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  • 1.
    Ahlström, Peter
    et al.
    University of Borås, School of Engineering.
    Gebäck, Tobias
    University of Borås, School of Engineering.
    Johansson, Erik
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    Water absorption in polymers2010Conference paper (Other academic)
    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.
    University of Borås, School of Engineering.
    Moodley, Suren
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    Ramjugernath, D.
    University of Borås, School of Engineering.
    Computer Simulations of Vapor-Liquid-Liquid Equilibria Involving Hydrocarbons and Water2008In: 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, 2008Conference paper (Other academic)
  • 3.
    Bazooyar, Faranak
    et al.
    University of Borås, Faculty of Textiles, Engineering and Business.
    Bohlén, Martin
    University of Borås, Faculty of Textiles, Engineering and Business.
    Bolton, Kim
    University of Borås, Faculty of Textiles, Engineering and Business.
    Computational Studies of Water and Carbon Dioxide Interactions with Cellobiose2015In: Journal of Molecular Modeling, ISSN 1610-2940, E-ISSN 0948-5023, Vol. 21, p. 2553-Article in journal (Refereed)
    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.

  • 4.
    Bazooyar, Faranak
    et al.
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    Molecular-level Simulations of Cellulose Dissolution by Steam and SC-CO2 Explosion2014Conference paper (Refereed)
    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.

  • 5.
    Bazooyar, Faranak
    et al.
    University of Borås, Faculty of Textiles, Engineering and Business.
    Bolton, Kim
    University of Borås, Faculty of Textiles, Engineering and Business.
    Molecular-level Simulations of Cellulose Steam Explosion2015In: Quantum Matter, ISSN 2164-7615, Vol. 4, no 2, p. 115-122Article in journal (Refereed)
    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.

  • 6.
    Bohlén, Martin
    et al.
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    Conformational studies of poly(vinylidene fluoride), poly(trifluoroethylene) and poly(vinylidene fluoride-co-trifluoroethylene) using density functional theory2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 25, p. 12929-12939Article in journal (Refereed)
    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.

  • 7.
    Bohlén, Martin
    et al.
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    Inducing the piezoelectric β-phase of PVDF: a DFT study2014Conference paper (Refereed)
  • 8.
    Bohlén, Martin
    et al.
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    Inducing the β-phase of poly(vinylidene fluoride): a review2014In: Annual Review of Nanoscience and Nanotechnology, ISSN 2159-9688, Vol. 1, no 1Article in journal (Refereed)
    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.

  • 9.
    Börjesson, Anders
    et al.
    University of Borås, School of Engineering.
    Erdtman, Edvin
    University of Borås, School of Engineering.
    Ahlström, Peter
    University of Borås, School of Engineering.
    Berlin, Mikael
    Andersson, Thorbjörn
    Bolton, Kim
    University of Borås, School of Engineering.
    Molecular modelling of oxygen and water permeation in polyethylene2013In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 54, no 12, p. 2988-Article in journal (Refereed)
    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.

  • 10. Erdtman, Edvin
    et al.
    Bohlén, Martin
    University of Borås, School of Engineering.
    Ahlström, Peter
    University of Borås, School of Engineering.
    Gkourmpis, Thomas
    Berlin, Mikael
    Andersson, Thorbjörn
    Bolton Kim, Kim
    University of Borås, School of Engineering.
    Permeation of water and oxygen through carbonaceous PE composites2014Conference paper (Refereed)
  • 11.
    Erdtman, Edvin
    et al.
    University of Borås, School of Engineering.
    Gebäck, Tobias
    University of Borås, School of Engineering.
    Ahlström, Peter
    University of Borås, School of Engineering.
    Atomistic Modelling of Protein Superabsorbents2012Conference paper (Other academic)
  • 12.
    Erdtman, Edvin
    et al.
    University of Borås, School of Engineering.
    Gebäck, Tobias
    Ahlström, Peter
    University of Borås, School of Engineering.
    Computational modeling of Protein based super-absorbents from waste2011Conference paper (Other academic)
    Abstract [en]

