The current thrust towards the compaction of electrical power equipment, resulting in increased insulation electrical stress levels, necessitates new electrical insulating materials. In the last few decades, polymeric materials that exhibit light weight, excellent mechanical properties, low cost, and some with unique non-wetting surface characteristics, have surpassed the use of the conventional porcelain and glass insulating materials. Despite these advantages, polymeric materials are incapable of withstanding the high heat from surface arcing that is instigated by the synergism of pollution, moisture, and voltage. Surface arcing results in material loss due to heat ablation and/or the electrical tracking of polymeric materials. To overcome such issues, inorganic fillers are added to the base polymers to enhance their resistance to surface discharge activities and other performances. Since their addition can significantly reduce material costs, their use is compelling. Micron-sized fillers, here after defined as microfillers, have been used to acquire these desirable properties, but due to limitations in material processability, the further application of such fillers is limited. Consequently, nano-sized fillers, here after defined as nanofillers, have been viewed as replacements or assistant combinations to microfillers. Nanofillers are characterized by large surface areas, resulting in increased bond strengths that yield significant improvements in the various properties at fill levels well below that of microfillers. However, the primary problem of using nanofillers is their characteristic property of agglomeration due to their physical size and the forces between the fillers. Conventional mechanical mixing of nanofillers does not adequately separate the nanofillers, leading to behaviour similarly to that of microfillers. Therefore, the implementation of nanofillers is not completely effective. In chemical dispersion techniques, for example, the use of surfactants, are normally very elaborate and complicated. Due to the negative impact of agglomeration, the successful dispersion of nanofillers is pivotal in the further development of nanodielectrics for various insulation applications. In this thesis, electrospinning is proposed and realized as a new dispersal method for nanofillers in polymeric materials. This novel technique facilitates polymeric nanocomposites with improved properties due to the uniform distribution of fillers. Scanning electron microscopy (SEM) images and energy dispersive X-ray analysis (EDX) clearly indicate that electrospun nanocomposites demonstrate a better filler distribution than nanocomposites, produced by conventional mechanical mixing. Also electrospinning introduces the possibility of separating different nanofillers in different base polymers. The mechanical properties: tensile strength and hardness; the electrical properties: permittivity, tracking, and erosion resistance; and the thermal properties: thermal conductivity, thermal degradation, and heat erosion resistance of electrospun nanocomposites are compared to those of conventional nanocomposites for silicone rubber and cycloaliphatic epoxy-based polymers. All the experimental studies in this thesis confirm that electrospun nanocomposites exhibit better thermal performances than the conventional composites which are attributed to the improved distribution of the nanofillers by the newly developed electrospinning process. Also in this investigation, a two-dimensional thermal model is developed in COMSOL MultiphysicsTM by using the finite element method (FEM) to theoretically address the benefits of using nanofillers and the effects of filler dispersion. The model confirms that electrospun nanocomposites have much more uniform temperature distribution than conventional nanocomposites. This thesis presents the possible mechanisms by which nanofillers improve the heat and erosion resistance of silicone rubber nanocomposites, and also addresses the possible mechanism by which electrospinning improves nanofiller dispersion.

