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  • 1.
    Ahlström, Peter
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Gebäck, Tobias
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Johansson, Erik
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Water absorption in polymers2010Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    In this work two different examples of water absorbtion in polymers are studied by Monte Carlo simulations. Both of them are of large technical and commercial impotance. The first example is the water absorption in polyethylene cables where the water absorption plays a crucial role in the degradation of the cable insulation and thus should be as low as possible. The second example is bio-based superabsorbents made from denatured protein where water absorption capability is the prime desired property. Methods Gibbs Ensemble Monte Carlo simulations [1] were used to study the hydration of polymers. All simulations are performed with two boxes, one of which is filled with water at the start of the simulation, whereas the other contains polymer molecules and possible ions. The polymer molecules are not allowed to swap boxes whereas the water molecules are allowed to do so thus constituting an osmotic Gibbs ensemble [2]. For the polyethylene a connectivity-altering algorithm was used whereas the protein molecules were simulated using a side-chain regrowth model in addition to traditional Monte Carlo moves. For the polyethylene, the TraPPE [3] force field was used and the protein molecules, the Amber force field [4] was used. Water was modelled using simple point charge models [5]. Electrostatic interactions are treated using Ewald summation methods. The protein molecules were of different amino acid compositions and in different conformations, e.g., β-turns and random coils obtained using the amorphous cell method[6]. Studies were made with different degrees of charging on, e.g., lysine side chains mimicking different ionization states. Results The studies of polyethylene revealed the importance of ions left from the polymerisation catalyst for the absorbtion of water and the concomitant degradation of polyethylene cable insulation. Also the absorption properties of the protein molecules is strongly related to the presence of charged groups and fully charged protein molecules absorb large amounts of water. However, neither native nor denatured protein molecules show superabsorbing properties (i.e. absorbing hundreds of times their own mass) as they show in experimental studies and the reasons for this discrepancy will be discussed. References 1. A.Z. Panagiotopoulos, Mol. Phys. 61, 813 (1987). 2. E. Johansson, K. Bolton, D.N. Theodorou, P. Ahlström, J. Chem. Phys., 126, 224902 (2007). 3. M.G. Martin, and J.I. Siepmann, J. Phys. Chem. B, 103, 4508-4517 (1999). 4. W.D. Cornell, P. Cieplak, C.I. Bayly, I.R. Gould, K.M. Merz Jr, D.M. Ferguson, D.C. Spellmeyer, T. Fox, J.W. Caldwell, P.A. Kollman (1995). J. Am. Chem. Soc. 117, 5179–5197. 5. H. J. C. Berendsen, J. P. M. Postma and W. F. van Gunsteren, in Intermolecular Forces, B. Pullman, ed. (Reidel, Dordrecht, 1981) p. 331; H. J. C. Berendsen, J. R. Grigera and T. P. Straatsma, J. Phys. Chem. 91, 6269 (1987). 6. D.N. Theodorou, U.W. Suter, Macromolecules, 18, 1467 (1985).

  • 2.
    Ahlström, Peter
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Moodley, Suren
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Ramjugernath, D.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Computer Simulations of Vapor-Liquid-Liquid Equilibria Involving Hydrocarbons and Water2008Inngår i: Proceedings of the 100th Annual Meeting of the American Institute for Chemical Engineering, 2008, CHPC National Meeting, Durban, South Africa, December 9-10, 2008, AlChe Annual Meeting, Philadelphia, November 15-21, 2008, 2008Konferansepaper (Annet vitenskapelig)
  • 3.
    Arja, Mina
    et al.
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Akbar Mirzaei, Ali
    University of Sistan and Baluchestan, Zahedan 98135-674, Iran.
    Mahmood Davarpanah, Abdol
    University of Sistan and Baluchestan, Zahedan 98135-674, Iran.
    Masoud Barakati, Seyed
    University of Sistan and Baluchestan, Zahedan 98135-674, Iran.
    Mohsenzadeh, Abas
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Atashi, Hossein
    University of Sistan and Baluchestan, Zahedan 98135-674, Iran.
    Bolton, Kim
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    DFT studies of hydrocarbon combustion on metal surfaces2018Inngår i: Journal of Molecular Modeling, ISSN 1610-2940, E-ISSN 0948-5023, Vol. 24, s. 47-Artikkel i tidsskrift (Fagfellevurdert)
  • 4.
    Bazooyar, Faranak
    et al.
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Bohlén, Martin
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Bolton, Kim
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Computational Studies of Water and Carbon Dioxide Interactions with Cellobiose2015Inngår i: Journal of Molecular Modeling, ISSN 1610-2940, E-ISSN 0948-5023, Vol. 21, s. 2553-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    B3LYP/6-311++G** with dispersion correction (DFT-D) was used to study local and global minimum energy structures of water (H2O) or carbon dioxide (CO2) bonding with a pair of cellobiose molecules. The calculations showed that neither the H2O nor the CO2 prefer to be between the cellobiose molecules, and that the minimum energy structures occur when these molecules bond to the outer surface of the cellobiose pair. The calculations also showed that the low energy structures have a larger number of inter-cellobiose hydrogen bonds than the high energy structures. These results indicate that penetration of H2O or CO2 between adjacent cellobiose pairs, which would assist steam or supercritical CO2 (SC-CO2) explosion of cellulose, is not energetically favored. Comparison of the energies obtained with DFT-D and DFT (the same method but without dispersion correction) show that both hydrogen bonds and van der Waals interactions play an important role in cellobiose-cellobiose interactions.

