| 1. |
- Bergenudd, Helena, et al.
(författare)
-
Predicting the Limit of Control in the ATRP Process : Results from Kinetic Simulations
- 2011
-
Ingår i: Macromolecular Theory and Simulations. - : Wiley. - 1022-1344 .- 1521-3919. ; 20:9, s. 814-825
-
Tidskriftsartikel (refereegranskat)abstract
- Kinetic simulations are reported, where the ATRP equilibrium constant K(ATRP) is varied and the rates and degree of control in different ATRP systems are evaluated. The apparent rate constant k(app) increases with increasing K(ATRP), but a maximum is reached. The limit of control is passed before the maximum, i.e. when K(ATRP) is increased further, apparent first-order kinetics and well-controlled molecular weights will no longer be obtained. The equilibrium constant at which the limit of control is reached varies linearly with the propagation rate constant. This enables the design of well controlled ATRP systems. The influence of the conversion and chain length dependence of the termination rate constant on the simulation results is discussed.
|
|
| 2. |
- Dahlgren, Björn, et al.
(författare)
-
Numerical Simulations of Nanogel Synthesis Using Pulsed Electron Beam
- 2020
-
Ingår i: Macromolecular Theory and Simulations. - : Wiley. - 1022-1344 .- 1521-3919. ; 29:1, s. 1900046-
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, a new method for numerical simulation of the radiation chemistry of aqueous polymer solutions exposed to a sequence of electron pulses is presented. The numerical simulations are based on a deterministic approach encompassing the conventional homogeneous radiation chemistry of water as well as the chemistry of polymer radicals. The multitude of possible reactions in the macromolecular system is handled by allowing for a large number of macromolecular species. The speciation of macromolecular species is done to account for variations in molecular weight, number of alkyl radicals per chain, number of peroxyl radicals per chain, number of oxyl radicals per chain, and number of internal loops. As benchmarking, previously published results from a series of experiments on pulsed irradiation of aqueous poly(N-vinylpyrrolidone) (PVP) solutions are used. The numerical simulations clearly show that the pulsed nature of the radiation must be accounted for. The simulations qualitatively reproduce the experimentally observed impact of initial gas saturation (air and N2O) and polymer concentration on the molecular chain length upon irradiation. The formation of double bonds as a function of dose as well as the impact of effective dose rate on the final chain length are also qualitatively reproduced in the simulations.
|
|
| 3. |
- Muntean, Stela Andrea, et al.
(författare)
-
Dynamics of water near oxidized polystyrene films
- 2012
-
Ingår i: Macromolecular Theory and Simulations. - : Wiley-Blackwell. - 1022-1344 .- 1521-3919. ; 21:8, s. 544-552
-
Tidskriftsartikel (refereegranskat)abstract
- Atomistic MD simulations of water in the vicinity of oxidized amorphous atactic polystyrene are presented. The changes in the orientational and translational dynamics of water near polymer surfaces with different hydrophilicity are studied. Two main orientational relaxation processes of water molecules are distinguished: a process on a fs timescale, associated with the ballistic motion of water molecules, and a process on a ps timescale, associated with the self-diffusion of water. The fast process is not affected by the presence of the polymeric surface. The second relaxation process differs at the interface from that in the bulk in that the dynamics of water molecules is more heterogeneous in the first. The effect of the representation of polystyrene films on the water dynamics is discussed. MD simulations for the dynamics of water near hydrophilic and hydrophobic polystyrene surfaces are presented. The quantities that characterize the dynamic behavior of water in the first layers near the interface are compared with those in bulk. The influence of the polystyrene model on the dynamic properties of water is studied. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
|
|
| 4. |
- Muntean, Stela Andrea, et al.
