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Structural Rheology of Polymer Melts, Solutions and Compositions on Their Base

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A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Physics and Theory".

Deadline for manuscript submissions: closed (30 September 2022) | Viewed by 17396

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Special Issue Editor

Prof. Dr. Valery Kulichikhin

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Guest Editor

Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, Russia
Interests: polymer physical chemistry; colloid chemistry; rheology; polymer processing; fiber spinning; additive technologies
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Rheology is the branch of sciences dealing with considering the response of polymer system on action of mechanical field. Knowledge of this response is important for both: polymer processing and polymer physics. In the first case, rheological parameters play the key role in estimation of processing regimes at production of plastics, films, fibers, composites, etc. In the second case, rheology “feels” structural transformations occurring with macromolecular conformations, orientation in space, interaction between them and other species presenting in melts or solutions, including micro- and nanoparticles (emulsions and suspensions), formation of aggregates and associates, as well as phase and relaxation transitions. In spite of the fact, that rheology is not structural method, it indicates on structural changes and sometimes combined with direct physical methods: optical, neutron-, X-ray-scattering, etc., and this combination reinforces tools allowing us to understand dipper structure and morphology of the nascent systems and their evolution at flow. The suggested SI is devoted to such kinds of tasks where rheology serves as an indicator of structural transformations appearing under action of stresses and strains.

Prof. Dr. Valery Kulichikhin
Guest Editor

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Keywords

polymer melts
solutions and composites
flow curves
dynamic moduli
morphology and structure at flow
rheo-X-ray

Published Papers (6 papers)

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Research

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15 pages, 6232 KiB

Open AccessArticle

Rheological, Surface Tension and Conductivity Insights on the Electrospinnability of Poly(lactic-co-glycolic acid)-hyaluronic Acid Solutions and Their Correlations with the Nanofiber Morphological Characteristics

by Ziqian Liu, Seeram Ramakrishna, Ifty Ahmed, Chris Rudd and Xiaoling Liu

Polymers 2022, 14(20), 4411; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14204411 - 19 Oct 2022

Cited by 2 | Viewed by 1802

Abstract

In this study, solutions were prepared with fixed concentrations of hyaluronic acid (HA) but varied concentrations of poly (lactic-co-glycolic acid) (PLGA) to emphasize the effects of PLGA concentration and HA addition on solution properties and to further evaluate their electrospinning performance. The dependence of specific viscosity on PLGA concentration was studied to determine the concentration regimes and evaluate the critical concentration (C_e) for successful fiber generation. The C_e of PLGA solutions is 12.07% compared to 10.09% for PLGA-HA solutions. Blending with HA results in a lower concentration dependence and better consistency to the theoretical scaling mechanisms due to the additional topological constrains, which thus result in more chain entanglements. Solutions in semi-dilute entangled regimes show the crossover of complex moduli, verifying the stable and reliable entanglement network. Higher concentrations and HA addition both led to lower crossover frequencies and, thus, a longer relaxation time. The effects of a higher PLGA concentration and HA addition on the surface tension were not evident. However, the HA addition significantly improved the solution conductivity up to three times in the pure PLGA solutions due to its polyelectrolyte nature. Defect-free and uniform nanofibers were generated from 35% to 40% of the PLGA-HA solutions, yet fibers with bead-on-string structures were produced from all studied pure PLGA solutions. Such solution characteristics and parametric correlations can provide predictive insights on tailoring the morphological characteristics of nanofibers for specific applications. Full article

(This article belongs to the Special Issue Structural Rheology of Polymer Melts, Solutions and Compositions on Their Base)

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21 pages, 7441 KiB

Open AccessArticle

Modelling of Elongational Flow of HDPE Melts by Hierarchical Multi-Mode Molecular Stress Function Model

by Leslie Poh, Esmaeil Narimissa and Manfred H. Wagner

Polymers 2021, 13(19), 3217; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13193217 - 23 Sep 2021

Cited by 5 | Viewed by 2164

Abstract

The transient elongational data set obtained by filament-stretching rheometry of four commercial high-density polyethylene (HDPE) melts with different molecular characteristics was reported by Morelly and Alvarez [Rheologica Acta 59, 797–807 (2020)]. We use the Hierarchical Multi-mode Molecular Stress Function (HMMSF) model of Narimissa and Wagner [Rheol. Acta 54, 779–791 (2015), and J. Rheology 60, 625–636 (2016)] for linear and long-chain branched (LCB) polymer melts to analyze the extensional rheological behavior of the four HDPEs with different polydispersity and long-chain branching content. Model predictions based solely on the linear-viscoelastic spectrum and a single nonlinear parameter, the dilution modulus

G_{D}

for extensional flows reveals good agreement with elongational stress growth data. The relationship of dilution modulus

G_{D}

to molecular characteristics (e.g., polydispersity index (PDI), long-chain branching index (LCBI), disengagement time

τ_{d}

) of the high-density polyethylene melts are presented in this paper. A new measure of the maximum strain hardening factor (MSHF) is proposed, which allows separation of the effects of orientation and chain stretching. Full article

(This article belongs to the Special Issue Structural Rheology of Polymer Melts, Solutions and Compositions on Their Base)

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18 pages, 4200 KiB

Open AccessArticle

On the Influence of Viscoelastic Modeling in Fluid Flow Simulations of Gum Acrylonitrile Butadiene Rubber

by Sebastian Stieger, Evan Mitsoulis, Matthias Walluch, Catharina Ebner, Roman Christopher Kerschbaumer, Matthias Haselmann, Mehdi Mostafaiyan, Markus Kämpfe, Ines Kühnert, Sven Wießner and Walter Friesenbichler

Polymers 2021, 13(14), 2323; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13142323 - 15 Jul 2021

