Polymers

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17 pages, 12503 KiB

Open AccessArticle

Development of a Digital Image Processing- and Machine Learning-Based Approach to Predict the Morphology and Thermal Properties of Polyurethane Foams

by Caglar Celik Bayar

Polymers 2025, 17(7), 928; https://doi.org/10.3390/polym17070928 - 29 Mar 2025

Viewed by 109

Abstract

Polyurethane foams are frequently used to provide thermal insulation. Thanks to the blowing agents used during their synthesis, pores are created in the structure and thermal insulation is achieved through these pores. In this study, five different insulating polyurethane foam samples containing water [...] Read more.

Polyurethane foams are frequently used to provide thermal insulation. Thanks to the blowing agents used during their synthesis, pores are created in the structure and thermal insulation is achieved through these pores. In this study, five different insulating polyurethane foam samples containing water and cyclohexane blowing agents were synthesized. Pore stabilities and their effects on pore neighboring were analyzed computationally (MP2/aug-cc-pVDZ). A digital image processing- and machine learning-based algorithm was developed to predict the mean neighboring effect distances of the produced foams. It was created using the Voronoi tessellation method used for the identification problems in industrial applications. This method showed that there was a close relationship between the calculated Voronoi neighboring effect distances of the samples and their thermal conductivity coefficients. Considering the Voronoi neighboring effect distances proposed in this study, the thermal conductivity coefficient of similar polyurethane foams could be predicted. This method required only a standard mobile phone to capture images of the samples and the algorithm developed using Python (version 3.13.2) programming language. In addition, when compared to the local surface imaging device SEM, it allowed the entire surface to be analyzed faster and at once, without any surface deterioration. Full article

(This article belongs to the Special Issue Computational Modeling and Simulations of Polymers)

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12 pages, 3859 KiB

Open AccessArticle

Chain Size and Knots of Ring Polymers in All-Crossing and Intra-Crossing Melts

by Jiangyang Mo, Jingqiao Guo, Xue Yu, Jianlei Yang, Guodong Hu, Jianhui Xin, Mengxia Yan, Yuan Wang, Yongjie Mo, Yuxi Jia, Lianyong Wu and Yongjin Ruan

Polymers 2025, 17(7), 854; https://doi.org/10.3390/polym17070854 - 23 Mar 2025

Viewed by 206

Abstract

Using dynamic Monte Carlo simulations based on the bond-fluctuation model, we systematically investigated the size and knots of ring polymers in all-crossing systems and intra-crossing systems. Our results demonstrate that the interchain constraint can increase the knotting probability, but does not alter the [...] Read more.

Using dynamic Monte Carlo simulations based on the bond-fluctuation model, we systematically investigated the size and knots of ring polymers in all-crossing systems and intra-crossing systems. Our results demonstrate that the interchain constraint can increase the knotting probability, but does not alter the scaling relationship between knotting probability and chain length for ring polymers in melts. Having established that, we derived the interchain constraint contribution to the free energy of ring polymers in intra-crossing systems based on the knotting probability and obtained the scaling relationship between the size R and chain length N, i.e., R~N^1/6. And, by calculating the mean-squared radius of gyration of ring polymers in intra-crossing systems, we validated these scaling results. Finally, we analyze the size of knotted ring polymers with different types and compare corresponding scaling exponents for size versus chain lengths of ring polymers with different knotting complexities. These results provide fundamental insights into the static properties of ring polymers in melts. Full article

(This article belongs to the Special Issue Computational Modeling and Simulations of Polymers)

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22 pages, 784 KiB

Open AccessArticle

Size-Exclusion Chromatography of Macromolecules: A Brief Tutorial Overview on Fundamentals with Computational Tools for Data Analysis and Determination of Structural Information

by José Ginés Hernández-Cifre, Mar Collado-González, Francisco Guillermo Díaz Baños and José García de la Torre

Polymers 2025, 17(5), 582; https://doi.org/10.3390/polym17050582 - 22 Feb 2025

Viewed by 421

Abstract

Size-exclusion chromatography (SEC) is presently a widely used and very informative technique for the characterization of macromolecules in solution. Beyond the first implementations of SEC—which required cumbersome column calibrations and were mainly intended for the determination of molecular weights—the modern SEC approach involving [...] Read more.

