juice particles are reported. The results indicate that there are three types of colloidal particles present viz., an aluminosilicate compound, silica and iron oxide, with the latter two being abundant. Proteins, polysaccharides and organic acids were identified on the surface of particles in juice. The overall particle charge varies from –2 mV to –6 mV. In comparison to juice expressed from burnt cane, the zeta potential values were more negative with juice particles originating from whole crop. This in part explains why these juices are difficult to clarify.

Environmental degradation of lignin/poly(hydroxybutyrate) blends

Blends of lignin and poly(hydroxybutyrate) (PHB) were obtained by melt extrusion. They were buried in a garden soil for up to 12 months, and the extent and mechanism of degradation were investigated by gravimetric analysis, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Fourier transform infra-red spectroscopy (FTIR) over the entire range of compositions. The PHB films were disintegrated and lost 45 wt% of mass within 12 months. This value dropped to 12 wt% of mass when only 10 wt% of lignin was present, suggesting that lignin both inhibited and slowed down the rate of PHB degradation. TGA and DSC indicated structural changes, within the lignin/PHB matrix, with burial time, while FTIR results confirmed the fragmentation of the PHB polymer. XPS revealed an accumulation of biofilms on the surface of buried samples, providing evidence of a biodegradation mechanism. Significant surface roughness was observed with PHB films due to microbial attack caused by both loosely and strongly associated micro-organisms. The presence of lignin in the blends may have inhibited the colonisation of the micro-organisms and caused the blends to be more resistant to microbial attack. Analysis suggested that lignin formed strong hydrogen bonds with PHB in the buried samples and it is likely that the rate of breakdown of PHB is reduced, preventing rapid degradation of the blends.

Prediction of pull-out force of multi-walled carbon nanotube (MWCNT) in sword-in-sheath mode

The pull-out force of some outer walls against other inner walls in multi-walled carbon nanotubes (MWCNTs) was systematically studied by molecular mechanics simulations. The obtained results reveal that the pull-out force is proportional to the square of the diameter of the immediate outer wall on the sliding interface, which highlights the primary contribution of the capped section of MWCNT to the pull-out force. A simple empirical formula was proposed based on the numerical results to predict the pull-out force for an arbitrary pull-out in a given MWCNT directly from the diameter of the immediate outer wall on the sliding interface. Moreover, tensile tests for MWCNTs with and without acid-treatment were performed with a nanomanipulator inside a vacuum chamber of a scanning electron microscope (SEM) to validate the present empirical formula. It was found that the theoretical pull-out forces agree with the present and some previous experimental results very well.

Studies on the surface properties of biodegradable polymer carriers in respiratory delivery of drug from Dry Powder Inhaler formulations

