Search results for "Gyration"

The escape transition of a compressed star polymer: Self-consistent field predictions tested by simulation

2013

The escape transition of a polymer "mushroom" (a flexible chain grafted to a flat non-adsorbing substrate surface in a good solvent) occurs when the polymer is compressed by a cylindrical piston of radius $R$, that by far exceeds the chain gyration radius. At this transition, the chain conformation abruptly changes from a two-dimensional self-avoiding walk of blobs (of diameter $H$, the height of the piston above the substrate) to a "flower conformation", i.e. stretched almost one-dimensional string of blobs (with end-to-end distance $\approx R$) and an "escaped" part of the chain, the "crown", outside the piston. The extension of this problem to the case of star polymers with $f$ arms is c…

Lösungseigenschaften von polymethylmethacrylat und polystyrol aus Röntgenkleinwinkelmessungen

1969

Die mit der Lichtstreuungsmethode an Losungen von Polymethylmethacrylat (PMMA) und Polystyrol (PST) im Bereich groser Molekulargewichte durchgefuhrten Untersuchungen werden mit Hilfe von Rontgenkleinwinkelmessungen auf das Gebiet Kleiner Molekulargewichte ausgedehnt. Es gibt einen Molekulargewichtsbereich (M = 103 bis 3·104), innerhalb dessen auch im guten Losungsmittel der Tragheitsradius der Wurzel aus dem Molekulargewicht proportional ist. Bei PMMA stimmen in diesem Bereich und auch bei kleineren Molekulargewichten die Tragheitsradein im guten Losungsmittel Aceton mit denen im verwendeten Θ-Losungsmittel innerhalb der Fehlergrenzen uberein; bei PST in Toluol gilt das nicht. Aus den Bezie…

New Development of Monte Carlo Techniques for Studying Bottle-brush Polymers

2011

Due to the complex characteristics of bottle-brush polymers, it became a challenge to develop an efficient algorithm for studying such macromolecules under various solvent conditions or some constraints in the space by using computer simulations. In the limit of a bottle-brush polymer with a rather stiff backbone (straight rigid backbone), we generalize the variant of the biased chain growth algorithm, the pruned-enriched Rosenbluth method, for simulating polymers with complex architecture, from star polymers to bottle-brush polymers, on the simple cubic lattice. With the high statistics of our Monte Carlo results, we check the theoretical predictions of side chain behavior and radial monom…

Single-chain conformations in symmetric binary polymer blends: Quantitative comparison between self-consistent field calculations and Monte Carlo sim…

1998

Single-chain properties in a symmetric binary polymer blend are studied by self-consistent field calculations and Monte Carlo simulations. Within the self-consistent field scheme, the statistical mechanics of a cluster of neighboring polymers is solved. Interactions among the polymers of a cluster and composition fluctuations within a cluster are incorporated exactly, a mean field approximation is invoked for intercluster interactions and long-range fluctuations. The results are compared to large scale Monte Carlo simulations for a broad range of chain lengths. While we find nearly quantitative agreement for single chain propertiese.g., the reduction of the chain dimensions of the minority …

Relaxation of self-entangled many-arm star polymers

1989

We present a description of the relaxation of star polymers based on the conformational scaling properties predicted by Daoud and Cotton and confirmed in our recent simulations. We identify three typical relaxation mechanisms. The first describes elastic deformation of the overall shape. Its relaxation time is nearly independent off. A second type of relaxation occurs via rotational diffusion. We predict that the relaxation time should scale with Nwlfz-v where Y is the correlation length exponent. A third relaxation process is the disentanglement of two or more arms. Here the longest relaxation time should increase exponentially with f llz. We measure various relaxation processes by molecul…

The Role of Internal Rotational Barriers in Polymer Melt Chain Dynamics

2002

We present molecular dynamics simulations on 1,4-polybutadiene comparing the dynamics of melt chains between chemically realistic models and a freely rotating chain version of one of the models. These models exhibit the same liquid structure, as measured by the structure factor, and meso- to large-scale chain structure, as measured by the Rouse-mode amplitudes. We show that in this case the Rouse-like chain dynamics as observable in the momentum transfer range of neutron spin-echo experiments is the same for the chains with and without torsion barriers. Our results bear on a recent comparative neutron spin-echo study of the chain dynamics of two polymers with similar chain structure which r…

Small-angle X-ray scattering reveals differences between the quaternary structures of oxygenated and deoxygenated tarantula hemocyanin

1996

Small-angle X-ray scattering (SAXS) curves have been recorded for the oxygenated and deoxygenated states of the 4 x 6-meric hemocyanin from the tarantula Eurypelma californicum. A comparison of the curves shows that the quaternary structures of the two states are different by three criteria, which all indicate that the hemocyanin is less compact in the oxygenated compared to the deoxygenated form: (a) The radius of gyration is 8.65 +/- 0.05 nm for the deoxy- and 8.80 +/- 0.05 nm for the oxy-form. (b) The maximum particle dimension amounts to 25.0 +/- 0.5 nm for the deoxy- and to 27.0 +/- 0.5 nm for the oxy-form. (c) A dip in the intramolecular distance distribution function p(r) is more pro…

2015

AbstractLight absorption can trigger biologically relevant protein conformational changes. The light-induced structural rearrangement at the level of a photoexcited chromophore is known to occur in the femtosecond timescale and is expected to propagate through the protein as a quake-like intramolecular motion. Here we report direct experimental evidence of such ‘proteinquake’ observed in myoglobin through femtosecond X-ray solution scattering measurements performed at the Linac Coherent Light Source X-ray free-electron laser. An ultrafast increase of myoglobin radius of gyration occurs within 1 picosecond and is followed by a delayed protein expansion. As the system approaches equilibrium i…

Homopolymer adsorption on periodically structured surfaces in systems with incommensurable lengths

2013

Surface-induced selective adsorption of homopolymers on a generic level is numerically analyzed for freely jointed chains (with a fixed bond length) whose monomers are attracted by the sites of regular periodic patterns. In particular, the behavior of the specific heat, the gyration tensor, and the bond order tensor are investigated as functions of the temperature. The properties of the transition are related to the interplay of the characteristic lengths. The adsorption proceeds in two steps for certain incommensurabilities of the bond length and the lattice constant. The corresponding adsorption mechanisms are elucidated by looking at the evolution of the inter bond angle distribution upo…

A soft-quadrumer model for diblock copolymers

2010

We present a new soft-particle type model for diblock copolymers and compare its phase diagram to experimental data as well as to results of other models. To determine the phase diagram we suggest studying geometrical characteristics of the mesophases. Diblock copolymer mesophases differ by the number and geometrical form of clusters of the two components formed in the mesophase. The form of these clusters can be characterized by values of the principle components of their gyration tensor and shape invariants determined from them. Alternatively, it has been suggested to use Minkowski functionals to characterize the global morphology of the different mesophases. We will also discuss the prac…