Zhaopeng Hu, Junwei Zhou, Yihu Song, Qiang Zheng, Wanjie Wang
Engineered rubber vulcanizates may contain a low content of short fibers and a high content of nanoparticles while the effects of the different fillers on the softening behavior are not yet explored. Herein, influences of carbon black (CB) and short aramid fiber (AF) on the Payne and Mullins effects of natural rubber composites are investigated for the first time by creating master curves of dynamic modulus or dissipation energy with respect to the straining responses of the matrix. It is revealed that the composite vulcanizates demonstrate the Payne effect characterized by decay of storage modulus, weak overshoot of loss modulus, and very weak high-order harmonics; this effect is mainly dominated by the rubber matrix experiencing microscopic strain amplitude enlarged by the filler. The composite vulcanizates exhibit the Mullins effect that becomes increasingly marked with increasing filler loading and is partially recovered by thermal annealing at relatively high temperatures. The energy dissipation during cyclic tensions is rooted in the viscoelastic deformation of the matrix and the filler-rubber interfacial debonding. The former is marked at room temperature where the rubber phase undergoes a crystallization-melting process during loading-unloading. The latter being marked in the presence of a small content of AF causes yieldinglike deformation for the virgin composites at low tensile strains, and its contribution to the softening is not recoverable during thermal annealing. The results show that the viscoelastic matrix is of importance in controlling the softening of the composite vulcanizates, which will be of guiding significance to conduct research studies on high-performance rubber composites products.
{"title":"Strain softening of natural rubber composites filled with carbon black and aramid fiber","authors":"Zhaopeng Hu, Junwei Zhou, Yihu Song, Qiang Zheng, Wanjie Wang","doi":"10.1122/8.0000474","DOIUrl":"https://doi.org/10.1122/8.0000474","url":null,"abstract":"Engineered rubber vulcanizates may contain a low content of short fibers and a high content of nanoparticles while the effects of the different fillers on the softening behavior are not yet explored. Herein, influences of carbon black (CB) and short aramid fiber (AF) on the Payne and Mullins effects of natural rubber composites are investigated for the first time by creating master curves of dynamic modulus or dissipation energy with respect to the straining responses of the matrix. It is revealed that the composite vulcanizates demonstrate the Payne effect characterized by decay of storage modulus, weak overshoot of loss modulus, and very weak high-order harmonics; this effect is mainly dominated by the rubber matrix experiencing microscopic strain amplitude enlarged by the filler. The composite vulcanizates exhibit the Mullins effect that becomes increasingly marked with increasing filler loading and is partially recovered by thermal annealing at relatively high temperatures. The energy dissipation during cyclic tensions is rooted in the viscoelastic deformation of the matrix and the filler-rubber interfacial debonding. The former is marked at room temperature where the rubber phase undergoes a crystallization-melting process during loading-unloading. The latter being marked in the presence of a small content of AF causes yieldinglike deformation for the virgin composites at low tensile strains, and its contribution to the softening is not recoverable during thermal annealing. The results show that the viscoelastic matrix is of importance in controlling the softening of the composite vulcanizates, which will be of guiding significance to conduct research studies on high-performance rubber composites products.","PeriodicalId":16991,"journal":{"name":"Journal of Rheology","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45904286","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Sara Tarashi, H. Nazockdast, A. Bandegi, Saeid Shafaghsorkh, G. Sodeifian, R. Foudazi
Double network (DN) hydrogels have been recognized as new tough materials for several industries due to their precise structural platforms and significant properties. However, a comprehensive understanding of microstructural changes of DN hydrogels under large deformations is required to extend their applications. In this work, we use the large amplitude oscillatory shear (LAOS) technique to study the nonlinear response of a thermoresponsive κ-carrageenan/polyacrylamide DN system and its nanocomposite containing graphene oxide (GO) in comparison to its single network components. The results show a combination of strain stiffening and shear thickening nonlinear responses. The elastic intracycle strain stiffening was mainly attributed to the shear-induced increase in the elasticity of network chains and non-Gaussian stretching of individual chains. In addition, the orientation of the κ-carrageenan double helix segments and their enhancing effect on molecular orientation could be proposed as another possible mechanism of strain stiffening. The viscous intracycle shear thickening is also interpreted by two mechanisms of shear-induced temporary structure formation and reformation of dissociated physical interactions. It is also found that the GO nanosheets could contribute to the viscoelastic response by increasing the molecular interactions and, thus, amplification of energy dissipation. Furthermore, temperature dependency of the DN hydrogel owing to the conformational changes of the κ-carrageenan network at sufficiently high temperatures is used to investigate the effect of temperature on nonlinear behaviors. Increasing the temperature is found to have a significant decreasing effect on viscous nonlinearity, while its effect on the elastic nonlinearity was strongly dependent on the strain amplitude. This study provides a better understanding of the correlation between the microstructure and viscoelastic properties for designing tough hydrogels.
