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31 pages, 13982 KiB

Open AccessArticle

A Contact Mechanics Model for Surface Wear Prediction of Parallel-Axis Polymer Gears

by Enis Muratović, Nedim Pervan, Adil Muminović and Muamer Delić

Polymers 2024, 16(20), 2858; https://doi.org/10.3390/polym16202858 - 10 Oct 2024

Viewed by 800

Abstract

As surface wear is one of the major failure mechanisms in many applications that include polymer gears, lifetime prediction of polymer gears often requires time-consuming and expensive experimental testing. This study introduces a contact mechanics model for the surface wear prediction of polymer [...] Read more.

As surface wear is one of the major failure mechanisms in many applications that include polymer gears, lifetime prediction of polymer gears often requires time-consuming and expensive experimental testing. This study introduces a contact mechanics model for the surface wear prediction of polymer gears. The developed model, which is based on an iterative numerical procedure, employs a boundary element method (BEM) in conjunction with Archard’s wear equation to predict wear depth on contacting tooth surfaces. The wear coefficients, necessary for the model development, have been determined experimentally for Polyoxymethylene (POM) and Polyvinylidene fluoride (PVDF) polymer gear samples by employing an abrasive wear model by the VDI 2736 guidelines for polymer gear design. To fully describe the complex changes in contact topography as the gears wear, the prediction model employs Winkler’s surface formulation used for the computation of the contact pressure distribution and Weber’s model for the computation of wear-induced changes in stiffness components as well as the alterations in the load-sharing factors with corresponding effects on the normal load distribution. The developed contact mechanics model has been validated through experimental testing of steel/polymer engagements after an arbitrary number of load cycles. Based on the comparison of the simulated and experimental results, it can be concluded that the developed model can be used to predict the surface wear of polymer gears, therefore reducing the need to perform experimental testing. One of the major benefits of the developed model is the possibility of assessing and visualizing the numerous contact parameters that simultaneously affect the wear behavior, which can be used to determine the wear patterns of contacting tooth surfaces after a certain number of load cycles, i.e., different lifetime stages of polymer gears. Full article

(This article belongs to the Special Issue Computational and Experimental Approaches in Polymeric Materials)

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19 pages, 10658 KiB

Open AccessArticle

Experimental and Simulation Study on Failure of Thermoplastic Carbon Fiber Composite Laminates under Low-Velocity Impact

by Lei Yang, Xiaolin Huang, Zhenhao Liao, Zongyou Wei and Jianchao Zou

Polymers 2024, 16(18), 2581; https://doi.org/10.3390/polym16182581 - 12 Sep 2024

Viewed by 845

Abstract

Numerous studies have demonstrated that under low-velocity, low-energy impact conditions, although the surface damage to fiber-reinforced composite laminates may be minimal, significant internal damage can occur. Consequently, a progressive damage finite element model was specifically developed for thermoplastic carbon fiber-reinforced composite laminates subjected [...] Read more.

Numerous studies have demonstrated that under low-velocity, low-energy impact conditions, although the surface damage to fiber-reinforced composite laminates may be minimal, significant internal damage can occur. Consequently, a progressive damage finite element model was specifically developed for thermoplastic carbon fiber-reinforced composite laminates subjected to low-speed impact loads, with the objective of analyzing the damage behavior of laminates under impacts of varying energy levels. The model utilizes a three-dimensional Hashin criterion for predicting intralayer damage initiation, with cohesive elements based on bilinear traction–separation law for predicting interlaminar delamination initiation, and incorporates a damage constitutive model based on equivalent displacement to characterize fiber damage evolution, along with the B-K criterion for interlaminar damage evolution. The impact response of laminates at energy levels of 5 J, 10 J, 15 J, 20 J, and 25 J was analyzed through numerical simulation, drop-hammer experiments, and XCT non-destructive testing. The results indicated that the simulation outcomes closely correspond with the experimental findings, with both the predicted peak error and absorbed energy error maintained within a 5% margin, and the trends of the mechanical response curves aligning closely with the experimental data. The damage patterns predicted by the numerical simulations were consistent with the results obtained from XCT scans. The study additionally revealed that the impact damage of the laminates primarily stems from interlaminar delamination and intralayer tensile failure. Initial damage typically presents as internal delamination; hence, enhancing interlaminar bonding performance can significantly augment the overall load-bearing capacity of the laminate. Full article

