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Publications (10 of 18) Show all publications
Kamerlin, N. & Elvingson, C. (2017). Deformation Behavior and Failure of Bimodal Networks. Macromolecules, 50(19), 7628-7635
Open this publication in new window or tab >>Deformation Behavior and Failure of Bimodal Networks
2017 (English)In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 50, no 19, p. 7628-7635Article in journal (Refereed) Published
Abstract [en]

Using computer simulations, we have investigated the deformation and stress-strain behavior of a series of ideal gels without any defects, with a bimodal molecular weight distribution, subject to tensile strains. These networks were prepared with a spatially homogeneous distribution of short and long chains, where all chains are elastically active, without needing to consider possible effects of chain aggregation or entanglements on the physical properties. For all fractions of short chains, the first chains to rupture were the short chains that were initially oriented along the strain axis. The average orientation of the short chains slightly increased with decreasing fraction of short chains. This could be explained by the detailed structure of the network at different compositions. Analysis of the stress-strain relation for the short and long chains showed that the stress was not uniformly shared. Instead, the short chains are more strongly deformed whereas the long chains only make a negligible contribution at smaller strains. The mechanical properties of the bimodal networks at lower fractions of short chains also deviated from the behavior of equivalent unimodal networks with the corresponding average chain length, showing that bimodality alone is sufficient to increase both the maximum extensibility and toughness.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-332557 (URN)10.1021/acs.macromol.7b01653 (DOI)000412965900023 ()
Available from: 2017-10-30 Created: 2017-10-30 Last updated: 2018-01-09Bibliographically approved
Kamerlin, N. & Elvingson, C. (2017). Deformation Behavior of Homogeneous and Heterogeneous Bimodal Networks. Macromolecules, 50(23), 9353-9359
Open this publication in new window or tab >>Deformation Behavior of Homogeneous and Heterogeneous Bimodal Networks
2017 (English)In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 50, no 23, p. 9353-9359Article in journal (Refereed) Published
Abstract [en]

In this study, the effect of spatial heterogeneities on the deformation behavior during uniaxial elongation as well as the ultimate properties of bimodal gels consisting of both short and long chains was investigated by molecular simulations. Defect-free networks were created containing dense short-chain clusters and compared with gels having a homogeneous distribution of chains. In both cases, the first chains to rupture were the ones already aligned along the strain axis prior to imposing a strain. The presence of clusters was generally not found to improve the ultimate stress or toughness; the short chains within the clusters were effectively shielded from deformation, even at large fractions of short chains. The heterogeneous network tended to be weaker than the corresponding homogeneous network at a given fraction of short chains, fracturing before any significant deformation of clusters had taken place. The deformation behavior was, however, found to be sensitive to the degree of heterogeneity and the number of intercluster connections. At large fractions of short chains, clustering offered an improvement in the ultimate strain compared to a homogeneous bimodal network and also an equivalent unimodal network with the corresponding number-average chain length, thus providing a small improvement in toughness.

National Category
Polymer Chemistry
Identifiers
urn:nbn:se:uu:diva-339797 (URN)10.1021/acs.macromol.7b02112 (DOI)000418206800027 ()
Available from: 2018-02-23 Created: 2018-02-23 Last updated: 2018-02-23Bibliographically approved
Kamerlin, N., Ekholm, T., Carlsson, T. & Elvingson, C. (2014). Construction of a closed polymer network for computer simulations. Journal of Chemical Physics, 141(15), 154113
Open this publication in new window or tab >>Construction of a closed polymer network for computer simulations
2014 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 141, no 15, p. 154113-Article in journal (Refereed) Published
Abstract [en]

Computer simulations are an important tool for linking the behaviour of polymer materials to the properties of the constituent polymer chains. In simulations, one normally uses periodic boundary conditions to mimic a macroscopic system. For a cross-linked polymer network, this will impose restrictions on the motion of the polymer chains at the borders of the simulation cell. We present a new method for constructing a three-dimensional closed network without periodic boundaries by embedding the system onto the surface of a sphere in four dimensions. This method can also be used to construct finite-sized gel particles for simulating the swelling of particles in a surrounding solvent. The method is described in algorithmic detail to allow the incorporation of the method into different types of simulation programs. We also present the results of Brownian dynamics simulations, analyzing the end-to-end distribution, radial distribution function, and the pore size distribution for different volume fractions and for chains with varying stiffness.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-239581 (URN)10.1063/1.4897447 (DOI)000344346000015 ()25338887 (PubMedID)
Available from: 2014-12-30 Created: 2014-12-29 Last updated: 2017-12-05Bibliographically approved
Siretskiy, A. & Elvingson, C. (2013). Role of non-uniform confinement in shape transitions of semi-stiff polymers. Molecular Physics, 111(1), 101-109
Open this publication in new window or tab >>Role of non-uniform confinement in shape transitions of semi-stiff polymers
2013 (English)In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 111, no 1, p. 101-109Article in journal (Refereed) Published
Abstract [en]

New types of nanostructures are constantly being developed synthetically but are also found in biological systems. Specific examples include the production of carbon nanocones as well as the conical core in some viruses. Such conical structures can be used to investigate the role of non-uniform confinement on the stability of e.g. toroidal structures formed by semi-stiff circular polymers, such as DNA. In this communication we are interested in the principal features of the compaction process. Using an external field and a conical confinement we observe several distinct shape transitions from a circle-like shape to several toroidal-like loops for both a two-dimensional and a three-dimensional system. The thermodynamic stability of these toroidal-like structures was investigated by evaluating their relative free energies using Monte Carlo simulations in the Extended Ensemble in the case of a two-dimensional system and by observing a hysteresis of the compaction-extension curve for the three-dimensional case.

