scholarly journals Kinetics of Loop Formation in Polymer Chains†

2008 ◽  
Vol 112 (19) ◽  
pp. 6094-6106 ◽  
Author(s):  
Ngo Minh Toan ◽  
Greg Morrison ◽  
Changbong Hyeon ◽  
D. Thirumalai
Keyword(s):  
Polymer Chains ◽  
Loop Formation ◽  
Kinetics Of

Simulations of High-Strain Electrostrictive Chlorinated Terpolymers

2003 ◽  
Vol 785 ◽  
Author(s):  
George J. Kavarnos ◽  
Thomas Ramotowski
Keyword(s):  
Vinylidene Fluoride ◽  
High Strain ◽  
Polymer Chains ◽  
X Ray Diffraction ◽  
X Ray ◽  
Lamellar Structures ◽  
Annealing Conditions ◽  
Poly Vinylidene Fluoride ◽  
Electromechanical Responses ◽  
Kinetics Of

ABSTRACTChlorinated poly(vinylidene fluoride/trifluoroethylene) terpolymers are remarkable examples of high strain electrostrictive materials. These polymers are synthesized by copolymerizing vinylidene fluoride and trifluoroethylene with small levels of a third chlorinated monomer. The electromechanical responses of these materials are believed to originate from the chlorine atom, which, by its presence in the polymer chains and by virtue of its large van der Waals radius, destroys the long-range crystalline polar macro-domains and transforms the polymer from a normal to a high-strain relaxor ferroelectric. To exploit the strain properties of the terpolymer, it is desirable to understand the structural implications resulting from the presence of the chlorinated monomer. To this end, computations have been performed on model superlattices of terpolymers using quantum-mechanical based force fields. The focus has been on determining the energetics and kinetics of crystallization of the various polymorphs that have been identified by x-ray diffraction and fourier transform infrared spectroscopy. The chlorinated monomer is shown to act as a defect that can be incorporated into the lamellar structures of annealed terpolymer without a high cost in energy. The degree of incorporation of the chlorinated monomer into the crystal lattice is controlled by annealing conditions and ultimately determines the ferroelectric behavior of the terpolymers.

Kinetics of polymer crystallization - II. Growth régimes

1988 ◽  
Vol 416 (1851) ◽  
pp. 463-476 ◽  
Keyword(s):  
Growth Rate ◽  
Continuum Model ◽  
Continuum Limit ◽  
Polymer Chains ◽  
Lamellar Crystal ◽  
Folding Rate ◽  
Edge Roughness ◽  
State Growth ◽  
Kinetics Of ◽  
The Continuum

From the models of paper I, exact expressions are found for the steady-state growth rate of a portion of the edge of a lamellar crystal in terms of the number of polymer segments M in the portion, the nucleation rate α on the edge and the folding rate v of polymer chains. Both hexagonal and square crystal structures are analysed. Simpler expressions are given in various limiting cases or régimes. One such régime is the continuum model of Bennett et al. (J. statist. Phys . 24, 419 (1981)). We find that the growth rates in our models differ substantially from this continuum limit when edge roughness is significant. The continuum growth rate provides an exact upper bound on the growth rate in Frank’s model (Frank, F. C. J. Cryst. Growth 22, 233 (1974)), which is sometimes exceeded by Frank’s approximation.

Morphology, Crystalline Structure and Isothermal Crystallization Kinetics of Polybutylene Terephthalate/Montmorillonite Nanocomposites

2005 ◽  
Vol 13 (1) ◽  
pp. 61-71 ◽  
Author(s):  
Defeng Wu ◽  
Chixing Zhou ◽  
Xie Fan ◽  
Dalian Mao ◽  
Zhang Bian
Keyword(s):  
Activation Energy ◽  
Crystallization Kinetics ◽  
Crystallization Temperature ◽  
Isothermal Crystallization ◽  
Polymer Chains ◽  
Isothermal Crystallization Kinetics ◽  
Clay Particles ◽  
Nucleation Sites ◽  
Kinetics Of ◽  
Montmorillonite Nanocomposites