Size-exclusion chromatography (SEC) is presently a widely used and very informative technique for the characterization of macromolecules in solution. Beyond the first implementations of SEC—which required cumbersome column calibrations and were mainly intended for the determination of molecular weights—the modern SEC approach involving multiple detectors (md-SEC) is based on solution properties such as intrinsic viscosity and light scattering. Thus, md-SEC enables the direct and more efficient determination of molecular weights, as well as the determination of relationships between property and molecular weight, which can be quite useful in structural studies. Here, we first present a review of the fundamental aspects of the dilute-solution properties of macromolecules—particularly the differential refractive index, intrinsic viscosity, and scattering-related properties—on which the various detectors involved in md-SEC are based. Then, we developed SECtools, a suite of public-domain, open-source computer programs, which allow for the full analysis of md-SEC chromatograms. These analyses range from just the recorded raw signals (mV) of the detectors to a full determination of molecular weight averages and distributions. The use of these programs is illustrated through experimental studies using various samples. Full article

(This article belongs to the Special Issue Computational Modeling and Simulations of Polymers)

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16 pages, 3165 KiB

Open AccessArticle

A Mixture Fraction Approach to Predict Polymer Burning

by Artem Shaklein, Alexander Karpov, Stanislav Trubachev, Gabriela Morar, Nikita Balobanov and Ekaterina Mitriukova

Polymers 2024, 16(23), 3313; https://doi.org/10.3390/polym16233313 - 27 Nov 2024

Viewed by 561

Abstract

A mixture fraction approach was applied to predict the combustion behavior of polymeric materials. In comparison to the combustion of gaseous mixtures, the presence of solid fuels complicates the description of the combustion. Accurate predictions of burning characteristics can only be achieved through [...] Read more.

A mixture fraction approach was applied to predict the combustion behavior of polymeric materials. In comparison to the combustion of gaseous mixtures, the presence of solid fuels complicates the description of the combustion. Accurate predictions of burning characteristics can only be achieved through the proper resolution of heat and mass transfer between the gas-phase flame and the solid fuel. We focused on a model case of flame spread over a solid fuel surface. Polymethyl methacrylate (PMMA) was selected as a polymeric material. An approach was proposed to account for heat loss from the gas phase to the solid material through calculations of counterflow diffusion flames with the flame positioned closely to the fuel supply. A combination of these solutions was applied to restore temperature and species mass fractions from tabulated chemistry. An analysis of the numerical results from previous studies on flame spread over PMMA, based on one-step combustion reaction and calculating the chemical source term at each time step, demonstrated a monotonic distribution of the mixture fraction in the flame region between the fuel and oxidizer streams. The shape of the flame tip was satisfactorily resolved using the proposed approach that employs a skeletal chemical mechanism for gas-phase combustion consisting of 29 species and 33 reactions. However, the heat flux from the flame to the solid fuel was overpredicted, resulting in higher flame spread rates compared to experimental data and previous calculations. Preliminary results show a promising opportunity for the mixture fraction approach to describe the combustion behavior of polymers. An analysis showed that oversimplifying the heat transfer process in the flame tip area is a main source of prediction inaccuracies. Multidimensional heat transfer has to be properly incorporated into a tabulated chemistry approach. Several potential directions for future work have been outlined. Full article

(This article belongs to the Special Issue Computational Modeling and Simulations of Polymers)

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16 pages, 8036 KiB

Open AccessArticle

Damage Investigation in PMMA Polymer: Experimental and Phase-Field Approaches

by Lotfi Ben Said, Hamdi Hentati, Mondher Wali, Badreddine Ayadi and Muapper Alhadri

Polymers 2024, 16(23), 3304; https://doi.org/10.3390/polym16233304 - 26 Nov 2024

Viewed by 696

Abstract

The prediction of crack patterns is one of the main tasks in the field of fracture mechanics in order to prevent the total damage of various materials, particularly Methyl Methacrylate Polymer (PMMA). The few data in the literature underscores the need for additional [...] Read more.

