Per Linse

Lund University, Lund, Skåne, Sweden

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Publications (167)377.68 Total impact

  • Erik Wernersson, Per Linse
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    ABSTRACT: We used isotension-ensemble Monte Carlo simulations to study the properties of brush layers of bottle-brush polymers under lateral compression. The polymers were represented by a freely jointed hard-bead model with one side chain grafted to each bead of the main chain, and we considered variations in side-chain length and bead size. Brush properties, including brush height and surface pressure, were analyzed in the context of a generalized box model. The surface pressure was found to have a steeper dependence on the grafting density than predicted by classical theories of polymer brushes. This discrepancy could be traced to the equation of state of the polymer fluid composing the brush, which was found to be more reminiscent of the concentrated regime than of the semidilute conditions normally expected in polymer brushes. The conformational properties of individual polymer molecules were found to be insensitive to lateral compression; in particular, the side-chain end-to-end distance remained essentially constant.
    Langmuir : the ACS journal of surfaces and colloids. 09/2014;
  • Daniel G Angelescu, Per Linse
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    ABSTRACT: Complexes formed by one charged and branched copolymer with an oppositely charged and linear polyion have been investigated by Monte Carlo simulations. A coarse-grained description has been used, in which the main chain of the branched polyion and the linear polyion possess the same absolute charge and charge density. The spatial extension and other structural properties, such as bond-angle orientational correlation function, asphericity, and scaling analysis of formed complexes, at varying branching density and side-chain length of the branched polyion, have been explored. In particular, the balance between cohesive Coulomb attraction and side-chain repulsions resulted in two main structures of a polyion complex. These structures are (i) a globular polyion core surrounded by side chains appearing at low branching density and (ii) an extended polyion core with side chains still being expelled at high branching density. The globule-to-extended transition occurred at a crossover branching density being practically independent of the side chain length.
    Soft Matter 07/2014; · 4.15 Impact Factor
  • Ran Zhang, per linse
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    ABSTRACT: On the basis of a T = 1 icosahedral capsid model, the capsomer-polyion co-assembly process has been investigated by molecular dynamics simulations using capsomers with different net charge and charge distribution as well as linear, branched, and hyper-branched polyions. The assembly process was characterized in terms of the time-dependent cluster size probabilities, averaged cluster size, encapsulation efficiency, and polyion extension. The kinetics of the capsid formation displayed a two-step process. The first one comprised adsorption of capsomers on the polyion, driven by their electrostatic attraction, whereas the second one involved a relocation and/or reorientation of adsorbed capsomers, which rate is reduced upon increasing electrostatic interaction. We found that increased polyion branching facilitated a more rapid encapsulation process towards a higher yield. Moreover, the hyper-branched polyions were entirely encapsulated at all polyion-capsid charge ratios considered.
    The Journal of Chemical Physics 06/2014; · 3.12 Impact Factor
  • Per Linse, Leo Lue
    The Journal of Chemical Physics. 01/2014; 140(4):-.
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    Daniel G. Angelescu, Per Linse
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    ABSTRACT: Multigraft polymers comprise a subclass of branched polymers where more than one side chain is attached to each node (branching point) of the main chain. We have investigated structural properties of single multigraft polymers under good solvent conditions by Monte Carlo simulations, employing a flexible bead–spring model. Beside the grafting density, denoting the linear density of grafted side chains, we have introduced the concept of branching density, denoting the linear density of nodes. At high branching density, both the branching density and the branching multiplicity controlled the structure of the side chains, whereas at lower branching density only the branching multiplicity influenced the side-chain structure. The spatial extension of the main chain and side chains as a function of side-chain length and grafting density was analyzed using scaling formalism. The dependence of the main-chain extension on side-chain length, branching density, and branching multiplicity could be collapsed on a universal curve upon relevant rescaling. Multigraft polymers with equal number of side-chain beads but unequal numbers and lengths of side chains displayed unconventional bending properties. Few and long side chains gave rise to a still relative low locally stiffness but considerable long-range rigidity, whereas more numerous and shorter side chains lead to a higher local stiffness but to a smaller long-range rigidity.
