Search results for "Length"
showing 10 items of 2188 documents
Reversible tuning of a block-copolymer nanostructure via electric fields
2007
Block copolymers consisting of incompatible components self-assemble into microphase-separated domains yielding highly regular structures with characteristic length scales of the order of several tens of nanometres. Therefore, in the past decades, block copolymers have gained considerable potential for nanotechnological applications, such as in nanostructured networks and membranes, nanoparticle templates and high-density data storage media. However, the characteristic size of the resulting structures is usually determined by molecular parameters of the constituent polymer molecules and cannot easily be adjusted on demand. Here, we show that electric d.c. fields can be used to tune the char…
Chalcogenide Fibers for Mid-IR Light Generation: Potentialities and Drawbacks of the Microstructured Design in Sulfide Waveguides
2014
We study optical and structural aging in As2S3 microstructured optical fibers, submitted to room atmosphere that may have, among others, an impact on mid-infrared supercontinuum generation.
Influence of polymer flexibility on nanoparticle dynamics in semidilute solutions
2018
The hierarchical structure and dynamics of polymer solutions control the transport of nanoparticles (NPs) through them. Here, we perform multi-particle collision dynamics simulations of solutions of semiflexible polymer chains with tunable persistence length lp to investigate the effect of chain stiffness on NP transport. The NPs exhibit two distinct dynamical regimes - subdiffusion on short time scales and diffusion on long time scales. The long-time NP diffusivities are compared with predictions from the Stokes-Einstein relation (SER), mode-coupling theory (MCT), and a recent polymer coupling theory (PCT). Increasing deviations from the SER as the polymer chains become more rigid (i.e. as…
Cylindrical polyelectrolyte-comb-surfactant complexes
2006
Abstract Quaternized polymer combs based on poly(2-vinylpyridine-macromonomers) and the surfactant sodium dodecylsulfate are employed in the synthesis of a novel cylindrical polyelectrolyte-comb-surfactant complex (PECSC). The complex formed has 1:1 stoichiometry with respect to the ratio of dodecylsulfate to pyridinium units. It is soluble in organic solvents such as 2-butanol or chloroform. Characterization of single particle properties of the complex in organic solution is possible and yields a radius of gyration of 〈Rg〉z = 78.4 nm, a hydrodynamic radius of 〈1/Rh〉z−1 = 51.4 nm and a cross-sectional radius of Rg,cross = 3.9 nm in chloroform. The characteristic ratio γ = 〈Rg〉z/〈1/Rh〉z−1 de…
Mapping onto ideal chains overestimates self-entanglements in polymer melts
2017
In polymer physics it is typically assumed that excluded volume interactions are effectively screened in polymer melts. Hence, chains could be described by an effective random walk without excluded volume interactions. In this letter, we show that this mapping is problematic by analyzing the occurrence of knots, their spectrum and sizes in polymer melts, corresponding random walks and chains in dilute solution. The effective random walk severely overrates the occurrence of knots and their complexity, particularly when compared to melts of flexible chains, indicating that non-trivial effects due to remnants of self-avoidance still play a significant role for the chain lengths considered in t…
Standard Definitions of Persistence Length Do Not Describe the Local “Intrinsic” Stiffness of Real Polymer Chains
2010
On the basis of extensive Monte Carlo simulations of lattice models for linear chains under good and Θ solvents conditions, and for bottle-brush polymers under good solvent conditions, different me...
Structure of bottle brush polymers on surfaces: weak versus strong adsorption.
2011
Large-scale Monte Carlo simulations are presented for a coarse-grained model of cylindrical molecular brushes adsorbed on a flat structureless substrate, varying both the chain length N of the side chains and the backbone chain length N(b). For the case of good solvent conditions, both the cases of weak adsorption (only 10 to 15% of the monomers being bound to the surface) and strong adsorption (~40% of the monomers being bound to the surface, forcing the bottle brush into an almost 2D conformation) are studied. We focus on the scaling of the total linear dimensions of the cylindrical brush with both chain lengths N and N(b), demonstrating a crossover from rod-like behavior (for not very la…
A Monte Carlo Study of Living Polymers in 2D: Effect of Small Chains on Static Properties
1996
A slithering snake algorithm is combined with a binding and breaking chain algorithm to simulate the static behavior of living polymers according to Cates' description. It is shown that this simple two-dimensional simulation on a square lattice gives good agreement with the mean field theory. However, the large amount of small contour length chains for small values of the mean average length 〈L 〉 appears to be one of the reasons for the discrepancies observed between the simulated results and the mean field theory. This finding could explain disagreements between experimental observation and theory. Also, the results are not in favor of a swelling of the greater chains by the smaller one.
Thermodynamics of Aqueous Poly(ethylene oxide)−Poly(propylene oxide)−Poly(ethylene oxide)/Surfactant Mixtures. Effect of the Copolymer Molecular Weig…
2004
A calorimetric study was performed to focus attention on the interactions between copolymers and anionic surfactants in aqueous solutions. Three aspects were analyzed: (1) the hydrophobicity of the surfactant, (2) the change of the copolymer molecular weight, and (3) the nature of the hydrophilicity of the copolymer. To this purpose, the family of sodium alkanoates (sodium octanoate through sodium dodecanoate) and the triblock copolymers EO76PO 29EO76 (F68), EO103PO39EO 103 and EO132PO50EO132 were investigated. Comparing F68 and EO13PO30EO13 (L64), previously studied by us, provided information on the effect of the copolymer hydrophilicity. The experimental data were analyzed by means of a …
A coarse-graining procedure for polymer melts applied to 1,4-polybutadiene
2009
We present a coarse-graining procedure for homopolymer melts mapping intra- as well as inter-molecular interactions from a chemically realistic united atom description to a bead-spring type molecular model. On the coarse-grained level the repeat units interact through bond-length and bond angle potentials and a non-bonded Lennard-Jones type interaction. The latter one is of the 7,4 form and softer than the typically employed 12,6 interactions. The coarse-graining of the intramolecular interactions follows well developed procedures, however, we point out in which way the non-bonded intramolecular interactions in the chemically realistic model should be treated. The parameters of the non-bond…