Dry Powder Inhaler (DPI) technology has a significant impact in the treatment of various respiratory disorders. DPI formulations consist of a micronized drug (<5ìm) blended with an inert coarse carrier, for which lactose is widely used to date. DPIs are one of the inhalation devices which are used to target the delivery of drugs to the lungs. Drug delivery via DPI formulations is influenced by the physico-chemical characteristics of lactose particles such as size, shape, surface roughness and adhesional forces. Commercially available DPI formulations, which utilise lactose as the carrier, are not efficient in delivering drug to the lungs. The reasons for this are the surface morphology, adhesional properties and surface roughness of lactose. Despite several attempts to modify lactose, the maximum efficient drug delivery to the lungs remains limited; hence, exploring suitable alternative carriers for DPIs is of paramount importance. Therefore, the objective of the project was to study the performance of spherical polymer microparticles as drug carriers and the factors controlling their performance. This study aimed to use biodegradable polymer microspheres as alternative carriers to lactose in DPIs for achieving efficient drug delivery into the lungs. This project focused on fabricating biodegradable polymer microparticles with reproducible surface morphology and particle shape. The surface characteristics of polymeric carriers and the adhesional forces between the drug and carrier particles were investigated in order to gain a better understanding of their influence on drug dispersion. For this purpose, two biodegradable polymers- polycaprolactone (PCL) and poly (DL-lactide-co-glycolide) (PLGA) were used as the carriers to deliver the anti-asthmatic drug - Salbutamol Sulphate (SS). The first study conducted for this dissertation was the aerosolization of SS from mixtures of SS and PCL or PLGA microparticles. The microparticles were fabricated using an emulsion technique and were characterized by laser diffraction for particle size analysis, Scanning Electron Microscopy (SEM) for surface morphology and X-ray Photoelectron Spectroscopy (XPS) to obtain surface elemental composition. The dispersion of the drug from the DPI formulations was determined by using a Twin Stage Impinger (TSI). The Fine particle Fraction (FPF) of SS from powder mixtures was analyzed by High Performance Liquid Chromatography (HPLC). It was found that the drug did not detach from the surface of PCL microspheres. To overcome this, the microspheres were coated with anti-adherent agents such as magnesium stearate and leucine to improve the dispersion of the drug from the carrier surfaces. It was found that coating the PCL microspheres helped in significantly improving the FPF of SS from the PCL surface. These results were in contrast to the PLGA microspheres which readily allowed detachment of the SS from their surface. However, coating PLGA microspheres with antiadherent agents did not further improve the detachment of the drug from the surface. Thus, the first part of the study demonstrated that the surface-coated PCL microspheres and PLGA microspheres can be potential alternatives to lactose as carriers in DPI formulations; however, there was no significant improvement in the FPF of the drug. The second part of the research studied the influence of the size of the microspheres on the FPF of the drug. For this purpose, four different sizes (25 ìm, 48 ìm, 100 ìm and 150 ìm) of the PCL and PLGA microspheres were fabricated and characterized. The dispersion of the drug from microspheres of different sizes was determined. It was found that as the size of the carrier increased there was a significant increase in the FPF of SS. This study suggested that the size of the carrier plays an important role in the dispersion of the drug from the carrier surface. Subsequent experiments in the third part of the dissertation studied the surface properties of the polymeric carrier. The adhesion forces existing between the drug particle and the polymer surfaces, and the surface roughness of the carriers were quantified using Atomic Force Microscopy (AFM). A direct correlation between adhesion forces and dispersion of the drug from the carrier surface was observed suggesting that adhesion forces play an important role in determining the detachment potential of the drug from the carrier surface. However, no direct relationship between the surface roughness of the PCL or PLGA carrier and the FPF of the drug was observed. In conclusion, the body of work presented in this dissertation demonstrated the potential of coated PCL microspheres and PLGA microspheres to be used in DPI formulations as an alternative carrier to sugar based carriers. The study also emphasized the role of the size of the carrier particles and the forces of interaction prevailing between the drug and the carrier particle surface on the aerosolization performances of the drug.

Characterisation of multi wall carbon nanotube–polymer composites for strain sensing applications

Carbon nanotubes (CNTs) have excellent electrical, mechanical and electromechanical properties. When CNTs are incorporated into polymers, electrically conductive composites with high electrical conductivity at very low CNT content (often below 1% wt CNT) result. Due to the change in electrical properties under mechanical load, carbon nanotube/polymer composites have attracted significant research interest especially due to their potential for application in in-situ monitoring of stress distribution and active control of strain sensing in composite structures or as strain sensors. To sucessfully develop novel devices for such applications, some of the major challenges that need to be overcome include; in-depth understanding of structure-electrical conductivity relationships, response of the composites under changing environmental conditions and piezoresistivity of different types of carbon nanotube/polymer sensing devices. In this thesis, direct current (DC) and alternating current (AC) conductivity of CNT-epoxy composites was investigated. Details of microstructure obtained by scanning electron microscopy were used to link observed electrical properties with structure using equivalent circuit modeling. The role of polymer coatings on macro and micro level electrical conductivity was investigated using atomic force microscopy. Thermal analysis and Raman spectroscopy were used to evaluate the heat flow and deformation of carbon nanotubes embedded in the epoxy, respectively, and related to temperature induced resistivity changes. A comparative assessment of piezoresistivity was conducted using randomly mixed carbon nanotube/epoxy composites, and new concept epoxy- and polyurethane-coated carbon nanotube films. The results indicate that equivalent circuit modelling is a reliable technique for estimating values of the resistance and capacitive components in linear, low aspect ratio-epoxy composites. Using this approach, the dominant role of tunneling resistance in determining the electrical conductivity was confirmed, a result further verified using conductive-atomic force microscopy analysis. Randomly mixed CNT-epoxy composites were found to be highly sensitive to mechanical strain and temperature variation compared to polymer-coated CNT films. In the vicinity of the glass transition temperature, the CNT-epoxy composites exhibited pronounced resistivity peaks. Thermal and Raman spectroscopy analyses indicated that this phenomenon can be attributed to physical aging of the epoxy matrix phase and structural rearrangement of the conductive network induced by matrix expansion. The resistivity of polymercoated CNT composites was mainly dominated by the intrinsic resistivity of CNTs and the CNT junctions, and their linear, weakly temperature sensitive response can be described by a modified Luttinger liquid model. Piezoresistivity of the polymer coated sensors was dominated by break up of the conducting carbon nanotube network and the consequent degradation of nanotube-nanotube contacts while that of the randomly mixed CNT-epoxy composites was determined by tunnelling resistance between neighbouring CNTs. This thesis has demonstrated that it is possible to use microstructure information to develop equivalent circuit models that are capable of representing the electrical conductivity of CNT/epoxy composites accurately. New designs of carbon nanotube based sensing devices, utilising carbon nanotube films as the key functional element, can be used to overcome the high temperature sensitivity of randomly mixed CNT/polymer composites without compromising on desired high strain sensitivity. This concept can be extended to develop large area intelligent CNT based coatings and targeted weak-point specific strain sensors for use in structural health monitoring.