The current thrust towards the compaction of electrical power equipment, resulting in increased insulation electrical stress levels, necessitates new electrical insulating materials. In the last few decades, polymeric materials that exhibit light weight, excellent mechanical properties, low cost, and some with unique non-wetting surface characteristics, have surpassed the use of the conventional porcelain and glass insulating materials. Despite these advantages, polymeric materials are incapable of withstanding the high heat from surface arcing that is instigated by the synergism of pollution, moisture, and voltage. Surface arcing results in material loss due to heat ablation and/or the electrical tracking of polymeric materials. To overcome such issues, inorganic fillers are added to the base polymers to enhance their resistance to surface discharge activities and other performances. Since their addition can significantly reduce material costs, their use is compelling. Micron-sized fillers, here after defined as microfillers, have been used to acquire these desirable properties, but due to limitations in material processability, the further application of such fillers is limited. Consequently, nano-sized fillers, here after defined as nanofillers, have been viewed as replacements or assistant combinations to microfillers. Nanofillers are characterized by large surface areas, resulting in increased bond strengths that yield significant improvements in the various properties at fill levels well below that of microfillers. However, the primary problem of using nanofillers is their characteristic property of agglomeration due to their physical size and the forces between the fillers. Conventional mechanical mixing of nanofillers does not adequately separate the nanofillers, leading to behaviour similarly to that of microfillers. Therefore, the implementation of nanofillers is not completely effective. In chemical dispersion techniques, for example, the use of surfactants, are normally very elaborate and complicated. Due to the negative impact of agglomeration, the successful dispersion of nanofillers is pivotal in the further development of nanodielectrics for various insulation applications. In this thesis, electrospinning is proposed and realized as a new dispersal method for nanofillers in polymeric materials. This novel technique facilitates polymeric nanocomposites with improved properties due to the uniform distribution of fillers. Scanning electron microscopy (SEM) images and energy dispersive X-ray analysis (EDX) clearly indicate that electrospun nanocomposites demonstrate a better filler distribution than nanocomposites, produced by conventional mechanical mixing. Also electrospinning introduces the possibility of separating different nanofillers in different base polymers. The mechanical properties: tensile strength and hardness; the electrical properties: permittivity, tracking, and erosion resistance; and the thermal properties: thermal conductivity, thermal degradation, and heat erosion resistance of electrospun nanocomposites are compared to those of conventional nanocomposites for silicone rubber and cycloaliphatic epoxy-based polymers. All the experimental studies in this thesis confirm that electrospun nanocomposites exhibit better thermal performances than the conventional composites which are attributed to the improved distribution of the nanofillers by the newly developed electrospinning process. Also in this investigation, a two-dimensional thermal model is developed in COMSOL MultiphysicsTM by using the finite element method (FEM) to theoretically address the benefits of using nanofillers and the effects of filler dispersion. The model confirms that electrospun nanocomposites have much more uniform temperature distribution than conventional nanocomposites. This thesis presents the possible mechanisms by which nanofillers improve the heat and erosion resistance of silicone rubber nanocomposites, and also addresses the possible mechanism by which electrospinning improves nanofiller dispersion.

Polymeric insulators are now a common replacement for conventional porcelain and glass string insulators on overhead distribution and transmission lines. The use of this mature technology represents many advantages to the utilities; however, in polluted environments and those with high moisture levels in the environment, electrical discharges will develop on the surface of the insulation. In the long term, electrical discharges cause degradation of the polymer insulation in the form of electrical tracking and material erosion, and both are detrimental to the life of the insulation. Inorganic fillers are added to polymer materials to make the insulation more resistant to discharges, and at the same time, to lower the cost of the insulation. However, there is a limit to the amount of filler that can be added as the processability of the polymer compound becomes extremely difficult and expensive. Microfillers are extensively used to modify the physical properties of the polymeric matrix, and the properties of these composites are well known. On the other hand, nanofillers are being used in some insulating composites for reinforcement of mechanical properties; their electrical characteristics have shown inconsistency in the literature, and this is attributable to the non-uniformity of the filler dispersion. Most researchers agree that particle dispersion is critical in the development of nanocomposites for electrical insulation applications. If the nanoparticles are well dispersed, the