{"title":"Large amplitude oscillatory shear behavior of thermoresponsive hydrogels: Single versus double network","authors":"Sara Tarashi, H. Nazockdast, A. Bandegi, Saeid Shafaghsorkh, G. Sodeifian, R. Foudazi","doi":"10.1122/8.0000457","DOIUrl":"https://doi.org/10.1122/8.0000457","url":null,"abstract":"Double network (DN) hydrogels have been recognized as new tough materials for several industries due to their precise structural platforms and significant properties. However, a comprehensive understanding of microstructural changes of DN hydrogels under large deformations is required to extend their applications. In this work, we use the large amplitude oscillatory shear (LAOS) technique to study the nonlinear response of a thermoresponsive κ-carrageenan/polyacrylamide DN system and its nanocomposite containing graphene oxide (GO) in comparison to its single network components. The results show a combination of strain stiffening and shear thickening nonlinear responses. The elastic intracycle strain stiffening was mainly attributed to the shear-induced increase in the elasticity of network chains and non-Gaussian stretching of individual chains. In addition, the orientation of the κ-carrageenan double helix segments and their enhancing effect on molecular orientation could be proposed as another possible mechanism of strain stiffening. The viscous intracycle shear thickening is also interpreted by two mechanisms of shear-induced temporary structure formation and reformation of dissociated physical interactions. It is also found that the GO nanosheets could contribute to the viscoelastic response by increasing the molecular interactions and, thus, amplification of energy dissipation. Furthermore, temperature dependency of the DN hydrogel owing to the conformational changes of the κ-carrageenan network at sufficiently high temperatures is used to investigate the effect of temperature on nonlinear behaviors. Increasing the temperature is found to have a significant decreasing effect on viscous nonlinearity, while its effect on the elastic nonlinearity was strongly dependent on the strain amplitude. This study provides a better understanding of the correlation between the microstructure and viscoelastic properties for designing tough hydrogels.","PeriodicalId":16991,"journal":{"name":"Journal of Rheology","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42714932","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Michael C. Burroughs, Yuan-Yin Zhang, A. Shetty, Christopher M. Bates, M. Helgeson, L. Leal
Shear banding in entangled polymer solutions is an elusive phenomenon in polymer rheology. One recently proposed mechanism for the existence of banded velocity profiles in entangled polymer solutions stems from a coupling of the flow to banded concentration profiles. Recent work [Burroughs et al., Phys. Rev. Lett . 126, 207801 (2021)] provided experimental evidence for the development of large gradients in concentration across the fluid. Here, a more systematic investigation is reported of the transient and steady-state banded velocity and concentration profiles of entangled polybutadiene in dioctyl phthalate solutions as a function of temperature [Formula: see text], number of entanglements ([Formula: see text]), and applied shear rate ([Formula: see text]), which control the susceptibility of the fluid to unstable flow-concentration coupling. The results are compared to a two-fluid model that accounts for coupling between elastic and osmotic polymer stresses, and a strong agreement is found between model predictions and measured concentration profiles. The interface locations and widths of the time-averaged, steady-state velocity profiles are quantified from high-order numerical derivatives of the data. At high levels of entanglement and large [Formula: see text], a significant wall slip is observed at both inner and outer surfaces of the flow geometry but is not a necessary criterion for a nonhomogeneous flow. Furthermore, the transient evolution of flow profiles for large Z indicate transitions from curved to “stair-stepped” and, ultimately, a banded steady state. These observed transitions provide detailed evidence for shear-induced demixing as a mechanism of shear banding in polymer solutions.
