The ability to accurately predict the rheological behavior of the blends of two incompatible polymers is critical to the polymer industry. The constitutive modeling of incompatible polymer blends requires understanding the structure and dynamics of the blends across different length scales. The polydispersity of chain length at the molecular level and nonuniformity of flow field due to dispersed domains at the mesoscopic level present significant challenges to this industrially relevant problem. This work proposes a modeling framework for linear and nonlinear rheology of industrial incompatible polymer blends with sea-island morphology. For the individual components, we adopt the Rolie-Double-Poly model and generate the relaxation spectrum from an optimized molecular weight distribution. We derive a new mixing rule without empirical parameters from the flow field analysis inside and outside the droplets. The phase interface, modeled by an ellipsoidal model, contributes to the apparent rheology only at low shear rates. Our modeling approach is verified by the shear and extensional rheology of eight polymer blends with a broad range of viscosity ratios (0.01–100). We also show that the model has the ability to predict the nonlinear rheological behaviors of incompatible polymer blends with known molecular weight distributions and phase morphology.
{"title":"Modeling linear and nonlinear rheology of industrial incompatible polymer blends","authors":"Xinyang Zhao, Benke Li, Sijun Liu, Li Peng, Xianbo Huang, Wei Yu","doi":"10.1122/8.0000728","DOIUrl":"https://doi.org/10.1122/8.0000728","url":null,"abstract":"The ability to accurately predict the rheological behavior of the blends of two incompatible polymers is critical to the polymer industry. The constitutive modeling of incompatible polymer blends requires understanding the structure and dynamics of the blends across different length scales. The polydispersity of chain length at the molecular level and nonuniformity of flow field due to dispersed domains at the mesoscopic level present significant challenges to this industrially relevant problem. This work proposes a modeling framework for linear and nonlinear rheology of industrial incompatible polymer blends with sea-island morphology. For the individual components, we adopt the Rolie-Double-Poly model and generate the relaxation spectrum from an optimized molecular weight distribution. We derive a new mixing rule without empirical parameters from the flow field analysis inside and outside the droplets. The phase interface, modeled by an ellipsoidal model, contributes to the apparent rheology only at low shear rates. Our modeling approach is verified by the shear and extensional rheology of eight polymer blends with a broad range of viscosity ratios (0.01–100). We also show that the model has the ability to predict the nonlinear rheological behaviors of incompatible polymer blends with known molecular weight distributions and phase morphology.","PeriodicalId":508264,"journal":{"name":"Journal of Rheology","volume":"11 6","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139687159","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
An aqueous dispersion of Laponite® has been studied in the literature for over the past three decades. Typically, the aqueous dispersion of Laponite® undergoes incessant evolution of its microstructure, wherein its elastic modulus and the mean relaxation time show a continuous increase as a function of time. A considerable amount of discussion has revolved around the nature of this dispersion, specifically whether it can be classified as a repulsive Wigner glass state, characterized by disconnected Laponite® particles stabilized by electrostatic repulsions, or an attractive gel state, in which the particles form a percolated space-spanning network. The proponents of the Wigner glass state also conjecture that this system experiences a glass–glass transition after a period of 2 days has elapsed since its preparation. In this Commentary, we explore this topic from a rheological point of view, analyzing the published literature and performing new experiments. Aided by additional evidence from the literature, we propose that rheological behavior overwhelmingly suggests that an aqueous dispersion of Laponite® undergoes a sol–attractive gel transition and remains in the attractive gel state over at least up to 7 days without undergoing any additional transition. Importantly, rheology, despite being a macroscopic tool governed by principles of mechanics, offers profound insight into the microstructure of this particular system. The corresponding analysis conclusively determines the state of an aqueous dispersion of Laponite® to be an attractive gel.