Cited by 11 | Viewed by 2607

Abstract

Computational fluid dynamics (CFD) simulation is an important tool as it enables engineers to study different design options without a time-consuming experimental workload. However, the prediction accuracy of any CFD simulation depends upon the set boundary conditions and upon the applied rheological constitutive equation. In the present study the viscoelastic nature of an unfilled gum acrylonitrile butadiene rubber (NBR) is considered by applying the integral and time-dependent Kaye–Bernstein–Kearsley–Zapas (K-BKZ) rheological model. First, exhaustive testing is carried out in the linear viscoelastic (LVE) and non-LVE deformation range including small amplitude oscillatory shear (SAOS) as well as high pressure capillary rheometer (HPCR) tests. Next, three abrupt capillary dies and one tapered orifice die are modeled in Ansys POLYFLOW. The pressure prediction accuracy of the K-BKZ/Wagner model was found to be excellent and insensitive to the applied normal force in SAOS testing as well as to the relation of first and second normal stress differences, provided that damping parameters are fitted to steady-state rheological data. Moreover, the crucial importance of viscoelastic modeling is proven for rubber materials, as two generalized Newtonian fluid (GNF) flow models severely underestimate measured pressure data, especially in contraction flow-dominated geometries. Full article

(This article belongs to the Special Issue Structural Rheology of Polymer Melts, Solutions and Compositions on Their Base)

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12 pages, 28048 KiB

Open AccessArticle

Simulation Approach for Hydrophobicity Replication via Injection Molding

by Tomás Baldi-Boleda, Ehsan Sadeghi, Carles Colominas and Andrés García-Granada

Polymers 2021, 13(13), 2069; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13132069 - 23 Jun 2021

Cited by 4 | Viewed by 2873

Abstract

Nanopattern replication of complex structures by plastic injection is a challenge that requires simulations to define the right processing parameters. Previous work managed to simulate replication for single cavities in 2D and 3D, showing high performance requirements of CPU to simulate periodic trenches in 2D. This paper presents two ways to approach the simulation of replication of complex 3D hydrophobic surfaces. The first approach is based on previous CFD Ansys Fluent and compared to FE based CFD Polyflow software for the analysis of laminar flows typical in polymer processing and glass forming as well as other applications. The results showed that Polyflow was able to reduce computing time from 72 h to only 5 min as desired in the project. Furthermore, simulations carried out with Polyflow showed that higher injection and mold temperature lead to better replication of hydrophobicity in agreement with the experiments. Polyflow simulations are proved to be a good tool to define process parameters such as temperature and cycle times for nanopattern replication. Full article

(This article belongs to the Special Issue Structural Rheology of Polymer Melts, Solutions and Compositions on Their Base)

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10 pages, 4028 KiB

Open AccessArticle

An Experimental Investigation of Viscoelastic Flow in a Contraction Channel

by Wei Wang and Linlin Wang

Polymers 2021, 13(11), 1876; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13111876 - 04 Jun 2021

Cited by 3 | Viewed by 1719

Abstract

In order to assess the predictive capability of the S–MDCPP model, which may describe the viscoelastic behavior of the low-density polyethylene melts, a planar contraction flow benchmark problem is calculated in this investigation. A pressure-stabilized iterative fractional step algorithm based on the finite increment calculus (FIC) method is adopted to overcome oscillations of the pressure field due to the incompressibility of fluids. The discrete elastic viscous stress splitting (DEVSS) technique in combination with the streamline upwind Petrov-Galerkin (SUPG) method are employed to calculate the viscoelastic flow. The equal low-order finite elements interpolation approximations for velocity-pressure-stress variables can be applied to calculate the viscoelastic contraction flows for LDPE melts. The predicted velocities agree well with the experimental results of particle imagine velocity (PIV) method, and the pattern of principal stress difference calculated by the S-MDCPP model has good agreement with the results measured by the flow induced birefringence (FIB) device. Numerical and experimental results show that the S-MDCPP model is capable of accurately capturing the rheological behaviors of branched polymers in complex flow. Full article

(This article belongs to the Special Issue Structural Rheology of Polymer Melts, Solutions and Compositions on Their Base)

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Review

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34 pages, 12225 KiB

Open AccessReview

The Role of Structure in Polymer Rheology: Review

by Valery G. Kulichikhin and Alexander Ya. Malkin

Polymers 2022, 14(6), 1262; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14061262 - 21 Mar 2022

Cited by 19 | Viewed by 5203

Abstract

The review is devoted to the analysis of the current state of understanding relationships among the deformation-induced structure transformations, observed rheological properties, and the occurrence of non-linear effects for polymer liquids (melts, solutions, and composites). Three levels of non-linearity are the base for consideration. The first one concerns changes in the relaxation spectra of viscoelastic liquids, which are responsible for weak non-linear phenomena. The second one refers to the strong non-linearity corresponding to such changes in the structure of a medium that leads to the emergence of a new relaxation state of a matter. Finally, the third one describes the deformation-induced changes in the phase state and/or the occurring of bifurcations and instability in flow and reflects the thermodynamic non-linear behavior. From a structure point of view, a common cause of the non-linear effects is the orientation of macromolecules and changes in intermolecular interaction, while a dominant factor in describing fluid dynamics of polymer liquids is their elasticity. The modern understanding of thixotropic effects, yielding viscoplastic materials, deformation-induced phase transition, and the experimental observations, demonstrating direct correlations between the structure and rheology of polymer liquids, are the main objects for discussion. All these topics are reviewed and discussed mainly on the basis of the latest five-year publications. Full article

(This article belongs to the Special Issue Structural Rheology of Polymer Melts, Solutions and Compositions on Their Base)

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