| 1. |
- Haghighatpanah, Shayesteh, et al.
(författare)
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Computational studies of catalyst-free single walled carbon nanotube growth
- 2013
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics. - 0021-9606 .- 1089-7690. ; 139:5, s. 054308-1
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Tidskriftsartikel (refereegranskat)abstract
- Semiempirical tight binding (TB) and density functional theory (DFT) methods have been used to study the mechanism of single walled carbon nanotube (SWNT) growth. The results are compared with similar calculations on graphene. Both TB and DFT geometry optimized structures of relevance to SWNT growth show that the minimum energy growth mechanism is via the formation of hexagons at the SWNT end. This is similar to the result for graphene where growth occurs via the formation of hexagons at the edge of the graphene flake. However, due to the SWNT curvature, defects such as pentagons are more stable in SWNTs than in graphene. Monte Carlo simulations based on the TB energies show that SWNTs close under conditions that are proper for growth of large defect-free graphene flakes, and that a particle such as a Ni cluster is required to maintain an open SWNT end under these conditions. The calculations also show that the proper combination of growth parameters such as temperature and chemical potential are required to prevent detachment of the SWNTs from the Ni cluster or encapsulation of the cluster by the feedstock carbon atoms.
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| 2. |
- Haghighatpanah, Shayesteh, 1973
(författare)
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Computational studies of graphene and single walled carbon nanotube growth and carbonaceous polymeric nanocomposites
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Graphene and single walled carbon nanotube (SWNT) has attracted a lot of attention in different fields of science due to its unique electrical, mechanical, and optical properties. Controlling the growth of graphene and SWNT is a very topical subject and critical for producing material with desired properties since their properties are highly dependent on their atomic structure and it is often desirable that the material contains very few or (if possible) no defects.There is great interest in using carbon nanotubes (CNTs) to design high performance materials, primarily due to their unique mechanical, electrical and thermal properties. These properties, as well as their light weight, make them suitable as reinforcement additives in polymeric nanocomposites. This includes composites of polyethylene (PE) and polyacrylonitrile (PAN), which are widely used in commercial applications.In this thesis, density functional theory (DFT) and Monte Carlo (MC) simulations based on a tight binding (TB) model are used to study the growth of graphene in the absence of a catalyst, and compare this with the growth mechanism on a Ni(111) surface. The growth of defect-free graphene at the atomic level was simulated which allowed for the study of the mechanisms of defect formation and healing. The growth of SWNT is also studied using the same computational methods and the role of Ni in maintaining an open SWNT end was investigated.A valid force field is selected to study the effect of SWNTs on the polymer morphology in large PE composite systems. The results show that the PE wrapped around the SWNT thereby increasing the radius of gyration of the PE. Interfacial shear strength, interfacial bonding energy and Young’s modulus is measured and results show that short SWNTs as reinforcement do not increase the Young’s modulus for the systems studied here, whereas longer, aligned SWNTs increased the Young’s modulus in the SWNT axial direction.Interfacial properties in SWNT-PE and SWNT-PAN composites is studied. These properties are critical for the other nanocomposite properties, such as interfacial shear stress and load transfer from the polymer to the SWNT additives. The effect of functionalization of SWNT on the interfacial properties were compared with those obtained for non-functionalized SWNTs. The results emphasize the improvement of interfacial properties after functionalizing the SWNTs with carboxylic acid groups. In addition, the changes in properties such as the interfacial shear stress are larger for the polar PAN systems than for the PE systems.
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| 3. |
- Haghighatpanah, Shayesteh, 1973
(författare)
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Computational Studies of Graphene Growth and Carbonaceous Polyethylene Nanocomposites
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Graphene, the youngest allotrope of carbon, has attracted a lot of attention in different fields of science due to its unique electrical, mechanical, and optical properties. Controlling the growth of graphene is a very topical subject and critical for producing material with desired properties since the properties of graphene are highly dependent on its atomic structure and it is often desirable that the material contains very few or (if possible) no defects. Another allotrope of carbon which has become of great interest in the field of polymeric nanocomposites (PNCs) is carbon nanotubes (CNTs); this is due to the unique mechanical, electrical and thermal properties as well as the light weight of CNTs which make them suitable as reinforcement additives in PNCs. This includes composites of polyethylene (PE), which is widely used in different commercial applications.In this study, Monte Carlo simulations based on a tight binding model is used to study the growth of graphene in the absence of a catalyst, and compare this with the growth mechanism on a Ni(111) surface. This is the first simulation of the growth of defect-free structures at the atomic level and also allows for the study of the mechanisms of defect formation and healing. A valid force field is selected to study the effect of SWCNTs on the polymer morphology in large PE composite systems. The results show that the PE wrapped around the SWCNT thereby increasing the radius of gyration of the PE. Interfacial shear strength, interfacial bonding energy and Young’s modulus is measured and results show that short SWCNTs as reinforcement do not increase the Young’s modulus for the systems studied here, whereas longer, aligned SWCNTs increased the Young’s modulus in the SWCNT axial direction.