{"title":"Aqueous Laponite® dispersions are attractive gels, not repulsive Wigner glasses: A critical commentary","authors":"Yogesh M Joshi, Shrajesh Patel, Khushboo Suman","doi":"10.1122/8.0000743","DOIUrl":"https://doi.org/10.1122/8.0000743","url":null,"abstract":"An aqueous dispersion of Laponite® has been studied in the literature for over the past three decades. Typically, the aqueous dispersion of Laponite® undergoes incessant evolution of its microstructure, wherein its elastic modulus and the mean relaxation time show a continuous increase as a function of time. A considerable amount of discussion has revolved around the nature of this dispersion, specifically whether it can be classified as a repulsive Wigner glass state, characterized by disconnected Laponite® particles stabilized by electrostatic repulsions, or an attractive gel state, in which the particles form a percolated space-spanning network. The proponents of the Wigner glass state also conjecture that this system experiences a glass–glass transition after a period of 2 days has elapsed since its preparation. In this Commentary, we explore this topic from a rheological point of view, analyzing the published literature and performing new experiments. Aided by additional evidence from the literature, we propose that rheological behavior overwhelmingly suggests that an aqueous dispersion of Laponite® undergoes a sol–attractive gel transition and remains in the attractive gel state over at least up to 7 days without undergoing any additional transition. Importantly, rheology, despite being a macroscopic tool governed by principles of mechanics, offers profound insight into the microstructure of this particular system. The corresponding analysis conclusively determines the state of an aqueous dispersion of Laponite® to be an attractive gel.","PeriodicalId":508264,"journal":{"name":"Journal of Rheology","volume":"122 48","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139453745","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Adeniyi Ogunkeye, Rebecca E. Hudson-Kershaw, Daniel J. Curtis
{"title":"Erratum: “The effect of instrument inertia on the initiation of oscillatory flow in stress controlled rheometry” [J. Rheol. 67, 1175 (2023)]","authors":"Adeniyi Ogunkeye, Rebecca E. Hudson-Kershaw, Daniel J. Curtis","doi":"10.1122/8.0000804","DOIUrl":"https://doi.org/10.1122/8.0000804","url":null,"abstract":"","PeriodicalId":508264,"journal":{"name":"Journal of Rheology","volume":" 65","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139392092","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We all instinctively poke, bounce, scoop, and observe materials to understand rheological properties quickly. Yet, these observations are rarely analyzed quantitatively. To address this, here we introduce the paradigm of protorheology: approximate quantitative inference from simple observations. Several case studies demonstrate how protorheology is an inclusive entry to rheology for a broad range of practitioners and strengthens the confidence and interpretation of accurate laboratory measurements. We survey a range of creative tests according to which rheological phenomenon is revealed. Some new working equations are derived, and all working equations are summarized for convenient reference and comparison across different methods. This establishes a framework to enable increased use of photos, videos, and quantitative inference and to support the increasing interest in digital image analysis, inverse methods, and high-throughput characterization being applied to rheological properties.
{"title":"Protorheology","authors":"Mohammad Tanver Hossain, Randy H. Ewoldt","doi":"10.1122/8.0000667","DOIUrl":"https://doi.org/10.1122/8.0000667","url":null,"abstract":"We all instinctively poke, bounce, scoop, and observe materials to understand rheological properties quickly. Yet, these observations are rarely analyzed quantitatively. To address this, here we introduce the paradigm of protorheology: approximate quantitative inference from simple observations. Several case studies demonstrate how protorheology is an inclusive entry to rheology for a broad range of practitioners and strengthens the confidence and interpretation of accurate laboratory measurements. We survey a range of creative tests according to which rheological phenomenon is revealed. Some new working equations are derived, and all working equations are summarized for convenient reference and comparison across different methods. This establishes a framework to enable increased use of photos, videos, and quantitative inference and to support the increasing interest in digital image analysis, inverse methods, and high-throughput characterization being applied to rheological properties.","PeriodicalId":508264,"journal":{"name":"Journal of Rheology","volume":"128 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139393750","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Diego D. Soetrisno, Carina D. V. Martínez Narváez, Mariah J. Gallegos, Vivek Sharma, J. Conrad
