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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 (31 January 2022) | Viewed by 18611

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Dr. Masoud Jabbari

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Guest Editor

Department of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester M13 9PL, UK
Interests: CFD; flow in porous media; rheology; functional polymers; 3D printing of polymers

Special Issue Information

Dear Colleagues,

This Special Issue is inviting original research papers as well as subjective reviews focused on improved numerical techniques and applied computer-aided simulations in all areas related to complex fluids. The Special Issue particularly welcomes research papers that use a combination of modelling, theory, and simulation to study systems that are complex due to the rheology of fluids (i.e., ceramic pastes, polymer solutions and melts, colloidal suspensions, emulsions, foams, nanofluids, etc.) and multiphysics phenomena in which the interactions of various effects (thermal, chemical, electric, or mechanical) lead to complex dynamics. The area of applications spans around materials processing, manufacturing, and biology. Topics of interest for publication include, but are not limited to:

Materials processing: micro-/macro-mixing of powders, melts, solutions and foams
Manufacturing: casting, extrusion, calendaring, injection moulding, 3D printing
Biological application: microfluidics, nano-/micro-droplets, haemodynamics
Emerging areas: LBM, SPH, FSI

Dr. Masoud Jabbari
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

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Keywords

Complex fluids
Rheology
Modelling and simulations
Materials processing
Extrusion
3D printing
Microfluidics
Emerging areas (LBM, SPH and FSI)

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Published Papers (6 papers)

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Research

33 pages, 1659 KiB

Open AccessArticle

Liquid-Crystal Ordering and Microphase Separation in the Lamellar Phase of Rod-Coil-Rod Triblock Copolymers. Molecular Theory and Computer Simulations

by Mikhail A. Osipov, Maxim V. Gorkunov, Alexander A. Antonov, Anatoly V. Berezkin and Yaroslav V. Kudryavtsev

Polymers 2021, 13(19), 3392; https://doi.org/10.3390/polym13193392 - 2 Oct 2021

Cited by 2 | Viewed by 2134

Abstract

A molecular model of the orientationally ordered lamellar phase exhibited by asymmetric rod-coil-rod triblock copolymers has been developed using the density-functional approach and generalizing the molecular-statistical theory of rod-coil diblock copolymers. An approximate expression for the free energy of the lamellar phase has been obtained in terms of the direct correlation functions of the system, the Flory-Huggins parameter and the Maier-Saupe orientational interaction potential between rods. A detailed derivation of several rod-rod and rod-coil density-density correlation functions required to evaluate the free energy is presented. The orientational and translational order parameters of rod and coil segments depending on the temperature and triblock asymmetry have been calculated numerically by direct minimization of the free energy. Different structure and ordering of the lamellar phase at high and low values of the triblock asymmetry is revealed and analyzed in detail. Asymmetric rod-coil-rod triblock copolymers have been simulated using the method of dissipative particle dynamics in the broad range of the Flory-Huggins parameter and for several values of the triblock asymmetry. It has been found that the lamellar phase appears to be the most stable one at strong segregation. The density distribution of the coil segments and the segments of the two different rods have been determined for different values of the segregation strength. The simulations confirm the existence of a weakly ordered lamellar phase predicted by the density-functional theory, in which the short rods separate from the long ones and are characterized by weak positional ordering. Full article

(This article belongs to the Special Issue Modelling and Simulation of Polymers)

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21 pages, 4488 KiB

Open AccessArticle

Unravelling Constant pH Molecular Dynamics in Oligopeptides with Explicit Solvation Model

by Cristian Privat, Sergio Madurga, Francesc Mas and Jaime Rubio-Martinez

Polymers 2021, 13(19), 3311; https://doi.org/10.3390/polym13193311 - 28 Sep 2021

Viewed by 2438

Abstract

An accurate description of the protonation state of amino acids is essential to correctly simulate the conformational space and the mechanisms of action of proteins or other biochemical systems. The pH and the electrochemical environments are decisive factors to define the effective pKa of amino acids and, therefore, the protonation state. However, they are poorly considered in Molecular Dynamics (MD) simulations. To deal with this problem, constant pH Molecular Dynamics (cpHMD) methods have been developed in recent decades, demonstrating a great ability to consider the effective pKa of amino acids within complex structures. Nonetheless, there are very few studies that assess the effect of these approaches in the conformational sampling. In a previous work of our research group, we detected strengths and weaknesses of the discrete cpHMD method implemented in AMBER when simulating capped tripeptides in implicit solvent. Now, we progressed this assessment by including explicit solvation in these peptides. To analyze more in depth the scope of the reported limitations, we also carried out simulations of oligopeptides with distinct positions of the titratable amino acids. Our study showed that the explicit solvation model does not improve the previously noted weaknesses and, furthermore, the separation of the titratable amino acids in oligopeptides can minimize them, thus providing guidelines to improve the conformational sampling in the cpHMD simulations. Full article

(This article belongs to the Special Issue Modelling and Simulation of Polymers)