{"title":"Flow-concentration coupling determines features of nonhomogeneous flow and shear banding in entangled polymer solutions","authors":"Michael C. Burroughs, Yuan-Yin Zhang, A. Shetty, Christopher M. Bates, M. Helgeson, L. Leal","doi":"10.1122/8.0000469","DOIUrl":"https://doi.org/10.1122/8.0000469","url":null,"abstract":"Shear banding in entangled polymer solutions is an elusive phenomenon in polymer rheology. One recently proposed mechanism for the existence of banded velocity profiles in entangled polymer solutions stems from a coupling of the flow to banded concentration profiles. Recent work [Burroughs et al., Phys. Rev. Lett . 126, 207801 (2021)] provided experimental evidence for the development of large gradients in concentration across the fluid. Here, a more systematic investigation is reported of the transient and steady-state banded velocity and concentration profiles of entangled polybutadiene in dioctyl phthalate solutions as a function of temperature [Formula: see text], number of entanglements ([Formula: see text]), and applied shear rate ([Formula: see text]), which control the susceptibility of the fluid to unstable flow-concentration coupling. The results are compared to a two-fluid model that accounts for coupling between elastic and osmotic polymer stresses, and a strong agreement is found between model predictions and measured concentration profiles. The interface locations and widths of the time-averaged, steady-state velocity profiles are quantified from high-order numerical derivatives of the data. At high levels of entanglement and large [Formula: see text], a significant wall slip is observed at both inner and outer surfaces of the flow geometry but is not a necessary criterion for a nonhomogeneous flow. Furthermore, the transient evolution of flow profiles for large Z indicate transitions from curved to “stair-stepped” and, ultimately, a banded steady state. These observed transitions provide detailed evidence for shear-induced demixing as a mechanism of shear banding in polymer solutions.","PeriodicalId":16991,"journal":{"name":"Journal of Rheology","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45782244","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
To predict the complex rheology and shear-rate inhomogeneities of lamellar gel networks, we propose a simple thixotropic constitutive model with an elastoplastic stress and a smoothly decreasing modulus near a solid boundary, motivated by the analysis of the effect of confinement and shear flow on lamellae orientation near surfaces. We show that the model qualitatively captures the important features of the lamellar gel shear rheology observed in experiments [Datta et al., J. Rheol. 64(4), 851–862 (2020)]. These include thixotropic shear thinning that is intermediate between constant viscosity and constant stress, a power-law slow creep under small constant shear stress and abrupt transition to fast creep at higher stress, as well as partial recovery of strain upon stress removal. In addition, the model correctly predicts a gap-dependent rheology and roughly predicts the amplitude dependence of storage and loss moduli in oscillatory tests despite having only a single thixotropic time constant. Most importantly, the introduction of the modulus gradient enables the model to predict the unique shear-banding phenomenon of lamellar gel networks wherein a thin, fast-shearing band exists near the boundary that widens only slowly with increased apparent shear rate until a very high rate is reached, while the bulk moves as a plug [Datta et al., J. Rheol. 64(4), 851–862 (2020)]. We discuss the influence of a lower modulus near the boundary and its possible origin in the underlying lamellar structure of the material.
为了预测层状凝胶网络的复杂流变学和剪切速率的不均匀性，我们提出了一个简单的触变本构模型，该模型具有弹塑性应力和接近固体边界的平滑下降的模量，并分析了约束和剪切流动对近表面层状凝胶取向的影响。我们表明，该模型定性地捕捉了实验中观察到的板层凝胶剪切流变学的重要特征[Datta et al.， J. Rheol. 64(4)， 851-862(2020)]。其中包括介于恒定粘度和恒定应力之间的触变剪切变薄，小恒定剪切应力下的幂律缓慢蠕变和高应力下的快速蠕变，以及应力去除后应变的部分恢复。此外，该模型正确地预测了间隙依赖的流变性，并大致预测了振荡试验中存储模量和损耗模量的振幅依赖，尽管只有一个触变时间常数。最重要的是，模量梯度的引入使模型能够预测层状凝胶网络独特的剪切带现象，其中在边界附近存在一条薄的快速剪切带，随着表观剪切速率的增加而缓慢变宽，直到达到非常高的剪切速率，而体块像塞一样移动[Datta等人，J. Rheol. 64(4)， 851-862(2020)]。讨论了边界附近低模量的影响及其在材料层状结构中的可能来源。
{"title":"Thixotropic constitutive modeling of shear banding by boundary-induced modulus gradient in lamellar gel networks","authors":"Futianyi Wang, R. Larson","doi":"10.1122/8.0000482","DOIUrl":"https://doi.org/10.1122/8.0000482","url":null,"abstract":"To predict the complex rheology and shear-rate inhomogeneities of lamellar gel networks, we propose a simple thixotropic constitutive model with an elastoplastic stress and a smoothly decreasing modulus near a solid boundary, motivated by the analysis of the effect of confinement and shear flow on lamellae orientation near surfaces. We show that the model qualitatively captures the important features of the lamellar gel shear rheology observed in experiments [Datta et al., J. Rheol. 64(4), 851–862 (2020)]. These include thixotropic shear thinning that is intermediate between constant viscosity and constant stress, a power-law slow creep under small constant shear stress and abrupt transition to fast creep at higher stress, as well as partial recovery of strain upon stress removal. In addition, the model correctly predicts a gap-dependent rheology and roughly predicts the amplitude dependence of storage and loss moduli in oscillatory tests despite having only a single thixotropic time constant. Most importantly, the introduction of the modulus gradient enables the model to predict the unique shear-banding phenomenon of lamellar gel networks wherein a thin, fast-shearing band exists near the boundary that widens only slowly with increased apparent shear rate until a very high rate is reached, while the bulk moves as a plug [Datta et al., J. Rheol. 