(This article belongs to the Special Issue Computational and Experimental Approaches in Polymeric Materials)

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9 pages, 1112 KiB

Open AccessArticle

Flame-Retardant Glass Fiber-Reinforced Epoxy Resins with Phosphorus-Containing Bio-Based Benzoxazines and Graphene

by Stanislav Trubachev, Alexander Paletsky, Egor Sosnin, Oleg Tuzhikov, Boris Buravov, Andrey Shmakov, Anatoliy Chernov, Ilya Kulikov, Albert Sagitov, Yuan Hu and Xin Wang

Polymers 2024, 16(16), 2333; https://doi.org/10.3390/polym16162333 - 18 Aug 2024

Viewed by 1092

Abstract

This paper presents a study of the flammability and thermal decomposition products of glass fiber-reinforced epoxy resin (GFRER) with the addition of cardanol-based phosphorus-containing benzoxazine monomer (CBz) and graphene and their combinations in different proportions (up to 20 wt.%). The addition of CBz [...] Read more.

This paper presents a study of the flammability and thermal decomposition products of glass fiber-reinforced epoxy resin (GFRER) with the addition of cardanol-based phosphorus-containing benzoxazine monomer (CBz) and graphene and their combinations in different proportions (up to 20 wt.%). The addition of CBz alone or in combination with graphene resulted in an increase in the limiting oxygen index (LOI) and self-extinguishing in the UL-94 HB test. The flame-retardant samples had better tensile mechanical properties than the sample without additives. The differential mass-spectrometric thermal analysis (DMSTA) of the thermal decomposition products of GFRER without additives and with the addition of CBz and graphene was carried out. CBz addition promoted the thermal decomposition of high-molecular-weight products of epoxy resin decomposition in the condensed phase and at the same time decreased the time of release of low-molecular-weight thermal decomposition products into the gas phase. Graphene addition resulted in an increase in the relative intensities of high-molecular-mass peaks compared to GFRER without additives. Full article

(This article belongs to the Special Issue Computational and Experimental Approaches in Polymeric Materials)

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25 pages, 4203 KiB

Open AccessEditor’s ChoiceArticle

Prediction of Short- to Long-Term Cyclic Deformation Behavior and Fatigue Life of Polymers

by Thierry Barriere, Stani Carbillet, Xavier Gabrion and Sami Holopainen

Polymers 2024, 16(12), 1640; https://doi.org/10.3390/polym16121640 - 10 Jun 2024

Viewed by 1195

Abstract

The prediction of mechanical behavior and fatigue life is of major importance for design and for replacing costly and time-consuming tests. The proposed approach for polymers is a combination of a fatigue model and a governing constitutive model, which is formulated using the [...] Read more.

The prediction of mechanical behavior and fatigue life is of major importance for design and for replacing costly and time-consuming tests. The proposed approach for polymers is a combination of a fatigue model and a governing constitutive model, which is formulated using the Haward–Thackray viscoplastic model (1968) and is capable of capturing large deformations. The fatigue model integrates high- and low-cycle fatigue and is based on the concept of damage evolution and a moving endurance surface in the stress space, therefore memorizing the load history without requesting vague cycle-counting approaches. The proposed approach is applicable for materials in which the fatigue development is ductile, i.e., damage during the formation of microcracks controls most of the fatigue life (up to 90%). Moreover, damage evolution shows a certain asymptote at the ultimate of the low-cycle fatigue, a second asymptote at the ultimate of the high-cycle fatigue (which is near zero), and a curvature of how rapidly the transition between the asymptotes is reached. An interesting matter is that similar to metals, many polymers satisfy these constraints. Therefore, all the model parameters for fatigue can be given in terms of the Basquin and Coffin–Manson model parameters, i.e., satisfying well-defined parameters. Full article