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18 pages, 5413 KiB

Open AccessArticle

Analysis of Bubble Growth in Supercritical CO₂ Extrusion Foaming Polyethylene Terephthalate Process Based on Dynamic Flow Simulation

by Shun Yao, Yichong Chen, Yijie Ling, Dongdong Hu, Zhenhao Xi and Ling Zhao

Polymers 2021, 13(16), 2799; https://doi.org/10.3390/polym13162799 - 20 Aug 2021

Cited by 13 | Viewed by 3213

Abstract

Bubble growth in the polymer extrusion foaming process occurs under a dynamic melt flow. For non-Newtonian fluids, this work successfully coupled the dynamic melt flow simulation with the bubble growth model to realize bubble growth predictions in an extrusion flow. The initial thermophysical properties and dynamic rheological property distribution at the cross section of the die exit were calculated based on the finite element method. It was found that dynamic rheological properties provided a necessary solution for predicting bubble growth during the supercritical CO₂ polyethylene terephthalate (PET) extrusion foaming process. The introduction of initial melt stress could effectively inhibit the rapid growth of bubbles and reduce the stable size of bubbles. However, the initial melt stress was ignored in previous work involving bubble growth predictions because it was not available. The simulation results based on the above theoretical model were consistent with the evolution trends of cell morphology and agreed well with the actual experimental results. Full article

(This article belongs to the Special Issue Modelling and Simulation of Polymers)

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10 pages, 25833 KiB

Open AccessArticle

Self-Stable Precipitation Polymerization Molecular Entanglement Effect and Molecular Weight Simulations and Experiments

by Jiali Qu, Yi Gao and Wantai Yang

Polymers 2021, 13(14), 2243; https://doi.org/10.3390/polym13142243 - 8 Jul 2021

Cited by 1 | Viewed by 2404

Abstract

In this paper, we developed a reactive molecular dynamics (RMD) scheme to simulate the Self-Stable Precipitation (SP) polymerization of 1-pentene and cyclopentene (C5) with maleic anhydride (MAn) in an all-atom resolution. We studied the chain propagation mechanism by tracking the changes in molecular conformation and analyzing end-to-end distance and radius of gyration. The results show that the main reason of chain termination in the reaction process was due to intramolecular cyclic entanglement, which made the active center wrapped in the center of the globular chain. After conducting the experiment in the same condition with the simulation, we found that the distribution trend and peak value of the molecular-weight-distribution curve in the simulation were consistent with experimental results. The simulated number average molecular weight (Mn) and weight average molecular weight (Mw) were in good agreement with the experiment. Moreover, the simulated molecular polydispersity index (PDI) for cyclopentene reaction with maleic anhydride was accurate, differing by 0.04 from the experimental value. These show that this model is suitable for C5–maleic anhydride self-stable precipitation polymerization and is expected to be used as a molecular weight prediction tool for other maleic anhydride self-stable precipitation polymerization system. Full article

(This article belongs to the Special Issue Modelling and Simulation of Polymers)

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14 pages, 1151 KiB

Open AccessArticle

Non-Newtonian Droplet Generation in a Cross-Junction Microfluidic Channel

by Maryam Fatehifar, Alistair Revell and Masoud Jabbari

Polymers 2021, 13(12), 1915; https://doi.org/10.3390/polym13121915 - 9 Jun 2021

Cited by 18 | Viewed by 3883

Abstract

A two-dimensional CFD model based on volume-of-fluid (VOF) is introduced to examine droplet generation in a cross-junction microfluidic using an open-source software, OpenFOAM together with an interFoam solver. Non-Newtonian power-law droplets in Newtonian liquid is numerically studied and its effect on droplet size and detachment time in three different regimes, i.e., squeezing, dripping and jetting, are investigated. To understand the droplet formation mechanism, the shear-thinning behaviour was enhanced by increasing the polymer concentrations in the dispersed phase. It is observed that by choosing a shear-dependent fluid, droplet size decreases compared to Newtonian fluids while detachment time increases due to higher apparent viscosity. Moreover, the rheological parameters—n and K in the power-law model—impose a considerable effect on the droplet size and detachment time, especially in the dripping and jetting regimes. Those parameters also have the potential to change the formation regime if the capillary number (

C a

) is high enough. This work extends the understanding of non-Newtonian droplet formation in microfluidics to control the droplet characteristics in applications involving shear-thinning polymeric solutions. Full article

(This article belongs to the Special Issue Modelling and Simulation of Polymers)

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12 pages, 3948 KiB

Open AccessArticle

Numerical Simulation of a Core–Shell Polymer Strand in Material Extrusion Additive Manufacturing

by Hamid Narei, Maryam Fatehifar, Ashley Howard Malt, John Bissell, Mohammad Souri, Mohammad Nasr Esfahani and Masoud Jabbari

Polymers 2021, 13(3), 476; https://doi.org/10.3390/polym13030476 - 2 Feb 2021

Cited by 13 | Viewed by 3756

Abstract

Material extrusion additive manufacturing (ME-AM) techniques have been recently introduced for core–shell polymer manufacturing. Using ME-AM for core–shell manufacturing offers improved mechanical properties and dimensional accuracy over conventional 3D-printed polymer. Operating parameters play an important role in forming the overall quality of the 3D-printed manufactured products. Here we use numerical simulations within the framework of computation fluid dynamics (CFD) to identify the best combination of operating parameters for the 3D printing of a core–shell polymer strand. The objectives of these CFD simulations are to find strands with an ultimate volume fraction of core polymer. At the same time, complete encapsulations are obtained for the core polymer inside the shell one. In this model, the deposition flow is controlled by three dimensionless parameters: (i) the diameter ratio of core material to the nozzle,

d / D

; (ii) the normalised gap between the extruder and the build plate,

t / D

; (iii) the velocity ratio of the moving build plate to the average velocity inside the nozzle,

V / U

. Numerical results of the deposited strands’ cross-sections demonstrate the effects of controlling parameters on the encapsulation of the core material inside the shell and the shape and size of the strand. Overall we find that the best operating parameters are a diameter ratio of

d / D = 0.7

, a normalised gap of

t / D = 1

, and a velocity ratio of

V / U = 1

. Full article

(This article belongs to the Special Issue Modelling and Simulation of Polymers)

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