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A special issue of Polymers (ISSN 2073-4360).

Deadline for manuscript submissions: closed (25 May 2018) | Viewed by 55004

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Prof. Dr. Roland G. Winkler

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Theoretical Soft Matter and Biophysics, Institute for Advanced Simulation, D-52425 Jülich, Germany
Interests: structure, dynamics, rheology of complex fluids (DNA, ultrasoft colloids, flexible and semiflexible polymers, actin filaments); dynamics of soft matter in microfluidic devices; polyelectrolytes; polyelectrolyte-colloid complexation; non-equilibrium phenomena; hydrodynamics; molecular dynamics simulations; mesoscale hydrodynamic simulations; coarse-grained simulations

Special Issue Information

Dear Colleagues,

There is a long-standing interest and drive to unravel the dynamical properties of long polymer chains. The driving force is, on the one hand, of fundamental importance for synthetic polymers in technical applications combined with novel and advanced microscale devices. On the other hand, biopolymers, such as DNA, proteins, or chainlike assemblies of proteins, e.g., actin filaments, are fundamental for living organisms. By combined experimental and theoretical efforts, major progress in elucidating the dynamical properties of polymers in melts and solution has been achieved over the last few decades. However, new synthetic polymeric materials, such as branched and hyper-branched polymers and mixtures of various kinds of polymer architectures, yield new material properties determined by the complex dynamical interplay of the underlaying individual components. Even more, the properties of polymers in presence of an active environment has recently come into focus, where non-thermal and correlated fluctuations determine their dynamical behaviors.

This Special Issue of Polymers is indented to cover a wide range of aspects of the dynamics of polymers from experiments, simulations, and theory. Various types of polymers are of interest: flexible and semiflexible linear chains, branched, ring, and polymer networks or gels. Their dynamical aspects in melts, solutions, and in mixtures of various architectures may be addressed. Moreover, studies on the dynamics of polymers under nonequilibrium conditions, e.g., under flow, confinement, or exposed to external stimuli, fields, or an active environment are welcome. Preferably, contributions focusing on fundamental aspects, highlighting the current state-of-the-art—specifically—possible applications. Both original contributions and brief reviews are welcome.

Prof. Dr. Roland Winkler
Guest Editor

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Keywords

flexible, semiflexible polymers
ring, branched polymers
polymer melts, solutions, and networks
mixtures
entanglements
hydrodynamic interactions
white and colored noise
biopolymers
flow fields
nonequilibrium dynamics
rheology
experiments
theory
simulations

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Published Papers (12 papers)

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Research

5 pages, 692 KiB

Open AccessArticle

Polymer Chain Mobility under Shear—A Rheo-NMR Investigation

by Brigitte Wiesner, Benjamin Kohn, Mandy Mende and Ulrich Scheler

Polymers 2018, 10(11), 1231; https://doi.org/10.3390/polym10111231 - 7 Nov 2018

Cited by 7 | Viewed by 3564

Abstract

The local dynamics in polymer melts and the impact of external shear in a Couette geometry have been investigated using rheological nuclear magnetic resonance (NMR). The spin-spin relaxation time, T₂, which is sensitive to chain-segment motion, has been measured as a function of shear rate for two samples of poly(dimethylsiloxane). For the low-molecular-weight sample, a mono-exponential decay is observed, which becomes slightly faster with shear, indicating restrictions of the polymer chain motion. For the high-weight sample, a much faster bi-exponential decay is observed, indicative of entanglements. Both components in this decay become longer with shear. This implies that the free polymer segments between entanglements become effectively longer as a result of shear. Full article

(This article belongs to the Special Issue Polymer Dynamics)