(This article belongs to the Special Issue Computational and Experimental Approaches in Polymeric Materials)

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21 pages, 4881 KiB

Open AccessArticle

A Theoretical Investigation of the Polyaddition of an AB₂+A₂+B₄ Monomer Mixture

by Sergei V. Karpov, Artem Iakunkov, Dmitry A. Chernyaev, Vladimir G. Kurbatov, Georgiy V. Malkov and Elmira R. Badamshina

Polymers 2024, 16(3), 426; https://doi.org/10.3390/polym16030426 - 3 Feb 2024

Viewed by 1043

Abstract

Hyperbranched polymers (HBPs) are widely applied nowadays as functional materials for biomedicine needs, nonlinear optics, organic semiconductors, etc. One of the effective and promising ways to synthesize HBPs is a polyaddition of AB₂+A₂+B₄ monomers that is generated in [...] Read more.

Hyperbranched polymers (HBPs) are widely applied nowadays as functional materials for biomedicine needs, nonlinear optics, organic semiconductors, etc. One of the effective and promising ways to synthesize HBPs is a polyaddition of AB₂+A₂+B₄ monomers that is generated in the A₂+CB₂, AA′+B₃, A₂+B′B₂, and A₂+C₂+B₃ systems or using other approaches. It is clear that all the foundational features of HBPs that are manufactured by a polyaddition reaction are defined by the component composition of the monomer mixture. For this reason, we have designed a structural kinetic model of AB₂+A₂+B₄ monomer mixture polyaddition which makes it possible to predict the impact of the monomer mixture’s composition on the molecular weight characteristics of hyperbranched polymers (number average (DP_n) and weight average (DP_w) degree of polymerization), as well as the degree of branching (DB) and gel point (p_g). The suggested model also considers the possibility of a positive or negative substitution effect during polyaddition. The change in the macromolecule parameters of HBPs formed by polyaddition of AB₂+A₂+B₄ monomers is described as an infinite system of kinetic equations. The solution for the equation system was found using the method of generating functions. The impact of both the component’s composition and the substitution effect during the polyaddition of AB₂+A₂+B₄ monomers on structural and molecular weight HBP characteristics was investigated. The suggested model is fairly versatile; it makes it possible to describe every possible case of polyaddition with various monomer combinations, such as A₂+AB₂, AB₂+B₄, AB₂, or A₂+B₄. The influence of each monomer type on the main characteristics of hyperbranched polymers that are obtained by the polyaddition of AB₂+A₂+B₄ monomers has been investigated. Based on the results obtained, an empirical formula was proposed to estimate the p_g = p_A during the polyaddition of an AB₂+A₂+B₄ monomer mixture: p_g = p_A = (−0.53([B]₀/[A]₀)^1/2 + 0.78)υAB₂ + (1/3)^1/2([B]₀/[A]₀)^1/2, where (1/3)^1/2([B]₀/[A]₀)^1/2 is the Flory equation for the A₂+B₄ polyaddition, [A]₀ and [B]₀ are the A and B group concentration from A₂ and B₄, respectively, and υAB₂ is the mole fraction of the AB₂ monomer in the mixture. The equation obtained allows us to accurately predict the p_g value, with an AB₂ monomer content of up to 80%. Full article

(This article belongs to the Special Issue Computational and Experimental Approaches in Polymeric Materials)

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19 pages, 5065 KiB

Open AccessArticle

Study on Self-Humidification in PEMFC with Crossed Flow Channels and an Ultra-Thin Membrane

by Chenlong Wang, Xiaosong Chen, Xin Xiang, Heng Zhang, Zhiping Huang, Xinhao Huang and Zhigang Zhan

Polymers 2023, 15(23), 4589; https://doi.org/10.3390/polym15234589 - 30 Nov 2023

Cited by 2 | Viewed by 1444

Abstract

In this study, a 3D model of a proton exchange membrane fuel cell (PEMFC) with crossed channels and an ultra-thin membrane is developed to investigate the feasibility of self-humidification; experiments utilizing a PEMFC stack with identical configurations are conducted to validate the simulation [...] Read more.