electrical properties of these materials will be significantly improved. The main problem in using nanofillers is that the nanoparticles agglomerate easily because of their high surface energy, such that conventional mixing techniques are unable to break apart the nanoparticle aggregates. A secondary problem is the incompatibility of the hydrophobic polymer with the hydrophilic nanoparticles which results in poor interfacial interactions. In this thesis, the reinforcement of a silicone rubber matrix is successfully accomplished with the combination of microfiller, nanofiller, and a commercial surfactant. To improve particle dispersion, several techniques are available apart from mixing. This includes surface modification of the nanoparticles by chemical and physical methods by using surfactants. While surfactants are commonly applied to liquids, their use to disperse nanoparticles in compositions forming solid dielectric materials has not yet been reported. The findings in this thesis have shown that Triton X-100, a common surfactant, significantly aids in the dispersion of nanosilica and nanoalumina in silicone rubber. The main advantage of the surfactant is that it lowers the surface energy and the interfacial tension of the nanoparticles. This reduces agglomeration and facilitates the separation of the particles during mixing, thereby allowing improved dispersion of the nanofillers, as observed through Scanning Electron Microscopy (SEM). However, also shown in the thesis is that Triton X-100 cannot interact efficiently with all types of nanofillers. A high concentration of surfactant can also compromise the adsorption of the matrix polymer chains on the filler particles, so it is necessary to establish a balance between matrix adsorption and the dispersion of the particles. Mechanical properties such as the tensile strength, elongation at break, and hardness may also suffer from the use of excess surfactant. In addition, excess surfactant can lead to surface wetting properties different from composites containing none. Better wetting due to the migration of excess surfactant to the surface of the silicone may favour arcing in a wet environment. The current investigation shows that for a specific filler and concentration, an optimal concentration of surfactant provides good erosion resistance without adversely affecting the mechanical characteristics of the nanocomposite. Stress–strain and hardness measurements are done to investigate the surfactant’s effect on the mechanical properties of the composites. The effect of the surfactant on the surface of the composites is analyzed with static contact angle measurements. The heat resistance of nanofilled silicone rubber is explored using an infrared laser simulating the heat developed by dry-band arcing. Also, several industry standard test methods such as salt fog and inclined plane tests are used to evaluate the erosion resistance of the filled composites. The results of all three tests confirm that the combination of microfiller and nanofiller with surfactant results in composites with improved erosion resistance to dry band arcing, with the exception of the case where calcinated filler is used in the formulation. In this thesis, the thermal conductivity is measured using a standard ASTM method and calculated using several theoretical, semi-theoretical, and empirical models. A thermal model developed in COMSOL Multiphysics and solved using a finite element method (FEM) shows a temperature distribution in the modelled nanocomposites which is comparable to the temperature distribution measured with an infrared camera under laser heating. In addition, this investigation aims to define the mechanism by which the nanofillers improve the heat and erosion resistance of the silicone composites. In order to understand this mechanism, nano fumed silica, nano natural silica, and nano alumina are used in a silicone rubber (SiR) matrix in order to study the thermally decomposed silicone and the residual char that is formed during laser ablation tests. The white residue remaining after laser ablation on the surface of composites with fumed silica, natural silica, and alumina is analyzed in a number of ways. Scanning Electron Microscopy, Energy Dispersive X-ray analysis (EDAX), and X-ray diffraction (XRD) techniques are used to analyze the thermally decomposed silicone residue after laser heating indicating that the protective mechanism of the three analyzed nanofillers – fumed silica, natural silica, and alumina – appears to be the same. The formation of a continuous layer on the surface behaves as a thermal insulator protecting the material underneath from further decomposition.

Polymeric insulators are now a common replacement for conventional porcelain and glass string insulators on overhead distribution and transmission lines. The use of this mature technology represents many advantages to the utilities; however, in polluted environments and those with high moisture levels in the environment, electrical discharges will develop on the surface of the insulation. In the long term, electrical discharges cause degradation of the polymer insulation in the form of electrical tracking and material erosion, and both are detrimental to the life of the insulation. Inorganic fillers are added to polymer materials to make the insulation more resistant to discharges, and at the same time, to lower the cost of the insulation. However, there is a limit to the amount of filler that can be added as the processability of the polymer compound becomes extremely difficult and