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11 pages, 1981 KiB

Open AccessArticle

Investigation of the Propagation of Electrical Trees in a Polymer Matrix in the Corona Condition

by Chunyu Shang, Hui Sun and Yongqin Hao

Polymers 2018, 10(9), 984; https://doi.org/10.3390/polym10090984 - 4 Sep 2018

Cited by 4 | Viewed by 2820

Abstract

In a corona environment, the initiation and propagation of electrical trees in a polymer matrix originate from the field enhancement effect. Driven by the macroscopic alternating electric field, a weak alternating current (AC) was passed through the decomposition channel of an electrical tree, and a small amount of alternating electric quantity was present on the tip of the electrical tree, resulting in an enhanced local electric field around the tip of the electrical tree. The emissions of electrons accelerated in the enhanced local electric field resulted in the decomposition of the polymer material, stimulating the propagation of the electrical tree. When inorganic nano-particles with high corona resistibility were introduced into the polymer matrix, the nano-particles were aggregately deposited as the polymer material decomposed. The decomposition channel of the electrical tree was blocked and the current passing through the decomposition channel was shut off, eliminating the enhanced local electric field. As a result, the propagation of electrical trees was restrained and an improved corona resistibility was achieved for the polymer/nano-particles composite material. Full article

(This article belongs to the Special Issue Polymer Dynamics)

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13 pages, 3529 KiB

Open AccessArticle

Viscoelastic Properties of Unentangled Multicyclic Polystyrenes

by Zhi-Chao Yan, Md. D. Hossain, Michael J. Monteiro and Dimitris Vlassopoulos

Polymers 2018, 10(9), 973; https://doi.org/10.3390/polym10090973 - 1 Sep 2018

Cited by 10 | Viewed by 4829

Abstract

We report on the viscoelastic properties of linear, monocyclic, and multicyclic polystyrenes with the same low molecular weight. All polymers investigated were found to exhibit unentangled dynamics. For monocyclic polymers without inner loops, a cyclic-Rouse model complemented by the contribution of unlinked chains (whose fraction was determined experimentally) captured the observed rheological response. On the other hand, multicyclic polymers with inner loops were shown to follow a hierarchical cyclic-Rouse relaxation with the outer loops relaxing first, followed by the inner loop relaxation. The influence of unlinked linear chains was less significant in multicyclic polymers with inner loops. The isofrictional zero-shear viscosity decreased with increasing number of constrained segments on the coupling sites, which was attributed to the decreasing loop size and the dilution effect due to the hierarchical relaxation. Full article

(This article belongs to the Special Issue Polymer Dynamics)

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17 pages, 2520 KiB

Open AccessArticle

Hydrodynamic Shear Effects on Grafted and Non-Grafted Collapsed Polymers

by Richard Schwarzl and Roland R. Netz

Polymers 2018, 10(8), 926; https://doi.org/10.3390/polym10080926 - 18 Aug 2018

Cited by 10 | Viewed by 4402

Abstract

We study collapsed homo-polymeric molecules under linear shear flow conditions using hydrodynamic Brownian dynamics simulations. Tensile force profiles and the shear-rate-dependent globular-coil transition for grafted and non-grafted chains are investigated to shine light on the different unfolding mechanisms. The scaling of the critical shear rate, at which the globular-coil transition takes place, with the monomer number is inverse for the grafted and non-grafted scenarios. This implicates that for the grafted scenario, larger chains have a decreased critical shear rate, while for the non-grafted scenario higher shear rates are needed in order to unfold larger chains. Protrusions govern the unfolding transition of non-grafted polymers, while for grafted polymers, the maximal tension appears at the grafted end. Full article

(This article belongs to the Special Issue Polymer Dynamics)

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18 pages, 998 KiB

Open AccessArticle

Efficient Determination of Slip-Link Parameters from Broadly Polydisperse Linear Melts

by Néstor E. Valadez-Pérez, Konstantin Taletskiy, Jay D. Schieber and Maksim Shivokhin

