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K Binder - One of the best experts on this subject based on the ideXlab platform.
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semiflexible polymers under Good Solvent conditions interacting with repulsive walls
arXiv: Soft Condensed Matter, 2016Co-Authors: Andrey Milchev, Sergei A Egorov, Peter Virnau, K BinderAbstract:Solutions of semiflexible polymers confined by repulsive planar walls are studied by density functional theory and Molecular Dynamics simulations, to clarify the competition between the chain alignment favored by the wall and the depletion caused by the monomer-wall repulsion. A coarse-grained bead-spring model with bond bending potential is studied, varying both the contour length and the persistence length of the polymers, as well as the monomer concentration in the solution (Good Solvent conditions are assumed throughout, and Solvent molecules are not included explicitly). The profiles of monomer density and pressure tensor components near the wall are studied, and the surface tension of the solution is obtained. While the surface tension slightly decreases with chain length for flexible polymers, it clearly increases with chain length for stiff polymers. Thus, at fixed density and fixed chain length the surface tension also increases with increasing persistence length. Chain ends always are enriched near the wall, but this effect is much larger for stiff polymers than for flexible ones. Also the profiles of the mean square gyration radius components near the wall and the nematic order parameter are studied to clarify the conditions where wall-induced nematic order occurs.
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scattering function of semiflexible polymer chains under Good Solvent conditions
Journal of Chemical Physics, 2012Co-Authors: Hsiaoping Hsu, Wolfgang Paul, K BinderAbstract:Using the pruned-enriched Rosenbluth Monte Carlo algorithm, the scattering functions of semiflexible macromolecules in dilute solution under Good Solvent conditions are estimated both in d = 2 and d = 3 dimensions, considering also the effect of stretching forces. Using self-avoiding walks of up to N = 25 600 steps on the square and simple cubic lattices, variable chain stiffness is modeled by introducing an energy penalty eb for chain bending; varying qb = exp (−eb/kBT) from qb = 1 (completely flexible chains) to qb = 0.005, the persistence length can be varied over two orders of magnitude. For unstretched semiflexible chains, we test the applicability of the Kratky-Porod worm-like chain model to describe the scattering function and discuss methods for extracting persistence length estimates from scattering. While in d = 2 the direct crossover from rod-like chains to self-avoiding walks invalidates the Kratky-Porod description, it holds in d = 3 for stiff chains if the number of Kuhn segments nK does not...
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scattering function of semiflexible polymer chains under Good Solvent conditions
arXiv: Soft Condensed Matter, 2012Co-Authors: Hsiaoping Hsu, Wolfgang Paul, K BinderAbstract:Using the pruned-enriched Rosenbluth Monte Carlo algorithm, the scattering functions of semiflexible macromolecules in dilute solution under Good Solvent conditions are estimated both in $d=2$ and $d=3$ dimensions, considering also the effect of stretching forces. Using self-avoiding walks of up to $N = 25600$ steps on the square and simple cubic lattices, variable chain stiffness is modeled by introducing an energy penalty $\epsilon_b$ for chain bending; varying $q_b=\exp (- \epsilon_b/k_BT)$ from $q_b=1$ (completely flexible chains) to $q_b = 0.005$, the persistence length can be varied over two orders of magnitude. For unstretched semiflexible chains we test the applicability of the Kratky-Porod worm-like chain model to describe the scattering function, and discuss methods for extracting persistence length estimates from scattering. While in $d=2$ the direct crossover from rod-like chains to self-avoiding walks invalidates the Kratky-Porod description, it holds in $d=3$ for stiff chains if the number of Kuhn segments $n_K$ does not exceed a limiting value $n^*_K$ (which depends on the persistence length). For stretched chains, the Pincus blob size enters as a further characteristic length scale. The anisotropy of the scattering is well described by the modified Debye function, if the actual observed chain extension $ $ (end-to-end distance in the direction of the force) as well as the corresponding longitudinal and transverse linear dimensions $ - ^2$, $ $ are used.