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| 4. |
- Haghighatpanah, Shayesteh, et al.
(författare)
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Computational studies of graphene growth mechanisms
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 85:20
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Tidskriftsartikel (refereegranskat)abstract
- Density functional theory (DFT) and semiempirical tight-binding (TB) methods have been used to study the mechanism of graphene growth in the presence and absence of a catalytic surface. Both DFT and TB geometry optimized structures relevant to graphene growth show that the minimum energy growth mechanism is via the sequential addition of carbon hexagons at the edge of the graphene sheet. Monte Carlo (MC) simulations based on the TB model show that defect-free graphene sheets can be grown provided one has the proper combination of temperature, chemical potential, and addition rate. In this work, growth of perfect graphene structures has been simulated at the atomic level. Comparison of the growth mechanism in the absence and presence of a nickel catalyst surface shows that the catalyst (i) allows for adsorption of carbon atoms at surface and subsurface sites, (ii) enables formation of long, stable strings of carbon atoms, and (iii) stabilizes small flakes of graphene that can act as precursors to subsequent growth.
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| 5. |
- Haghighatpanah, Shayesteh, et al.
(författare)
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Molecular level computational studies of polyethylene and polyacrylonitrile composites containing single walled carbon nanotubes : effect of carboxylic acid functionalization on nanotube-polymer interfacial properties
- 2014
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Ingår i: Frontiers in Chemistry. - : Frontiers Media S.A.. - 2296-2646. ; 2:74
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Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamics and molecular mechanics methods have been used to investigate additive – polymer interfacial properties in single walled carbon nanotube – polyethylene and single walled carbon nanotube – polyacrylonitrile composites. Properties such as the interfacial shear stress and bonding energy are similar for the two composites. In contrast, functionalizing the single walled carbon nanotubes with carboxylic acid groups leads to an increase in these properties, with a larger increase for the polar polyacrylonitrile composite. Increasing the percentage of carbon atoms that were functionalized from 1% to 5% also leads to an increase in the interfacial properties. In addition, the interfacial properties depend on the location of the functional groups on the single walled carbon nanotube wall.
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| 6. |
- Haghighatpanah, Shayesteh, et al.
(författare)
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Molecular-level computational studies of single wall carbon nanotube : polyethylene composites
- 2013
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Ingår i: Computational materials science. - : Elsevier. - 0927-0256 .- 1879-0801. ; 69, s. 443-454
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Tidskriftsartikel (refereegranskat)abstract
- Minimum energy structures of short (3,3) single wall carbon nanotube (SWCNT)–polyethylene (PE) structures, as well as the binding energy between the SWCNT and PE, were obtained from three commonly used molecular mechanics force fields and first principles methods. The molecular force fields were the Dreiding, Universal and Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force fields and the first principles methods included the B3LYP density functional and MP2 post-Hartree Fock methods with, typically, 6-311G, 6-311G(d,p) and 6-311G(2d,2p) basis sets. These calculations show that the results obtained from all force fields are in qualitative agreement with the first principles results, and that PE prefers to be aligned with a non-zero angle along the SWCNT axis, where the angle depends on the force field or first principles method used. This indicates that longer PE chains may wrap around SWCNTs. This was studied using the COMPASS force field with longer (5,5) SWCNTs interacting with a PE chain and, in agreement with the minimum energy calculations, the PE wrapped around the SWCNT thereby increasing the radius of gyration of the PE. This force field was also used to assess the effect of (5,5) SWCNTs on the mechanical properties of PE nanocomposites. The calculated interfacial shear stress and interfacial bonding energy of SWCNT–PE structures was 141.09 MPa and 0.14 N/m. The simulations show that using short SWCNTs as reinforcement does not increase the Young’s modulus for the systems studied here, whereas longer, aligned SWCNTs increased the Young’s modulus in the SWCNT axial direction.