We study the extensional flow properties by characterizing the capillarity-driven pinching dynamics of dense colloidal suspensions at a constant volume fraction ϕ=0.40 with polymer-induced depletion interactions using a dripping-onto-substrate (DoS) protocol. Methacrylate copolymer particles with dimethylacrylamide copolymer brushes are suspended in a refractive-index- and density-matched mixture of 80 (w/w)% glycerol in water with NaCl added to screen the electrostatic repulsions. Depletion attractions between the colloids are introduced by adding polyacrylamide polymers of weight and dispersity. The addition of polymer delays and modifies the pinch-off dynamics of the dense suspensions, depending on the size and dispersity of the polymer. The extensional relaxation time λE of suspensions collapses as a function of the normalized free volume polymer concentration c/c∗ with the corresponding polymer solutions, indicating that the elastic properties of the polymer solutions control the extensional time scale. Following the results of our previous study [Soetrisno et al., Macromolecules 56, 4919–4928 (2023)], the polymer size determines the scaling exponent of λE for colloid-polymer mixtures in the dilute regime and high dispersity shifts the concentration where the scaling of λE transitions from power-law to linear. The filament lifespans tf of colloid-polymer mixtures and of polymer solutions collapse onto a master curve as a function of c/c∗ when normalized by the filament lifespan of the corresponding fluid without polymer tf,0. These results provide insight into the role of the polymer size in dictating the pinching dynamics and extensional rheology of colloid-polymer mixtures and further suggest that the shear and extensional responses of these mixtures can be separately tuned through the concentrations of the two constituents.
{"title":"Pinching dynamics and extensional rheology of dense colloidal suspensions with depletion attractions","authors":"Diego D. Soetrisno, Carina D. V. Martínez Narváez, Mariah J. Gallegos, Vivek Sharma, J. Conrad","doi":"10.1122/8.0000717","DOIUrl":"https://doi.org/10.1122/8.0000717","url":null,"abstract":"We study the extensional flow properties by characterizing the capillarity-driven pinching dynamics of dense colloidal suspensions at a constant volume fraction ϕ=0.40 with polymer-induced depletion interactions using a dripping-onto-substrate (DoS) protocol. Methacrylate copolymer particles with dimethylacrylamide copolymer brushes are suspended in a refractive-index- and density-matched mixture of 80 (w/w)% glycerol in water with NaCl added to screen the electrostatic repulsions. Depletion attractions between the colloids are introduced by adding polyacrylamide polymers of weight and dispersity. The addition of polymer delays and modifies the pinch-off dynamics of the dense suspensions, depending on the size and dispersity of the polymer. The extensional relaxation time λE of suspensions collapses as a function of the normalized free volume polymer concentration c/c∗ with the corresponding polymer solutions, indicating that the elastic properties of the polymer solutions control the extensional time scale. Following the results of our previous study [Soetrisno et al., Macromolecules 56, 4919–4928 (2023)], the polymer size determines the scaling exponent of λE for colloid-polymer mixtures in the dilute regime and high dispersity shifts the concentration where the scaling of λE transitions from power-law to linear. The filament lifespans tf of colloid-polymer mixtures and of polymer solutions collapse onto a master curve as a function of c/c∗ when normalized by the filament lifespan of the corresponding fluid without polymer tf,0. These results provide insight into the role of the polymer size in dictating the pinching dynamics and extensional rheology of colloid-polymer mixtures and further suggest that the shear and extensional responses of these mixtures can be separately tuned through the concentrations of the two constituents.","PeriodicalId":508264,"journal":{"name":"Journal of Rheology","volume":" 8","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139144539","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Parallel superposition rheology has been explored using Brownian dynamics simulations on a model colloidal gel by imposing a small amplitude probing oscillation parallel to the main shear flow. This study aims to investigate the constituting principles behind the material functions in parallel superposition rheometry (PSR) and to elucidate the principles behind the structure responses. The viscoelastic spectra under frequency sweeps show that in a high-frequency region, each curve can be superimposed onto a single master curve using horizontal shift factors equal to viscosity which is a reminiscence of time-shear rate superposition in orthogonal superposition rheometry. This corresponds to the region where a parallel superposition analysis can be adequately performed as the shear rate controls the viscoelastic spectra of the gel independently from probing perturbation. On the other hand, in the low-frequency region, this principle breaks down and even negative storage modulus is observed due to the strong flow coupling effect, which is also found in experiments. By introducing the spatial moduli, it is found that the negative modulus originates from the attractive potential region. In the flow conditions where negative modulus occurs, the shear force is strong enough to break down every surface bond between the particles. In this state, the increase in structural factor in response to the rise in the shear rate dominates particle stress, even within the attractive potential region. This arises because the isolated particles have more opportunities to interact with other particles as the shear rate of the imposed perturbation increases. This structural response, influenced by the attractive potential, results in a negative storage modulus and a positive loss modulus after performing Fourier transformation. This paper, for the first time by a simulation approach, demonstrates the essential characteristics of the material functions obtained using PSR. Also, this study is expected to enhance our understanding on the flowing materials and suggest a criterion for the reliable application of superposition rheology using a viscoelastic master curve.