    12/2013; 47(1).
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    ABSTRACT: The role of the genome in the assembly of icosahedral viral capsids has been investigated by molecular dynamics simulation of a coarse-grained model, in which the capsomers carry explicit charges and the polynucleic acid is represented by a bead-spring chain. The co-assembly process was contrasted with the self-assembly of uncharged capsomers. In the co-assembly, the capsomers first associated to the polyion and then rearrange into a capsid, whereas the self-assembly proceeded through a spontaneous nucleation and growth of partial capsids. The polyion backbone stiffness was found to have a significant effect on the co-assembly process; polyions of intermediate flexibility gave the fastest and most faithful assembly process. Addition of a small amount of monovalent salt also improved both speed and fidelity of the co-assembly process.
    RSC Advances 10/2013; 2013(2):25258. · 3.71 Impact Factor
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  • Erik Wernersson, Per Linse
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    ABSTRACT: We investigate structural and thermodynamic properties of surface-grafted layers of model "bottle-brush" polymers by Monte Carlo simulation. The polymers consist of a longer main chain densely grafted with shorter side chains, of which the latter have some degree of affinity to the surface. Our focus is on the effect of the side-chain surface affinity on the brush properties, which we study in terms of compression isotherms spanning a broad range of grafting densities. For low grafting densities, side-chain adsorption causes the polymers to spread on the surface. As the grafting density is increased, the layer goes through a "pancake-to-brush" transition to form a brush with the main chains aligned perpendicular to the surface. We find that side-chain adsorption is decisive for the structure of dilute layers and in the transition region but has little influence on the properties of dense brushes. The close relation between compression and adsorption isotherms is discussed, and the implications of side-chain adsorption for the ability of the polymer to form a dense brush are investigated. This analysis suggests that side-chain surface affinity alone will not give rise to "brush of bottle-brushes" layers by adsorption of polymers from solution, in agreement with recent experimental results.
    Langmuir 08/2013; · 4.38 Impact Factor
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    Ran Zhang, Per Linse
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    ABSTRACT: Kinetical and structural aspects of the capsomer-polyion co-assembly into icosahedral viruses have been simulated by molecular dynamics using a coarse-grained model comprising cationic capsomers and short anionic polyions. Conditions were found at which the presence of polyions of a minimum length was necessary for capsomer formation. The largest yield of correctly formed capsids was obtained at which the driving force for capsid formation was relatively weak. Relatively stronger driving forces, i.e., stronger capsomer-capsomer short-range attraction and∕or stronger electrostatic interaction, lead to larger fraction of kinetically trapped structures and aberrant capsids. The intermediate formation was investigated and different evolving scenarios were found by just varying the polyion length.
    The Journal of Chemical Physics 04/2013; 138(15):154901. · 3.12 Impact Factor
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    ABSTRACT: A series of cationic diblock copolymers, poly(N-isopropylacrylamide)(48)-block-poly((3-acrylamidopropyl)trimethylammonium chloride)(X), abbreviated as PNIPAAM(48)-b-PAMPTMA(+)(X) (X = 0, 6, 10, 14, and 20), has been synthesized, and their adsorption onto silicon oxynitride from aqueous solution has been investigated using dual polarization interferometry. The polymer adsorption was modeled by using a lattice mean-field theory, and a satisfactory consistency between theory and experiments was found in terms of surface excess and layer thickness. Both theory and experiments show that the adsorption is limited by steric repulsion for X < X(max) and by electrostatic interactions for X > X(max). Modeling demonstrates that significant surface charge regulation occurs due to adsorption. Both the nonionic and cationic block exhibit nonelectrostatic affinity to silicon oxynitride and thus contribute to the driving force for adsorption, and modeling is used for clarifying how changes in the nonelectrostatic affinity affects the surface excess. The segments of the nonionic and cationic blocks seem less segregated when both have a nonelectrostatic affinity for the surface compared to the case where the segments had no surface affinity. Adsorption kinetics was investigated experimentally. Two kinetic regimes were observed: the adsorption rate is initially controlled by the mass transfer rate to the surface and at higher coverage is limited by the attachment rate.