In this study, a 3D model of a proton exchange membrane fuel cell (PEMFC) with crossed channels and an ultra-thin membrane is developed to investigate the feasibility of self-humidification; experiments utilizing a PEMFC stack with identical configurations are conducted to validate the simulation results and further investigate the effects of various operating conditions (OCs) on self-humidification. The results indicate that the crossed flow channel leads to enhanced uniformity of water distribution, resulting in improved cell performance under low/no humidification conditions. External humidifiers for the anode can be removed since the performance difference is negligible (≤3%) between RHa = 0% and 100%. Self-humidification can be achieved in the stack at 90 °C or below with an appropriate back pressure among 100–200 kPa. As the current density increases, there is a gradual convergence and crossing of the voltage at low RH with that at high RH, and the crossover points are observed at 60–80 °C with suitable pressure when successful self-humidification is achieved. Below the current density of the point, the stack’s performance is inferior at lower RH due to membrane unsaturation, and conversely, the performance is inferior at higher RH due to flooding; this current density decreases with higher pressure and lower temperature. Full article

(This article belongs to the Special Issue Computational and Experimental Approaches in Polymeric Materials)

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13 pages, 8449 KiB

Open AccessArticle

Origin of Optoelectronic Contradictions in 3,4-Cycloalkyl[c]-chalcogenophenes: A Computational Study

by Ganesh Masilamani, Gamidi Rama Krishna, Sashi Debnath and Anjan Bedi

Polymers 2023, 15(21), 4240; https://doi.org/10.3390/polym15214240 - 27 Oct 2023

Cited by 2 | Viewed by 1170

Abstract

The planar morphology of the backbone significantly contributes to the subtle optoelectronic features of π-conjugated polymers. On the other hand, the atomistic tuning of an otherwise identical π-backbone could also impact optoelectronic properties systematically. In this manuscript, we compare a series of 3,4-cycloalkylchalcogenophenes [...] Read more.

The planar morphology of the backbone significantly contributes to the subtle optoelectronic features of π-conjugated polymers. On the other hand, the atomistic tuning of an otherwise identical π-backbone could also impact optoelectronic properties systematically. In this manuscript, we compare a series of 3,4-cycloalkylchalcogenophenes by tuning them atomistically using group-16 elements. Additionally, the effect of systematically extending these building blocks in the form of oligomers and polymers is studied. The size of the 3,4-substitution affected the morphology of the oligomers. In addition, the heteroatoms contributed to a further alteration in their geometry and resultant optoelectronic properties. The chalcogenophenes, containing smaller 3,4-cycloalkanes, resulted in lower bandgap oligomers or polymers compared to those with larger 3,4-cycloalkanes. Natural bonding orbital (NBO) calculations were performed to understand the disparity alongside the contour maps of frontier molecular orbitals (FMO). Full article

(This article belongs to the Special Issue Computational and Experimental Approaches in Polymeric Materials)

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18 pages, 6547 KiB

Open AccessArticle

Evaluating the Cooling Efficiency of Polymer Injection Molds by Computer Simulation Using Conformal Channels

by Carlos Vargas-Isaza, Adrian Benitez-Lozano and Johnnatan Rodriguez

Polymers 2023, 15(20), 4044; https://doi.org/10.3390/polym15204044 - 10 Oct 2023

Cited by 7 | Viewed by 2171

Abstract

Injection molds are production tools that require detailed analysis based on the quality of the resulting part, the impact on cycle times, and the expected production volume. Cooling channels also play a critical role in mold performance and product quality as they largely [...] Read more.