(författare)
-
Myoglobin interactions with polystyrene surfaces of different hydrophobicity
- 2014
-
Ingår i: Macromolecular Theory and Simulations. - : Wiley-Blackwell. - 1022-1344 .- 1521-3919. ; 23:2, s. 63-75
-
Tidskriftsartikel (refereegranskat)abstract
- The atomistic molecular-dynamics simulations of the initial stage of myoglobin adsorption on amorphous polystyrene surfaces with varying hydrophobicity are presented. The polystyrene surfaces as non-oxidized (hydrophobic) and oxidized (hydrophilic) films, both in united-atoms and dummy-hydrogen atoms representations are modeled. The protein is placed initially at different distances and orientations from the polymer. We monitor the interactions between the protein and the polystyrene surface for the same polystyrene surface in contact with the protein in different initial orientations and for one initial orientation of the protein in contact with different polystyrene surfaces. By comparing the stability and the number of myoglobin-polystyrene atomic contacts and the interaction energies, it is found that the initial contact of the protein with the hydrophobic polystyrene surfaces is stronger than with the hydrophilic ones. The orientations of the myoglobin in which the more rigid protein parts face the polymer exhibit stronger initial contact with the polymeric surface. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
|
|
| 5. |
- Muntean, Stela Andrea, et al.
(författare)
-
Representation of hydrogen atoms in molecular dynamics simulations : The influence on the computed properties of thin polystyrene films
- 2012
-
Ingår i: Macromolecular Theory and Simulations. - : Wiley-Blackwell. - 1022-1344 .- 1521-3919. ; 21:2, s. 90-97
-
Tidskriftsartikel (refereegranskat)abstract
- The united atoms (UA) and dummy hydrogen atom (DHA) approaches for molecular dynamics simulations of the interface between oxidized atactic polystyrene (aPS) thin films and water are compared. For both oxidized and non-oxidized aPS films the polymer density profile decays steepest when using the UA model. The surface roughness of the aPS film and the ordering of the phenyl rings near the surface decrease upon changing from vacuum to water for the UA, but not for the DHA model. This also supports the fact that the non-oxidized aPS films modeled in DHA representation become less hydrophobic. The water structure close to the interface also suggests that the aPS films modeled using UA are more hydrophobic compared to the aPS films modeled with DHA in the phenyl rings. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
|
|
| 6. |
- Volkov, Nikolai, et al.
(författare)
-
Two-Dimensional Wang–Landau Algorithm for Osmotic Pressure Calculations in a Polyelectrolyte–Membrane System
- 2011
-
Ingår i: Macromolecular Theory and Simulations. - : Wiley-VCH Verlagsgesellschaft. - 1022-1344 .- 1521-3919. ; 20:7, s. 496-509
-
Tidskriftsartikel (refereegranskat)abstract
- The Monte Carlo method based on two-dimensional entropic sampling within the Wang–Landau (WL) algorithm is applied to simulation of a continuous model of a polyelectrolyte between membrane surfaces. Membranes are presented by parallel plane surfaces holding either fixed or mobile dipoles (representing lipid headgroups). A strongly charged polyion accompanied by neutralizing counterions is placed between the membranes. Periodic boundary conditions are imposed along X- and Y-axes. The volume of the main cell is varied during the simulation by shifting one of the surfaces along Z-axis. Within two-dimensional WL sampling algorithm we obtain joint density of states as a function of energy and volume in a single run. In order to increase efficiency of our calculations we introduce a number of modifications to the original WL-approach. Various properties of the system over wide temperature and volume or pressure ranges, i.e., conformational energy, heat capacity, and free energy, are obtained from the two-dimensional density of states by simple integration. The osmotic pressure is calculated as a derivative of Helmholtz free energy. Alternatively, properties of the system, including average volume, can be obtained under condition of NPT ensemble. It is shown that the both approaches produce coinciding Posm(V) isotherms. In all considered cases we observe repulsive effective interaction between the membrane surfaces, and repulsion is stronger for the surfaces with fixed dipoles.
|
|
| 7. |
- Yang, G., et al.