通过对模型胶体凝胶施加与主剪切流平行的小振幅探测振荡，利用布朗动力学模拟探索了平行叠加流变学。本研究旨在探究平行叠加流变学（PSR）中材料函数背后的构成原理，并阐明结构响应背后的原理。频率扫描下的粘弹性频谱显示，在高频区域，每条曲线都可以通过与粘度相等的水平移动因子叠加到一条主曲线上，这是对正交叠加流变仪中时间-剪切速率叠加的再现。由于剪切速率控制着凝胶的粘弹性光谱，而不受探测扰动的影响，因此在这一区域可以充分进行平行叠加分析。另一方面，在低频区域，这一原则会被打破，由于强烈的流动耦合效应，甚至会观察到负的存储模量，这在实验中也有发现。通过引入空间模量，可以发现负模量源于吸引力势区。在出现负模量的流动条件下，剪切力足以破坏颗粒之间的每一个表面键。在这种状态下，随着剪切速率的上升，结构因子的增加会主导颗粒应力，即使在吸引力势能区域内也是如此。这是因为随着外加扰动的剪切速率增加，孤立的粒子有更多机会与其他粒子相互作用。这种受吸引力影响的结构响应在进行傅立叶变换后会产生负的存储模量和正的损耗模量。本文首次通过模拟方法展示了利用 PSR 获得的材料函数的基本特征。此外，这项研究有望加深我们对流动材料的理解，并为使用粘弹性主曲线可靠地应用叠加流变学提出一个标准。
{"title":"Brownian dynamics simulation on the parallel superposition rheology of a colloidal gel","authors":"Young Jin Lee, Howon Jin, Kyung Hyun Ahn","doi":"10.1122/8.0000672","DOIUrl":"https://doi.org/10.1122/8.0000672","url":null,"abstract":"Parallel superposition rheology has been explored using Brownian dynamics simulations on a model colloidal gel by imposing a small amplitude probing oscillation parallel to the main shear flow. This study aims to investigate the constituting principles behind the material functions in parallel superposition rheometry (PSR) and to elucidate the principles behind the structure responses. The viscoelastic spectra under frequency sweeps show that in a high-frequency region, each curve can be superimposed onto a single master curve using horizontal shift factors equal to viscosity which is a reminiscence of time-shear rate superposition in orthogonal superposition rheometry. This corresponds to the region where a parallel superposition analysis can be adequately performed as the shear rate controls the viscoelastic spectra of the gel independently from probing perturbation. On the other hand, in the low-frequency region, this principle breaks down and even negative storage modulus is observed due to the strong flow coupling effect, which is also found in experiments. By introducing the spatial moduli, it is found that the negative modulus originates from the attractive potential region. In the flow conditions where negative modulus occurs, the shear force is strong enough to break down every surface bond between the particles. In this state, the increase in structural factor in response to the rise in the shear rate dominates particle stress, even within the attractive potential region. This arises because the isolated particles have more opportunities to interact with other particles as the shear rate of the imposed perturbation increases. This structural response, influenced by the attractive potential, results in a negative storage modulus and a positive loss modulus after performing Fourier transformation. This paper, for the first time by a simulation approach, demonstrates the essential characteristics of the material functions obtained using PSR. Also, this study is expected to enhance our understanding on the flowing materials and suggest a criterion for the reliable application of superposition rheology using a viscoelastic master curve.","PeriodicalId":508264,"journal":{"name":"Journal of Rheology","volume":"28 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139176353","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
To meet the challenge of efficient modeling of film blowing with realistic constitutive equations for commercial thermoplastic melts, we present a multistage optimization modeling framework that integrates polymerization reaction modeling, rheology modeling, and bubble-shape prediction. A direct link is thereby created between the polymer architecture and the bubble shape of low-density polyethylene (LDPE) through a three-stage modeling protocol. Stage 1 aims to get complete polymer structure information from a limited set of linear and nonlinear rheological data and the measured averaged molecular weight. An optimization loop uses the Tobita algorithm for polymer reaction and the BoB model for rheology to minimize the deviation between experimental data and model predictions. Stage 2 is designed to obtain a representative