  • 5.
    Bazooyar, Faranak
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Molecular-level Simulations of Cellulose Dissolution by Steam and SC-CO2 Explosion2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Dissolution of cellulose is an important but tough step in biofuel production from lignocellulosic materials. Steam and supercritical carbon dioxide (SC-CO2) explosion are two effective methods for dissolution of some lignocellulosic materials. Loading and explosion are the major processes of these methods. Studies of these processes were performed using grand canonical Monte Carlo and molecular dynamics simulations at different pressure/ temperature conditions on the crystalline structure of cellulose. The COMPASS force field was used for both methods. The validity of the COMPASS force field for the calculations was confirmed by comparing the energy and structures obtained from molecular mechanics simulations of cellobiose (the repeat unit of cellulose), water–cellobiose, water-cellobiose pair and CO2-cellobiose pair systems with those obtained from first principle calculations with and without dispersion correction. A larger disruption of the cellulose crystal structure was seen during loading than that during the explosion process. This is seen by an increased separation of the cellulose chains from the centre of mass of the crystal during the initial stages of the loading, especially for chains in the outer shell of the crystalline structure. Reducing and non-reducing ends of the cellulose crystal show larger disruption than the central core; this leads to increasing susceptibility to enzymatic attack in these end regions. There was also change from the syn to the anti torsion angle conformations, especially for chains in the outer cellulose shell. Increasing the temperature increases the disruption of the crystalline structure during loading and explosion.

  • 6.
    Bazooyar, Faranak
    et al.
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Bolton, Kim
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Molecular-level Simulations of Cellulose Steam Explosion2015Inngår i: Quantum Matter, ISSN 2164-7615, Vol. 4, nr 2, s. 115-122Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Grand canonical Monte Carlo and molecular dynamics simulations are used to study steam explosion of crystalline cellulose using 100, 160, 210 and 250 °C saturated steam. The simulations are based on the COMPASS force field, which provides a valid description of the cellulose crystal structure and water-cellobiose interactions. Disruption of the crystal structure during steaming is typically larger than that during the explosion stage and the restructuring is larger at increased temperature and pressure. This is seen by an increased separation of the cellulose chains from the center of mass of the crystal during the initial stages of the steaming, especially for chains in the outer shell of the elementary fibril. There is a large change in the radius of gyration and fraction of anti torsion angle conformers for chains in the outer shell of the elementary fibril. In addition, the disruption at the reducing and non-reducing ends of the cellulose crystal is larger than in the central core, increasing susceptibility to enzymatic attack in these end regions.

  • 7.
    Bazooyar, Faranak
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Momany, Frank A.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Validating Empirical Force Fields for Molecular-level Simulation of Cellulose Dissolution2012Inngår i: Computational and Theoretical Chemistry, ISSN 2210-271X, E-ISSN 2210-2728, Vol. 984, s. 119-127Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The calculations presented here, which include dynamics simulations using molecular mechanics forcefields and first principles studies, indicate that the COMPASS forcefield is preferred over the Dreiding and Universal forcefields for studying dissolution of large cellulose structures. The validity of these forcefields was assessed by comparing structures and energies of cellobiose, which is the shortest cellulose chain, obtained from the forcefields with those obtained from MP2 and DFT methods. In agreement with the first principles methods, COMPASS is the only forcefield of the three studied here that favors the anti form of cellobiose in the vacuum. This forcefield was also used to compare changes in energies when hydrating cellobiose with 1–4 water molecules. Although the COMPASS forcefield does not yield the change from anti to syn minimum energy structure when hydrating with more than two water molecules – as predicted by DFT – it does predict that the syn conformer is preferred when simulating cellobiose in bulk liquid water and at temperatures relevant to cellulosedissolution. This indicates that the COMPASS forcefield yields valid structures of cellulose under these conditions. Simulations based on the COMPASS forcefield show that, due to entropic effects, the syn form of cellobiose is energetically preferred at elevated temperature, both in vacuum and in bulk water. This is also in agreement with DFT calculations.

  • 8. Bazooyar, Faranak
    et al.
    Taherzadeh, M.J.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Niklasson, C.
    Bolton, K.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Molecular modeling of cellulose dissolution2013Inngår i: Journal of Computational and Theoretical Nanoscience, ISSN 1546-1955, E-ISSN 1546-1963, Vol. 10, nr 11, s. 2639-2648Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work we present computational studies that shed light on the molecular mechanism of the initial stages of cellulose dissolution in saturated steam, which is an important pretreatment step in the conversion of lignocellulose to biofuel. The COMPASS, Dreiding and Universal molecular mechanics force fields and the B3LYP density functional with 6-311G, 6-311++G(d,p) and 6-311++G(2d,2p) basis sets were used to study systems containing glucose, cellobiose and water. These molecular systems were studied since they are sufficiently small to perform the density functional theory calculations in a tractable time, while also being relevant to the dissolution of cellulose in saturated steam. Comparison of the energies and structures obtained from the three force fields with those obtained from the first principles method showed that the COMPASS force field is preferred to the other two and that this force field gives similar structures obtained from the first principles method. This supports the validity of the COMPASS force field for studying cellulose dissolution in saturated steam, and preliminary simulations were performed using grand canonical Monte Carlo and molecular dynamics simulations of cellulose dissolution in saturated steam at 100 °C and 1 bar, 160 °C and 6.2 bar, and 250 °C and 39.7 bar. The results show that the cellulose crystal dissolves in saturated steam at the higher temperatures and pressures.

