Tough elastomers and gels have garnered broad research interest due to their wide-ranging potential applications.However,during the loading and unloading cycles,a clear stress softening behavior can be observed in man...Tough elastomers and gels have garnered broad research interest due to their wide-ranging potential applications.However,during the loading and unloading cycles,a clear stress softening behavior can be observed in many material systems,which is also named as the Mullins effect.In this work,we aim to provide a complete review of the Mullins effect in soft yet tough materials,specifically focusing on nanocomposite gels,double-network hydrogels,and multi-network elastomers.We first revisit the experimental observations for these soft materials.We then discuss the recent developments of constitutive models,emphasizing novel developments in the damage mechanisms or network representations.Some phenomenological models will also be briefly introduced.Particular attention is then placed on the anisotropic and multiaxial modeling aspects.It is demonstrated that most of the existing models fail to accurately predict the multiaxial data,posing a significant challenge for developing future anisotropic models tailored for tough gels and elastomers.展开更多
The damage models based on the eight-chain model and the affine full-chain network model are not adequate to describe the damage behaviors in double-network(DN)hydrogels.To overcome this limitation,we propose a combin...The damage models based on the eight-chain model and the affine full-chain network model are not adequate to describe the damage behaviors in double-network(DN)hydrogels.To overcome this limitation,we propose a combined chain stretch model with new damage flow rules.It is demonstrated that the new proposed micro-chain stretch is a reduced form of the complete representation for the transversely isotropic tensor function.As a result,the damage models based on the eight-chain model and the affine model are incorporated as special cases.The effects of chain affineness and network entangling are simultaneously involved in the new model,while only one of these two effects can be characterized in either the eight-chain model or the affine model.It is further shown that the new model can effectively capture the Mullins features of the DN hydrogels and achieve better agreement with the experimental data than the affine model and the eight-chain model.展开更多
As polymer networks infiltrated with water, hydrogels are major constituents of animal and plant bodies and have diverse engineering applications. While natural hydrogels can robustly adhere to other biological materi...As polymer networks infiltrated with water, hydrogels are major constituents of animal and plant bodies and have diverse engineering applications. While natural hydrogels can robustly adhere to other biological materials, such as bonding of tendons and cartilage on bones and adhesive plaques of mussels, it is challenging to achieve such tough adhesions between synthetic hydrogels and engineering materials. Recent experiments show that chemically anchoring long-chain polymer networks of tough synthetic hydrogels on solid surfaces create adhesions tougher than their natural counterparts, but the underlying mechanism has not been well understood. It is also challenging to tune systematically the adhesion of hydrogels on solids. Here, we provide a quantitative understanding of the mechanism for tough adhesions of hydrogels on solid materials via a combination of experiments, theory, and numerical simulations. Using a coupled cohesive-zone and Mullins-effect model validated by experiments, we reveal the interplays of intrinsic work of adhesion, interfacial strength, and energy dissipation in bulk hydrogels in order to achieve tough adhesions. We further show that hydrogel adhesion can be systematically tuned by tailoring the hydrogel geometry and silanization time of solid substrates, corresponding to the control of energy dissipation zone and intrinsic work of adhesion, respectively. The current work further provides a theoretical foundation for rational design of future biocompatible and underwater adhesives.展开更多
Incorporation of carbon black(CB)in natural rubber(NR)enhances the Mullins effect and Payne effect of their vulcanizates,but the strain softening mechanisms and the microstructure evolution in the vulcanizates have no...Incorporation of carbon black(CB)in natural rubber(NR)enhances the Mullins effect and Payne effect of their vulcanizates,but the strain softening mechanisms and the microstructure evolution in the vulcanizates have not been clearly concluded so far.We investigate the Mullins effect and Payne effect of CB filled NR vulcanizates by using cyclic tensile tests at different temperatures and dynamic rheological measurements combined with simultaneous electric conduction.During cyclic stretching,the normalized recovery hysteresis energy and accumulative softening energy for NR/CB vulcanizates with different loadings can be both superimposed on a master curve,indicating that the Mullins effect is mainly dominated by the rubber matrix.The irreversible simultaneous resistance evolution also reveals that the structural evolution of nanoparticles(NPs)network is not directly related to the Mullins effect.Moreover,the extension of linear viscoelastic region and the hysteresis of Payne effect for filled vulcanizates subjected to cyclic stretching indicate the destruction of CB aggregated structure and the interfacial layers between CB and rubber chains during cyclic stretching.This investigation would be illuminating for the microstructure evolution and strain softening of rubber nanocomposites under harsh service conditions.展开更多