64(4), 851–862 (2020)]. We discuss the influence of a lower modulus near the boundary and its possible origin in the underlying lamellar structure of the material.","PeriodicalId":16991,"journal":{"name":"Journal of Rheology","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47637768","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Formation and coalescence of solvent droplets on a thread of polymer solution at the final stage of capillary pinching is studied theoretically. It is considered that macromolecules are already almost completely stretched along the extension axis and their contour length exceeds the diameter of the thread. In this regime, the radius of polymer string decreases slowly with time under the action of capillary forces and the solvent squeezes out to the thread surface forming annular droplets of different sizes. The thinning process stops when the capillary pressure is balanced by the osmotic pressure of the polymer. As a result, a quasistationary two-phase structure of polydisperse solvent droplets on a polymer string is formed. We develop a rigorous theory showing that the polymer core is swollen in the droplet regions but still remains much thinner than the solvent phase. We also demonstrate that such a blistering structure is unstable with respect to droplet coalescence and elucidate two mechanisms of this process due to the solvent flow between the droplets and due to diffusion of solvent droplets along the polymer string. Both mechanisms lead to the same long-time power law ( t1/7) for the droplet radius. It is shown that a breakage of the polymer string may occur at time scales exceeding the Rouse time of polymer chains.
{"title":"Dynamics of annular solvent droplets under capillary thinning of non-entangled polymer solution","authors":"A. Subbotin, A. Semenov","doi":"10.1122/8.0000518","DOIUrl":"https://doi.org/10.1122/8.0000518","url":null,"abstract":"Formation and coalescence of solvent droplets on a thread of polymer solution at the final stage of capillary pinching is studied theoretically. It is considered that macromolecules are already almost completely stretched along the extension axis and their contour length exceeds the diameter of the thread. In this regime, the radius of polymer string decreases slowly with time under the action of capillary forces and the solvent squeezes out to the thread surface forming annular droplets of different sizes. The thinning process stops when the capillary pressure is balanced by the osmotic pressure of the polymer. As a result, a quasistationary two-phase structure of polydisperse solvent droplets on a polymer string is formed. We develop a rigorous theory showing that the polymer core is swollen in the droplet regions but still remains much thinner than the solvent phase. We also demonstrate that such a blistering structure is unstable with respect to droplet coalescence and elucidate two mechanisms of this process due to the solvent flow between the droplets and due to diffusion of solvent droplets along the polymer string. Both mechanisms lead to the same long-time power law ( t1/7) for the droplet radius. It is shown that a breakage of the polymer string may occur at time scales exceeding the Rouse time of polymer chains.","PeriodicalId":16991,"journal":{"name":"Journal of Rheology","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49164949","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
R. Sengupta, Mukul D. Tikekar, James V. Raj, K. Delaney, Michael C. Villet, G. Fredrickson
Reactive blending is an efficient method for synthesizing polymer blends. Industrially, this process is carried out in extruders, where the reacting polymers and the generated copolymer are subjected to high shear stresses. The dynamics of the process, and the resulting morphology is dictated by a coupling of the hydrodynamic forces in the extruder, the thermodynamic interactions between species, and the reaction kinetics on a complex interfacial manifold. We use phase-field simulations to quantify the evolution of the reactive blending process under an external shear flow. Specifically, we consider a model system of two homopolymers of equal length, which react via an end-coupling reaction to form a diblock copolymer of double the length. We compare the morphology development in two different initial geometries of the homopolymers—a cylindrical thread and a drop of one homopolymer in a matrix of the second. We investigate the effect of flow strength, measured by the shear rate, and reaction kinetics, quantified by a Damkohler number, on the progress of the reaction and morphology development. Cylindrical threads are susceptible to breakup via the Rayleigh capillary instability. We demonstrate that this instability can be suppressed by imposing shear along the direction of the thread and increasing the extent of the reaction. The reaction rate in this geometry is unaffected by shear imposed along the cylinder axis. Drops deform significantly under an imposed flow, eventually stretching to long cylindrical threads for sufficient shear rates. In the case of drops, shear stresses enhance the reaction rate by deforming the drop, enabling more homopolymers to come in contact at the expanded interface. We show that shear stresses significantly impact the morphology development and reaction dynamics in reactive polymer blending.