Keywords
semi-stiff polymers, Monte Carlo, Wang-Landau, Extended Ensemble, compact structures, shape transitions, confinement, nanocone
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-196086 (URN)10.1080/00268976.2012.705024 (DOI)000313633400011 ()
Available from: 2013-03-04 Created: 2013-03-04 Last updated: 2017-12-06Bibliographically approved
Siretskiy, A., Elvingson, C. & Vorontsov-Velyaminov, P. (2013). Stepwise conformation transitions for a semi-stiff ring polymer confined in a conical trap induced by the increasing external field or by cone's opening angle variation. Nanosystems: Physics, Chemistry, Mathematics, 4(2), 225-235
Open this publication in new window or tab >>Stepwise conformation transitions for a semi-stiff ring polymer confined in a conical trap induced by the increasing external field or by cone's opening angle variation
2013 (English)In: Nanosystems: Physics, Chemistry, Mathematics, ISSN 2220-8054, Vol. 4, no 2, p. 225-235Article in journal (Refereed) Published
Abstract [en]

In this paper a stepwise compaction process of a ring semi-stiff polymer chain placed in a 3d conical nano-cavity and being under the action of the increasing external field is studied. Compaction from a circle- like shape to several toroidal-like loops for a three-dimensional system was observed. The thermodynamic stability of these toroidal-like structures was investigated by observing a hysteresis of the compaction- extension curves. This study extends our previous work [1] with investigation of the effect of the cone opening angle variation on the distinct shape transitions. 

Place, publisher, year, edition, pages
St. Petersburg National Research University of Information Technologies, Mechanics and Optics, 2013
Keywords
semi-stiff ring polymers, Monte Carlo, compact structures, shape transitions, confinement, nanocone
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-206386 (URN)
Available from: 2013-08-30 Created: 2013-08-30 Last updated: 2013-09-04Bibliographically approved
Carlsson, T., Kamerlin, N., Arteca, G. A. & Elvingson, C. (2011). Brownian dynamics of a compressed polymer brush model: Off-equilibrium response as a function of surface coverage and compression rate. Physical Chemistry, Chemical Physics - PCCP, 13(35), 16084-16094
Open this publication in new window or tab >>Brownian dynamics of a compressed polymer brush model: Off-equilibrium response as a function of surface coverage and compression rate
2011 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 35, p. 16084-16094Article in journal (Refereed) Published
Abstract [en]

We study the compressive behaviour of a polymer-covered surface (i.e., a "polymer brush'') using Brownian dynamics simulations. The model consists of grafted chains with variable flexibility, variable intra-and inter-chain interactions, as well as different surface coverage. We discuss the polymer brush response to confinement by considering variable rates of compression under a hard plane. Our results show a small degree of inter-chain entanglement, regardless of whether the interaction is attractive or merely excluded volume. We observe that the molecular shape depends strongly on the surface coverage. Dense brushes exhibit a limited degree of lateral deformation under compression; instead, chains undergo a transition that produces a local patch with near-solid packing. This effect due to surface density can be undone partially by increasing the attractive nature of the chain interaction, by modulating the rate of compression, or by allowing "soft anchoring'', i.e., the possible Brownian drift of the grafting bead on the surface. We have also studied the polymer brush relaxation while maintaining the compressing plane, as well as after its sudden removal. We find evidence that also the relaxation depends on surface density; dense brushes appear to be configurationally frustrated at high compression and are unable to undergo swelling, regardless of the pressure applied.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-158668 (URN)10.1039/c1cp21433k (DOI)000294167700042 ()
Available from: 2011-09-13 Created: 2011-09-13 Last updated: 2017-12-08Bibliographically approved
Siretskiy, A., Elvingson, C., Vorontsov-Velyaminov, P. & Khan, M. (2011). Method for sampling compact configurations for semistiff  polymers. Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, 84(1), 016702
Open this publication in new window or tab >>Method for sampling compact configurations for semistiff  polymers
2011 (English)In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 84, no 1, p. 016702-Article in journal (Refereed) Published
Abstract [en]