Polymers 2018, 10(8), 908; https://doi.org/10.3390/polym10080908 - 12 Aug 2018

Cited by 10 | Viewed by 4718

Abstract

We investigate the ability of a coarse-grained slip-link model and a simple double reptation model to describe the linear rheology of polydisperse linear polymer melts. Our slip-link model is a well-defined mathematical object that can describe the equilibrium dynamics and non-linear rheology of flexible polymer melts with arbitrary polydispersity and architecture with a minimum of inputs: the molecular weight of a Kuhn step, the entanglement activity, and Kuhn step friction. However, this detailed model is computationally expensive, so we also examine predictions of the cheaper double reptation model, which is restricted to only linear rheology near the terminal zone. We report the storage and loss moduli for polydisperse polymer melts and compare with experimental measurements from small amplitude oscillatory shear. We examine three chemistries: polybutadiene, polypropylene and polyethylene. We also use a simple double reptation model to estimate parameters for the slip-link model and examine under which circumstances this simplified model works. The computational implementation of the slip-link model is accelerated with the help of graphics processing units, which allow us to simulate in parallel large ensembles made of up to 50,000 chains. We show that our simulation can predict the dynamic moduli for highly entangled polymer melts over nine decades of frequency. Although the double reptation model performs well only near the terminal zone, it does provide a convenient and inexpensive way to estimate the entanglement parameter for the slip-link model from polydisperse data. Full article

(This article belongs to the Special Issue Polymer Dynamics)

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21 pages, 5708 KiB

Open AccessArticle

Rotation Dynamics of Star Block Copolymers under Shear Flow

by Diego Jaramillo-Cano, Christos N. Likos and Manuel Camargo

Polymers 2018, 10(8), 860; https://doi.org/10.3390/polym10080860 - 3 Aug 2018

Cited by 5 | Viewed by 4024

Abstract

Star block-copolymers (SBCs) are macromolecules formed by a number of diblock copolymers anchored to a common central core, being the internal monomers solvophilic and the end monomers solvophobic. Recent studies have demonstrated that SBCs constitute self-assembling building blocks with specific softness, functionalization, shape and flexibility. Depending on different physical and chemical parameters, the SBCs can behave as flexible patchy particles. In this paper, we study the rotational dynamics of isolated SBCs using a hybrid mesoscale simulation technique. We compare three different approaches to analyze the dynamics: the laboratory frame, the non-inertial Eckart’s frame and a geometrical approximation relating the conformation of the SBC to the velocity profile of the solvent. We find that the geometrical approach is adequate when dealing with very soft systems, while in the opposite extreme, the dynamics is best explained using the laboratory frame. On the other hand, the Eckart frame is found to be very general and to reproduced well both extreme cases. We also compare the rotational frequency and the kinetic energy with the definitions of the angular momentum and inertia tensor from recent publications. Full article

(This article belongs to the Special Issue Polymer Dynamics)

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19 pages, 9287 KiB

Open AccessArticle

A Comparative Study of Intramolecular Mobility of Single Siloxane and Carbosilane Dendrimers via Molecular Dynamics Simulations

by Andrey O. Kurbatov, Nikolay K. Balabaev, Mikhail A. Mazo and Elena Yu. Kramarenko

Polymers 2018, 10(8), 838; https://doi.org/10.3390/polym10080838 - 30 Jul 2018

Cited by 10 | Viewed by 4785

Abstract

A comparative analysis of intramolecular dynamics of four types of isolated dendrimers from the fourth to the seventh generations belonging to the siloxane and carbosilane families, differing in spacer length, core functionality, and the type of chemical bonds, has been performed via atomic molecular dynamics simulations. The average radial and angular positions of all Si branching atoms of various topological layers within the dendrimer interior, as well as their variations, have been calculated, and the distributions of the relaxation times of their radial and angular motions have been found. It has been shown that the dendrons of all the dendrimers elongate from the center and decrease in a solid angle with an increasing generation number. The characteristic relaxation times of both angular and radial motions of Si atoms are of the order of a few nanoseconds, and they increase with an increasing generation number and decrease with temperature, with the angular relaxation times being larger than the radial ones. The relaxation times in the carbosilanes are larger than those in the siloxanes. The rotational angle dynamics of the carbosilane dendrimers show that the chain bending is mainly realized via trans-gauche transitions in the Si branching bonds. Full article