  • 9.
    Björk, Hans
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Lindecrantz, Kaj
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Ericsson, Dag
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Sarv, Hans
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Börjesson, Anders
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Bazooyar, Faranak
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Ahlström, Peter
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Taherzadeh, Mohammad
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Andersson, Bengt-Åke
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Johansson, Andreas
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Skrifvars, Mikael
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    20 år med Institutionen Ingenjörshögskolan: historik, nuläge och framtid2009Rapport (Annet vitenskapelig)
  • 10.
    Bohlén, Martin
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Conformational studies of poly(vinylidene fluoride), poly(trifluoroethylene) and poly(vinylidene fluoride-co-trifluoroethylene) using density functional theory2014Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, nr 25, s. 12929-12939Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Different conformations of systems consisting of poly(vinylidene fluoride) (PVDF), poly(trifluoroethylene) (PTrFE) and poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) were investigated using density functional theory with dispersion correction. It was found that the trans-gauche-trans-gauche´ (TGTG´) conformation of a single PVDF chain is the lowest energy conformer. Crystals of PVDF were modelled using between two to five chains with up to 12 repeat units in each chain and, in agreement with experiment, structures comprised partly or completely of chains with the TGTG´ conformation are more stable than structures built up from chains with all-trans (TTTT) conformation. This indicates that an all-trans segment or chain will not induce the growth of a larger crystal with the same chain conformations. In contrast, the energetically preferred structure of PTrFE chains is an all-trans (TTTT) conformation, and the results indicate that copolymerization of vinylidene fluoride with trifluoroethylene can facilitate the formation of the all-trans PVDF conformations. This is probably due to increased intramolecular repulsion between the fluorine atoms and an increased intermolecular attraction in the crystal structure.

  • 11.
    Bohlén, Martin
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Effect of single wall carbon nanotubes on the conformation of Poly(vinylidene fluoride)2014Inngår i: Quantum Matter, ISSN 2164-7615, Vol. 3, nr 4, s. 339-343Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Structures consisting of single Poly(vinylidene fluoride) (PVDF) chains, single wall carbon nanotubes (SWCNTs), a PVDF chain interacting with a SWCNT and of five PVDF chains arranged to resemble the α and β crystal structures of PVDF were evaluated using geometry optimizations and single point energy calculations. Density functional theory with dispersion correction was used for all calculations. The conformer of PVDF is the lowest energy structure, irrespective of whether the SWCNT is present or not. Interaction with the SWCNT reduces the energy difference between the β and α conformers by approximately 30%, indicating that SWCNTs can increase the relative amount of the β conformers at higher temperatures. However, even in the presence of the SWCNT this energy difference is approximately 1.67 kcal/mol per –CH2CF2– repeat unit, which is larger than kT at 300 K (0.6 kcal/mol). Hence, the presence of the SWCNTs is not expected to substantially increase the relative amount of the β conformers at these conditions. Compression of the α and β crystal structures, which occurs during fibre extrusion, and which may be increased if nanoparticles are present in the polymer matrix, further decreases the energy difference between the β and α conformers but only to a very small extent at pressures relevant to fibre extrusion.

  • 12.
    Bohlén, Martin
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Inducing the piezoelectric β-phase of PVDF: a DFT study2014Konferansepaper (Fagfellevurdert)
  • 13.
    Bohlén, Martin
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Inducing the β-phase of poly(vinylidene fluoride): a review2014Inngår i: Annual Review of Nanoscience and Nanotechnology, ISSN 2159-9688, Vol. 1, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Poly(vinylidene fluoride) (PVDF) is a versatile material with numerous applications in many fields of industry and science. The extent of applications, ranging from approved contact materials in the food industry to monitors for respiration and heart-rate in medicine, drives the research and development by the materials science community. The largest limiting factor when using PVDF in applications where its piezo- and pyroelectricity is important, is the amount of the highly polar crystalline β-phase in the material. PVDF is polymorphic and usually crystallizes from melt or solution into the non-polar α-phase, which is of little use in piezoelectric applications. Many studies have therefore aimed at increasing the amount of the β-phase crystal structure in the material. Cold drawing of α-phase PVDF, poling in high electric fields, copolymerization with trifluoroethylene, and inclusion of different types of additives to PVDF have been studied using both experimental and computational techniques. This review presents the current status and understanding of these processes, and summarizes results from previous studies. © Global Scientific Publishers 2015.

  • 14.
    Bohlén, Martin
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Molecular Dynamics Studies of the Influence of Single Wall Carbon Nanotubes on the Mechanical Properties of Poly(vinylidene fluoride)2013Inngår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 68, s. 73-80Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Molecular dynamics simulations and geometry optimizations based on the Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force field were performed to understand the effect of Single Wall Carbon Nanotubes (SWCNTs) on the mechanical properties of Poly(vinylidene fluoride) (PVDF). In particular, the Young’s modulus, bulk and shear modulus, pullout energy, pullout force, interfacial shear stress and interfacial bonding energy were calculated. The presence of the SWCNTs can increase the Young’s modulus of the systems studied here by 1 GPa in the direction of the SWCNT axis, although this depends on the distance between neighboring SWCNTs. The calculated interfacial shear stress was between 100 and 129 MPa, which is in agreement with results obtained for other SWCNT-polymer systems. The results, and in particular those obtained for the bulk and shear modulus, show that SWCNTs do not have a significant effect on the bulk mechanical properties. Functionalizing the SWCNTs may yield stronger adhesion between the nanotube and the polymer, thereby achieving improved mechanical properties. ⺠Computational studies using molecular dynamics and molecular mechanics. ⺠Effect of single wall carbon nanotubes on the mechanical properties of Poly(vinylidene fluoride). ⺠Alignment of the nanotubes plays a crucial role for the reinforcing effect. ⺠When aligned, an increase in Young’s modulus of approximately 1 GPa could be observed. ⺠The interfacial shear stress was calculated to be in the range of 100–129 MPa.

