59 research outputs found
Force-Extension Relation and Plateau Modulus for Wormlike Chains
We derive the linear force-extension relation for a wormlike chain of
arbitrary stiffness including entropy elasticity, bending and thermodynamic
buckling. From this we infer the plateau modulus of an isotropic
entangled solution of wormlike chains. The entanglement length is
expressed in terms of the characteristic network parameters for three different
scaling regimes in the entangled phase. The entanglement transition and the
concentration dependence of are analyzed. Finally we compare our findings
with experimental data.Comment: 5 pages, 1 eps-figure, to appear in PR
A molecular dynamics simulation of polymer crystallization from oriented amorphous state
Molecular process of crystallization from an oriented amorphous state was
reproduced by molecular dynamics simulation for a realistic polyethylene model.
Initial oriented amorphous state was obtained by uniaxial drawing an isotropic
glassy state at 100 K. By the temperature jump from 100 K to 330 K, there
occurred the crystallization into the fiber structure, during the process of
which we observed the developments of various order parameters. The real space
image and its Fourier transform revealed that a hexagonally ordered domain was
initially formed, and then highly ordered crystalline state with stacked
lamellae developed after further adjustment of the relative heights of the
chains along their axes.Comment: 4 pages, 3 figure
Early Stages of Homopolymer Collapse
Interest in the protein folding problem has motivated a wide range of
theoretical and experimental studies of the kinetics of the collapse of
flexible homopolymers. In this Paper a phenomenological model is proposed for
the kinetics of the early stages of homopolymer collapse following a quench
from temperatures above to below the theta temperature. In the first stage,
nascent droplets of the dense phase are formed, with little effect on the
configurations of the bridges that join them. The droplets then grow by
accreting monomers from the bridges, thus causing the bridges to stretch.
During these two stages the overall dimensions of the chain decrease only
weakly. Further growth of the droplets is accomplished by the shortening of the
bridges, which causes the shrinking of the overall dimensions of the chain. The
characteristic times of the three stages respectively scale as the zeroth, 1/5
and 6/5 power of the the degree of polymerization of the chain.Comment: 11 pages, 3 figure
Complex linkages between agriculture and air pollution pose a major threat to food security in India
Fiber optical laser spot microscope: A new concept for photoelectrochemical characterization of semiconductor electrodes
A fiber optical laser spot microscope, which allows the simultaneous measurements of photocurrent and reflected light intensity or the measurement of laser spot photocurrent under the illumination of other light sources, has been developed to study semiconductor/electrolyte interfaces. The capability of this microscope was demonstrated on as-cleaved and Pt-treated p-InSe. The Pt treatment increased the photocurrent and improved the lateral resolution due to the increase of surface reaction rate. The higher photocurrent was observed at the spot where the reflectivity was higher. This behavior is considered to be due to an uneven distribution of platinum. The laser spot photocurrent image under the illumination of other light sources provided useful information to clarify whether the rate was controlled by surface or bulk properties of InSe
Fiber optical laser spot microscope: A new concept for photoelectrochemical characterization of semiconductor electrodes
Conformation of interacting polymer chains: Effects of temperature, bias, polymer concentration, and porosity
The conformations of interacting polymer chains driven by a biased field in heterogeneous media are studied using Monte Carlo simulations in three dimensions. In addition to excluded volume, a nearest-neighbor interaction is considered with polymer-polymer repulsion and polymer-solvent attraction. Two types of heterogeneous media are considered: (i) a homogeneous-annealed system consisting of mobile polymer chains and solvents and (ii) quenched porous media, generated by adding a random distribution of quenched barriers. Effects of polymer concentration (p), bias (B), temperature (T), and porosity (ps) on the magnitude of the radius of gyration (Rg) of the chains and its scaling with the chain length (Lc) are studied. In an annealed system, we observe a crossover in power-law variation of the radius of gyration with the chain length, Rgā¼Lyc, from an extended conformation with Ī³ā0.7 at low bias (B=0.2), low p, and high T to a collapsed conformation with Ī³ā¼0.20-0.31 at high bias (Bā©¾0.5) and low T. In a quenched porous medium, we observe a somewhat lower value of the power-law exponent, Ī³ā¼0.60-0.70, from its annealed value at high T and low bias. At low temperatures, in contrast, the magnitude of Ī³ā¼0.39-0.47 is enhanced with respect to its annealed value. Various nonlinear responses of Rg to bias are observed in different ranges of B, Lc, ps and T. In particular, we find that the response is nonmonotonic at low temperatures (Tā0.1) in the annealed system and at high temperatures (Tā100.0) in a porous medium with a relatively high barrier concentration (pbā©¾0.3
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