Dynamics Of Linear Polymers Research Articles

Hidden Symmetry Effects in the Dynamics of Linear Polymers and Biopolymers

Hidden Symmetry Effects in the Dynamics of Linear Polymers and Biopolymers

A unified approach to the dynamics of a polymer melt

Stretched exponentials are often used to describe quasi-elastic neutron scattering (QENS)and nuclear magnetic resonance (NMR) relaxation data from polymer melts. In thispaper, we attempt to derive a more physically meaningful model of the local(∼0.1 nm),short-time (∼10 ps) dynamics of linear polymers that takes into account (i) orientationaldiffusion along the polymer chain, (ii) local conformational transitions, and(iii) long-time, large-scale motions. The model takes into account the spatialcomponent of the local dynamics, described in terms of the scattering vectorQ. Themodel is applied to QENS results on highly entangled polyethylene oxide (PEO) melt at 373 K. We findthe Q dependences of the three correlation times of the model to be consistent withQ0,Q−2 andQ−4 power laws,respectively. The high-Q limit of the model closely resembles the NMR-based DLM model (Dejean de la Batie et al 1988 Macromolecules 21 2045) but the physical interpretation is different. At 373 K,the polymer dynamics is described in terms of transverse motions of the chainsegments over a distance of a few nm, with a local monomeric diffusion coefficient of1.78 × 10−9 m2 s−1. From this value, we derive a monomeric friction coefficientξ0 = 2.89 × 10−12 N s m−1 that,used as numerical input to the Doi–Edwards theory, leads to a chain centre-of-mass diffusion coefficientDcm = 9.4 × 10−15 m2 s−1. This value is in good agreement with pulsed field gradient NMR data (Appeland Fleischer 1993 Macromolecules 26 5520) and validates the proposed model.

Dynamics of linear polymers in random media

We study phenomenological scaling theories of the polymer dynamics in random media, employing the existing scaling theories of polymer chains and the percolation statistics. We investigate both the Rouse and the Zimm model for Brownian dynamics and estimate the diffusion constant of the center-of-mass of the chain in such disordered media. For internal dynamics of the chain, we estimate the dynamic exponents. We propose similar scaling theory for the reptation dynamics of the chain in the framework of Flory theory for the disordered medium. The modifications in the case of correlated disorders are also discussed.

Contribution of Polymer-Solvent Interactions to Dynamics of Linear Polymers in Dilute Solutions

In this work a theoretical approach to dynamics of linear vinyl polymers in dilute solutions of high viscosity solvents is presented. The calculations for the relaxation time spectra, polymer intrinsic viscosity [η (ω)], complex elastic modulus G*(ω), total intrinsic viscosity [ηT (ω)] and specific heat capacity C (ω) were carried out in the non-free-draining limits. The relaxation time spectrum calculated for dynamics of low frequency modes exhibits a Rouse-like character. Its position and shape corresponds to the ultrasonic relaxation time spectrum observed in the system at 106 Hz. On the other hand, the relaxation time spectrum associated with moderate frequency mode dynamics is narrower and typical for ultrasonic relaxation observed at 107 Hz. The polymer intrinsic viscosity [η (ω)] and elastic modulus G*(ω) are shown to be represented by the model within a low-frequency range. In turn, the specific heat capacity C (ω) is displayed as a representation of the model in the acoustic region mentioned above. In the high-frequency range the dynamics is described by the total intrinsic viscosity [ηT (ω)] tending to a plateau where the value is equal to the sum of the single-bead intrinsic viscosity [ηN] and effective solvent viscosity [ηeff].

Molecular approach in linear polymer dynamics: Theory and numerical experiment

A constitutive equation for polymer solutions and melts is obtained on the basis of the dynamics of noninteracting dumbbells moving in a nonlinear anisotropic fluid. The equation obtained is used to describe nonlinear effects under conditions of simple shear and steady-state flow in a circular tube and for the numerical investigation of a flow in a finite cylinder with a rotating end face.

Dynamics of linear polymers in dilute solutions

We present an exactly soluble Rouse-like model of the linear polymer chain dynamics in which the effects of solvent molecule dynamics and ultrasonic absorption are treated. Calculations for the relaxation time spectra, total intrinsic viscosity [ η T( ω)], intrinsic viscosity [ η( ω)], elastic modulus G( ω) and specific heat capacity C( ω) of the polymer are presented in the free-draining limit. The calculations were carried out according to the configuration interaction method currently used in quantum mechanics. The relaxation time spectrum corresponding to dynamics of low frequency modes shows a Rouse-like character, whereas the relaxation time spectrum associated with dynamics of moderate frequency modes is narrower. The behaviour of the intrinsic viscosity [ η( ω)] and elastic modulus G( ω) are shown to be represented by the model within the low frequency range. In the moderate- and high-frequency regions, [ η( ω)] drops to zero and [ η T( ω)] reaches a plateau value equal to the sum of both the single bead intrinsic viscosity [ η N] and the effective solvent intrinsic viscosity [ η eff]. Behaviour of the specific heat capacity C( ω) is shown to be represented by the model at acoustic frequency region. The model is shown to be Rouse-like and representative for the description of ultrasonic absorption studies.