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interactions between polymer brush coated spherical nanoparticles the Good Solvent case
Journal of Chemical Physics, 2011Co-Authors: Federica Lo Verso, Leonid Yelash, S A Egorov, K BinderAbstract:The interaction between two spherical polymer brushes is studied by molecular dynamics simulation varying both the radius of the spherical particles and their distance, as well as the grafting density and the chain length of the end-grafted flexible polymer chains. A coarse-grained bead-spring model is used to describe the macromolecules, and purely repulsive monomer-monomer interactions are taken throughout, restricting the study to the Good Solvent limit. Both the potential of mean force between the particles as a function of their distance is computed, for various choices of the parameters mentioned above, and the structural characteristics are discussed (density profiles, average end-to-end distance of the grafted chains, etc.). When the nanoparticles approach very closely, some chains need to be squeezed out into the tangent plane in between the particles, causing a very steep rise of the repulsive interaction energy between the particles. We consider as a complementary method the density functional theory approach. We find that the quantitative accuracy of the density functional theory is limited to large nanoparticle separation and short chain length. A brief comparison to Flory theory and related work on other models also is presented.
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computer simulation of bottle brush polymers with flexible backbone Good Solvent versus theta Solvent conditions
arXiv: Soft Condensed Matter, 2011Co-Authors: Panagiotis E. Theodorakis, Hsiaoping Hsu, Wolfgang Paul, K BinderAbstract:By Molecular Dynamics simulation of a coarse-grained bead-spring type model for a cylindrical molecular brush with a backbone chain of $N_b$ effective monomers to which with grafting density $\sigma$ side chains with $N$ effective monomers are tethered, several characteristic length scales are studied for variable Solvent quality. Side chain lengths are in the range $5 \le N \le 40$, backbone chain lengths are in the range $50 \le N_b \le 200$, and we perform a comparison to results for the bond fluctuation model on the simple cubic lattice (for which much longer chains are accessible, $N_b \le 1027$, and which corresponds to an athermal, very Good, Solvent). We obtain linear dimensions of side chains and the backbone chain and discuss their $N$-dependence in terms of power laws and the associated effective exponents. We show that even at the Theta point the side chains are considerably stretched, their linear dimension depending on the Solvent quality only weakly. Effective persistence lengths are extracted both from the orientational correlations and from the backbone end-to-end distance; it is shown that different measures of the persistence length (which would all agree for Gaussian chains) are not mutually consistent with each other, and depend distinctly both on $N_b$ and the Solvent quality. A brief discussion of pertinent experiments is given.
Andrea Pelissetto - One of the best experts on this subject based on the ideXlab platform.
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Polymer models with optimal Good-Solvent behavior.
Journal of physics. Condensed matter : an Institute of Physics journal, 2017Co-Authors: Giuseppe D'adamo, Andrea PelissettoAbstract:We consider three different continuum polymer models, which all depend on a tunable parameter r that determines the strength of the excluded-volume interactions. In the first model, chains are obtained by concatenating hard spherocylinders of height b and diameter rb (we call them thick self-avoiding chains). The other two models are generalizations of the tangent hard-sphere and of the Kremer-Grest models. We show that for a specific value [Formula: see text], all models show optimal behavior: asymptotic long-chain behavior is observed for relatively short chains. For [Formula: see text], instead, the behavior can be parametrized by using the two-parameter model, which also describes the thermal crossover close to the θ point. The bonds of the thick self-avoiding chains cannot cross each other, and therefore the model is suited for the investigation of topological properties and for dynamical studies. Such a model also provides a coarse-grained description of double-stranded DNA, so that we can use our results to discuss under which conditions DNA can be considered as a model Good-Solvent polymer.
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polymer models with optimal Good Solvent behavior
arXiv: Soft Condensed Matter, 2017Co-Authors: Giuseppe Dadamo, Andrea PelissettoAbstract:We consider three different continuum polymer models, that all depend on a tunable parameter r that determines the strength of the excluded-volume interactions. In the first model chains are obtained by concatenating hard spherocylinders of height b and diameter rb (we call them thick self- avoiding chains). The other two models are generalizations of the tangent hard-sphere and of the Kremer-Grest models. We show that, for a specific value r*, all models show an optimal behavior: asymptotic long-chain behavior is observed for relatively short chains. For r < r*, instead, the behavior can be parametrized by using the two-parameter model that also describes the thermal crossover close to the {\theta} point. The bonds of thick self-avoiding chains cannot cross each other and, therefore, the model is suited for the investigation of topological properties and for dynamical studies. Such a model also provides a coarse-grained description of double-stranded DNA, so that we can use our results to discuss under which conditions DNA can be considered as a model Good-Solvent polymer.
