Search results for "Persistence"
showing 10 items of 243 documents
Persistence and career choices of female Finnish university physics students
2019
Entropic Unmixing in Nematic Blends of Semiflexible Polymers.
2020
Binary mixtures of semiflexible polymers with the same chain length, but different persistence lengths, separate into two coexisting different nematic phases when the osmotic pressure of the lyotropic solution is varied. Molecular Dynamics simulations and Density Functional Theory predict phase diagrams either with a triple point, where the isotropic phase coexists with two nematic phases or a critical point of unmixing within the nematic mixture. The difference in locally preferred bond angles between the constituents drives this unmixing without any attractive interactions between monomers.
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…
Individual Differences in DNA Repair Capacities in Man
1987
After metabolic activation of benzo[a]pyrene to the 7,8-dihydrodiol- 9,10-epoxide, this ultimate carcinogen preferentially binds to the exocyclic amino group of guanine. In order to investigate possible interindividual differenes in the capacity of repair of the DNA adducts formed from benzo[a]- pyrene 7,8-dihydrodiol 9,10-epoxide, their persistence in freshly isolated lymphocytes of several donors was studied. The results show a surprisingly large interindividual variation in DNA adduct formation and their persistence in freshly isolated lymphocytes. This range included several individuals with an apparent complete lack of repair capability for these adducts. Compared with controls, smoker…
Adult Lactose Tolerance Is Not an Advantageous Evolutionary Trait
2004
To the Editor. I read with great interest the recent article from Fomon1 in which he refers to the well-known hypothesis that views the variable frequencies of lactase persistence in different human populations and, consequently, the possibility for some adults to feed on milk (lactose tolerance) as an advantageous evolutionary trait that has been genetically determined and brought about through centuries of natural selection. This notion stands as a common statement in current medical literature, and most authors have accepted its validity since the 1970s.2,3 Because adult mammals are lactose-intolerant, this hypothesis is, moreover, based on the low percentage of lactose malabsorption and…