The sampling of compact configurations is crucial when investigating structural properties of semistiff polymers, like proteins and DNA, using Monte Carlo methods. A sampling scheme for a continuous model based on configuration biasing is introduced, tested, and compared with conventional methods. The proposed configuration biased Monte Carlo method, used together with the Wang-Landau sampling scheme, enables us to obtain any thermodynamic property within the statistical ensemble in use. Using the proposed method, it is possible to collect statistical data of interest for a wide range of compactions (from stretched up to several toroid loops) in a single computer experiment. A second-order-like stretched-toroid phase transition is observed for a semistiff polymer, and the critical temperature is estimated.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-151616 (URN)10.1103/PhysRevE.84.016702 (DOI)000293399500004 ()
Available from: 2011-04-14 Created: 2011-04-14 Last updated: 2017-12-11Bibliographically approved
Carlsson, T., Ekholm, T. & Elvingson, C. (2010). Algorithm for generating a Brownian motion on a sphere. Journal of physics A: Mathematical and theoretical, 43(50), 505001
Open this publication in new window or tab >>Algorithm for generating a Brownian motion on a sphere
2010 (English)In: Journal of physics A: Mathematical and theoretical, ISSN 1751-8113, Vol. 43, no 50, p. 505001-Article in journal (Refereed) Published
Abstract [en]

We present a new algorithm for generation of a random walk on a two-dimensional sphere. The algorithm is obtained by viewing the 2-sphere as the equator in the 3-sphere surrounded by an infinitesimally thin band with boundary which reflects Brownian particles and then applying known effective methods for generating Brownian motion on the 3-sphere. To test the method, the diffusion coefficient was calculated in computer simulations using the new algorithm and, for comparison, also using a commonly used method in which the particle takes a Brownian step in the tangent plane to the 2-sphere and is then projected back to the spherical surface. The two methods are in good agreement for short time steps, while the method presented in this paper continues to give good results also for larger time steps, when the alternative method becomes unstable.

National Category
Mathematics Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-134231 (URN)10.1088/1751-8113/43/50/505001 (DOI)000284879400003 ()
Available from: 2010-11-23 Created: 2010-11-23 Last updated: 2012-08-01Bibliographically approved
Bergman, K., Elvingson, C., Hilborn, J., Svensk, G. & Bowden, T. (2007). Hyaluronic acid derivatives prepared in aqueous media by triazine-activated amidation. Biomacromolecules, 8(7), 2190-2195
Open this publication in new window or tab >>Hyaluronic acid derivatives prepared in aqueous media by triazine-activated amidation
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2007 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 8, no 7, p. 2190-2195Article in journal (Refereed) Published
Abstract [en]

A method is presented for the preparation of hyaluronic acid derivatives obtained through triazine-activated amidation. A number of amines were successfully reacted with hyaluronic acid carboxyl groups using 2-chloro-4,6-dimethoxy-1,3,5-triazine as an activating species in a mixture of water and acetonitrile under neutral conditions. By varying the amount of triazine reagent, it was possible to control the degree of modification. Depending on the amine chosen, degrees of modification ranging from 3 to 20% were obtained when using 0.5 equiv of the triazine to hyaluronic acid carboxyl groups. The possibility to perform the reaction in a mixture of water and acetonitrile facilitates the introduction of a wide range of both hydrophilic and hydrophobic amines. Triazine-activated amidation appears to be a highly versatile, controllable, and relatively mild technique for modification of hyaluronic acid, and we predict that it will be useful in the design of novel hyaluronic acid based biomaterials.

Keywords
Oside polymer, Experimental study, Mild operating conditions, Aqueous medium, Triazine derivatives, Activation, Primary amine, Amidation, Chemical modification, Preparation, Modified material, Hyaluronic acid
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-97729 (URN)10.1021/bm0701604 (DOI)000247820000022 ()17579475 (PubMedID)
Available from: 2008-11-14 Created: 2008-11-14 Last updated: 2017-12-14Bibliographically approved
Råsmark, P. J., Ekholm, T. & Elvingson, C. (2005). Computer simulations of polymer chain structure and dynamics on a hypersphere in four-space. Journal of Chemical Physics, 122(18), 184110
Open this publication in new window or tab >>Computer simulations of polymer chain structure and dynamics on a hypersphere in four-space
2005 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 18, p. 184110-Article in journal (Refereed) Published
Abstract [en]

There is a rapidly growing interest in performing computer simulations in a closed space, avoiding periodic boundary conditions. To extend the range of potential systems to include also macromolecules, we describe an algorithm for computer simulations of polymer chain molecules on S3, a hypersphere in four dimensions. In particular, we show how to generate initial conformations with a bond angle distribution given by the persistence length of the chain and how to calculate the bending forces for a molecule moving on S3. Furthermore, we discuss how to describe the shape of a macromolecule on S3, by deriving the radius of gyration tensor in this non-Euclidean space. The results from both Monte Carlo and Brownian dynamics simulations in the infinite dilution limit show that the results on S3 and in R3 coincide, both with respect to the size and shape as well as for the diffusion coefficient. All data on S3 can also be described by master curves by suitable scaling by the corresponding values in R3. We thus show how to extend the use of spherical boundary conditions, which are most effective for calculating electrostatic forces, to polymer chain molecules, making it possible to perform simulations on S3 also for polyelectrolyte systems.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-73804 (URN)10.1063/1.1896950 (DOI)15918697 (PubMedID)
Available from: 2007-01-16 Created: 2007-01-16 Last updated: 2017-12-14Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-5115-5481

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