    Langmuir 08/2012; 28(39):14028-38. · 4.38 Impact Factor
  • Per Linse
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    ABSTRACT: Adsorption of uncharged homopolymers in good and theta solvents onto planar surfaces at various chain flexibility and polymer–surface attraction strengths was investigated by using a coarse-grained bead–spring polymer model and simulation techniques. Equilibrium properties of the interfacial systems were obtained from Monte Carlo simulations by monitoring the bead and polymer density profiles, the number of adsorbed beads and polymers, the components of the radius of gyration perpendicular and parallel to the surface as well as tail, loop, and train characteristics. The adsorption process starting with a polymer-free zone adjacent to the surface was examined by Brownian dynamic simulations. At equilibrium, the adsorbed amount increased upon increasing chain stiffness and in poorer solvent conditions, and the structural characteristics depended also on the chain stiffness and solvent condition. The initial adsorption was diffusion controlled, but soon it became governed by the probability of a polymer to be captured by the surface attraction. Flexible polymers became flattened after attaching, but their final relaxation mechanism involved an increase in perpendicular extension. There were fewer adsorbed beads and longer tails, which was driven by the surface pressure originating from the surrounding adsorbed polymers. This structural rearrangement became more prominent in poorer solvent conditions. Finally, the integration time, which denotes the adsorption time for adsorbed polymers to become fully integrated into the adsorbed layer, and the residence times of integrated polymers were analyzed. In particular, the latter became longer with increasing chain stiffness and shorter in poorer solvent conditions.
    Soft Matter 04/2012; 8(19):5140-5150. · 4.15 Impact Factor
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    ABSTRACT: The structure of charge-stabilized colloidal dispersions has been studied through a one-component model using a Yukawa potential with density-dependent parameters examined with integral equation theory and Monte Carlo simulations. Partial thermodynamic consistency was guaranteed by considering the osmotic pressure of the dispersion from the approximate mean-field renormalized jellium and Poisson-Boltzmann cell models. The colloidal structures could be accurately described by the Ornstein-Zernike equation with the Rogers-Young closure by using the osmotic pressure from the renormalized jellium model. Although we explicitly show that the correct effective pair-potential obtained from the inverse Monte Carlo method deviates from the Yukawa shape, the osmotic pressure constraint allows us to have a good description of the colloidal structure without losing information on the system thermodynamics. Our findings are corroborated by primitive model simulations of salt-free colloidal dispersions.
    Journal of Physics Condensed Matter 02/2012; 24(6):065102. · 2.22 Impact Factor
  • Per Linse, Håkan Wennerström
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    ABSTRACT: A model for the adsorption of colloidal particles on a planar surface is analyzed by using a thermodynamic chemical equilibrium model and Monte Carlo simulations. Central to this investigation are that (i) particles and surface are considered to be of the same material and (ii) the particle–surface and particle–particle interactions are related using the Derjaguin approximation using a surface–surface square-well potential as a basis. Thereby, all interactions within the system are characterized by the same parameters, and hence the difference between particle adsorption on the surface and particle aggregation in bulk is solely due to geometrical effects. Equilibrium constants for the different binary associations are calculated from the interaction potentials enabling a direct comparison between predictions based on a chemical equilibrium model and on computer simulations with no adjustable parameters. As the interaction gradually is made more attractive for a given particle concentration, we find the following sequence of events: (A) a weak particle adsorption onto the surface, (B) particle association on the surface forming a denser single adsorbed layer, (C) formation of a second adsorbed layer on the surface, (D) multiple adsorbed layers on the surface, and (E) bulk phase separation. There is a semi-quantitative agreement between the predictions of the equilibrium model and the results of the simulations. The equilibrium model calculations facilitate a conceptual understanding of the competition between association on a surface and in bulk. Our study is relevant both for understanding processes where colloidal particle adsorption is used to modify surface properties and also for the understanding of heterogeneous versus homogeneous nucleation.