expensive. Microfillers are extensively used to modify the physical properties of the polymeric matrix, and the properties of these composites are well known. On the other hand, nanofillers are being used in some insulating composites for reinforcement of mechanical properties; their electrical characteristics have shown inconsistency in the literature, and this is attributable to the non-uniformity of the filler dispersion. Most researchers agree that particle dispersion is critical in the development of nanocomposites for electrical insulation applications. If the nanoparticles are well dispersed, the electrical properties of these materials will be significantly improved. The main problem in using nanofillers is that the nanoparticles agglomerate easily because of their high surface energy, such that conventional mixing techniques are unable to break apart the nanoparticle aggregates. A secondary problem is the incompatibility of the hydrophobic polymer with the hydrophilic nanoparticles which results in poor interfacial interactions. In this thesis, the reinforcement of a silicone rubber matrix is successfully accomplished with the combination of microfiller, nanofiller, and a commercial surfactant. To improve particle dispersion, several techniques are available apart from mixing. This includes surface modification of the nanoparticles by chemical and physical methods by using surfactants. While surfactants are commonly applied to liquids, their use to disperse nanoparticles in compositions forming solid dielectric materials has not yet been reported. The findings in this thesis have shown that Triton X-100, a common surfactant, significantly aids in the dispersion of nanosilica and nanoalumina in silicone rubber. The main advantage of the surfactant is that it lowers the surface energy and the interfacial tension of the nanoparticles. This reduces agglomeration and facilitates the separation of the particles during mixing, thereby allowing improved dispersion of the nanofillers, as observed through Scanning Electron Microscopy (SEM). However, also shown in the thesis is that Triton X-100 cannot interact efficiently with all types of nanofillers. A high concentration of surfactant can also compromise the adsorption of the matrix polymer chains on the filler particles, so it is necessary to establish a balance between matrix adsorption and the dispersion of the particles. Mechanical properties such as the tensile strength, elongation at break, and hardness may also suffer from the use of excess surfactant. In addition, excess surfactant can lead to surface wetting properties different from composites containing none. Better wetting due to the migration of excess surfactant to the surface of the silicone may favour arcing in a wet environment. The current investigation shows that for a specific filler and concentration, an optimal concentration of surfactant provides good erosion resistance without adversely affecting the mechanical characteristics of the nanocomposite. Stress–strain and hardness measurements are done to investigate the surfactant’s effect on the mechanical properties of the composites. The effect of the surfactant on the surface of the composites is analyzed with static contact angle measurements. The heat resistance of nanofilled silicone rubber is explored using an infrared laser simulating the heat developed by dry-band arcing. Also, several industry standard test methods such as salt fog and inclined plane tests are used to evaluate the erosion resistance of the filled composites. The results of all three tests confirm that the combination of microfiller and nanofiller with surfactant results in composites with improved erosion resistance to dry band arcing, with the exception of the case where calcinated filler is used in the formulation. In this thesis, the thermal conductivity is measured using a standard ASTM method and calculated using several theoretical, semi-theoretical, and empirical models. A thermal model developed in COMSOL Multiphysics and solved using a finite element method (FEM) shows a temperature distribution in the modelled nanocomposites which is comparable to the temperature distribution measured with an infrared camera under laser heating. In addition, this investigation aims to define the mechanism by which the nanofillers improve the heat and erosion resistance of the silicone composites. In order to understand this mechanism, nano fumed silica, nano natural silica, and nano alumina are used in a silicone rubber (SiR) matrix in order to study the thermally decomposed silicone and the residual char that is formed during laser ablation tests. The white residue remaining after laser ablation on the surface of composites with fumed silica, natural silica, and alumina is analyzed in a number of ways. Scanning Electron Microscopy, Energy Dispersive X-ray analysis (EDAX), and X-ray diffraction (XRD) techniques are used to analyze the thermally decomposed silicone residue after laser heating indicating that the protective mechanism of the three analyzed nanofillers – fumed silica, natural silica, and alumina – appears to be the same. The formation of a continuous layer on the surface behaves as a thermal insulator protecting the material underneath from further decomposition.

This masters’s thesis study electric properties of nanocomposites based on epoxy resins, production of samples and measuring their electrical properties. In this thesis there are observed temperature dependences of the dissipation factor, relative permittivity and internal resistivity.