{"title":"Phase-field simulations of morphology development in reactive polymer blending","authors":"R. Sengupta, Mukul D. Tikekar, James V. Raj, K. Delaney, Michael C. Villet, G. Fredrickson","doi":"10.1122/8.0000523","DOIUrl":"https://doi.org/10.1122/8.0000523","url":null,"abstract":"Reactive blending is an efficient method for synthesizing polymer blends. Industrially, this process is carried out in extruders, where the reacting polymers and the generated copolymer are subjected to high shear stresses. The dynamics of the process, and the resulting morphology is dictated by a coupling of the hydrodynamic forces in the extruder, the thermodynamic interactions between species, and the reaction kinetics on a complex interfacial manifold. We use phase-field simulations to quantify the evolution of the reactive blending process under an external shear flow. Specifically, we consider a model system of two homopolymers of equal length, which react via an end-coupling reaction to form a diblock copolymer of double the length. We compare the morphology development in two different initial geometries of the homopolymers—a cylindrical thread and a drop of one homopolymer in a matrix of the second. We investigate the effect of flow strength, measured by the shear rate, and reaction kinetics, quantified by a Damkohler number, on the progress of the reaction and morphology development. Cylindrical threads are susceptible to breakup via the Rayleigh capillary instability. We demonstrate that this instability can be suppressed by imposing shear along the direction of the thread and increasing the extent of the reaction. The reaction rate in this geometry is unaffected by shear imposed along the cylinder axis. Drops deform significantly under an imposed flow, eventually stretching to long cylindrical threads for sufficient shear rates. In the case of drops, shear stresses enhance the reaction rate by deforming the drop, enabling more homopolymers to come in contact at the expanded interface. We show that shear stresses significantly impact the morphology development and reaction dynamics in reactive polymer blending.","PeriodicalId":16991,"journal":{"name":"Journal of Rheology","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46691225","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Rheological measurements typically require at least 20–50 mg of sample. We set up a miniaturized sliding-plates shear rheometer (mgRheo) that requires only 2 mg sample or even less. We designed a flexure-based force-sensing device that could measure force ranging from the micronewton to millinewton scale, e.g., 40 μN–400 mN for one particular spring constant. The setup was strain-controlled by a piezostage and could perform standard rheological tests such as small amplitude oscillatory shear, step strain, and stress relaxation. The accuracy and consistencies were evaluated on polydimethylsiloxane viscoelastic standard, entangled poly(hexyl methacrylate), and polystyrene. The obtained phase angles quantitatively agreed with those from commercial rheometers. The exact values of the modulus are prone to the overfilling of the sample. The storage G′ and loss G″ moduli from the mgRheo were systematically higher than those from commercial rheometers (i.e., within 5% with careful trimming or 30% with excessive overfilling). Between 102 and 106 Pa, G′ and G″ were in good agreement with commercial rheometers. Such a setup allowed for general rheometric characterizations, especially obtaining linear viscoelasticity on soft matters that are synthetically difficult to obtain in a large quantity.
