Search results for "Biomolecules"
showing 10 items of 549 documents
Dynamic force spectroscopy: analysis of reversible bond-breaking dynamics
2008
The problem of diffusive bond-dissociation in a double well potential under application of an external force is scrutinized. We compute the probability distribution of rupture forces and present a detailed discussion of the influence of finite rebinding probabilities on the dynamic force spectrum. In particular, we focus on barrier crossing upon extension, i.e. under linearly increased load, and upon relaxation starting from completely separated bonds. For large loading rates the rupture force and the rejoining force depend on the loading rate in the expected manner determined by the shape of the potential. For small loading rates the mean forces obtained from pull and relax modes approach …
Polyelectrolyte Molecule in an Elongational Flow
1995
The theory describing the stretching of a weakly charged polyelectrolyte molecule by elongational shear flow is developed. It is shown that for a polyelectrolyte immersed in a salt-added solution two critical values of shear flow gradient exist: the lower critical point corresponds to the chain stretching on the scale of superblobs of size equal to the Debye screening length and the upper critical point corresponds to the complete stretching of the chain on the scale of monomer units.
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…
Polymer brushes on flat and curved surfaces: How computer simulations can help to test theories and to interpret experiments
2012
Theoretical descriptions of static properties of polymer brushes are reviewed, with an emphasis on monodisperse macromolecules grafted to planar, cylindrical, or spherical substrates. Blob concepts and resulting scaling relations are outlined, and various versions of the self-consistent field theory are summarized: the classical approximation and the strong stretching limit, as well as the lattice formulation. The physical justification of various inherent assumptions is discussed, and computer simulation results addressing the test of the validity of these approximations are reviewed. Also, alternative theories, such as the single chain mean field theory and the density functional theory, …
Stretching of Free Chains Confined in Concave Brush-Coated Nanocylinders
2012
The structure of a free flexible macromolecule confined in a cylindrical nanopore whose wall is coated by a polymer brush is studied by Monte Carlo simulation, varying the grafting density as well as the radius of the cylindrical pore. Because of this confinement, the free chain is stretched in axial direction; while for small grafting densities of the brush the end-to-end distance increases monotonously with decreasing pore radius, a nonmonotonic variation occurs for larger grafting densities. We show that this effect is due to strong interpenetration of the free chain and the brush chains; for very narrow pores a strong layering of cylindrical shells is found, and comparison with self-con…
Phase Diagram of Random Copolymer Melts: A Computer Simulation Study
2004
We investigate the phase behavior of random copolymer melts via large-scale Monte Carlo simulations. The AB multiblock copolymers have, on average, symmetric composition and are characterized by a ...
Interface and Surface Properties of Short Polymers in Solution: Monte Carlo Simulations and Self-Consistent Field Theory
2000
We investigate the structure and thermodynamics of inhomogeneous polymer solutions in the framework of a coarse-grained off-lattice model. Properties of the liquidvapor interface and the packing of...
Shear induced deformation of polystyrene coils in dilute solution from small angle neutron scattering
1985
The deformation of the overall conformation of polystyrene,Mw=280000 g/ mole in dilute solution in a constant shear gradient has been investigated by small angle neutron scattering (SANS).
A new method for data evaluation of small angle neutron scattering experiments and its application to amorphous polycarbonate
1981
The conformation of single chains in bulk polymer materials can be evaluated from coherent neutron scattering on mixtures of normal and deuterated polymers. It is shown that the single-chain structure factor can be also obtained from measurements of highly concentrated mixtures and the procedure of evaluation is described. The application to amorphous polycarbonate demonstrates the advantages of the method.
Structural and conformational dynamics of supercooled polymer melts: Insights from first-principles theory and simulations
2007
We report on quantitative comparisons between simulation results of a bead-spring model and mode-coupling theory calculations for the structural and conformational dynamics of a supercooled, unentangled polymer melt. We find semiquantitative agreement between simulation and theory, except for processes that occur on intermediate length scales between the compressibility plateau and the amorphous halo of the static structure factor. Our results suggest that the onset of slow relaxation in a glass-forming melt can be described in terms of monomer-caging supplemented by chain connectivity. Furthermore, a unified atomistic description of glassy arrest and of conformational fluctuations that (as…