Injection molds are production tools that require detailed analysis based on the quality of the resulting part, the impact on cycle times, and the expected production volume. Cooling channels also play a critical role in mold performance and product quality as they largely determine cycle time. Designs that incorporate conformal cooling channel (CCC) geometries that conform to or align with the part contour are currently being explored as an alternative to conventional cooling channel designs in injection molds. In this study, a simulation of CCC geometries was performed and their effects on mold temperatures and warpage were investigated. Two cross-sectional geometries, circular and square, were selected for a three-factor level design of experiments (DOE) analysis. The response variables used were mold temperatures and part warpage. A cup-shaped part with upper and lower diameters of 54 and 48 mm, respectively, a height of 23 mm and a thickness of 3 mm was used for the injection molded part. A comparison was also made between two materials for the injection mold, steel and polycarbonate. The DOE results showed that the distance between the CCC and the injected part and the diameter or side of the square have significant effects on the response variables for both systems (steel and polycarbonate molds). In addition, a comparison between conventional and conformal cooling channels was analyzed using a cup-shaped part and a less rigid part geometry. The finite element simulation results show a 9.26% reduction in final warpage in the cup-shaped part using CCCs compared with the conventional cooling methods in steel. When using parts with lower geometry stiffness, the use of CCCs reduced final part warpage by 32.4% in metal molds and by 59.8% in polymer molds. Full article

(This article belongs to the Special Issue Computational and Experimental Approaches in Polymeric Materials)

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15 pages, 5165 KiB

Open AccessArticle

Effect of Rice Husk and Wood Flour on the Structural, Mechanical, and Fire-Retardant Characteristics of Recycled High-Density Polyethylene

by Atta Ur Rehman Shah, Abdul Jalil, Atiya Sadiq, Meshal Alzaid, Muhammad Shoaib Naseem, Rakan Alanazi, Sultan Alanazi, Abdullatyf Obaid Alanzy, Ibrahim Hotan Alsohaimi and Rizwan Ahmed Malik

Polymers 2023, 15(19), 4031; https://doi.org/10.3390/polym15194031 - 9 Oct 2023

Cited by 4 | Viewed by 2017

Abstract

Given the rising consumption of plastic products, it is becoming imperative to prioritize the recycling of plastic items as a solution to reducing plastic waste and environmental pollution. In this context, this research focuses on assessing the impact of incorporating rice husk and [...] Read more.

Given the rising consumption of plastic products, it is becoming imperative to prioritize the recycling of plastic items as a solution to reducing plastic waste and environmental pollution. In this context, this research focuses on assessing the impact of incorporating rice husk and wood flour into recycled high-density polyethylene (rec-HDPE) to analyze its mechanical properties, flammability, and thermal stability. The combined rec-HDPE content of wood flour and rice husk varied between 0% and 20%. The rec-HDPE content of maleic anhydride grafted polyethylene (MAPE) was fixed at 3%. Mechanical characteristics such as flexural, tensile, and impact strengths were assessed. Cone calorimetry (CC) tests, limited oxygen index (LOI) tests, and horizontal and vertical burning tests were performed to determine the flammability or fire retardancy of these composites. On the other hand, to characterize the thermal characteristics of these composites, thermogravimetric analysis (TGA) was used. To further characterize the fluctuation in these characteristics, scanning electron microscopy (SEM) and infrared spectroscopy (FTIR) studies were carried out. The mechanical characteristics were found to be increased in response to adding rice husk or wood flour. An 8% increase in tensile strength and a 20% increase in elastic modulus enhancement were recorded for a 20% rice husk-added composite. SEM revealed the reason for the variation in tensile properties, based on the extent of agglomeration and the extent of uniform distribution of fillers in rec-HDPE. Following these lines, the 20% rice husk-added composite also showed a maximum increase of around 6% in its flexural strength and a maximum increase of 50% in its flexural modulus. A decrease in impact strength was recorded for rice husk and wood flour-reinforced composites, compared with unreinforced rec-HDPE. Hybrid composites displayed a lack of mechanical strength due to changes in their nature. FTIR tests were performed for a much more elaborate analysis to confirm these results. Twenty percent of rice husk-added rec-HDPE displayed the best thermal properties that were tested, based on TGA and derivative thermogravimetric (DTG) analysis. This 20% composite also displayed the best fire-retardancy characteristics according to UL 94 tests, cone calorimetry tests, and limited oxygen index tests, due to the barrier created by the silica protective layer. These tests demonstrated that the incorporation of both fillers—rice husk and wood flour—effectively enhanced the thermal, mechanical, and fire-retardant attributes of recycled HDPE. Full article