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phase diagram and structure of mixtures of large colloids and linear polymers under Good Solvent conditions
Macromolecules, 2016Co-Authors: Giuseppe Dadamo, Andrea Pelissetto, Carlo PierleoniAbstract:Efficient Monte Carlo simulations are used to determine the liquid–liquid binodal line of mixtures of hard-sphere colloids and neutral polymers under Good-Solvent conditions for two values of the polymer-to-colloid size ratio q, q = 0.5 and 1. We use a multiblob coarse-graining approach, in which groups of monomers are mapped onto a single pseudoatom (a blob) and blob–blob interactions are obtained by requiring the model to reproduce some large-scale properties of the polymer solution in the dilute limit. We also compute several experimentally relevant quantities at a few selected points along the binodal: thermodynamic properties (pressure, isothermal compressibility, chemical potentials), partial structure factors, and polymer form factor. Finally, we discuss how the polymers become more compact with increasing colloidal crowding.
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Consistent and transferable coarse-grained model for semidilute polymer solutions in Good Solvent.
The Journal of chemical physics, 2012Co-Authors: Giuseppe D'adamo, Andrea Pelissetto, Carlo PierleoniAbstract:We present a coarse-grained model for linear polymers with a tunable number of effective atoms (blobs) per chain interacting by intra- and intermolecular potentials obtained at zero density. We show how this model is able to accurately reproduce the universal properties of the underlying solution of athermal linear chains at various levels of coarse-graining and in a range of chain densities which can be widened by increasing the spatial resolution of the multiblob representation, i.e., the number of blobs per chain. The present model is unique in its ability to quantitatively predict thermodynamic and large scale structural properties of polymer solutions deep in the semidilute regime with a very limited computational effort, overcoming most of the problems related to the simulations of semidilute polymer solutions in Good Solvent conditions.
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Coarse-grained models for semi-dilute polymer solutions under Good-Solvent conditions
Journal of physics. Condensed matter : an Institute of Physics journal, 2009Co-Authors: Andrea PelissettoAbstract:We determine coarse-grained models with a relatively small number of units which reproduce the universal behavior of polymer solutions in the semi-dilute regime under Good-Solvent conditions. We check both the thermodynamical behavior (osmotic pressure and chemical potential) and structural properties (polymer size).
Jimmy W Mays - One of the best experts on this subject based on the ideXlab platform.
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forces of interaction between surfaces bearing looped polymer brushes in Good Solvent
Soft Matter, 2009Co-Authors: Jose Alonzo, Jimmy W Mays, Michael S KilbeyAbstract:In a previous publication we suggested [Huang et al., Macromolecules, 2008, 41, 1745–1752] that looped polymer brushes formed by tethering chains by both ends to a surface may exhibit a polydispersity-like effect due to a distribution of distances between tethering points, leading to segment density profiles dominated by a long and diffuse exponentially-decaying tail. To study this issue in more detail, the force profiles (forces of interaction as a function of separation distance) of a series of looped polymer brushes made by preferential adsorption of poly(2-vinylpyridine)–polystyrene–poly(2-vinylpyridine) (PVP-b-PS-b-PVP) triblock copolymers of varying molecular weight and asymmetry ratio are measured using the surface forces apparatus. The force profiles are analyzed using an equivalent diblock model, which considers the triblock copolymer brushes as being comprised of two diblock copolymers of half the PS molecular weight. While scaling the dependencies of the interaction energy and distance on molecular weight, the tethering density and segment size coalesce the measured force profiles to the “universal profile”, it is necessary to include polydispersity in the description of the equilibrium structure. This is done using the self-consistent field model of Milner et al. [Macromolecules, 1988, 21, 2610–2619]. For looped brushes formed from the symmetric and moderately symmetric triblock copolymers we find that the polydispersity due to molecular weight distribution effectively accounts for the observed force profiles. On the other hand, agreement between the measured and predicted force profiles of looped brushes formed from highly asymmetric copolymers at low degrees-of-compression is achieved only if a much smaller value of the polydispersity index is used in the fitting. The implication of these results is that the shape of the segment density profiles is not due to the previously proposed anchor-induced polydispersity arising due to loop formation; however in the case of highly asymmetric copolymers, loop formation may constrain the stretching of the chains relative to what is expected for brushes formed from the equivalent diblock copolymer.