    Hydrogels are used for various applications, for example as transporters in drug delivery, in control lenses, and as superabsorbent material in diapers.[1] Most synthetic produced hydrogels are based on synthetic polymers. Even though they are efficient and cheap, they are not biodegradable and sometimes even toxic. To produce more environmental friendly and biodegradable superabsorbent polymers (Bio- SAPs), other building blocks can be used, such as polysaccharides[2] and various protein structures, for example fish shells[3], collagen[4], soy protein[5] and egg protein[6]. Experimental studies at the University of Boras show that it is possible to produce Bio-SAPs from by-products of ethanol production from ligno-cellulose.[2, 6, 7] 2. Method We have studied the absorption properties of protein structures in silico as a comparison to experimental studies. The NPT Gibbs Ensemble Monte Carlo (GEMC) simulation scheme with two phases is used in order to calculate the absorption capacity of the protein. Pure water was simulated in the first GEMC-phase and the peptide in the second phase. The simulations were made with SPC/E water model [8] and the AMBER99 atomistic force field for the peptides [9]. Furthermore, mesoscopic studies with coarse grained force fields have been done. To facilitate faster computations, we used cell lists for the atom-atom interactions, configurational bias algorithm to build the water molecules and the peptide side-chains, and the cavity bias algorithm [10] for molecule insertions. Model peptides have been studied with varying secondary structure, temperature and protonation (pH). We also plan to study how cross-links affect the absorption. One of the peptides we study is a 20 amino acid long peptide called SSP1.[11] This peptide is designed to form a fibrous structure a hydrogel, and its structure is well defined. We have also studied a peptide which changes secondary structure when changing the pH, and concentration.[12] This makes it possible to compare absorption properties with respect to the secondary structure. 3. Conclusion We have simulated peptides with the Gibbs Ensemble Monte Carlo scheme in order to study the water absorption rate dependent of structure, charge, pH and temperature. This information is useful when developing new biodegradable superabsorbent materials.

  • 13. Haghighatpanah, Shayesteh
    et al.
    Bohlén, Martin
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    Molecular level computational studies of polyethylene and polyacrylonitrile composites containing single walled carbon nanotubes: effect of carboxylic acid functionalization on nanotube-polymer interfacial properties2014In: Frontiers in Chemistry, E-ISSN 2296-2646, Vol. 2, no 74Article in journal (Refereed)
    Abstract [en]

    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.

  • 14.
    Mohsenzadeh, Abas
    et al.
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    Richards, Tobias
    University of Borås, School of Engineering.
    Oxidation and dissociation of formyl on Ni(111), Ni(110) and Ni(100) surfaces: A comparative density functional theory study2014Conference paper (Refereed)
    Abstract [en]

    Formyl (CHO) is an important adsorbate and a key intermediate in industrial processes such as water gas shift (WGS), Fischer Tropsch synthesis (FTS) and catalytic hydrocarbon combustion reactions. Density functional theory (DFT) with the PBE functional was used to calculate the adsorption, reaction and activation energies of formyl oxidation and dissociation on Ni(111), Ni(110) and Ni(100) surfaces. The results show that these energies are sensitive to the surface structure. The dissociation barrier for CHO → CH + O (FTS process) is higher than that for CHO → CO + H (catalytic combustion) on all three surfaces. This means that the dissociation to CO and H is kinetically favored. The dissociation reaction rate decreases in the order Ni(110) > Ni(111) > Ni(100) for both dissociation reactions. The formation of formate (CHO + O → HCOO), which is included in one of the pathways for the WGS reaction, has lowest activation energy on the Ni(111) surface, and the energy increases in the order Ni(111) < Ni(110) < Ni(100). However, the reaction rate at 463 K, which is a typical temperature for industrial processes that involve these reactions, is at least five orders of magnitude higher for the CHO → CO + H reaction than for the other two reactions, irrespective of the crystallographic structure of the Ni surface. This means that Ni surfaces studied here are better catalysts for this reaction. The results also show that the WGS reaction on a Ni catalyst does not primarily occur via the formate pathway.