(This article belongs to the Special Issue Computational and Experimental Approaches in Polymeric Materials)

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15 pages, 4188 KiB

Open AccessArticle

Understanding the Behavior of Sodium Polyacrylate in Suspensions of Silica and Monovalent Salts

by Gonzalo R. Quezada, Francisco Retamal, Matías Jeldres and Ricardo I. Jeldres

Polymers 2023, 15(19), 3861; https://doi.org/10.3390/polym15193861 - 22 Sep 2023

Cited by 1 | Viewed by 1622

Abstract

This study investigated the interaction of monovalent cations with different sizes on quartz surfaces and the rheological impact that this causes in concentrated suspensions when subjected to the action of a rheological modifier, in this case, sodium polyacrylate (NaPA). Yield stress was determined [...] Read more.

This study investigated the interaction of monovalent cations with different sizes on quartz surfaces and the rheological impact that this causes in concentrated suspensions when subjected to the action of a rheological modifier, in this case, sodium polyacrylate (NaPA). Yield stress was determined using a rheometer with a vane-in-cup configuration to establish the relationship between shear stress and strain. Experiments were carried out in LiCl, NaCl, KCl, and CsCl solutions. The results show that the yield stress increases following the order Li < Na < K < Cs in the absence of PAA. However, the addition of NaPA significantly reduced the yield stress in all cases. This reduction was more noticeable in the LiCl and NaCl solutions than in the KCl and CsCl solutions, suggesting a more pronounced effect of PA in maker salts. We conducted molecular dynamics simulations to understand how PA interacts with dissolved salts on the quartz surface. Our results showed that Li had the highest adsorption, followed by Na, K, and Cs. As the salt concentration increased, so did the adsorption. We validated these simulation results with rheological experiments, which helped us understand the observed differences. The molecular interactions indicate that, in the lithium system, cationic bridges and the synergy between hydrogen bridges and hydrophobic bridges predominate mainly. This tendency decreases as the type of cation is changed due to the decrease in the electrical density of the cation in the following order: Li < Na < K < Cs. This reduces bridging with the quartz surface and, therefore, directly impacts the system’s rheological properties. Full article

(This article belongs to the Special Issue Computational and Experimental Approaches in Polymeric Materials)

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14 pages, 3653 KiB

Open AccessArticle

Modeling and Simulation of a Multizone Circulating Reactor for Polyethylene Production with Internal Cooling

by Nayef Ghasem

Polymers 2023, 15(18), 3741; https://doi.org/10.3390/polym15183741 - 13 Sep 2023

Cited by 2 | Viewed by 1777

Abstract

Polyolefins play a role in industries and are typically manufactured using two types of reactors: high-pressure tubular reactors and fluidized bed reactors. An innovative technology called the Multizone Circulating reactor (MZCR) has emerged, which introduces an innovative approach with interconnected polymerization zones creating [...] Read more.

Polyolefins play a role in industries and are typically manufactured using two types of reactors: high-pressure tubular reactors and fluidized bed reactors. An innovative technology called the Multizone Circulating reactor (MZCR) has emerged, which introduces an innovative approach with interconnected polymerization zones creating a continuous loop of polymer flow. This study focuses on modeling and simulating ethylene gas phase polymerization within the MZCR in the presence of internal cooling to gain insights into its behavior. To achieve this, a comprehensive computational fluid dynamics (CFD) simulation was developed. It considered momentum, material, and energy balance aspects. The model equations were solved using the finite difference method in COMSOL Multiphysics version 6.1. The investigation primarily focused on studying the impact of incorporating a cooler into the riser section on the temperature profile within the reactor and ethylene conversion. The presence of this cooler resulted in a reduction in temperature change along the riser from approximately 8.0 °C to 4.0 °C. Moreover, it led to an increase of 7%, in ethylene single-pass conversion. Full article

(This article belongs to the Special Issue Computational and Experimental Approaches in Polymeric Materials)