(författare)
-
A Study of a Novel Synergy Definition for Ternary CB/CNT Composites Suggesting a Representative Model for CB and CNT
- 2020
-
Ingår i: Macromolecular Theory and Simulations. - : Wiley-VCH Verlag. - 1022-1344 .- 1521-3919. ; 29:5
-
Tidskriftsartikel (refereegranskat)abstract
- For polymer composites containing two types of conductive fillers, the electrical conductivity can be predicted with a ternary mixing equation. However, a slight deviation from the foreseen trend is recently observed for ternary polymethyl methacrylate (PMMA) nanocomposites containing carbon nanotubes (CNT) and carbon black (CB). In this study, the reason for the deviation is examined. Representative composite geometries are generated with Monte-Carlo technique and the composite conductivity is calculated with Finite Element Modeling (FEM) Traditional FEM strategies would give results resembling the ternary mixing equation, but when the CB particles are modeled as solid spheres whereas the CNT are modeled as solid cylinders surrounded by soft, conductive shells, the composite conductivity gained the same shape as observed experimentally. One possible interpretation is that a small geometrical rearrangement of the CNT fibers has a larger impact on the composite conductivity than a corresponding movement of the spherical CB particles. As a consequence, the CNT/CB/PMMA nanocomposite exhibits a special kind of synergy ("synergism"), caused by the grape-shaped morphology. These findings can be utilized in the future development and optimization of conductive polymer nanocomposites.
|
|
| 8. |
- Yang, Guanda, et al.
(författare)
-
A Study of Finite Size Effects and Periodic Boundary Conditions to Simulations of a Novel Theoretical Self-Consistent Mean-Field Approach
- 2019
-
Ingår i: Macromolecular Theory and Simulations. - : Wiley-VCH Verlagsgesellschaft. - 1022-1344 .- 1521-3919.
-
Tidskriftsartikel (refereegranskat)abstract
- In a previous work, a very promising mathematical model for predicting the electrical conductivity below the electrical percolation threshold, for both isotropic and anisotropic composites, was published by Schubert. In this work, periodic boundary condition of the simulation is utilized. The results are also compared to the previous work and other theoretical models. The truncated fibers due to finite size of the simulation volume are considered as two individual pieces so that the real aspect ratios will also be taken into consideration. A comparison is made between two groups, in which the length and the radius of the carbon fibers are changed, respectively, under certain aspect ratios. With three different sizes of the simulation volumes, the influence on the results due to the finite size effect is calculated.
|
|
| 9. |
- Yang, Guanda, et al.
(författare)
-
Novel Theoretical Self-Consistent Mean-Field Approach to Describe the Conductivity of Carbon Fiber-Filled Thermoplastics : PART II. Validation by Computer Simulation
- 2018
-
Ingår i: Macromolecular Theory and Simulations. - : Wiley-VCH Verlagsgesellschaft. - 1022-1344 .- 1521-3919. ; 27:4
-
Tidskriftsartikel (refereegranskat)abstract
- The electrical conductivity of polymeric fiber composites is generally strongly dependent on the constituent conductivities, the fiber filler fraction, the fiber aspect ratio, and on the orientation of the fibers. Even though electrically conductive polymer composites are emerging materials of high scientific and commercial interest, accurate mathematical models for describing such materials are rare. A very promising mathematical model for predicting the electrical conductivity below the electrical percolation threshold, for both isotropic and anisotropic composites, is however recently published by Schubert. The shortcomings of that study are that the model includes so far only one predicted parameter and that it is not sufficiently validated. In the current study, finite element modeling is used to successfully validate the model of Schubert for isotropic fiber composites and to accurately determine the predicted parameter. These theoretical predictions are finally compared with experimental conductivity data for isotropic carbon fiber/poly(methyl methacrylate) (PMMA) composites with fiber filler fractions in the range 0-12 vol% and fiber aspect ratios from 5 to 30. The model forecasts, without any adjustable parameters, are satisfactory close to the experimental data.
|
|
| 10. |
- Arteca, GA
(författare)
-
Shape transitions in confined polymer mushrooms with excluded-volume interaction
- 1999
-
Ingår i: MACROMOLECULAR THEORY AND SIMULATIONS. - : WILEY-V C H VERLAG GMBH. - 1022-1344. ; 8:2, s. 137-146
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- This work deals with some aspects of the molecular shape deformation of a single grafted poly mer (a "polymer mushroom") compressed by a repulsive wall. Compression not only changes the size of the polymer but also modifies its entanglements, i.e., how th
|
|