Characterisation of sugarcane juice particles that influence the clarification process

Problems associated with processing whole sugarcane crop can be minimised by removing impurities during the clarification stage. As a first step, it is important to understand the colloidal chemistry of juice particles on a molecular level to assist development of strategies for effective clarification performance. This paper presents the composition and surface characteristics of colloidal particles originating from various juice types by using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray photoelectron spectroscopy(XPS) and zeta potential measurements. The composition and surface characteristics of colloidal juice particles are reported. The results indicate that there are three types of colloidal particles present, viz. an aluminosilicatecompound, silica and iron oxide, with the latter two being abundant. Proteins, polysaccharides and organic acids were identified on the surface of particles in juice. The overall particle charge varies from -2 mV to -6 mV. In comparison to juice expressed from burnt cane, the zeta potential values were more negative with juice particles originating from whole crop. This in part explains why these juices are difficult to clarify.

Melting, ablation, and vapor phase condensation during atmospheric passage of the Bjurbole Meteorite

A detailed study of the Bjurbole fusion crust using scanning electron microscopy (SEM) and energy dispersive analysis (EDS) shows that filamentary crystals and ablation spheres may form on the meteoroid surface. Filamentary crystals, hollow spheres, and porous regions of the surface point to a period of intense vapor phase activity during atmospheric passage. Filamentary crystals can be divided into three categories on the basis of bulk composition and morphology. Two types of filamentary crystals are vapor phase condensation products formed during atmospheric entry of the meteoroid. The other type forms by the interaction of seawater with the fusion surface. The density and composition of ablation spheres varies with the flight orientation of the meteorite. The size range and composition of iron-nickel spheres on the surface of Bjurbole are similar to spheres collected in the stratosphere. A comparison of stratospheric dust collections with meteorite surfaces may provide further insight into the mechanisms of meteoroid entry into planetary atmospheres.

Melt textured Y123 bulk and thick film

YBa2Cu3O7-δ - 25mol%Y2BaCuO5 bars and thick films have been melt textured using a stationary furnace with a temperature gradient of 3 or 6°C/cm. Samples are heated above the peritectic reaction temperature and quenched to just above the solidification temperature and then slowly cooled below the solidification temperature. All bar shaped samples consist of 2-5 mm grains though the grain orientations strongly depend on the heat treatment conditions. The bar shows the maximum Jc of above 3,000 A/cm2, whereas the maximum Jc of 200 A/cm2 and Tczero of 88K are obtained for the thick film on (100) LaAlO3 single crystal.

Microstructural studies of quenched partially-melted Y-123 materials and Y-123 with Y-211, PtO2 and CeO2 additions

The microstructure of YBa2Cu3O7-delta (Y-123) materials partially-melted in air and quenched from the temperature range 900-1100 degrees C, has been characterized using a combination of X-ray diffractometry, optical microscopy, scanning electron microscopy, electron microprobe analyses, transmission electron microscopy and energy and wave dispersive X-ray spectrometries. The microstructural studies reveal significant changes in the character of the quenched partial-melt as a function of temperature and time before quenching. BaCu2O2 and BaCuO2 are found to co-exist in stoichiometric samples quenched from the temperature range 920-960 degrees C. Under suitable cooling conditions, large pockets of melt cristallize as BaCuO2 with an exsolution of BaCu2O2 in the form of thin plates (approximate to 50-100 nm thick) along facets. Y2BaCuO5 (Y-211) additions are associated with the formation of BaCu2O2 at 1100 degrees C. Preliminary results on the effects of PtO2 and CeO2 additions to Y-123 (and Y-123 with Y-211 additions) show that these enhace the formation of BaCu2O2 at the melting temperature of 1100 degrees C. (C) 1998 Elsevier Science S.A. All rights reserved.