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18 pages, 4104 KiB

Open AccessArticle

Calcium-Alginate-Chitosan Nanoparticle as a Potential Solution for Pesticide Removal, a Computational Approach

by Osvaldo Yáñez, Melissa Alegría-Arcos, Reynier Suardiaz, Luis Morales-Quintana, Ricardo I. Castro, Jonathan Palma-Olate, Christian Galarza, Ángel Catagua-González, Víctor Rojas-Pérez, Gabriela Urra, Erix W. Hernández-Rodríguez and Daniel Bustos

Polymers 2023, 15(14), 3020; https://doi.org/10.3390/polym15143020 - 12 Jul 2023

Cited by 4 | Viewed by 2183

Abstract

Pesticides have a significant negative impact on the environment, non-target organisms, and human health. To address these issues, sustainable pest management practices and government regulations are necessary. However, biotechnology can provide additional solutions, such as the use of polyelectrolyte complexes to encapsulate and [...] Read more.

Pesticides have a significant negative impact on the environment, non-target organisms, and human health. To address these issues, sustainable pest management practices and government regulations are necessary. However, biotechnology can provide additional solutions, such as the use of polyelectrolyte complexes to encapsulate and remove pesticides from water sources. We introduce a computational methodology to evaluate the capture capabilities of Calcium-Alginate-Chitosan (CAC) nanoparticles for a broad range of pesticides. By employing ensemble-docking and molecular dynamics simulations, we investigate the intermolecular interactions and absorption/adsorption characteristics between the CAC nanoparticles and selected pesticides. Our findings reveal that charged pesticide molecules exhibit more than double capture rates compared to neutral counterparts, owing to their stronger affinity for the CAC nanoparticles. Non-covalent interactions, such as van der Waals forces, π-π stacking, and hydrogen bonds, are identified as key factors which stabilized the capture and physisorption of pesticides. Density profile analysis confirms the localization of pesticides adsorbed onto the surface or absorbed into the polymer matrix, depending on their chemical nature. The mobility and diffusion behavior of captured compounds within the nanoparticle matrix is assessed using mean square displacement and diffusion coefficients. Compounds with high capture levels exhibit limited mobility, indicative of effective absorption and adsorption. Intermolecular interaction analysis highlights the significance of hydrogen bonds and electrostatic interactions in the pesticide-polymer association. Notably, two promising candidates, an antibiotic derived from tetracycline and a rodenticide, demonstrate a strong affinity for CAC nanoparticles. This computational methodology offers a reliable and efficient screening approach for identifying effective pesticide capture agents, contributing to the development of eco-friendly strategies for pesticide removal. Full article

(This article belongs to the Special Issue Computational and Experimental Approaches in Polymeric Materials)

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13 pages, 2244 KiB

Open AccessArticle

Simulation of Nondilute Dendrimer Systems with the Bond Fluctuation Model

by Juan J. Freire

Polymers 2022, 14(24), 5363; https://doi.org/10.3390/polym14245363 - 8 Dec 2022

Viewed by 958

Abstract

Using the bond fluctuation model, we performed Monte Carlo simulations for solutions of generation 4 and 5 dendrimers with only an intermediate unit between the branching points at different concentrations, ranging from moderately dilute solutions to concentrated systems close to the melt behavior. [...] Read more.

Using the bond fluctuation model, we performed Monte Carlo simulations for solutions of generation 4 and 5 dendrimers with only an intermediate unit between the branching points at different concentrations, ranging from moderately dilute solutions to concentrated systems close to the melt behavior. This model may represent different real types of dendrimer families. We obtained the mean sizes, asphericities, displacement of units, scattering functions, radial distribution functions and structure factors. We compared the results obtained for the last two properties with much faster Monte Carlo simulations of point-like dendrimers using global potentials obtained through the study of binary interactions. The latter procedure provided good reproductions of these properties but failed in the reproduction of the scattering functions in the range of higher concentrations. In this range, the scattering function cannot be described as the product of the structure function and the form factor, because the intensity decreases when the density of the dendrimer units becomes more homogenous. Full article