  • 15.
    Bohlén, Martin
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Satyanarayana, Kavitha Chelakara
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Computational Studies of Poly(vinylidene fluoride)-Single Wall Carbon Nanotube Systems2013Inngår i: Journal of Computational and Theoretical Nanoscience, ISSN 1546-1955, E-ISSN 1546-1963, Vol. 10, nr 6, s. 1317-1325Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    First principles and molecular mechanics methods have been used to study poly(vinylidene fluoride)—single wall carbon nanotube systems. First principles calculations (Møller-Plesset second order perturbation theory and density functional theory with B3LYP exchange correlation functional with and without dispersion correction) using short poly(vinylidene fluoride) segments and short hydrogen-capped single wall carbon nanotubes show that the polymer segments prefer to have the β-rather than the β-conformation both in the absence and presence of the single wall carbon nanotube. The lowest energy structure is obtained when the poly(vinylidene fluoride) has an β-conformation and is located parallel to the single wall carbon nanotube wall. In contrast to the Dreiding and Universal force fields, the COMPASS force field predicts the structures containing the β-conformation of poly(vinylidene fluoride) to be the lowest in energy in agreement with first principles results. The COMPASS force field was consequently used in preliminary studies of a longer poly(vinylidene fluoride) chain and a longer single wall carbon nanotube using molecular dynamics.

  • 16.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Modelling carbon nanotube growth2008Konferansepaper (Annet vitenskapelig)
  • 17.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Simulations of water, metal and carbon clustering2008Konferansepaper (Annet vitenskapelig)
  • 18.
    Bolton, Kim
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Börjesson, Anders
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Computational studies of single-walled carbon nanotube growth2011Inngår i: SNIC Progress Report (2008-2009), s. 40-46Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    Allocation of time on the Swedish national supercomputing facilities since 2000, as well as support from other sources, has allowed us to perform computational studies on a wide variety of systems. These include properties and growth of carbon nanotubes [1–36], icecatalysed reactions of importance to stratospheric ozone depletion[37], calculations of vapour-liquid, liquid-liquid and vapour-liquid-liquid phase equilibrium of single, binary and ternary component systems[38], and, more recently, carbonaceous polymer nanocomposites and cellulose decomposition. More details of these projects are available at the web page given above.

  • 19.
    Bolton, Kim
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Börjesson, Anders
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Ahlström, Peter
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Bazooyar, Faranak
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Beräkningsteknik2009Inngår i: Vetenskap för profession, ISSN 1654-6520, nr 10, s. 63-68Artikkel i tidsskrift (Annet vitenskapelig)
  • 20.
    Bolton, Kim
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Börjesson, Anders
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Zhu, Wuming
    Amara, Hakim
    Bichara, Christophe
    Density functional theory and tight binding-based dynamical studies of carbon metal systems of relevance to carbon nanotube growth2009Inngår i: Nano Reseach, ISSN 1998-0124, E-ISSN 1998-0000, Vol. 2, nr 10, s. 774-782Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Density functional theory (DFT) and tight binding (TB) models have been used to study systems containing single-walled carbon nanotubes (SWNTs) and metal clusters that are of relevance to SWNT growth and regrowth. In particular, TB-based Monte Carlo (TBMC) simulations at 1000 or 1500 K show that Ni atoms that are initially on the surface of the SWNT or that are clustered near the SWNT end diffuse to the nanotube end so that virtually none of the Ni atoms are located inside the nanotube. This occurs, in part, due to the lowering of the Ni atom energies when they retract from the SWNT to the interior of the cluster. Aggregation of the atoms at the SWNT end does not change the chirality within the simulation time, which supports the application of SWNT regrowth (seeded growth) as a potential route for chirality-controlled SWNT production. DFT-based geometry optimisation and direct dynamics at 2000 K show that Cr and Mo atoms in Cr5Co50 and Mo5Co50 clusters prefer to be distributed in the interior of the clusters. Extension of these calculations should deepen our understanding of the role of the various alloy components in SWNT growth.

  • 21.
    Bolton, Kim
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Christie, Michael
    Ingerman, Åke
    Linder, Cedric
    Saalman, Elisabeth
    SimChemistry as an active learning tool in chemical education2008Inngår i: Chemistry Education Research and Practice, ISSN 1756-1108, E-ISSN 1756-1108, Vol. 9, nr 3, s. 277-284Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The publicly available free computer program, SimChemistry, was used as an active learning tool in the chemical engineering curriculum at the University College of Borås, Sweden. The activity involved students writing their own simulation programs on topics in the area of molecular structure and interactions. Evaluation of the learning experience was done using interviews and by comparing learning outcomes with previous teachings of the topics. Overall, the outcome was interactively engaging group work, high quality construction of simulations, and a much better ability to explain molecular-level chemical concepts and their relations. An interesting perception that emerged during the interviews was that many of the students were unable to explicitly describe the improvement in learning that they had experienced. However, they did recognize that learning had occurred, and all firmly and positively recommended that the initiative be continued for subsequent courses.

  • 22.
    Bolton, Kim
    et al.
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    De Mena, Barbara
    ttz Bremerhaven.
    Schories, Gerhard
    ttz Bremerhaven.
    Sustainable Management of Solid Waste2016Inngår i: Resource Recovery to approach zero municipal wastes / [ed] M. J. Taherzadeh and T. Richards, CRC Press, 2016, s. 23-41Kapittel i bok, del av antologi (Fagfellevurdert)
  • 23.
    Bolton, Kim
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Ding, F.
    Börjesson, Arne
    Zhu, W.M.
    Duan, H.M.
    Harutyunyan, A.R.
    Curtarlo, S.
    Computational Studies of Catalytic Particles for Carbon Nanotube Growth2009Inngår i: Journal of Computational and Theoretical Nanoscience, ISSN 1546-1955, E-ISSN 1546-1963, Vol. 6, nr 1, s. 1-15Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We review our computational studies of the melting temperatures and mechanisms of iron and iron-carbide clusters. Both isolated and supported clusters have been considered, and substrates with different shapes or pores have been simulated. It has been seen, for example, that the surface curvature—or local surface curvature—of the particle plays a dominant role in the melting mechanism and temperature. It has also been observed that the melting mechanism for small clusters is different to that of larger clusters.