The melt intercalation method was employed to prepare poly(butylene terepathalate)/montmorillonite nanocomposites, and their microstructure was characterized by wide angle X-ray diffraction and transmission electron microscopy. The XRD results showed that the crystalline plane such as (010), (111), (100) was smaller than that of pristine PBT, which indicates that the crystallite size of PBT in the nanocomposites could be diminished by adding clay. Moreover, the isothermal crystallization kinetics of PBT and PBT/MMT nanocomposites was investigated by differential scanning calorimetry (DSC). During isothermal crystallization, the development of crystallinity with time was analysed by the Avrami equation. The results show that very small amounts of clay dramatically increased the rate of crystallization and high clay concentrations reduced the rate of crystallization at the low crystallization temperatures. At low concentrations of clay, the distance between dispersed platelets was large so it was relatively easy for the additional nucleation sites to incorporate surrounding polymer, and the crystal nucleus was formatted easily. However, at high concentrations of clay, the diffusion of polymer chains to the growing crystallites was hindered by large clay particles, despite the formation of additional nucleation sites by the clay layers. At the higher crystallization temperature, the crystallization of the nanocomposites was slower than that of the pure PBT under the experimental conditions, which means that with the increase in chains mobility at the high crystallization temperature, the crystal nuclei are harder to format, and the hindering effect of clay particles on the polymer chains was stronger than the nucleating effect of the layers. In addition, the activation energies of crystallization for PBT and its nanocomposites were calculated by the Arrhenius relationship, and the results showed that the nanocomposites with a low clay content had the lower activation energy values than PBT, while high amounts of clay increased the activation energy of PBT.

scholarly journals Kinetics of anchoring of polymer chains on substrates with chemically active sites

1998 ◽  
Vol 58 (5) ◽  
pp. 6134-6144 ◽  
Author(s):  
G. Oshanin ◽  
S. Nechaev ◽  
A. M. Cazabat ◽  
M. Moreau
Keyword(s):  
Active Sites ◽  
Polymer Chains ◽  
Kinetics Of

Study of the kinetics of mushroom-to-brush transition of charged polymer chains

Polymer ◽  
2006 ◽  
Vol 47 (9) ◽  
pp. 3157-3163 ◽  
Author(s):  
Guangming Liu ◽  
Lifeng Yan ◽  
Xi Chen ◽  
Guangzhao Zhang
Keyword(s):  
Polymer Chains ◽  
Charged Polymer ◽  
Kinetics Of

scholarly journals Kinetics of Internal-Loop Formation in Polypeptide Chains: A Simulation Study

2007 ◽  
Vol 92 (7) ◽  
pp. 2281-2289 ◽  
Author(s):  
Dana Doucet ◽  
Adrian Roitberg ◽  
Stephen J. Hagen
Keyword(s):  
Simulation Study ◽  
Loop Formation ◽  
Internal Loop ◽  
Polypeptide Chains ◽  
Kinetics Of

Kinetics of Loop Formation and Breakage in the Denatured State of Iso-1-cytochrome c

2005 ◽  
Vol 353 (3) ◽  
pp. 730-743 ◽  
Author(s):  
Eydiejo Kurchan ◽  
Heinrich Roder ◽  
Bruce E. Bowler
Keyword(s):  
Cytochrome C ◽  
Loop Formation ◽  
Denatured State ◽  
Kinetics Of

Kinetics of polymer chains in elongational flow

1994 ◽  
Vol 172-174 ◽  
pp. 932-934 ◽  
Author(s):  
A.A. Darinskii ◽  
M.G. Saphiannikova
Keyword(s):  
Elongational Flow ◽  
Polymer Chains ◽  
Kinetics Of

scholarly journals The accidental ally: Nucleosomal barriers can accelerate cohesin mediated loop formation in chromatin

2019 ◽  
Author(s):  
Ajoy Maji ◽  
Ranjith Padinhateeri ◽  
Mithun K. Mitra
Keyword(s):  
Effective Diffusion ◽  
Diffusion Constant ◽  
Loop Formation ◽  
Base Pairs ◽  
Diffusion Constants ◽  
Dna Backbone ◽  
The Mean ◽  
The Times ◽  
Lower Loop ◽  
Kinetics Of

AbstractAn important question in the context of the 3D organization of chromosomes is the mechanism of formation of large loops between distant base pairs. Recent experiments suggest that the formation of loops might be mediated by Loop Extrusion Factor proteins like cohesin. Experiments on cohesin have shown that cohesins walk diffusively on the DNA, and that nucleosomes act as obstacles to the diffusion, lowering the permeability and hence reducing the effective diffusion constant. An estimation of the times required to form the loops of typical sizes seen in Hi-C experiments using these low effective diffusion constants leads to times that are unphysically large. The puzzle then is the following, how does a cohesin molecule diffusing on the DNA backbone achieve speeds necessary to form the large loops seen in experiments? We propose a simple answer to this puzzle, and show that while at low densities, nucleosomes act as barriers to cohesin diffusion, beyond a certain concentration, they can reduce loop formation times due to a subtle interplay between the nucleosome size and the mean linker length. This effect is further enhanced on considering stochastic binding kinetics of nucleosomes on the DNA backbone, and leads to predictions of lower loop formation times than might be expected from a naive obstacle picture of nucleosomes.

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