(This article belongs to the Special Issue Computational and Experimental Approaches in Polymeric Materials)

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11 pages, 3869 KiB

Open AccessArticle

Entanglement Characteristic Time from Complex Moduli via i-Rheo GT

by Dongdong Li, Lukun Feng, Yin Tang and Caizhen Zhu

Polymers 2022, 14(23), 5208; https://doi.org/10.3390/polym14235208 - 30 Nov 2022

Viewed by 1533

Abstract

Tassieri et al. have introduced a novel rheological tool called “i-Rheo GT” that allows the evaluation of the frequency-dependent materials’ linear viscoelastic properties from a direct Fourier transform of the time-dependent relaxation modulus G(t), without artifacts. They adopted i-Rheo [...] Read more.

Tassieri et al. have introduced a novel rheological tool called “i-Rheo GT” that allows the evaluation of the frequency-dependent materials’ linear viscoelastic properties from a direct Fourier transform of the time-dependent relaxation modulus G(t), without artifacts. They adopted i-Rheo GT to exploit the information embedded in G(t) derived from molecular dynamics simulations of atomistic and quasi-atomistic models, and they estimated the polymers’ entanglement characteristic time (

τ_{e}

) from the crossover point of the moduli at intermediate times, which had never been possible before because of the poor fitting performance, at short time scales, of the commonly used generalized Maxwell models. Here, we highlight that the values of

τ_{e}

reported by Tassieri et al. are significantly different (i.e., an order of magnitude smaller) from those reported in the literature, obtained from either experiments or molecular dynamics simulations of different observables. In this work, we demonstrate that consistent values of

τ_{e}

can be achieved if the initial values of G(t), i.e., those governed by the bond-oscillation dynamics, are discarded. These findings have been corroborated by adopting i-Rheo GT to Fourier transform the outcomes of three different molecular dynamics simulations based on the following three models: a dissipative particle dynamics model, a Kremer–Grest model, and an atomistic polyethylene model. Moreover, we have investigated the variations of

τ_{e}

as function of (i) the ‘cadence’ at which G(t) is evaluated, (ii) the spring constant of the atomic bone, and (iii) the initial value of the shear relaxation modulus G(O). The ensemble of these results confirms the effectiveness of i-Rheo GT and provide new insights into the interpretation of molecular dynamics simulations for a better understanding of polymer dynamics. Full article

(This article belongs to the Special Issue Computational and Experimental Approaches in Polymeric Materials)

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Review

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45 pages, 2915 KiB

Open AccessReview

Applications of Long Short-Term Memory (LSTM) Networks in Polymeric Sciences: A Review

by Ivan Malashin, Vadim Tynchenko, Andrei Gantimurov, Vladimir Nelyub and Aleksei Borodulin

Polymers 2024, 16(18), 2607; https://doi.org/10.3390/polym16182607 - 14 Sep 2024

Viewed by 1416

Abstract

This review explores the application of Long Short-Term Memory (LSTM) networks, a specialized type of recurrent neural network (RNN), in the field of polymeric sciences. LSTM networks have shown notable effectiveness in modeling sequential data and predicting time-series outcomes, which are essential for [...] Read more.

This review explores the application of Long Short-Term Memory (LSTM) networks, a specialized type of recurrent neural network (RNN), in the field of polymeric sciences. LSTM networks have shown notable effectiveness in modeling sequential data and predicting time-series outcomes, which are essential for understanding complex molecular structures and dynamic processes in polymers. This review delves into the use of LSTM models for predicting polymer properties, monitoring polymerization processes, and evaluating the degradation and mechanical performance of polymers. Additionally, it addresses the challenges related to data availability and interpretability. Through various case studies and comparative analyses, the review demonstrates the effectiveness of LSTM networks in different polymer science applications. Future directions are also discussed, with an emphasis on real-time applications and the need for interdisciplinary collaboration. The goal of this review is to connect advanced machine learning (ML) techniques with polymer science, thereby promoting innovation and improving predictive capabilities in the field. Full article

(This article belongs to the Special Issue Computational and Experimental Approaches in Polymeric Materials)

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