{"title":"Micronewton shear rheometer performing SAOS using 2 mg of sample","authors":"Weiwei Wu, Jintian Luo, Xikai Ouyang, Wangjing He, Kangle Bao, Hui Li, GengXin Liu (刘庚鑫)","doi":"10.1122/8.0000494","DOIUrl":"https://doi.org/10.1122/8.0000494","url":null,"abstract":"Rheological measurements typically require at least 20–50 mg of sample. We set up a miniaturized sliding-plates shear rheometer (mgRheo) that requires only 2 mg sample or even less. We designed a flexure-based force-sensing device that could measure force ranging from the micronewton to millinewton scale, e.g., 40 μN–400 mN for one particular spring constant. The setup was strain-controlled by a piezostage and could perform standard rheological tests such as small amplitude oscillatory shear, step strain, and stress relaxation. The accuracy and consistencies were evaluated on polydimethylsiloxane viscoelastic standard, entangled poly(hexyl methacrylate), and polystyrene. The obtained phase angles quantitatively agreed with those from commercial rheometers. The exact values of the modulus are prone to the overfilling of the sample. The storage G′ and loss G″ moduli from the mgRheo were systematically higher than those from commercial rheometers (i.e., within 5% with careful trimming or 30% with excessive overfilling). Between 102 and 106 Pa, G′ and G″ were in good agreement with commercial rheometers. Such a setup allowed for general rheometric characterizations, especially obtaining linear viscoelasticity on soft matters that are synthetically difficult to obtain in a large quantity.","PeriodicalId":16991,"journal":{"name":"Journal of Rheology","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44276041","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The macroscopic stretchability of ionomer melts strongly relies on the structural evolution during the elongational flow. It has been noted that the introduction of the secondary associations weaker than the ionic association can improve the stretchability. To understand the mechanism, this study examines the stretchability of unentangled ionomers containing a fixed number of ionic groups per chain, [Formula: see text], but a varied number of hydrogen bonds per chain, fH = 5.5–27. The stretchability that is reflected in the maximum Hencky strain achieved before rupture shows nonmonotonous change with fH: the stretchability improves with increasing fH from 5.5 to 14 while it decreases upon further increasing fH to 27. The former improvement is attributed to the slowing down of chain retraction after the strain-induced dissociation of ionic groups. The slowing down would suppress the formation of defects or small cracks that potentially grow into the fracture. This mechanism, i.e., strain-induced dissociation followed by the chain retraction, holds only in a window where the elongational rate is faster than the ionic dissociation rate but slower than the chain retraction rate. This window narrows down with increasing fH, which probably leads to the decrease of stretchability at high fH = 27.
{"title":"Improving stretchability of associative polymers through tuning density of the secondary interactions","authors":"Shilong Wu, Huanhuan Yang, Quan Chen","doi":"10.1122/8.0000508","DOIUrl":"https://doi.org/10.1122/8.0000508","url":null,"abstract":"The macroscopic stretchability of ionomer melts strongly relies on the structural evolution during the elongational flow. It has been noted that the introduction of the secondary associations weaker than the ionic association can improve the stretchability. To understand the mechanism, this study examines the stretchability of unentangled ionomers containing a fixed number of ionic groups per chain, [Formula: see text], but a varied number of hydrogen bonds per chain, fH = 5.5–27. The stretchability that is reflected in the maximum Hencky strain achieved before rupture shows nonmonotonous change with fH: the stretchability improves with increasing fH from 5.5 to 14 while it decreases upon further increasing fH to 27. The former improvement is attributed to the slowing down of chain retraction after the strain-induced dissociation of ionic groups. The slowing down would suppress the formation of defects or small cracks that potentially grow into the fracture. This mechanism, i.e., strain-induced dissociation followed by the chain retraction, holds only in a window where the elongational rate is faster than the ionic dissociation rate but slower than the chain retraction rate. This window narrows down with increasing fH, which probably leads to the decrease of stretchability at high fH = 27.","PeriodicalId":16991,"journal":{"name":"Journal of Rheology","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49035420","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Laboratory experiments were conducted to study particle migration and flow properties of non-Brownian, noncolloidal suspensions ranging from 10% to 40% particle volume fraction in a pressure-driven flow over and through a porous structure at a low Reynolds number. Particle concentration maps, velocity maps, and corresponding profiles were acquired using a magnetic resonance imaging technique. The model porous medium consists of square arrays of circular rods oriented across the flow in a rectangular microchannel. It was observed that the square arrays of the circular rods modify the velocity profiles and result in heterogeneous concentration fields for various suspensions. As the bulk particle volume fraction of the suspension increases, particles tend to concentrate in the free channel relative to the porous medium while the centerline velocity profile along the lateral direction becomes increasingly blunted. Within the porous structure, concentrated suspensions exhibit smaller periodic axial velocity variations due to the geometry compared to semidilute suspensions (bulk volume fraction ranges from 10% to 20%) and show periodic concentration variations, where the average particle concentration is slightly greater between the rods than on top of the rods. For concentrated systems, high particle concentration pathways aligned with the flow direction are observed in regions that correspond to gaps between rods within the porous medium.