reduced ensemble of LDPE in the Rolie-double-poly (RDP) model to reduce the computational cost of rheology calculations during processing. The parameters of the reduced molecular components are obtained by fitting the RDP model to a wide range of rheology data predicted by the BoB model applied to the full ensemble of polymer architectures obtained in stage 1. In stage 3, the reduced-ensemble RDP model is coupled to measured temperature profiles using time–temperature superposition, and the bubble shape and strain rate history of a fluid particle in the bubble are obtained by minimizing error in the momentum balance equations. We show that each stage of the process yields successful fitting, and at the end, we obtain an a priori prediction of height-dependent bubble radius and velocity in agreement with experiment. With this multistage optimization strategy, we link the polymer compositions to the bubble properties during the film blowing of LDPE.
为了应对利用商用热塑性熔体的现实构成方程对吹膜进行高效建模的挑战，我们提出了一个多阶段优化建模框架，该框架集成了聚合反应建模、流变建模和气泡形状预测。通过三阶段建模方案，在聚合物结构和低密度聚乙烯（LDPE）气泡形状之间建立了直接联系。第一阶段旨在从有限的线性和非线性流变数据集以及测量的平均分子量中获取完整的聚合物结构信息。优化循环使用聚合物反应的 Tobita 算法和流变学的 BoB 模型，以尽量减少实验数据与模型预测之间的偏差。第二阶段的目的是在罗利-双聚物（RDP）模型中获得具有代表性的低密度聚乙烯还原组合，以降低加工过程中流变计算的计算成本。通过将 RDP 模型与应用于第 1 阶段获得的聚合物结构全集合的 BoB 模型所预测的各种流变数据进行拟合，可获得还原分子成分的参数。在第 3 阶段，利用时间-温度叠加法将还原组合 RDP 模型与测量的温度曲线相结合，并通过最小化动量平衡方程中的误差来获得气泡形状和气泡中流体粒子的应变率历史。我们的研究表明，该过程的每个阶段都能成功拟合，最后，我们获得了与实验一致的随高度变化的气泡半径和速度的先验预测。通过这种多阶段优化策略，我们将聚合物成分与低密度聚乙烯吹膜过程中的气泡特性联系起来。
{"title":"Linking polymer architecture to bubble shape in LDPE film blowing through multistage modeling","authors":"Zhiqiang Shen, Yanan Gong, Ronald G. Larson","doi":"10.1122/8.0000735","DOIUrl":"https://doi.org/10.1122/8.0000735","url":null,"abstract":"To meet the challenge of efficient modeling of film blowing with realistic constitutive equations for commercial thermoplastic melts, we present a multistage optimization modeling framework that integrates polymerization reaction modeling, rheology modeling, and bubble-shape prediction. A direct link is thereby created between the polymer architecture and the bubble shape of low-density polyethylene (LDPE) through a three-stage modeling protocol. Stage 1 aims to get complete polymer structure information from a limited set of linear and nonlinear rheological data and the measured averaged molecular weight. An optimization loop uses the Tobita algorithm for polymer reaction and the BoB model for rheology to minimize the deviation between experimental data and model predictions. Stage 2 is designed to obtain a representative reduced ensemble of LDPE in the Rolie-double-poly (RDP) model to reduce the computational cost of rheology calculations during processing. The parameters of the reduced molecular components are obtained by fitting the RDP model to a wide range of rheology data predicted by the BoB model applied to the full ensemble of polymer architectures obtained in stage 1. In stage 3, the reduced-ensemble RDP model is coupled to measured temperature profiles using time–temperature superposition, and the bubble shape and strain rate history of a fluid particle in the bubble are obtained by minimizing error in the momentum balance equations. We show that each stage of the process yields successful fitting, and at the end, we obtain an a priori prediction of height-dependent bubble radius and velocity in agreement with experiment. With this multistage optimization strategy, we link the polymer compositions to the bubble properties during the film blowing of LDPE.","PeriodicalId":508264,"journal":{"name":"Journal of Rheology","volume":"33 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139213589","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Spyridakis, P. Moschopoulos, S. Varchanis, Y. Dimakopoulos, J. Tsamopoulos