    Soft Matter 02/2012; 8(8):2486-2493. · 4.15 Impact Factor
  • Leo Lue, Per Linse
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    ABSTRACT: Aqueous solutions of charged spherical macroions with variable dielectric permittivity and their associated counterions are examined within the cell model using a field theory and Monte Carlo simulations. The field theory is based on separation of fields into short- and long-wavelength terms, which are subjected to different statistical-mechanical treatments. The simulations were performed by using a new, accurate, and fast algorithm for numerical evaluation of the electrostatic polarization interaction. The field theory provides counterion distributions outside a macroion in good agreement with the simulation results over the full range from weak to strong electrostatic coupling. A low-dielectric macroion leads to a displacement of the counterions away from the macroion.
    The Journal of Chemical Physics 12/2011; 135(22):224508. · 3.12 Impact Factor
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    ABSTRACT: A heuristic model based on dielectric continuum theory for the long-range solvation free energy of a dipolar system possessing periodic boundary conditions (PBCs) is presented. The predictions of the model are compared to simulation results for Stockmayer fluids simulated using three different cell geometries. The boundary effects induced by the PBCs are shown to lead to anisotropies in the apparent dielectric constant and the long-range solvation free energy of as much as 50%. However, the sum of all of the anisotropic energy contributions yields a value that is very close to the isotropic one derived from dielectric continuum theory, leading to a total system energy close to the dielectric value. It is finally shown that the leading-order contribution to the energetic and structural anisotropy is significantly smaller in the noncubic simulation cell geometries compared to when using a cubic simulation cell.
    Journal of Chemical Theory and Computation 12/2011; 7(12):4165-4174. · 5.39 Impact Factor
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    ABSTRACT: Structural properties and the topology of polyelectrolyte complexes (PECs) formed in solution have been investigated under different conditions by Monte Carlo simulations using a coarse-grained model. The extension of individual polyions has been characterized by their radius of gyration, whereas the composition of the complexes has been investigated by their net charge and their internal topological structure by a novel analysis describing how the shorter polycations link to monomers of the longer polyanion. Conditions have been found at which the polyanion and a given number of polycations form distinguishable complexes differing in (i) the polyanion conformation and (ii) the fraction of polycations being in extended and collapsed states. Thus, at equilibrium, these PECs display a stepwise variation of the degree of intrachain disproportionation within the polyanion (also referred to as intrachain segregation), concomitant with the interchain disproportionation of the polycations, which is in agreement with previous theoretical predictions. The coexistence of the different polyelectrolyte complex structures appears, generally, at mixing ratios close to but different from charge equivalence and, as a consequence, broad polyelectrolyte size distributions are commonly obtained.
    Journal of Computational Chemistry 09/2011; 32(12):2697-707. · 3.84 Impact Factor
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    ABSTRACT: A new two-state polymer folding model is proposed, in which the folding of a stiff helical polymer is enabled by allowing for short sequences of coils connecting shorter and separated helices. The folding is driven by short-range attraction energy among stacked helices and is opposed by the free-energy cost of forming coils from helical monomers. Principal outcomes of the model are equilibrium distribution of the number of helices and their length in helical polymers. The proposed model is applied to α-helical polyalanine. The distribution of the number of α-helices as a function of number of alanine residues is fitted to the corresponding result from molecular dynamics simulation employing an all-atom potential model with very good agreement. The influence and significance of the fitting parameters and possible use of the two-state folding model are discussed.