The prediction of crack patterns is one of the main tasks in the field of fracture mechanics in order to prevent the total damage of various materials, particularly Methyl Methacrylate Polymer (PMMA). The few data in the literature underscores the need for additional experiments on PMMA to analyze the performance of the phase-field approach to predict crack trajectories. The main purpose of this study is to verify the accuracy of the phase-field approach with a staggered scheme, based on spectral decomposition, for predicting crack propagation in PMMA specimens by comparing it with the experimental results presented in this work. Based on the tensile test and SEM analysis, this material exhibits brittle behavior. The numerical approach considers cracks as diffuse damage rather than sharp discontinuities, enabling a more accurate representation of brittle fracture processes. Experimental determination of material properties is used in the development of the numerical model. The main aim of these experiments is to explore how variations in load and specific geometries influence fracture initiation and crack trajectory. Consequently, these experiments will establish a dataset to further validate numerical advancements. Full article

(This article belongs to the Special Issue Computational Modeling and Simulations of Polymers)

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16 pages, 26612 KiB

Open AccessArticle

Prediction of Dielectric Constant in Series of Polymers by Quantitative Structure-Property Relationship (QSPR)

by Estefania Ascencio-Medina, Shan He, Amirreza Daghighi, Kweeni Iduoku, Gerardo M. Casanola-Martin, Sonia Arrasate, Humberto González-Díaz and Bakhtiyor Rasulev

Polymers 2024, 16(19), 2731; https://doi.org/10.3390/polym16192731 - 26 Sep 2024

Cited by 2 | Viewed by 1378

Abstract

This work is devoted to the investigation of dielectric permittivity which is influenced by electronic, ionic, and dipolar polarization mechanisms, contributing to the material’s capacity to store electrical energy. In this study, an extended dataset of 86 polymers was analyzed, and two quantitative [...] Read more.

This work is devoted to the investigation of dielectric permittivity which is influenced by electronic, ionic, and dipolar polarization mechanisms, contributing to the material’s capacity to store electrical energy. In this study, an extended dataset of 86 polymers was analyzed, and two quantitative structure–property relationship (QSPR) models were developed to predict dielectric permittivity. From an initial set of 1273 descriptors, the most relevant ones were selected using a genetic algorithm, and machine learning models were built using the Gradient Boosting Regressor (GBR). In contrast to Multiple Linear Regression (MLR)- and Partial Least Squares (PLS)-based models, the gradient boosting models excel in handling nonlinear relationships and multicollinearity, iteratively optimizing decision trees to improve accuracy without overfitting. The developed GBR models showed high R² coefficients of 0.938 and 0.822, for the training and test sets, respectively. An Accumulated Local Effect (ALE) technique was applied to assess the relationship between the selected descriptors—eight for the GB_A model and six for the GB_B model, and their impact on target property. ALE analysis revealed that descriptors such as TDB09m had a strong positive effect on permittivity, while MLOGP2 showed a negative effect. These results highlight the effectiveness of the GBR approach in predicting the dielectric properties of polymers, offering improved accuracy and interpretability. Full article

(This article belongs to the Special Issue Computational Modeling and Simulations of Polymers)

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23 pages, 7330 KiB

Open AccessArticle

Entropy-Driven Crystallization of Hard Colloidal Mixtures of Polymers and Monomers

by Olia Bouzid, Daniel Martínez-Fernández, Miguel Herranz and Nikos Ch. Karayiannis

Polymers 2024, 16(16), 2311; https://doi.org/10.3390/polym16162311 - 15 Aug 2024

Cited by 1 | Viewed by 1058

Abstract

The most trivial example of self-assembly is the entropy-driven crystallization of hard spheres. Past works have established the similarities and differences in the phase behavior of monomers and chains made of hard spheres. Inspired by the difference in the melting points of the [...] Read more.

The most trivial example of self-assembly is the entropy-driven crystallization of hard spheres. Past works have established the similarities and differences in the phase behavior of monomers and chains made of hard spheres. Inspired by the difference in the melting points of the pure components, we study, through Monte Carlo simulations, the phase behavior of athermal mixtures composed of fully flexible polymers and individual monomers of uniform size. We analyze how the relative number fraction and the packing density affect crystallization and the established ordered morphologies. As a first result, a more precise determination of the melting point for freely jointed chains of tangent hard spheres is extracted. A synergetic effect is observed in the crystallization leading to synchronous crystallization of the two species. Structural analysis of the resulting ordered morphologies shows perfect mixing and thus no phase separation. Due to the constraints imposed by chain connectivity, the local environment of the individual spheres, as quantified by the Voronoi polyhedron, is systematically more spherical and more symmetric compared to that of spheres belonging to chains. In turn, the local environment of the ordered phase is more symmetric and more spherical compared to that of the initial random packing, demonstrating the entropic origins of the phase transition. In general, increasing the polymer content reduces the degree of crystallinity and increases the melting point to higher volume fractions. According to the present findings, relative concentration is another determining factor in controlling the phase behavior of hard colloidal mixtures based on polymers. Full article