We propose an enhanced model for the rheological characterization of human blood that accounts for thixotropy, viscoelasticity, and yield-stress. Blood plasma is assumed to act as a Newtonian solvent. We introduce a scalar variable, λ, to macroscopically describe the structure of blood. The temporal evolution of λ is governed by an equation that accounts for aggregation of red blood cells and breakdown of rouleaux structures. We introduce a Gaussian function that qualitatively describes experimental findings on rouleaux restructuring and the expression that was proposed by Stephanou and Georgiou for the breakdown term. The constitutive equation for stresses is based on the elastoviscoplastic formalism by Saramito. However, the max term of the viscoplastic deformation rate has been replaced by a continuous function of λ to account for smooth solid-fluid transition, following the experimental evidence. The continuous yielding description provides improved rheological predictions, especially in small amplitude oscillatory shear. The model predicts finite viscous dissipation at small amplitude oscillation, as we would expect from a gel material-like human blood. Overall, it has nine adjustable parameters that are fitted simultaneously to experimental data by nonlinear regression. The model can accurately predict numerous flow conditions: steady shear, step shear, hysteresis loops, and oscillatory shear. We compare this model (TEVP 9) to our previous formulation for human blood (TEVP 11), and we show that the predictions of the new model are more accurate, despite using fewer parameters. We provide additional predictions for uniaxial elongation, which include finite normal stress difference, extensional hardening at large values of the extensional rate, and extensional thinning at extremely large extensional rates.
{"title":"Thixo-elastoviscoplastic modeling of human blood","authors":"A. Spyridakis, P. Moschopoulos, S. Varchanis, Y. Dimakopoulos, J. Tsamopoulos","doi":"10.1122/8.0000711","DOIUrl":"https://doi.org/10.1122/8.0000711","url":null,"abstract":"We propose an enhanced model for the rheological characterization of human blood that accounts for thixotropy, viscoelasticity, and yield-stress. Blood plasma is assumed to act as a Newtonian solvent. We introduce a scalar variable, λ, to macroscopically describe the structure of blood. The temporal evolution of λ is governed by an equation that accounts for aggregation of red blood cells and breakdown of rouleaux structures. We introduce a Gaussian function that qualitatively describes experimental findings on rouleaux restructuring and the expression that was proposed by Stephanou and Georgiou for the breakdown term. The constitutive equation for stresses is based on the elastoviscoplastic formalism by Saramito. However, the max term of the viscoplastic deformation rate has been replaced by a continuous function of λ to account for smooth solid-fluid transition, following the experimental evidence. The continuous yielding description provides improved rheological predictions, especially in small amplitude oscillatory shear. The model predicts finite viscous dissipation at small amplitude oscillation, as we would expect from a gel material-like human blood. Overall, it has nine adjustable parameters that are fitted simultaneously to experimental data by nonlinear regression. The model can accurately predict numerous flow conditions: steady shear, step shear, hysteresis loops, and oscillatory shear. We compare this model (TEVP 9) to our previous formulation for human blood (TEVP 11), and we show that the predictions of the new model are more accurate, despite using fewer parameters. We provide additional predictions for uniaxial elongation, which include finite normal stress difference, extensional hardening at large values of the extensional rate, and extensional thinning at extremely large extensional rates.","PeriodicalId":508264,"journal":{"name":"Journal of Rheology","volume":"16 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139249540","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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