(This article belongs to the Special Issue Polymer Dynamics)

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18 pages, 4137 KiB

Open AccessArticle

Active Brownian Filamentous Polymers under Shear Flow

by Aitor Martín-Gómez, Gerhard Gompper and Roland G. Winkler

Polymers 2018, 10(8), 837; https://doi.org/10.3390/polym10080837 - 30 Jul 2018

Cited by 27 | Viewed by 5391

Abstract

The conformational and rheological properties of active filaments/polymers exposed to shear flow are studied analytically. Using the continuous Gaussian semiflexible polymer model extended by the activity, we derive analytical expressions for the dependence of the deformation, orientation, relaxation times, and viscosity on the persistence length, shear rate, and activity. The model yields a Weissenberg-number dependent shear-induced deformation, alignment, and shear thinning behavior, similarly to the passive counterpart. Thereby, the model shows an intimate coupling between activity and shear flow. As a consequence, activity enhances the shear-induced polymer deformation for flexible polymers. For semiflexible polymers/filaments, a nonmonotonic deformation is obtained because of the activity-induced shrinkage at moderate and swelling at large activities. Independent of stiffness, activity-induced swelling facilitates and enhances alignment and shear thinning compared to a passive polymer. In the asymptotic limit of large activities, a polymer length- and stiffness-independent behavior is obtained, with universal shear-rate dependencies for the conformations, dynamics, and rheology. Full article

(This article belongs to the Special Issue Polymer Dynamics)

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13 pages, 811 KiB

Open AccessArticle

Analysis of the Models of Motion of Aqueous Solutions of Polymers on the Basis of Their Exact Solutions

by Oxana A. Frolovskaya and Vladislav V. Pukhnachev

Polymers 2018, 10(6), 684; https://doi.org/10.3390/polym10060684 - 19 Jun 2018

Cited by 17 | Viewed by 3422

Abstract

The qualitative properties of solutions of a hereditary model of motion of aqueous solutions of polymers, its modification in the limiting case of short relaxation times, and a similar second grade fluid model are studied. Unsteady shear flows are considered. In the first case, their properties are similar to those of motion of a usual viscous fluid. Other models can include weak discontinuities, which are retained in the course of fluid motion. Exact solutions are found by using the group analysis of the examined systems of equations. These solutions describe the fluid motion in a gap between coaxial rotating cylinders, the stagnation point flow, and the motion in a half-space induced by plane rotation (analog of the Karman vortex). The problem of motion of an aqueous solution of a polymer in a cylindrical tube under the action of a streamwise pressure gradient is considered. In this case, a flow with straight-line trajectories is possible (analog of the Hagen-Poiseuille flow). In contrast to the latter, however, the pressure in the flow considered here depends on all three spatial variables. Full article

(This article belongs to the Special Issue Polymer Dynamics)

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15 pages, 6143 KiB

Open AccessArticle

Microflow Mechanism of Oil Displacement by Viscoelastic Hydrophobically Associating Water-Soluble Polymers in Enhanced Oil Recovery

by Huiying Zhong, Yuanyuan Li, Weidong Zhang, Hongjun Yin, Jun Lu and Daizong Guo