Soft elastomers with mechanical properties similar to biological tissues have shown encouraging potential in applications of biomedical devices and stretchable electronics.With the ability to enhance electric and ther...Soft elastomers with mechanical properties similar to biological tissues have shown encouraging potential in applications of biomedical devices and stretchable electronics.With the ability to enhance electric and thermal conductivity,embedding low melting alloys into soft elastomer matrix has received considerable attention in recent years.However,the mechanical properties,especially the fatigue behaviors of these soft composites,have not been extensively investigated.Here,we fabricate two silicone elastomers filled with eutectic gallium-indium,a liquid metal alloy,which has a melting temperature around room temperature.The cyclic loading–unloading tests are first performed on the composites with low melting alloys in either solid or fluid state.The results show that the modulus and energy dissipation density of the composite increase with the ratio of the alloys when the deformation temperature is below the melting temperature,while these properties decrease with the ratio of alloys when they are in the fluid state.In contrast,the failure strain shows an opposite trend.Mechanical tests are further performed on specimens with a precut to measure the fracture energy and fatigue threshold.It is demonstrated that both fracture energy and fatigue threshold are significantly enhanced in the presence of low melting alloys regardless of their states.Finally,we apply a continuum damage model to describe the Mullins effect of the soft composites observed in the loading–unloading cycles,which further reveals the change of mechanical properties with deformation for different compositions of soft composites.展开更多
Plasticized polyvinyl chloride(PVC)gel is a type of electroactive polymers,which has potentials to be applied as soft actuators.However,few studies have been performed to investigate the mechanical responses of PVC ge...Plasticized polyvinyl chloride(PVC)gel is a type of electroactive polymers,which has potentials to be applied as soft actuators.However,few studies have been performed to investigate the mechanical responses of PVC gels in cyclic loading conditions.In this work,we combined experiments and theory to characterize the mechanical responses of two plasticized PVC gels.The gels were subjected to different types of loading-unloading-reloading cycles.The experimental results showed that the plasticized PVC gels exhibited stress softening response(the Mullins effect)in the cyclic tests.Meanwhile,the gels regained some strength after annealing at room temperature for several hours,indicating the self-healing ability of gels.We further extended the eight-chain model with incorporation of the chain dissociation and reassociation mechanism.The developed constitutive model is able to reproduce the Mullins effect and the recovery of the Mullins effect observed in the experiments.Our results clearly show that understanding the complex mechanical response is crucial for the applications of plasticized PVC gels.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12321002,12211530061,12022204,and 12202378)the Zhejiang Provincial Natural Science Foundation of China(Grant No.LD22A020001)the 111 Project(Grant No.B21034).
文摘Tough elastomers and gels have garnered broad research interest due to their wide-ranging potential applications.However,during the loading and unloading cycles,a clear stress softening behavior can be observed in many material systems,which is also named as the Mullins effect.In this work,we aim to provide a complete review of the Mullins effect in soft yet tough materials,specifically focusing on nanocomposite gels,double-network hydrogels,and multi-network elastomers.We first revisit the experimental observations for these soft materials.We then discuss the recent developments of constitutive models,emphasizing novel developments in the damage mechanisms or network representations.Some phenomenological models will also be briefly introduced.Particular attention is then placed on the anisotropic and multiaxial modeling aspects.It is demonstrated that most of the existing models fail to accurately predict the multiaxial data,posing a significant challenge for developing future anisotropic models tailored for tough gels and elastomers.
基金supported by the National Natural Science Foundation of China under Grant No.12022204,the Zhejiang Provincial Natural Science Foundation of China under Grant No.LD22A020001,and the Fundamental Research Funds for the Central Universities,China(Grant No.2021FZZX001-16).
文摘The damage models based on the eight-chain model and the affine full-chain network model are not adequate to describe the damage behaviors in double-network(DN)hydrogels.To overcome this limitation,we propose a combined chain stretch model with new damage flow rules.It is demonstrated that the new proposed micro-chain stretch is a reduced form of the complete representation for the transversely isotropic tensor function.As a result,the damage models based on the eight-chain model and the affine model are incorporated as special cases.The effects of chain affineness and network entangling are simultaneously involved in the new model,while only one of these two effects can be characterized in either the eight-chain model or the affine model.It is further shown that the new model can effectively capture the Mullins features of the DN hydrogels and achieve better agreement with the experimental data than the affine model and the eight-chain model.