(This article belongs to the Special Issue Computational Modeling and Simulations of Polymers)

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24 pages, 11838 KiB

Open AccessArticle

Lagrangian Split-Step Method for Viscoelastic Flows

by Martina Bašić, Branko Blagojević, Branko Klarin, Chong Peng and Josip Bašić

Polymers 2024, 16(14), 2068; https://doi.org/10.3390/polym16142068 - 19 Jul 2024

Cited by 1 | Viewed by 1097

Abstract

This research addresses and resolves current challenges in meshless Lagrangian methods for simulating viscoelastic materials. A split-step scheme, or pressure Poisson reformulation of the Navier–Stokes equations, is introduced for incompressible viscoelastic flows in a Lagrangian context. The Lagrangian differencing dynamics (LDD) method, which [...] Read more.

This research addresses and resolves current challenges in meshless Lagrangian methods for simulating viscoelastic materials. A split-step scheme, or pressure Poisson reformulation of the Navier–Stokes equations, is introduced for incompressible viscoelastic flows in a Lagrangian context. The Lagrangian differencing dynamics (LDD) method, which is a thoroughly validated Lagrangian method for Newtonian and non-Newtonian incompressible flows, is extended to solve the introduced split-step scheme to simulate viscoelastic flows based on the Oldroyd-B constitutive model. To validate and evaluate the new method’s capabilities, the following benchmarks were used: lid-driven cavity flow, droplet impact response, 4:1 planar sudden contraction, and die swelling. These findings highlight the LDD method’s effectiveness in accurately simulating viscoelastic flows and capturing large deformations and memory effects. Even though the extra stress was directly modeled without any regularization approach, the method produced stable simulations for high Weissenberg numbers. The stability and performance of the the Lagrangian numerics for complex temporal evolution of material properties and stress responses encourage its use for industrial problems dealing with polymers. Full article

(This article belongs to the Special Issue Computational Modeling and Simulations of Polymers)

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17 pages, 7439 KiB

Open AccessArticle

Enhancing Polymer Blend Compatibility with Linear and Complex Star Copolymer Architectures: A Monte Carlo Simulation Study with the Bond Fluctuation Model

by Juan J. Freire and Costas Vlahos

Polymers 2024, 16(12), 1626; https://doi.org/10.3390/polym16121626 - 8 Jun 2024

Viewed by 1877

Abstract

A Monte Carlo study of the compatibilization of A/B polymer blends has been performed using the bond fluctuation model. The considered compatibilizers are copolymer molecules composed of A and B blocks. Different types of copolymer structures have been included, namely, linear diblock and [...] Read more.

A Monte Carlo study of the compatibilization of A/B polymer blends has been performed using the bond fluctuation model. The considered compatibilizers are copolymer molecules composed of A and B blocks. Different types of copolymer structures have been included, namely, linear diblock and 4-block alternating copolymers, star block copolymers, miktoarm stars, and zipper stars. Zipper stars are composed of two arms of diblock copolymers arranged in alternate order (AB and BA) from the central unit, along with two homogeneous arms of A and B units. The compatibilization performance has been characterized by analyzing the equilibration of repulsion energy, the simulated scattering intensity obtained with opposite refractive indices for A and B, the profiles along a coordinate axis, the radial distribution functions, and the compatibilizer aggregation numbers. According to the results, linear alternate block copolymers, star block copolymers, and zipper stars exhibit significantly better compatibilization, with zipper stars showing slightly but consistently better performance. Full article

(This article belongs to the Special Issue Computational Modeling and Simulations of Polymers)

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16 pages, 2973 KiB

Open AccessArticle

Geant4 Simulation of Photon- and Neutron-Shielding Capabilities of Biopolymer Blends of Poly(lactic acid) and Poly(hydroxybutyrate)

by Hanan Akhdar and Maryam Alshehri

Polymers 2023, 15(21), 4257; https://doi.org/10.3390/polym15214257 - 29 Oct 2023

Cited by 5 | Viewed by 2015

Abstract

Simulation is used by scientists to imitate a real-life experimental setup in order to save time, costs and effort. Geant4, a toolkit based on the Monte Carlo method, has been widely used in investigating the radiation-shielding properties of different materials. In many recent [...] Read more.