  • 24.
    Bolton, Kim
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Johansson, Erik
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Jönsson, Lennart
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Ahlström, Peter
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Simulation of water clusters in vapour, alkanes and polyethylenes2009Inngår i: Molecular Simulation, ISSN 0892-7022, E-ISSN 1029-0435, Vol. 35, nr 10/11, s. 888-896Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Gibbs Ensemble Monte Carlo (GEMC) technique has been used to study the clustering of water in vapour, alkanes and polyethylene, where the water clusters are in equilibrium with liquid phase water. The effect of an external electric field and ionic impurities on the clustering of water in the hydrocarbons (alkanes and polyethylene) has also been studied. The simulations of water clustering in polyethylene were made more efficient by using a connectivity altering osmotic Gibbs ensemble method. It was found that trends in the size distribution of water clusters in the hydrocarbons are similar to those found in the pure vapour, but that fewer and smaller clusters are formed as the length of the hydrocarbon chain increased. Also, large external electric fields decrease the solubility of water in hydrocarbons, whereas the presence of ionic species dramatically increases the solubility.

  • 25.
    Bolton, Kim
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Richards, Tobias
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Mohsenzadeh Syouki, Abas
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    DFT study of the adsorption and dissociation of water on Ni(111), Ni(110) and Ni(100) surfaces2014Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 627, s. 1-10Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Water adsorption and dissociation on catalytic metal surfaces play a key role in a variety of industrial processes, and a detailed understanding of this process and how it is effected by the surface structure will assist in developing improved catalysts. Hence, a comparative study of the adsorption and dissociation of water on Ni(111), Ni(110) and Ni(100) surfaces, which is often used as catalyst, has been performed using density functional theory. The results show that the adsorption energies and dissociation rates depend on the surface structure. The adsorption energies for H2O and OH decrease in the order Ni(110) > Ni(100) > Ni(111), and for the O and H atoms the adsorption energies decrease in the order Ni(100) > Ni(111) > Ni(110). In addition, the splitting of water to OH and H has lower activation energies over less packed Ni(110) and Ni(100) surfaces compared to the highly packed Ni(111) surface. The subsequent splitting of the OH to O and H also has the lowest activation energy on the Ni(110) surface. At 463 K, which is typical for industrial processes that include the water gas shift reaction, the H2O splitting is approximately 6000 and 10 times faster on the Ni(110) surface compared to the Ni(111) and Ni(100) surfaces, respectively, and OH splitting is 200 and 3000 times faster, respectively. The complete water dissociation reaction rate decreases in the order Ni(110) > Ni(100) > Ni(111).

  • 26.
    Bolton, Kim
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Zhu, Wuming
    Börjesson, Anders
    Progress in understanding controlled single-wall carbon nanotube growth from computer simulations2012Inngår i: Journal of Computational and Theoretical Nanoscience, ISSN 1546-1955, E-ISSN 1546-1963, Vol. 9, nr 6, s. 819-825Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Density functional theory based on the PW91 and PBE exchange-correlation functionals was used to study processes that are expected to play a key role in single-walled carbon nanotube (SWNT) growth and continued growth. It is shown that Ni clusters adapt their shape to the shape of the SWNT end to which they are attached. The results also show that the presence of SWNTs affects Ostwald ripening of the catalyst metal clusters and that, under certain conditions, the net diffusion may be from larger to smaller clusters. Also, Ostwald ripening may affect the chiral distribution of the SWNTs.

  • 27.
    Brancoli, Pedro
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Life Cycle Assessment of Waste Management Systems2019Inngår i: Sustainable Resource Recovery and Zero Waste Approaches / [ed] Mohammad J. Taherzadeh, Kim Bolton, Jonathan Wong and Ashok Pandey, Elsevier, 2019Kapittel i bok, del av antologi (Fagfellevurdert)
  • 28.
    Brancoli, Pedro
    et al.
    Högskolan i Borås, Akademin för textil, teknik och ekonomi. University of Borås.
    Bolton, Kim
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Rousta, Kamran
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    LCA as a Supporting Tool for Supermarket Food Waste Management2016Konferansepaper (Annet vitenskapelig)
  • 29.
    Brancoli, Pedro
    et al.
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Bolton, Kim
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Rousta, Kamran
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Life cycle assessment of supermarket food waste2017Inngår i: Resources, Conservation and Recycling, ISSN 0921-3449, E-ISSN 1879-0658, Vol. 118, s. 39-46Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Retail is an important actor regarding waste throughout the entire food supply chain. Although it produces lower amounts of waste compared to other steps in the food value chain, such as households and agriculture, it has a significant influence on the supply chain, including both suppliers in the upstream processes and consumers in the downstream. The research presented in this contribution analyses the impacts of food waste at a supermarket in Sweden. In addition to shedding light on which waste fractions have the largest environmental impacts and what part of the waste life cycle is responsible for the majority of the impacts, the results provide information to support development of strategies and actions to reduce of the supermarket's environmental footprint. Therefore, the food waste was categorised and quantified over the period of one year, the environmental impacts of waste that were generated regularly and in large amounts were assessed, and alternative waste management practices were suggested. The research revealed the importance of not only measuring the food waste in terms of mass, but also in terms of environmental impacts and economic costs. The results show that meat and bread waste contributes the most to the environmental footprint of the supermarket. Since bread is a large fraction of the food waste for many Swedish supermarkets, this is a key item for actions aimed at reducing the environmental footprint of supermarkets. Separation of waste packaging from its food content at the source and the use of bread as animal feed were investigated as alternative waste treatment routes and the results show that both have the potential to lead to a reduction in the carbon footprint of the supermarket.