{"title":"Particle migration of suspensions in a pressure-driven flow over and through a porous structure","authors":"P. Mirbod, N. Shapley","doi":"10.1122/8.0000505","DOIUrl":"https://doi.org/10.1122/8.0000505","url":null,"abstract":"Laboratory experiments were conducted to study particle migration and flow properties of non-Brownian, noncolloidal suspensions ranging from 10% to 40% particle volume fraction in a pressure-driven flow over and through a porous structure at a low Reynolds number. Particle concentration maps, velocity maps, and corresponding profiles were acquired using a magnetic resonance imaging technique. The model porous medium consists of square arrays of circular rods oriented across the flow in a rectangular microchannel. It was observed that the square arrays of the circular rods modify the velocity profiles and result in heterogeneous concentration fields for various suspensions. As the bulk particle volume fraction of the suspension increases, particles tend to concentrate in the free channel relative to the porous medium while the centerline velocity profile along the lateral direction becomes increasingly blunted. Within the porous structure, concentrated suspensions exhibit smaller periodic axial velocity variations due to the geometry compared to semidilute suspensions (bulk volume fraction ranges from 10% to 20%) and show periodic concentration variations, where the average particle concentration is slightly greater between the rods than on top of the rods. For concentrated systems, high particle concentration pathways aligned with the flow direction are observed in regions that correspond to gaps between rods within the porous medium.","PeriodicalId":16991,"journal":{"name":"Journal of Rheology","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2022-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45409095","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Nelya Malbranche, Bulbul Chakraborty, Jeffrey F. Morris
Discrete-particle simulations of bidisperse shear thickening suspensions are reported. The work considers two packing parameters, the large-to-small particle radius ratio ranging from <span><math altimg="eq-00001.gif" display="inline" overflow="scroll"><mi>δ</mi><mo>=</mo><mn>1.4</mn></math></span><span></span> (nearly monodisperse) to <span><math altimg="eq-00002.gif" display="inline" overflow="scroll"><mi>δ</mi><mo>=</mo><mn>4</mn></math></span><span></span>, and the large particle fraction of the total solid loading with values <span><math altimg="eq-00003.gif" display="inline" overflow="scroll"><mi>ζ</mi><mo>=</mo><mn>0.15</mn></math></span><span></span>, 0.5, and 0.85. Particle-scale simulations are performed over a broad range of shear stresses using a simulation model for spherical particles accounting for short-range lubrication forces, frictional interaction, and repulsion between particles. The variation of rheological properties and the maximum packing fraction <span><math altimg="eq-00004.gif" display="inline" overflow="scroll"><msub><mi>ϕ</mi><mi>J</mi></msub></math></span><span></span> with shear stress <span><math altimg="eq-00005.gif" display="inline" overflow="scroll"><mi>σ</mi></math></span><span></span> are reported. At a fixed volume fraction <span><math altimg="eq-00006.gif" display="inline" overflow="scroll"><mi>ϕ</mi></math></span><span></span>, bidispersity decreases the suspension relative viscosity <span><math altimg="eq-00007.gif" display="inline" overflow="scroll"><msub><mi>η</mi><mi>r</mi></msub><mo>=</mo><msub><mi>η</mi><mi>s</mi></msub><mo>/</mo><msub><mi>η</mi><mn>0</mn></msub></math></span><span></span>, where <span><math altimg="eq-00008.gif" display="inline" overflow="scroll"><msub><mi>η</mi><mi>s</mi></msub></math></span><span></span> is the suspension viscosity and <span><math altimg="eq-00009.gif" display="inline" overflow="scroll"><msub><mi>η</mi><mn>0</mn></msub></math></span><span></span> is the suspending fluid viscosity, over the entire range of shear stresses studied. However, under low shear stress conditions, the suspension exhibits an unusual rheological behavior: the minimum viscosity does not occur as expected at <span><math altimg="eq-00010.gif" display="inline" overflow="scroll"><mi>ζ</mi><mo>≈</mo><mn>0.5</mn></math></span><span></span>, but