Simulation is used by scientists to imitate a real-life experimental setup in order to save time, costs and effort. Geant4, a toolkit based on the Monte Carlo method, has been widely used in investigating the radiation-shielding properties of different materials. In many recent studies, researchers have focused on polymers and their shielding capabilities. Poly(lactic acid) (PLA) is a widely used biopolymer in many applications due to its excellent mechanical properties. However, it has limitations related to its degree of crystallinity and molecular characteristics, which could be improved through blending with other biodegradable polymers such as poly(hydroxybutyrate) (PHB). Previous published studies have shown that the mechanical properties of such blends can be improved further. In this work, the effect of blending PHB with PLA on the photon- and neutron-shielding capabilities will be investigated using Geant4 over a wide energy range, as well as the effect of doping those blends with metal oxides. The results show that the shielding properties of the polymers are affected by blending with other polymers and by doping the polymer blends with different metal oxides, and they confirm that Geant4 is a very reliable tool that can simulate any material’s shielding properties against photons and neutrons. Full article

(This article belongs to the Special Issue Computational Modeling and Simulations of Polymers)

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11 pages, 6839 KiB

Open AccessArticle

Thermal Reflow Simulation for PMMA Structures with Nonuniform Viscosity Profile

by Fedor Sidorov and Alexander Rogozhin

Polymers 2023, 15(18), 3731; https://doi.org/10.3390/polym15183731 - 11 Sep 2023

Cited by 3 | Viewed by 1660

Abstract

This paper presents a new approach to the simulation of the thermal reflow of e-beam-exposed polymethyl methacrylate (PMMA) taking into account its nonuniform viscosity profile. This approach is based on numerical “soapfilm” modeling of the surface evolution, processed by the free software “Surface [...] Read more.

This paper presents a new approach to the simulation of the thermal reflow of e-beam-exposed polymethyl methacrylate (PMMA) taking into account its nonuniform viscosity profile. This approach is based on numerical “soapfilm” modeling of the surface evolution, processed by the free software “Surface Evolver” in area normalization mode. The PMMA viscosity profile is calculated via the simulation of the exposed PMMA number average molecular weight distribution using the Monte-Carlo method and empirical formulas. The relation between the PMMA viscosity and the mobility of PMMA surface vertices was determined via the thermal reflow simulation for uniform PMMA gratings using analytical and numerical approaches in a wide viscosity range. The agreement between reflowed profiles simulated with these two approaches emphasizes the applicability of “soapfilm” modeling in the simulation of polymer thermal reflow. The inverse mobility of PMMA surface vertices appeared to be proportional to the PMMA viscosity with a high precision. The developed approach enables thermal reflow simulations for complex nonuniform structures, which allows the use of predictable reflow as a stage of 3D microfabrication. Full article

(This article belongs to the Special Issue Computational Modeling and Simulations of Polymers)

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22 pages, 31131 KiB

Open AccessArticle

Investigation of Auxetic Structural Deformation Behavior of PBAT Polymers Using Process and Finite Element Simulation

by Yanling Schneider, Vinzenz Guski, Ahmet O. Sahin, Siegfried Schmauder, Javad Kadkhodapour, Jonas Hufert, Axel Grebhardt and Christian Bonten

Polymers 2023, 15(14), 3142; https://doi.org/10.3390/polym15143142 - 24 Jul 2023

Cited by 1 | Viewed by 1477

Abstract

The current work investigates the auxetic tensile deformation behavior of the inversehoneycomb structure with 5 × 5 cells made of biodegradable poly(butylene adipate-coterephthalate) (PBAT). Fused deposition modeling, an additive manufacturing method, was used to produce such specimens. Residual stress (RS) and warpage, more [...] Read more.