  • 15.
    Mohsenzadeh, Abas
    et al.
    University of Borås, School of Engineering.
    Börjesson, Anders
    Wang, Jeng-Han
    Richards, Tobias
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    The Effect of Carbon Monoxide Co-Adsorption on Ni-Catalysed Water Dissociation2013In: International Journal of Molecular Sciences, ISSN 1422-0067, E-ISSN 1422-0067, Vol. 14, no 12, p. 23301-23314Article in journal (Refereed)
    Abstract [en]

    The effect of carbon monoxide (CO) co-adsorption on the dissociation of water on the Ni(111) surface has been studied using density functional theory. The structures of the adsorbed water molecule and of the transition state are changed by the presence of the CO molecule. The water O–H bond that is closest to the CO is lengthened compared to the structure in the absence of the CO, and the breaking O–H bond in the transition state structure has a larger imaginary frequency in the presence of CO. In addition, the distances between the Ni surface and H2O reactant and OH and H products decrease in the presence of the CO. The changes in structures and vibrational frequencies lead to a reaction energy that is 0.17 eV less exothermic in the presence of the CO, and an activation barrier that is 0.12 eV larger in the presence of the CO. At 463 K the water dissociation rate constant is an order of magnitude smaller in the presence of the CO. This reveals that far fewer water molecules will dissociate in the presence of CO under reaction conditions that are typical for the water-gas-shift reaction.

  • 16.
    Mohsenzadeh, Abas
    et al.
    University of Borås, School of Engineering.
    Richards, Tobias
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    Hydrocarbon combustion and synthesis on Ni(111), Ni(110) and Ni(100) surfaces: A comparative density functional theory study2014Conference paper (Other academic)
    Abstract [en]

    Combustion and synthesis of hydrocarbons may occur directly (CH → C + H and CO → C + O) via a formyl intermediate (CH + O → CHO followed by CHO → CO + H and CO + H → CHO followed by CHO → CH + O) . The activation and reaction energies of these reactions on the Ni(111), Ni(110) and Ni(100) surfaces were investigated using density functional theory (DFT). Calculations show that the barriers are sensitive to the surface structure. The barrier for CH dissociation (catalytic hydrocarbon combustion) is lower than that of for its oxidation reaction (CH + O → CHO) on the Ni(110) and Ni(100) surfaces. In contrast, the barrier for oxidation is lower than that for dissociation on the Ni(111) surface. This means CH will preferably dissociate on the Ni(110) and Ni(100) surfaces, but not on the Ni(111) surface. The barrier for dissociation increases in the order Ni(110) < Ni(100) < Ni(111). The barrier of CHO dissociation to CO and H is almost the same on the Ni(111) and Ni(110) surfaces and it is lower compared to the Ni(100) surface. The energy barrier for carbon monoxide dissociation (catalytic hydrocarbon synthesis) is higher than that of for its hydrogenation reaction on all three surfaces. This means that the hydrogenation to CHO favored over the nickel surfaces studied here. The barrier for both reactions increases in the order Ni(110) < Ni(100) < Ni(111). Formyl dissociation to CH + O barrier is the lowest on the Ni(110) surface and follows the order Ni(100) > Ni(111) > Ni(110). Our DFT results show that the Ni(110) surface has a larger catalytic activity compared to the other surfaces, and that Ni is a better catalyst for hydrocarbon combustion than synthesis.

  • 17. Tian, Bo-Xue
    et al.
    Erdtman, Edvin
    University of Borås, School of Engineering.
    Eriksson, Leif A.
    Catalytic Mechanism of Porphobilinogen Synthase: The Chemical Step Revisited by QM/MM Calculations2012In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 116, no 40, p. 12105-12112Article in journal (Refereed)
    Abstract [en]

    Porphobilinogen synthase (PBGS) catalyzes the asymmetric condensation and cyclization of two 5-aminolevulinic acid (5-ALA) substrate molecules to give porphobilinogen (PBG). The chemical step of PBGS is herein revisited using QM/MM (ONIOM) calculations. Two different protonation states and several different mechanisms are considered. Previous mechanisms based on DFT-only calculations are shown unlikely to occur. According to these new calculations, the deprotonation step rather than ring closure is rate-limiting. Both the C–C bond formation first mechanism and the C–N bond formation first mechanism are possible, depending on how the A-site ALA binds to the enzyme. We furthermore propose that future work should focus on the substrate binding step rather than the enzymatic mechanism.

1 - 17 of 17
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