Polymers 2018, 10(6), 628; https://doi.org/10.3390/polym10060628 - 7 Jun 2018

Cited by 34 | Viewed by 5318

Abstract

Polymer flooding plays an important role in enhanced oil recovery (EOR), particularly in China, where partially hydrolyzed polyacrylamide (HPAM) and hydrophobically associating water-soluble polymers (HAWP) are used in onshore and offshore reservoirs, respectively. Many researchers have highlighted the elasticity of HPAM, which can be used to improve the sweep efficiency, i.e., the ratio of the area swept by an injected fluid to the oil area. On the other hand, fewer studies exist on the elasticity of HAWP. In this study, we investigate the flow of HAWP and Xanthan solutions with identical viscosities in core experiments in terms of elasticity; results reveal that the HAWP can produce shear thickening in the core. The constitutive equation for the HAWP can be obtained using the simulation results matched with the experimental data. On the basis of these experiments, we established a two-phase flow model of a polymer and oil, including the continuity, momentum, constitutive, and phase equations. The volume-of-fluid (VOF) method was used to track the interface between the two phases. A complex pore model was established based on the glass-etched model used in the experiment. We used the OpenFOAM platform to solve the mathematical model. The saturation, pressure, and stress tensor distributions were obtained. The results show that the displacement efficiency increased as the elasticity of the polymer increased; accordingly, the elasticity can enlarge the sweep area and decrease the residual oil saturation. As the elasticity increases, the stresses (the first normal stress, second normal stress, and shear stress) increase. Finally, the results obtained in this study can be used as a guideline in polymer design, screening, and optimization in the polymer flooding oilfields. Full article

(This article belongs to the Special Issue Polymer Dynamics)

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15 pages, 641 KiB

Open AccessArticle

Flow Behavior of Chain and Star Polymers and Their Mixtures

by Deepika Srivastva and Arash Nikoubashman

Polymers 2018, 10(6), 599; https://doi.org/10.3390/polym10060599 - 29 May 2018

Cited by 13 | Viewed by 6318

Abstract

Star-shaped polymers show a continuous change of properties from flexible linear chains to soft colloids, as the number of arms is increased. To investigate the effect of macromolecular architecture on the flow properties, we employ computer simulations of single chain and star polymers as well as of their mixtures under Poiseuille flow. Hydrodynamic interactions are incorporated through the multi-particle collision dynamics (MPCD) technique, while a bead-spring model is used to describe the polymers. For the ultradilute systems at rest, the polymers are distributed uniformly in the slit channel, with a weak dependence on their number of arms. Once flow is applied, however, we find that the stars migrate much more strongly towards the channel center as the number of arms is increased. In the star-chain mixtures, we find a flow-induced separation between stars and chains, with the stars located in the channel center and the chains closer to the walls. In order to identify the origin of this flow-induced partitioning, we conduct additional simulations without hydrodynamic interactions, and find that the observed cross-stream migration originates from a combination of wall-induced hydrodynamic lift forces and viscoelastic effects. The results from our study give valuable insights for designing microfluidic devices for separating polymers based on their architecture. Full article

(This article belongs to the Special Issue Polymer Dynamics)

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18 pages, 3537 KiB

Open AccessArticle

Tumbling-Snake Model for Polymeric Liquids Subjected to Biaxial Elongational Flows with a Focus on Planar Elongation

by Pavlos S. Stephanou and Martin Kröger

Polymers 2018, 10(3), 329; https://doi.org/10.3390/polym10030329 - 16 Mar 2018

Cited by 6 | Viewed by 4432

Abstract

We have recently solved the tumbling-snake model for concentrated polymer solutions and entangled melts in the presence of both steady-state and transient shear and uniaxial elongational flows, supplemented by a variable link tension coefficient. Here, we provide the transient and stationary solutions of the tumbling-snake model under biaxial elongation both analytically, for small and large elongation rates, and via Brownian dynamics simulations, for the case of planar elongational flow over a wide range of rates, times, and the model parameters. We show that both the steady-state and transient first planar viscosity predictions are similar to their uniaxial counterparts, in accord with recent experimental data. The second planar viscosity seems to behave in all aspects similarly to the shear viscosity, if shear rate is replaced by elongation rate. Full article

(This article belongs to the Special Issue Polymer Dynamics)

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