The current work investigates the auxetic tensile deformation behavior of the inversehoneycomb structure with 5 × 5 cells made of biodegradable poly(butylene adipate-coterephthalate) (PBAT). Fused deposition modeling, an additive manufacturing method, was used to produce such specimens. Residual stress (RS) and warpage, more or less, always exist in such specimens due to their layer-by-layer fabrication, i.e., repeated heating and cooling. The RS influences the auxetic deformation behavior, but its measurement is challenging due to its very fine structure. Instead, the finite-element (FE)-based process simulation realized using an ABAQUS plug-in numerically predicts the RS and warpage. The predicted warpage shows a negligibly slight deviation compared to the design topology. This process simulation also provides the temperature evolution of a small-volume material, revealing the effects of local cyclic heating and cooling. The achieved RS serves as the initial condition for the FE model used to investigate the auxetic tensile behavior. With the outcomes from FE calculation without consideration of the RS, the effect of the RS on the deformation behavior is discussed for the global force–displacement curve, the structural Poisson’s ratio evolution, the deformed structural status, the stress distribution, and the evolution, where the first three and the warpage are also compared with the experimental results. Furthermore, the FE simulation can easily provide the global stress–strain flow curve with the total stress calculated from the elemental stresses. Full article

(This article belongs to the Special Issue Computational Modeling and Simulations of Polymers)

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17 pages, 5684 KiB

Open AccessArticle

Chemical Feedback in Templated Reaction-Assembly of Polyelectrolyte Complex Micelles: A Molecular Simulation Study of the Kinetics and Clustering

by Christos Gioldasis, Apostolos Gkamas, Othonas A. Moultos and Costas Hristos Vlahos

Polymers 2023, 15(14), 3024; https://doi.org/10.3390/polym15143024 - 12 Jul 2023

Cited by 1 | Viewed by 1266

Abstract

The chemical feedback between building blocks in templated polymerization of diblock copolymers and their consecutive micellization was studied for the first time by means of coarse-grained molecular dynamics simulations. Using a stochastic polymerization model, we were able to reproduce the experimental findings on [...] Read more.

The chemical feedback between building blocks in templated polymerization of diblock copolymers and their consecutive micellization was studied for the first time by means of coarse-grained molecular dynamics simulations. Using a stochastic polymerization model, we were able to reproduce the experimental findings on the effect of chemical feedback on the polymerization rates at low and high solution concentrations. The size and shape of micelles were computed using a newly developed software in Python conjugated with graph theory. In full agreement with the experiments, our simulations revealed that micelles formed by the templated micellization are more spherical and have a lower radius of gyration than those formed by the traditional two-step micellization method. The advantage of molecular simulation over the traditional kinetic models is that with the simulation, one studies in detail the heterogeneous polymerization in the presence of the oppositely charged template while also accounting for the incompatibility between reacted species, which significantly influences the reaction process. Full article

(This article belongs to the Special Issue Computational Modeling and Simulations of Polymers)

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14 pages, 3228 KiB

Open AccessArticle

Computer Simulation Insight into the Adsorption and Diffusion of Polyelectrolytes on Oppositely Charged Surface

by Anna A. Glagoleva, Alexander A. Yaroslavov and Valentina V. Vasilevskaya

Polymers 2023, 15(13), 2845; https://doi.org/10.3390/polym15132845 - 28 Jun 2023

Cited by 2 | Viewed by 1440

Abstract

In the present work, by means of computer simulation, we studied the adsorption and diffusion of polyelectrolyte macromolecules on oppositely charged surfaces. We considered the surface coverage and the charge of the adsorbed layer depending on the ionization degree of the macromolecules and [...] Read more.