    The Journal of Physical Chemistry B 08/2011; 115(39):11448-54. · 3.61 Impact Factor
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    ABSTRACT: The adsorption of and conformation adopted by a branched-linear polymer conjugate to the hydrophilic silica-aqueous solution interface have been studied by in situ null ellipsometry and Monte Carlo simulations. The conjugate is a highly branched polyethyleneimine structure with ethyleneoxide chains grafted to its primary and secondary amino groups. In situ null ellipsometry demonstrated that the polymer conjugate adsorbs to the silica surface from water and aqueous solution of 1 mM asymmetric divalent salt (calcium and magnesium chloride to emulate hard water) over a large pH range. The adsorbed amount is hardly affected by pH and large charge reversal on the negatively charged silica surface occurred at pH = 4.0, due to the adsorption of the cationic polyelectrolyte. The Monte Carlo simulations using an appropriate coarse-grained model of the polymer in solution predicted a core-shell structure with no sharp boundary between the ethyleneimine and ethyleneoxide moieties. The structure at the interface is similar to that in solution when the polymer degree of protonation is low or moderate while at high degree of protonation the strong electrostatic attraction between the ethyleneimine core and oppositely charged silica surface distorts the ethyleneoxide shell so that an "anemone"-like configuration is adopted. The adsorption of alkyl benzene sulfonic acid (LAS) to a preadsorbed polymer layer was also investigated by null ellipsometry. The adsorption data brought additional support for the existence of a strong polymer adsorption and showed the presence of a binding which was further enhanced by the decreased solvency of the surfactant in the salt solution and confirmed the surface charge reversal by the polymer adsorption at pH = 4.0.
    Langmuir 08/2011; 27(16):9961-71. · 4.38 Impact Factor
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    ABSTRACT: A review of the literature on the calculation of electrostatic potentials, fields, and field gradients in systems consisting of charges and dipoles using the Ewald summation technique is presented. Discrepancies between the previous formulas are highlighted, and an error in the derivation of the reciprocal contributions to the electrostatic field and field gradient is corrected. The new formulas for the field and field gradient are shown to exhibit a termwise identity with the ones for the electrostatic energy.
    The Journal of Chemical Physics 06/2011; 134(22):224104. · 3.12 Impact Factor
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    ABSTRACT: Delayed asymmetric Coulomb fission in size-selected molecular dication clusters has been recorded for the first time. Observations on (NH(3))(n)(2+) clusters show that fragmentation accompanied by charge separation can occur on a microsecond time scale, exhibits considerable asymmetry, and involves a kinetic energy release of ∼0.9 eV. The fission process has been modeled by representing the fragments as charged dielectric spheres and the calculated maximum in the electrostatic interaction energy between the fragments gives a good account of the measured kinetic energy release. A simple kinetic model shows that instrumental factors may contribute to the observation of asymmetric fragmentation.
    The Journal of Chemical Physics 01/2011; 134(3):031103. · 3.12 Impact Factor

Publication Stats

2k Citations
377.68 Total Impact Points

Institutions

  • 1990–2014
    • Lund University
      • Department of Physical Chemistry
      Lund, Skåne, Sweden
  • 2012
    • Universidad de Guanajuato
      • División de Ciencias e Ingenierías
      Guanajuato, Guanajuato, Mexico
    • KTH Royal Institute of Technology
      • Department of Chemistry
      Stockholm, Stockholm, Sweden
  • 2011
    • University of North Carolina at Chapel Hill
      • Department of Chemistry
      Chapel Hill, NC, United States
    • University of Nottingham
      • School of Chemistry
      Nottingham, ENG, United Kingdom
    • University of Strathclyde
      • Department of Chemical and Process Engineering
      Glasgow, SCT, United Kingdom
  • 2008
    • University of Ljubljana
      • Faculty of Chemistry and Chemical Technology
      Ljubljana, Ljubljana, Slovenia
  • 2002–2008
    • University of Coimbra
      • • Departamento de Química
      • • Departamento de Engenharia Química
      Coimbra, Distrito de Coimbra, Portugal
  • 2007
    • University of Leipzig
      • Institut für Experimentelle Physik
      Leipzig, Saxony, Germany
  • 2006
    • Институт молекулярной биологии им. В.А. Энгельгардта Российской академии наук
      Moskva, Moscow, Russia
  • 2005
    • Al-Quds University
      • Department of Physics
      Abū Dīs, WE, Palestinian Territory
  • 2001
    • Université de Fribourg
      • Institut de Physique Théorique
      Fribourg, FR, Switzerland