Over the past two decades one class of oligomers, polyhedral oligomeric silsesquioxanes (POSS), has attracted considerable attention because of their unique hybrid organic/inorganic molecular structures and nanoscopic sizes. While surface and interfacial properties may play a key role in many potential POSS applications, relatively little is actually known about the surface properties of POSS. This dissertation provides studies of the interfacial aspects of both POSS molecules and POSS/polymer blends at the air/water interface (A/W) through surface pressure-area per molecule (π-<i>A</i>) isotherm, Brewster angle microscopy (BAM), and interfacial stress rheometry (ISR) studies. Results for POSS Langmuir thin films at A/W show that trisilanol-POSS derivatives are a new class of amphiphiles, that exhibit multiple phase transitions in going from traditional 2D Langmuir monolayers (1 POSS molecule thick) to various 3D multilayer films upon compression. With small length/diameter ratios and bulky shapes, the monolayer phase behavior and packing states of different POSS are simpler than the traditional rod-like lipids. Meanwhile trisilanol-POSS derivatives have very different collapse behavior and multilayer organization showing strong substituent effects even though they have similar molecular sizes. While trisilanolisobutyl-POSS (TiBuP) monolayers undergo collapse around π ≈ 18 mNm⁻¹ and form various ordered or disordered solid-like 3D aggregates at different compression rates, trisilanolcyclohexyl-POSS (TCyP) monolayers collapse into trilayers via instantaneous nucleation with hemispherical edge growth around π ≈ 3.7 mNm⁻¹. ISR results reveal three different non-Newtonian flow regimes that correlate with phase transitions in the Pi-A isotherms. Further symmetric compression after trilayer formation induces TCyP thin films to self-assemble into highly ordered crystalline-like hydrophobic multilayers (≈8 POSS molecule thick) with unique rod-like morphologies, which are dramatically different from –collapsed– morphologies seen in other systems. By treating POSS derivatives as ideal nanofiller for studying confinement effects on filled polymer systems, amphiphilic poly(dimethylsiloxane) (PDMS) derivatives with different polar functional groups are studied as blends with TiBuP and octaisobutyl-POSS at A/W to resolve one of the key challenges for current nanocomposite applications: How to control nanofiller dispersion in polymer matrices? The results in this dissertation reveal that introducing polar groups into polymeric matrix polymers is a good way to control dispersion. / Ph. D.

More and more, advanced polymer and composite materials are being applied in engineering situations where a high resistance to loading at high rates of strain, such as by impact or blast deformation, are a vital requirement. Specific examples exist in the fields of defence and sport research and development for personal, and in the case of the former, vehicular, protection. There are obvious advantages to the use of polymer materials for these applications in augmenting the more widely used metals and ceramics, most notably the evident reduction in weight, and it is believed that with suitable nano-reinforcement these materials may exhibit improved combat survivability. The current study concerns the effect that nano-reinforcements in the form of Carbon Black, Titanium Dioxide, Exfoliated Hectorite Nanoclay and Carbon Nanotubes; have upon the high strain rate mechanical properties of structural variants of Polyethylene (Linear Low Density Polyethylene, LLDPE; High Density Polyethylene, HDPE; Ultra-High Molecular Weight Polyethylene, UHMWPE) and blends of UHMWPE and HDPE. The testing samples were manufactured using a novel process developed in the Loughborough University Materials Department, which has produced well-dispersed specimens. The formed nanocomposite samples were studied using an in-house four-bar Split Hopkinson Pressure Bar (SHPB) system for high strain rate performance, instrumented dropweight for intermediate strain rates and a conventional commercial Hounsfield H50KM universal testing machine for quasi-static strain rate compressive tests. The experimental results recorded for un-reinforced materials are used as a reference to allow comparative analysis of any effect the nano-reinforcements or the blending process have upon the structure, performance and properties of the composite material. From the mechanical testing, it was seen that the stress-strain behaviour of Polyethylene is highly strain-rate-dependent, as plots of the average representative yield stress as a function of strain rate show a bilinear relationship when plotted on a logarithmic strain rate scale, with the gradient of the curve rising sharply at around 103s-1. Concerning the addition of the nanofiller materials, it was seen that there was an increase in the flow and yield stresses and the energy absorption characteristics of the resulting composite with the magnitude dependent upon whether it was a pure or blended polymer that was reinforced. Of the aforementioned fillers it was seen that the addition of Carbon Nanotubes in the small concentrations studied resulted in the greatest increase in properties compared to the pure polymers, closely followed by the Carbon Black fillers. Also of note, the un-reinforced blended samples showed significant increases in flow stress, yield stress and energy absorption when compared to the constituent UHMWPE and HDPE polymers. Additionally, a complete set of Differential Scanning Calorimetry and density measurements were made before testing to assess any changes in the properties after reinforcement or blending, and to help in the interpretation of the results from the different mechanical tests.