  • 30.
    Brancoli, Pedro
    et al.
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Ferreira, Jorge A.
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Bolton, Kim
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Taherzadeh, Mohammad J
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Changes in carbon footprint when integrating production of filamentous fungi in 1st generation ethanol plants2017Inngår i: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Integrating the cultivation of edible filamentous fungi in the thin stillage from ethanol production is presently being considered. This integration can increase the ethanol yield while simultaneously producing a new value-added protein-rich biomass that can be used for animal feed. This study uses life cycle assessment to determine the change in greenhouse gas (GHG) emissions when integrating the cultivation of filamentous fungi in ethanol production. The result shows that the integration performs better than the current scenario when the fungal biomass is used as cattle feed for system expansion and when energy allocation is used. It performs worse if the biomass is used as fish feed. Hence, integrating the cultivation of filamentous fungi in 1st generation ethanol plants combined with proper use of the fungi can lead to a reduction of GHG emissions which, considering the number of existing ethanol plants, can have a significant global impact.

  • 31.
    Brancoli, Pedro
    et al.
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Lundin, Magnus
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Bolton, Kim
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Eriksson, Mattias
    Bread loss rates at the supplier-retailer interface – Analysis of risk factors tosupport waste prevention measures2019Inngår i: Resources, Conservation and Recycling, ISSN 0921-3449, E-ISSN 1879-0658, s. 128-136Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper quantifies bread waste throughout the Swedish supply chain and investigates the loss rate of prepackagedbread products at the supplier-retailer interface. The goal is to understand the extent of bread waste inSweden and to identify risk factors for high quantities of waste at the supplier-retailer interface, in order toprovide information supporting waste prevention measures. The study uses primary data, in combination withnational statistics and data from sustainability reports and the literature. Primary data were collected from 380stores of a Swedish retail company and a bakery. Bread waste was calculated to be 80 410 tons/year in Sweden,the equivalent of 8.1 kg per person/year, and was found to be concentrated at households and in retail, specificallyat the supplier-retailer interface. The results provide evidence that take-back agreements between suppliersand retailers, where the retailer only pays for sold products and the supplier bears the cost of the unsoldproducts and their collection and treatment, are risk factors for high waste generation. Current business modelsmay need to be changed to achieve a more sustainable bread supply chain with less waste.

  • 32.
    Brancoli, Pedro
    et al.
    Högskolan i Borås, Akademin för textil, teknik och ekonomi. University of Borås.
    Rousta, Kamran
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Bolton, Kim
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Environmental impacts of supermarket food waste in a life cycle perspective2016Konferansepaper (Annet vitenskapelig)
  • 33.
    Börjesson, A.
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Zhu, W.
    Amara, H.
    Bichara, C.
    Ducastelle, F.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Theoretical investigation of the Nanotube-metal junction2008Konferansepaper (Annet vitenskapelig)
  • 34.
    Börjesson, Anders
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    First Principles Studies of the Effect of Nickel Carbide Catalyst Composition on Carbon Nanotube Growth2010Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, nr 42, s. 18045-18050Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Density functional theory calculations were used to investigate the stability of single-walled carbon nanotubes (CNTs) attached to nanoparticles. The total energies and the adhesion energies between the CNTs and the nanoparticles were calculated for systems where the nanoparticles were either pure Ni or Ni carbide. It was found that the adhesion between the CNT and a pure Ni cluster is stronger than between the same CNT and a Ni carbide cluster although the energy difference was small compared to the total adhesion energies. This adhesion strength implies that CNTs are likely to remain attached to both pure Ni and Ni carbide clusters and that either pure Ni or Ni carbide clusters may be docked onto the open CNT ends to achieve continued growth or electronic contacts between CNTs and electrode materials. The system with a CNT attached to a pure Ni cluster was found to be energetically favored compared to a system containing the same CNT attached to a Ni carbide. The difference in total energy implies that a CNT should act as a sink for C atoms dissolved in the Ni carbide cluster, which means that the dissolved C atoms will be drained from the cluster, yielding a pure metal in the zero Kelvin thermodynamic limit. It is argued that this draining procedure is likely to occur even if carbon is added to the cluster at a proper rate, for example, during CNT growth.

  • 35.
    Börjesson, Anders
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    First Principles Studies of the Effect of Ostwald Ripening on Carbon Nanotube Chirality Distributions2011Inngår i: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 5, nr 2, s. 771-779Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of Ostwald ripening of metal particles attached to carbon nanotubes has been studied using density functional theory. It has been confirmed that Ostwald ripening may be responsible for the termination of growth of carbon nanotube forests. It was seen that the Ostwald ripening of metal particles attached to carbon nanotubes is governed by a critical factor that depends on both the cluster size and the carbon nanotube chirality. For example, clusters attached to armchair and zigzag nanotubes of similar diameters will have different critical factors although the exact behavior may depend on which molecules are present in the surrounding medium. The critical factor was also observed to have a critical point with the effect that clusters with a narrow size distribution close to the critical point may experience a narrowing rather than a widening of the size distribution, as is the case for free clusters.

