Search results for "polymers"
showing 10 items of 3567 documents
Osmotic pressure, atomic pressure and the virial equation of state of polymer solutions: Monte Carlo simulations of a bead-spring model
1994
A recently introduced coarse-grained model of polymer chains is studied analyzing various contributions to the pressure as obtained from the virial theorem as a function of chain length N, temperature T and density ϕ. The off-lattice model of the polymer chains has anharmonic springs between the beads, but of finite extensibility, and the Morse-type interaction between beads is repulsive at very short distances and attractive at intermediate distances. Solvent molecules are not explicitly included. It is found that the covalent forces along the chain (modelled by the spring potentials) contribute a negative term to the pressure, irrespective of temperature, which vanishes linearly in ϕ as ϕ…
Recent Developments in Monte Carlo Simulations of Lattice Models for Polymer Systems
2008
A brief review is given of methodological advances made during the past decade with the Monte Carlo sampling of equilibrium properties of simple lattice models of polymer systems, and representative applications of these new algorithms are summarized. These algorithms include Wang−Landau (WL) sampling, the pruned-enriched Rosenbluth method (PERM), and topology violating dynamic Monte Carlo algorithms such as combinations of local moves, slithering snake moves, and “double bridging” moves for the bond fluctuation model. The applications mentioned concern phase-transition-like phenomena of single chains (collapse and crystallization in bad solvents; interplay of collapse and adsorption; escap…
Stimuli-responsive brushes with active minority components: Monte Carlo study and analytical theory
2015
Using a combination of analytical theory, Monte Carlo simulations, and three dimensional self-consistent field calculations, we study the equilibrium properties and the switching behavior of adsorption-active polymer chains included in a homopolymer brush. The switching transition is driven by a conformational change of a small fraction of minority chains, which are attracted by the substrate. Depending on the strength of the attractive interaction, the minority chains assume one of two states: An exposed state characterized by a stem-crown-like conformation, and an adsorbed state characterized by a flat two-dimensional structure. Comparing the Monte Carlo simulations, which use an Edwards-…
Glass transition of polymer melts: Test of theoretical concepts by computer simulation.
2003
Abstract Polymers are good glass formers and allow for the study of melts near the glass transition in (meta-)stable equilibrium. Theories of the glass transition imply such an equilibrium and can, hence, be tested by the study of polymer melts. After a brief summary of the basic experimental facts about the glass transition in polymers, the main theoretical concepts are reviewed: mode coupling theory (MCT), entropy theory, free-volume theory, the idea of a growing length describing the size of cooperative regions, etc. Then, two basic coarse-grained models of polymers are described, which have been developed aiming at a test of these concepts. The first model is the bond-fluctuation model …
Adsorption Transition of a Polymer Chain at a Weakly Attractive Surface: Monte Carlo Simulation of Off-Lattice Models
2002
A bead-spring model of a polymer chain with one end attached to a wall is studied by Monte Carlo simulations for chain lengths 16 ≤ N ≤ 256. Two types of adsorption potentials, 9-3 and 10-4 Lennard-Jones (LJ) potentials, between the effective monomers and the wall are assumed. For both cases the adsorption transition where the chain changes its asymptotic statistical properties from a three-dimensional to a two-dimensional configuration is located using a scaling analysis. It is shown that the crossover exponent φ = 0.50 ± 0.02 is the same for both LJ potentials. This value is compatible with recent theoretical predictions and simulation results for lattice models with short-range wall pote…
Combining Orthogonal Reactive Groups in Block Copolymers for Functional Nanoparticle Synthesis in a Single Step.
2017
We report on the synthesis of polysarcosine-block-poly(S-alkylsulfonyl)-l-cysteine block copolymers, which combine three orthogonal addressable groups enabling site-specific conversion of all reactive entities in a single step. The polymers are readily obtained by ring-opening polymerization (ROP) of corresponding α-amino acid N-carboxyanhydrides (NCAs) combining azide and amine chain ends, with a thiol-reactive S-alkylsulfonyl cysteine. Functional group interconversion of chain ends using strain-promoted azide–alkyne cycloaddition (SPAAC) and activated ester chemistry with NHS- and DBCO-containing fluorescent dyes could be readily performed without affecting the cross-linking reaction betw…
Orthogonally reactive amino acids and end groups in NCA polymerization
2017
Functional amino acids whose reactivity is compatible with the polymerization of α-amino acid-N-carboxyanhydrides (NCAs) have received a lot of attention in recent years. The appeal of these reactive monomers lies in the fact that the resulting polymers can be easily modified in one controlled post-polymerization step, leading to a variety of polypeptidic materials like helical non-natural polycations or glycopeptides. This review highlights recent developments in the field and focuses on the different reactive groups like alkynes, alkenes, azides, chlorides and S-alkylsulfonyls. Furthermore, the modifications after polymerization are discussed, pointing out advantages and challenges. Besid…
Saccharide modified silica particles by enzymatic grafting
1997
The surface of silica particles has been chemically modified with oligo- or poly-(α,1→4)-D-glucopyranose (amylose) chains of various length by covalently attaching maltoheptaose derivatives to the solid support and enzymatic polymerization of glucose-1-phosphate with a potato phosphorylase as catalyst. The characterization of the products by solid-state NMR spectroscopy showed an interesting dependence of the linewidth with the grafting density of the glucan chains. The modified silica particles showed chiral discrimination in liquid chromatography.
Some examples of the modification of polymers
1986
Reactions avec des groupes amide et amino dans la chaine principale, et avec un groupe terminal bromoacetyl. Polymerisation de la conidine en presence d'un polystyrene vivant
Molecular dynamics simulations of the glass transition in polymer melts
2004
Computer simulations of polymer models have contributed strongly to our understanding of the glass transition in polymer melts. The ability of the simulation to provide information on experimentally not directly accessible quantities like the detailed spatial arrangement of the particles allows for stringent tests of theoretical concepts about the glass transition and provides additional insight for the interpretation of experimental data. Comparing coarse-grained simulations of a bead-spring model and chemically realistic simulations of 1,4-polybutadiene the importance of dihedral barriers for the glass transition phenomenon can be elucidated.