In the present work, by means of computer simulation, we studied the adsorption and diffusion of polyelectrolyte macromolecules on oppositely charged surfaces. We considered the surface coverage and the charge of the adsorbed layer depending on the ionization degree of the macromolecules and the charge of the surface and carried out a computer experiment on the polymer diffusion within the adsorbed layers, taking into account its strong dependency on the surface coverage and the macromolecular ionization degree. The different regimes were distinguished that provided maximal mobility of the polymer chains along with a high number of charged groups in the layer, which could be beneficial for the development of the functional coatings. The results were compared with those of previous experiments on the adsorption of polyelectrolyte layers that may be applied as biocidal renewable coatings that can reversibly desorb from the surface. Full article

(This article belongs to the Special Issue Computational Modeling and Simulations of Polymers)

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Review

Jump to: Research

26 pages, 9349 KiB

Open AccessReview

Micromechanical Models for FDM 3D-Printed Polymers: A Review

by Rowin J. M. Bol and Branko Šavija

Polymers 2023, 15(23), 4497; https://doi.org/10.3390/polym15234497 - 23 Nov 2023

Cited by 12 | Viewed by 2275

Abstract

Due to its large number of advantages compared to traditional subtractive manufacturing techniques, additive manufacturing (AM) has gained increasing attention and popularity. Among the most common AM techniques is fused filament fabrication (FFF), usually referred to by its trademarked name: fused deposition modeling [...] Read more.

Due to its large number of advantages compared to traditional subtractive manufacturing techniques, additive manufacturing (AM) has gained increasing attention and popularity. Among the most common AM techniques is fused filament fabrication (FFF), usually referred to by its trademarked name: fused deposition modeling (FDM). This is the most efficient technique for manufacturing physical three-dimensional thermoplastics, such that FDM machines are nowadays the most common. Regardless of the 3D-printing methodology, AM techniques involve layer-by-layer deposition. Generally, this layer-wise process introduces anisotropy into the produced parts. The manufacturing procedure creates parts possessing heterogeneities at the micro (usually up to 1 mm) and meso (mm to cm) length scales, such as voids and pores, whose size, shape, and spatial distribution are mainly influenced by the so-called printing process parameters. Therefore, it is crucial to investigate their influence on the mechanical properties of FDM 3D-printed parts. This review starts with the identification of the printing process parameters that are considered to affect the micromechanical composition of FDM 3D-printed polymers. In what follows, their (negative) influence is attributed to characteristic mechanical properties. The remainder of this work reviews the state of the art in geometrical, numerical, and experimental analyses of FDM-printed parts. Finally, conclusions are drawn for each of the aforementioned analyses in view of microstructural modeling. Full article

(This article belongs to the Special Issue Computational Modeling and Simulations of Polymers)

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41 pages, 1747 KiB

Open AccessReview

Simulational Tests of the Rouse Model

by George David Joseph Phillies

Polymers 2023, 15(12), 2615; https://doi.org/10.3390/polym15122615 - 8 Jun 2023

Cited by 3 | Viewed by 3213

Abstract

An extensive review of literature simulations of quiescent polymer melts is given, considering results that test aspects of the Rouse model in the melt. We focus on Rouse model predictions for the mean-square amplitudes [...] Read more.

An extensive review of literature simulations of quiescent polymer melts is given, considering results that test aspects of the Rouse model in the melt. We focus on Rouse model predictions for the mean-square amplitudes

⟨ {(X_{p} (0))}^{2} ⟩

and time correlation functions

⟨ X_{p} (0) X_{p} (t) ⟩

of the Rouse mode

X_{p} (t)

. The simulations conclusively demonstrate that the Rouse model is invalid in polymer melts. In particular, and contrary to the Rouse model, (i) mean-square Rouse mode amplitudes

⟨ {(X_{p} (0))}^{2} ⟩

do not scale as

{sin}^{- 2} (p π / 2 N)

, N being the number of beads in the polymer. For small p (say,

p \leq 3

)

⟨ {(X_{p} (0))}^{2} ⟩

scales with p as

p^{- 2}

; for larger p, it scales as

p^{- 3}

. (ii) Rouse mode time correlation functions

⟨ X_{p} (t) X_{p} (0) ⟩

do not decay with time as exponentials; they instead decay as stretched exponentials

exp (- α t^{β})

.

β

depends on p, typically with a minimum near

N / 2

or

N / 4

. (iii) Polymer bead displacements are not described by independent Gaussian random processes. (iv) For

p \neq q

,

⟨ X_{p} (t) X_{q} (0) ⟩

is sometimes non-zero. (v) The response of a polymer coil to a shear flow is a rotation, not the affine deformation predicted by Rouse. We also briefly consider the Kirkwood–Riseman polymer model. Full article

(This article belongs to the Special Issue Computational Modeling and Simulations of Polymers)

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