  • 36.
    Börjesson, Anders
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan. Högskolan i Borås, Institutionen Textilhögskolan.
    Modelling of Ostwald ripening of metal clusters attached to carbon nanotubes2011Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, nr 50, s. 24454-24462Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a model of Ostwald ripening of nanosized clusters and apply it to study the time evolution of metal particles attached to carbon nanotubes. The Ostwald ripening of metal clusters attached to carbon nanotubes differs from that of free metal clusters. While free clusters experience a rapid broadening in the size dispersion, this may be delayed by the nanotubes, which may therefore limit the ripening. The diameter and chirality of the carbon nanotubes were also seen to affect the Ostwald ripening of the catalyst particles. For a collection of carbon nanotubes that contains different diameters and chiralities, the clusters attached to carbon nanotubes with large diameters and strong carbon–metal adhesion are the most likely to survive the Ostwald ripening.

  • 37.
    Börjesson, Anders
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Curtarolo, Stefano
    Harutyunyan, Avetik R.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Computational study of the thermal behavior of iron clusters on a porous substrate2008Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, nr 11Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermal behavior of iron nanoclusters on a porous substrate has been studied using classical molecular dynamics simulations. The substrate has been modeled with a simple Morse potential and pores with different shapes have been modeled in order to mimic the porous substrates used for carbon nanotube growth. It has been confirmed that the presence of the substrate increases the cluster melting temperature compared to the free cluster. In addition, the magnitude of this increase in melting point depends on the existence, shape, and diameter of the pore. For example, the increase in melting point is larger for clusters supported on flat (nonporous) substrates than for clusters which straddle pores with smaller diameters than the cluster diameter.

  • 38.
    Börjesson, Anders
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Erdtman, Edvin
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Ahlström, Peter
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Berlin, Mikael
    Andersson, Thorbjörn
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Molecular modelling of oxygen and water permeation in polyethylene2013Inngår i: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 54, nr 12, s. 2988-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Monte Carlo and molecular dynamics simulations were performed to calculate solubility, S, and diffusion, D, coefficients of oxygen and water in polyethylene, and to obtain a molecular-level understanding of the diffusion mechanism. The permeation coefficient, P, was calculated from the product of S and D. The AMBER force field, which yields the correct polymer densities under the conditions studied, was used for the simulations, and it was observed that the results were not sensitive to the inclusion of atomic charges in the force field. The simulated S for oxygen and water are higher and lower than experimental data, respectively. The calculated diffusion coefficients are in good agreement with experimental data. Possible reasons for the discrepancy in the simulated and experimental solubilities, which results in discrepancies in the permeation coefficients, are discussed. The diffusion of both penetrants occurs mainly by large amplitude, infrequent jumps of the molecules through the polymer matrix.

  • 39.
    Börjesson, Anders
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Harutyunyan, Avetik R.
    Curtarolo, Stefano
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Computational study of the thermal behavior of iron clusters on a porous substrate2008Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, nr 11Artikkel i tidsskrift (Fagfellevurdert)
  • 40.
    Börjesson, Anders
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Zhu, Wuming
    Amara, Hakim
    Bichara, Christophe
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Computational studies of metal-carbon nanotube interfaces for regrowth and electronic transport2009Inngår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 9, nr 3, s. 1117-1120Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    First principles and tight binding Monte Carlo simulations show that junctions between single-walled carbon nanotubes (SWNTs) and nickel clusters are on the cluster surface, and not at subsurface sites, irrespective of the nanotube chirality, temperature, and whether the docking is gentle or forced. Gentle docking helps to preserve the pristine structure of the SWNT at the metal interface, whereas forced docking may partially dissolve the SWNT in the cluster. This is important for SWNT-based electronics and SWNT-seeded regrowth.

  • 41. Chelakara Satyanarayana, Kavitha
    et al.
    Bohlén, Martin
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Lund, Anja
    Rychwalski, Rodney
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Analysis of the torsion angle distribution of poly(vinylidene fluoride) in the melt2012Inngår i: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 53, nr 4, s. 1109-1114Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Analysis of the torsionangledistribution of poly(vinylidene fluoride) (PVDF) structures at temperatures above its melting point is addressed by combining first principles methods, atomistic simulations and laboratory experiments. Amorphous, α- and β-conformations of PVDF structures have been considered. The results from the atomistic simulations as well as the experiments show that there is a larger probability of the PVDF torsions to be near ±180° at temperatures above the melting point, which is associated more with the β-conformation than the α-conformation.

  • 42. Chelakara Satyanarayana, Kavitha
    et al.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Molecular dynamics simulations of α- to β-poly (vinylidene fluoride) phase change by stretching and poling2012Inngår i: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 53, nr 14, s. 2927-2934Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The mechanism of inducing a phase change from α-poly(vinylidene fluoride) (α-PVDF) to β-PVDF is addressed using molecular dynamics simulations based on a molecular mechanics force field. The effect of applying a strain to the α-PVDF crystal along the axis of the molecules is investigated, as well as poling the crystal before or after stretching. Rather large (at least 1010 V/m) electric fields that are perpendicular to the axis of the PVDF molecules are required to induce α- to β-PVDF phase change when no strain is applied to the α-PVDF crystal. However, at a strain of 1.0475 (i.e., when the crystal is stretched by 4.75%) α-PVDF changes to a β-PVDF like structure, where the β-PVDF molecules orientate anti-parallel relative to each other. Transformation of the anti-parallel β-PVDF to β-PVDF can be induced by poling (even at the lowest electric field of 105 V/m studied here) or by thermal annealing.