基金supported by the Office Naval Research (Grant N00014-14-1-0528)Draper Laboratory+4 种基金MIT Institute for Soldier Nanotechnologiesthe National Science Foundation (Grant CMMI-1253495)the financial support from Samsung Scholarshipthe supports from the National Institutes Health (Grant UH3TR000505)the support from MIT research computing resources and the Extreme Science and Engineering Discovery Environment (XSEDE) (Grant TG-MSS160007)
文摘As polymer networks infiltrated with water, hydrogels are major constituents of animal and plant bodies and have diverse engineering applications. While natural hydrogels can robustly adhere to other biological materials, such as bonding of tendons and cartilage on bones and adhesive plaques of mussels, it is challenging to achieve such tough adhesions between synthetic hydrogels and engineering materials. Recent experiments show that chemically anchoring long-chain polymer networks of tough synthetic hydrogels on solid surfaces create adhesions tougher than their natural counterparts, but the underlying mechanism has not been well understood. It is also challenging to tune systematically the adhesion of hydrogels on solids. Here, we provide a quantitative understanding of the mechanism for tough adhesions of hydrogels on solid materials via a combination of experiments, theory, and numerical simulations. Using a coupled cohesive-zone and Mullins-effect model validated by experiments, we reveal the interplays of intrinsic work of adhesion, interfacial strength, and energy dissipation in bulk hydrogels in order to achieve tough adhesions. We further show that hydrogel adhesion can be systematically tuned by tailoring the hydrogel geometry and silanization time of solid substrates, corresponding to the control of energy dissipation zone and intrinsic work of adhesion, respectively. The current work further provides a theoretical foundation for rational design of future biocompatible and underwater adhesives.
基金financially supported by the National Natural Science Foundation of China(Nos.51790503,52273084 and 51873181).
文摘Incorporation of carbon black(CB)in natural rubber(NR)enhances the Mullins effect and Payne effect of their vulcanizates,but the strain softening mechanisms and the microstructure evolution in the vulcanizates have not been clearly concluded so far.We investigate the Mullins effect and Payne effect of CB filled NR vulcanizates by using cyclic tensile tests at different temperatures and dynamic rheological measurements combined with simultaneous electric conduction.During cyclic stretching,the normalized recovery hysteresis energy and accumulative softening energy for NR/CB vulcanizates with different loadings can be both superimposed on a master curve,indicating that the Mullins effect is mainly dominated by the rubber matrix.The irreversible simultaneous resistance evolution also reveals that the structural evolution of nanoparticles(NPs)network is not directly related to the Mullins effect.Moreover,the extension of linear viscoelastic region and the hysteresis of Payne effect for filled vulcanizates subjected to cyclic stretching indicate the destruction of CB aggregated structure and the interfacial layers between CB and rubber chains during cyclic stretching.This investigation would be illuminating for the microstructure evolution and strain softening of rubber nanocomposites under harsh service conditions.
基金supported the Zhejiang Provincial Natural Science Foundation of China under Grant Nos.LD22A020001 and LGG20E050011the Fundamental Research Funds for the Central Universities,China(Grant No.2021FZZX001-16)the funding support from Institute of Systems Engineering,China Academy of Engineering Physics.
文摘Soft elastomers with mechanical properties similar to biological tissues have shown encouraging potential in applications of biomedical devices and stretchable electronics.With the ability to enhance electric and thermal conductivity,embedding low melting alloys into soft elastomer matrix has received considerable attention in recent years.However,the mechanical properties,especially the fatigue behaviors of these soft composites,have not been extensively investigated.Here,we fabricate two silicone elastomers filled with eutectic gallium-indium,a liquid metal alloy,which has a melting temperature around room temperature.The cyclic loading–unloading tests are first performed on the composites with low melting alloys in either solid or fluid state.The results show that the modulus and energy dissipation density of the composite increase with the ratio of the alloys when the deformation temperature is below the melting temperature,while these properties decrease with the ratio of alloys when they are in the fluid state.In contrast,the failure strain shows an opposite trend.Mechanical tests are further performed on specimens with a precut to measure the fracture energy and fatigue threshold.It is demonstrated that both fracture energy and fatigue threshold are significantly enhanced in the presence of low melting alloys regardless of their states.Finally,we apply a continuum damage model to describe the Mullins effect of the soft composites observed in the loading–unloading cycles,which further reveals the change of mechanical properties with deformation for different compositions of soft composites.
基金This work is supported by the National Natural Science Foundation of China(Grant No.12022204)the Fundamental Research Funds for the Central Universities(Grant No.2021FZZX001-16).
文摘Plasticized polyvinyl chloride(PVC)gel is a type of electroactive polymers,which has potentials to be applied as soft actuators.However,few studies have been performed to investigate the mechanical responses of PVC gels in cyclic loading conditions.In this work,we combined experiments and theory to characterize the mechanical responses of two plasticized PVC gels.The gels were subjected to different types of loading-unloading-reloading cycles.The experimental results showed that the plasticized PVC gels exhibited stress softening response(the Mullins effect)in the cyclic tests.Meanwhile,the gels regained some strength after annealing at room temperature for several hours,indicating the self-healing ability of gels.We further extended the eight-chain model with incorporation of the chain dissociation and reassociation mechanism.The developed constitutive model is able to reproduce the Mullins effect and the recovery of the Mullins effect observed in the experiments.Our results clearly show that understanding the complex mechanical response is crucial for the applications of plasticized PVC gels.