instead decreases with further increase of <span><math altimg="eq-00011.gif" display="inline" overflow="scroll"><mi>ζ</mi></math></span><span></span> to <span><math altimg="eq-00012.gif" display="inline" overflow="scroll"><mn>0.85</mn></math></span><span></span>. The second normal stress difference <span><math altimg="eq-00013.gif" display="inline" overflow="scroll"><msub><mi>N</mi><mn>2</mn></msub></math></span><span></span> acts similarly. This behavior is caused by particles ordering into a layered structure, as is also reflected by the zero slope with respect to time of the mean-square displacement in the velocity gradient direction. The relative viscosi
{"title":"Shear thickening in dense bidisperse suspensions","authors":"Nelya Malbranche, Bulbul Chakraborty, Jeffrey F. Morris","doi":"10.1122/8.0000495","DOIUrl":"https://doi.org/10.1122/8.0000495","url":null,"abstract":"Discrete-particle simulations of bidisperse shear thickening suspensions are reported. The work considers two packing parameters, the large-to-small particle radius ratio ranging from <span><math altimg=\"eq-00001.gif\" display=\"inline\" overflow=\"scroll\"><mi>δ</mi><mo>=</mo><mn>1.4</mn></math></span><span></span> (nearly monodisperse) to <span><math altimg=\"eq-00002.gif\" display=\"inline\" overflow=\"scroll\"><mi>δ</mi><mo>=</mo><mn>4</mn></math></span><span></span>, and the large particle fraction of the total solid loading with values <span><math altimg=\"eq-00003.gif\" display=\"inline\" overflow=\"scroll\"><mi>ζ</mi><mo>=</mo><mn>0.15</mn></math></span><span></span>, 0.5, and 0.85. Particle-scale simulations are performed over a broad range of shear stresses using a simulation model for spherical particles accounting for short-range lubrication forces, frictional interaction, and repulsion between particles. The variation of rheological properties and the maximum packing fraction <span><math altimg=\"eq-00004.gif\" display=\"inline\" overflow=\"scroll\"><msub><mi>ϕ</mi><mi>J</mi></msub></math></span><span></span> with shear stress <span><math altimg=\"eq-00005.gif\" display=\"inline\" overflow=\"scroll\"><mi>σ</mi></math></span><span></span> are reported. At a fixed volume fraction <span><math altimg=\"eq-00006.gif\" display=\"inline\" overflow=\"scroll\"><mi>ϕ</mi></math></span><span></span>, bidispersity decreases the suspension relative viscosity <span><math altimg=\"eq-00007.gif\" display=\"inline\" overflow=\"scroll\"><msub><mi>η</mi><mi>r</mi></msub><mo>=</mo><msub><mi>η</mi><mi>s</mi></msub><mo>/</mo><msub><mi>η</mi><mn>0</mn></msub></math></span><span></span>, where <span><math altimg=\"eq-00008.gif\" display=\"inline\" overflow=\"scroll\"><msub><mi>η</mi><mi>s</mi></msub></math></span><span></span> is the suspension viscosity and <span><math altimg=\"eq-00009.gif\" display=\"inline\" overflow=\"scroll\"><msub><mi>η</mi><mn>0</mn></msub></math></span><span></span> is the suspending fluid viscosity, over the entire range of shear stresses studied. However, under low shear stress conditions, the suspension exhibits an unusual rheological behavior: the minimum viscosity does not occur as expected at <span><math altimg=\"eq-00010.gif\" display=\"inline\" overflow=\"scroll\"><mi>ζ</mi><mo>≈</mo><mn>0.5</mn></math></span><span></span>, but instead decreases with further increase of <span><math altimg=\"eq-00011.gif\" display=\"inline\" overflow=\"scroll\"><mi>ζ</mi></math></span><span></span> to <span><math altimg=\"eq-00012.gif\" display=\"inline\" overflow=\"scroll\"><mn>0.85</mn></math></span><span></span>. The second normal stress difference <span><math altimg=\"eq-00013.gif\" display=\"inline\" overflow=\"scroll\"><msub><mi>N</mi><mn>2</mn></msub></math></span><span></span> acts similarly. This behavior is caused by particles ordering into a layered structure, as is also reflected by the zero slope with respect to time of the mean-square displacement in the velocity gradient direction. The relative viscosi","PeriodicalId":16991,"journal":{"name":"Journal of Rheology","volume":"85 2 1","pages":""},"PeriodicalIF":3.3,"publicationDate":"2022-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138542758","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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