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on line measurement of molecular weight and radius of gyration of polystyrene in a Good Solvent and in a theta Solvent measured with a two angle light scattering detector
European Polymer Journal, 2004Co-Authors: Ken Terao, Jimmy W MaysAbstract:Abstract On-line two-angle (15° and 90°) light scattering measurements with a gel permeation chromatography for linear and branched polystyrene in tetrahydrofuran (a Good Solvent) and in trans -decalin (a theta Solvent) were made and compared with data from a multi-angle light scattering detector and literature values. Theoretically, weight-average molecular weight and the radius of gyration R g can be determined accurately in the range where R g 2 k 2 is less than 1.2 (rod)∼1.7 (random coil); here, k is the absolute value of the scattering vector for a right angle detector with the Berry square root method. Molecular weight dependence of the radius of gyration obtained from the two-angle light scattering detector for linear and branched polystyrenes under different thermodynamic conditions were measured and found to be almost the same as values measured with a multi-angle light scattering detector and literature values in the appropriate range of molecular weight.
Masahiro Kitabata - One of the best experts on this subject based on the ideXlab platform.
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wettability of a poly vinylidene fluoride surface by a pure Good Solvent and a Good Solvent nonSolvent mixture all atom molecular dynamics study
Langmuir, 2020Co-Authors: Masahiro Kitabata, Tseden Taddese, Susumu OkazakiAbstract:This study investigated the wettability of poly(vinylidene fluoride) (PVDF) surfaces by a Good pure Solvent and a Good Solvent/nonSolvent mixture based on all-atom molecular dynamics (MD) simulatio...
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Wettability of a Poly(vinylidene fluoride) Surface by a Pure Good Solvent and a Good Solvent/NonSolvent Mixture: All-Atom Molecular Dynamics Study
Langmuir : the ACS journal of surfaces and colloids, 2020Co-Authors: Masahiro Kitabata, Tseden Taddese, Susumu OkazakiAbstract:This study investigated the wettability of poly(vinylidene fluoride) (PVDF) surfaces by a Good pure Solvent and a Good Solvent/nonSolvent mixture based on all-atom molecular dynamics (MD) simulatio...
Michael S Kilbey - One of the best experts on this subject based on the ideXlab platform.
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forces of interaction between surfaces bearing looped polymer brushes in Good Solvent
Soft Matter, 2009Co-Authors: Jose Alonzo, Jimmy W Mays, Michael S KilbeyAbstract:In a previous publication we suggested [Huang et al., Macromolecules, 2008, 41, 1745–1752] that looped polymer brushes formed by tethering chains by both ends to a surface may exhibit a polydispersity-like effect due to a distribution of distances between tethering points, leading to segment density profiles dominated by a long and diffuse exponentially-decaying tail. To study this issue in more detail, the force profiles (forces of interaction as a function of separation distance) of a series of looped polymer brushes made by preferential adsorption of poly(2-vinylpyridine)–polystyrene–poly(2-vinylpyridine) (PVP-b-PS-b-PVP) triblock copolymers of varying molecular weight and asymmetry ratio are measured using the surface forces apparatus. The force profiles are analyzed using an equivalent diblock model, which considers the triblock copolymer brushes as being comprised of two diblock copolymers of half the PS molecular weight. While scaling the dependencies of the interaction energy and distance on molecular weight, the tethering density and segment size coalesce the measured force profiles to the “universal profile”, it is necessary to include polydispersity in the description of the equilibrium structure. This is done using the self-consistent field model of Milner et al. [Macromolecules, 1988, 21, 2610–2619]. For looped brushes formed from the symmetric and moderately symmetric triblock copolymers we find that the polydispersity due to molecular weight distribution effectively accounts for the observed force profiles. On the other hand, agreement between the measured and predicted force profiles of looped brushes formed from highly asymmetric copolymers at low degrees-of-compression is achieved only if a much smaller value of the polydispersity index is used in the fitting. The implication of these results is that the shape of the segment density profiles is not due to the previously proposed anchor-induced polydispersity arising due to loop formation; however in the case of highly asymmetric copolymers, loop formation may constrain the stretching of the chains relative to what is expected for brushes formed from the equivalent diblock copolymer.