  • 43. Curtarolo, S.
    et al.
    Awasthi, N.
    Setyawan, W.
    Jiang, A.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Tokune, T.
    Harutyunyan, A. R.
    Influence of Mo on the Fe:Mo:C nanocatalyst thermodynamics for singlewalled carbon nanotube growth2008Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, nr 5Artikkel i tidsskrift (Fagfellevurdert)
  • 44. Curtarolo, Stefano
    et al.
    Awasthi, Neha
    Setyawan, Wahyu
    Mora, Elena
    Tokune, Toshio
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Harutyunyan, Avetik R.
    The role of carbon solubility in Fe-C nano-clusters on the growth of small single-walled carbon nanotubes2008Konferansepaper (Annet vitenskapelig)
  • 45. Curtarolo, Stefano
    et al.
    Awasthi, Neha
    Setyawan, Wahyu
    Tokune, Toshio
    Mora, Elena
    Kuznetsov, O.
    Harutyunyan, Avetik R.
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    The apparent paradox of the Gibbs-Thompson phenomenon is the thermodynamic limit for the activity of Fe anf Fe:Mo catalysts for carbon nanotubes growth2008Konferansepaper (Annet vitenskapelig)
  • 46. Cutrarolo, Stefano
    et al.
    Awastahi, Neha
    Setyawan, Wahyu
    Li, Na
    Jiang, Aiqin
    Mora, Elena
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Harutyunyan, Avetik R.
    Thermodynamics of carbon in iron nanoparticles at low temperature: reduced solubility and size-induced nucleation of cementite2010Inngår i: Physics Procedia, ISSN 1875-3892, E-ISSN 1875-3892, Vol. 6, s. 16-26Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this manuscript we present the thermodynamics of iron-carbon nano particles at low temperature. By combining classical molecular dynamics simulations, ab initio calculations, finite temperature thermodynamics modeling, and the “size/pressure approximation”, we address carbon-induced fluidization, size-induced eutectic point shift, and reduced solubility at the nanoscale. The results are used to describe, as functions of particle size, three scenarios in the catalytic chemical vapor deposition growth of single single-walled carbon nanotubes, corresponding to steady state-, limitedand no-growth.

  • 47. Ding, Feng
    et al.
    Larsson, Peter
    Larsson, Andreas J.
    Ahuja, Rajeev
    Duan, Haiming
    Rosén, Arne
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    The importance of strong carbon-metal adhesion for catalytic nucleation of single-walled carbon nanotubes2008Inngår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 8, nr 2, s. 463-468Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Density functional theory is used to show that the adhesion between single-walled carbon nanotubes (SWNTs) and the catalyst particles from which they grow needs to be strong to support nanotube growth. It is found that Fe, Co, and Ni, commonly used to catalyze SWNT growth, have larger adhesion strengths to SWNTs than Cu, Pd, and Au and are therefore likely to be more efficient for supporting growth. The calculations also show that to maintain an open end of the SWNT it is necessary that the SWNT adhesion strength to the metal particle is comparable to the cap formation energy of the SWNT end. This implies that the difference between continued and discontinued SWNT growth to a large extent depends on the carbon-metal binding strength, which we demonstrate by molecular dynamics (MD) simulations. The results highlight that first principles computations are vital for the understanding of the binding strength's role in the SWNT growth mechanism and are needed to get accurate force field parameters for MD.

  • 48. Duan, Haiming
    et al.
    Ding, Feng
    Rosén, Arne
    Harutyunyang, Avetik R.
    Curtarolo, Stefano
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Size dependent melting mechanisms of iron nanoclusters2007Inngår i: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 333, nr 1, s. 57-62Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Molecular dynamics simulations were used to study the change in the mechanism of iron cluster melting with increasing cluster size. Melting of smaller clusters (e.g., Fe-55 and Fe-100) occurs over a large temperature interval where the phase of the cluster repeatedly oscillates between liquid and solid. In contrast, larger clusters (e.g., Fe-300) have sharper melting points with surface melting preceding bulk melting. The importance of the simulation time, the force field and the definition of cluster melting is also discussed.

  • 49. Duan, Haiming
    et al.
    Ding, Feng
    Rosén, Arne
    Harutyunyang, Avetik
    Tokune, Toshio
    Curtarolo, Stefano
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Initial growth of single-walled carbon nanotubes on supported iron clusters: a molecular dynamics study2007Inngår i: European Physical Journal D: Atomic, Molecular and Optical Physics, ISSN 1434-6060, E-ISSN 1434-6079, Vol. 43, nr 1-3, s. 185-189Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Molecular dynamics simulations were used to study the initial growth of single-walled carbon nanotubes (SWNTs) on a supported iron cluster (Fe-50). Statistical analysis shows that the growth direction of SWNTs becomes more perpendicular to the substrate over time due to the weak interaction between carbon nanotube and the substrate. The diameter of the nanotube also increases with the simulation time and approaches the size of the supported iron cluster.

  • 50. Duan, Haiming
    et al.
    Rosén, Arne
    Harutyunyan, Avetik
    Curtarolo, Stefano
    Bolton, Kim
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Computational studies of small carbon and iron-carbon systems relevant to carbon nanotube growth2008Inngår i: Journal of Nanoscience and Nanotechnology, ISSN 1533-4880, E-ISSN 1533-4899, Vol. 8, nr 11, s. 6170-6177Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Density functional theory (DFT) calculations show that dimers and longer carbon strings are more stable than individual atoms on Fe(111) surfaces. It is therefore necessary to consider the formation of these species on the metal surfaces and their effect on the mechanism of single-walled nanotube (SWNT) growth. The good agreement between the trends (energies and structures) obtained using DFT and those based on the Brenner and AIREBO models indicate that these analytic models provide adequate descriptions of the supported carbon systems needed for valid molecular dynamics simulations of SWNT growth. In contrast, the AIREBO model provides a better description of the relative energies for isolated carbon species, and this model is preferred over the Brenner potential when simulating SWNT growth in the absence of metal particles. However, the PM3 semiempirical model appears to provide an even better description for these systems and, given sufficient computer resources, direct dynamics methods based on this model may be preferred.

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