No description available.

Yes / The development of ultra-high performance cementitious composite (UHPCC) represents a significant advancement in the field of concrete science and technology, but insufficient hydration and high autogenous shrinkage relatively increase the pores inside UHPCC, in turn, affecting the macro-performance of UHPCC. This paper, initially, optimized the pore structure of UHPCC using different types and dimensions of nanofillers. Subsequently, the pore structure characteristics of nano-modified UHPCC were investigated by the mercury intrusion porosimeter method and fractal theory. Finally, the fluid permeability of nano-modified UHPCC was estimated by applying the Katz-Thompson equation. Experimental results showed that all incorporated nanofillers can refine the pore structure of UHPCC, but nanofillers with different types and dimensions have various effects on the pore structure of UHPCC. Specifically, CNTs, especially the thin-short one, can significantly reduce the porosity of UHPCC, whereas nanoparticles, especially nano-SiO2, are more conducive to refine the pore size. Among all nanofillers, nano-SiO2 has the most obvious effect on pore structure, reducing the porosity, specific pore volume and most probable pore radius of UHPCC by 31.9%, 35.1% and 40.9%, respectively. Additionally, the pore size distribution of nano-modified UHPCC ranges from 10-1nm to 105nm, and the gel pores and fine capillary pores in the range of 3-50nm account for more than 70% of the total pore content, confirming nanofillers incorporation can effectively weaken pore connectivity and induce pore distribution to concentrate at nanoscale. Fractal results indicated the provision of nanofillers reduces the structural heterogeneity of gel pores and fine capillary pores, and induces homogenization and densification of UHPCC matrix, in turn, decreasing the UHPCC fluid permeability by 15.7%-79.2%. / The full-text of this article will be released for public view at the end of the publisher embargo on 11 May 2024.

Yes / The development of ultra-high performance cementitious composite (UHPCC) represents a significant advancement in the field of concrete science and technology, but insufficient hydration and high autogenous shrinkage relatively increase the pores inside UHPCC, in turn, affecting the macro-performance of UHPCC. This paper, initially, optimized the pore structure of UHPCC using different types and dimensions of nanofillers. Subsequently, the pore structure characteristics of nano-modified UHPCC were investigated by the mercury intrusion porosimeter method and fractal theory. Finally, the fluid permeability of nano-modified UHPCC was estimated by applying the Katz-Thompson equation. Experimental results showed that all incorporated nanofillers can refine the pore structure of UHPCC, but nanofillers with different types and dimensions have various effects on the pore structure of UHPCC. Specifically, CNTs, especially the thin-short one, can significantly reduce the porosity of UHPCC, whereas nanoparticles, especially nano-SiO2, are more conducive to refine the pore size. Among all nanofillers, nano-SiO2 has the most obvious effect on pore structure, reducing the porosity, specific pore volume and most probable pore radius of UHPCC by 31.9%, 35.1% and 40.9%, respectively. Additionally, the pore size distribution of nano-modified UHPCC ranges from 10-1nm to 105nm, and the gel pores and fine capillary pores in the range of 3-50nm account for more than 70% of the total pore content, confirming nanofillers incorporation can effectively weaken pore connectivity and induce pore distribution to concentrate at nanoscale. Fractal results indicated the provision of nanofillers reduces the structural heterogeneity of gel pores and fine capillary pores, and induces homogenization and densification of UHPCC matrix, in turn, decreasing the UHPCC fluid permeability by 15.7%-79.2%. / The authors thank the funding supported from the National Science Foundation of China (51978127, 52178188 and 51908103), the China Postdoctoral Science Foundation (2022M720648 and 2022M710973) and the Fundamental Research Funds for the Central Universities (DUT21RC(3)039). / The full-text of this article will be released for public view at the end of the publisher embargo on 11 May 2024.