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| 7. |
- Storesund, Karolina, et al.
(författare)
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Fire safe furniture in a sustainable perspective
- 2019
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Loose furnishings, such as upholstered furniture, mattresses and textiles, are very important for the early stages of fires. Such products can be easily ignited, contribute to rapid spread of fire and produce a lot of smoke and heat when they burn. This limits the time and opportunity for evacuation and fire rescue. The regulation of fire properties of interior textiles, armchairs, sofas and mattresses has been discussed nationally and internationally for many years, without resulting in more stringent requirements for such products, at least not on a harmonized level. Fire safety and environmental considerations are important factors that are often set against each other. It is therefore important to promote the development of safe and fireproof furnishings that are environmentally friendly throughout their life cycle, and which satisfy other requirements that are usually imposed on this product group. The main objective of this project has been to contribute to new knowledge about how fire safety associated with loose interior design can be improved through developing products that meet sustainability and circularity requirements. These new products shall have fire performance comparable to flame retarded reference products but will rely on construction techniques and materials containing small amounts or no flame retardants. The new products shall be safe while in use and shall be recyclable at the end of life. Sustainability and environmental impact analyses including life cycle analyses of furnishing materials have been performed, as well as fire tests for screening the fire performance of a selection of material combinations. Combining a requirement for both sustainable yet fire safe furnishing is a complex task to solve. The more complex the material combination, the more difficult to predict both factors in parallel. Slight variations in components can potentially change the overall scoring of their performance. Cotton, wool and polyester has been shown to have equally high sustainability scores, although cotton had relatively high environmental impact. Polyamide was identified as the fabric with the best environmental performer but scoring lower on sustainability. The cushion material has great impact on fire safety because it may contribute with large amounts of heat energy and smoke. Polyurethane is by far the most common cushion material and comes in many variations, some including chemical fire retardants (FR). FR’s have not been included in in the sustainability and environmental impact analyses in this study, instead focus has been on exploring alternative methods of achieving comparable fire performance. In the case of cushion material, latex was identified as performing much higher on both sustainability and environmental impact than polyurethane. Unfortunately, latex was not a part of the fire testing series and was therefore not explored with regard to fire performance. Future studies should explore the interaction of the fire performance properties of different materials identified as high sustainability and environmental impact performers, especially in full scale room fire experiments. Thorough knowledge about how different components (of high sustainability and low environmental impact) contribute to the fire performance and how these are maintained throughout the furniture’s lifetime, would improve the possibility of fire safe furniture to be part of a circular economy.
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| 8. |
- Storesund, Karolina, et al.
(författare)
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Fire safe, sustainable loose furnishing
- 2019
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Ingår i: Interflam 2019.
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Konferensbidrag (refereegranskat)abstract
- The aim of this study has been to investigate the fire properties and environmental aspects of different upholstery material combinations. An analysis of the sustainability and circularity of selected textiles, along with lifecycle assessment, is used to qualitatively evaluate materials from an environmental perspective. The cone calorimeter was the primary tool used to screen 20 different material combinations from a fire performance perspective. It was found that textile covers of conventional fibres such as wool, cotton and polyester, can be improved by blending them with fire resistant speciality fibres. A new three-dimensional web structure has been examined, showing preliminary promising fire properties with regard to ignition time, heat release rates and smoke production.
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| 9. |
- Storesund, Karolina, et al.
(författare)
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Fire safe, sustainable loose furnishing
- 2021
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Ingår i: Fire and Materials. - : John Wiley and Sons Ltd. - 0308-0501 .- 1099-1018. ; , s. 181-190
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this exploratory study has been to investigate the fire properties and environmental aspects of different upholstery material combinations, mainly for domestic applications. An analysis of the sustainability and circularity of selected textiles, along with lifecycle assessment, is used to qualitatively evaluate materials from an environmental perspective. The cone calorimeter was the primary tool used to screen 20 different material combinations from a fire performance perspective. It was found that textile covers of conventional fibres such as wool, cotton and polyester, can be improved by blending them with fire resistant speciality fibres. A new three-dimensional web structure has been examined as an alternative padding material, showing preliminary promising fire properties with regard to ignition time, heat release rates and smoke production.
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