scholarly journals Capturing the Transient Microstructure of a Physically Assembled Gel Subjected to Temperature and Large Deformation

2021 ◽  
Author(s):  
Rosa Maria Badani Prado ◽  
Satish Mishra ◽  
Wesley R. Burghardt ◽  
Santanu Kundu
Keyword(s):  
Stress Relaxation ◽  
Relaxation Process ◽  
Triblock Copolymer ◽  
Large Strain ◽  
Real Life ◽  
Exponential Model ◽  
Complex Nature ◽  
Gelation Process ◽  
Oriented Structure ◽  
Step Strain

The microstructure of physically assembled gels depends on mechanical loading and environmental stimuli such as temperature. Here, we report the real-time change in the structure of physically assembled triblock copolymer gels that consist of 10 wt% and 20 wt% of poly(styrene)-poly(isoprene)-poly(styrene) [PS-PI-PS] triblock copolymer in mineral oil (i) during the gelation process with decreasing temperature, (ii) subjected to large oscillatory deformation, and (iii) during the stress-relaxation process after the application of a step-strain. The presence of loosely bounded PS-aggregates at temperatures higher than the rheometrically determined gelation temperature (Tgel) captures the progressive gelation process spanning over a broad temperature range. However, the microstructure fully develops at temperatures suciently lower than Tgel, and the storage modulus (G0 ) also reaches a plateau at those temperatures. The microstructure orients in the stretching direction with the applied strain. In an oscillation strain cycle, such oriented structure has been observed at low-strain. But, at large-strain, the oriented structure splits, and only a fraction of midblock participates in load-bearing. This has been attributed to the endblock pullout from the aggregates, likely caused by the strain localization in the samples. Both microstructure recovery and time-dependent moduli during the stress-relaxation process after the application of a step-strain can be captured using a stretched-exponential model. However, the microstructure recovery time has been found to be two orders of magnitude slower than the stress-relaxation time at room temperature, indicating a complex nature of relaxation process involving midblock relaxation, endblock pullout and reassociation process. Due to their viscoelastic nature, these gels' mechanical responses are sensitive to strain, temperature, and rate of deformation. Therefore, insights into the microstructural information as a function of these parameters will assist these gels' real-life applications and design new gels with improved properties<br>

scholarly journals Capturing the Transient Microstructure of a Physically Assembled Gel Subjected to Temperature and Large Deformation

2021 ◽  
Author(s):  
Rosa Maria Badani Prado ◽  
Satish Mishra ◽  
Wesley R. Burghardt ◽  
Santanu Kundu
Keyword(s):  
Stress Relaxation ◽  
Relaxation Process ◽  
Triblock Copolymer ◽  
Large Strain ◽  
Real Life ◽  
Exponential Model ◽  
Complex Nature ◽  
Gelation Process ◽  
Oriented Structure ◽  
Step Strain

The microstructure of physically assembled gels depends on mechanical loading and environmental stimuli such as temperature. Here, we report the real-time change in the structure of physically assembled triblock copolymer gels that consist of 10 wt% and 20 wt% of poly(styrene)-poly(isoprene)-poly(styrene) [PS-PI-PS] triblock copolymer in mineral oil (i) during the gelation process with decreasing temperature, (ii) subjected to large oscillatory deformation, and (iii) during the stress-relaxation process after the application of a step-strain. The presence of loosely bounded PS-aggregates at temperatures higher than the rheometrically determined gelation temperature (Tgel) captures the progressive gelation process spanning over a broad temperature range. However, the microstructure fully develops at temperatures suciently lower than Tgel, and the storage modulus (G0 ) also reaches a plateau at those temperatures. The microstructure orients in the stretching direction with the applied strain. In an oscillation strain cycle, such oriented structure has been observed at low-strain. But, at large-strain, the oriented structure splits, and only a fraction of midblock participates in load-bearing. This has been attributed to the endblock pullout from the aggregates, likely caused by the strain localization in the samples. Both microstructure recovery and time-dependent moduli during the stress-relaxation process after the application of a step-strain can be captured using a stretched-exponential model. However, the microstructure recovery time has been found to be two orders of magnitude slower than the stress-relaxation time at room temperature, indicating a complex nature of relaxation process involving midblock relaxation, endblock pullout and reassociation process. Due to their viscoelastic nature, these gels' mechanical responses are sensitive to strain, temperature, and rate of deformation. Therefore, insights into the microstructural information as a function of these parameters will assist these gels' real-life applications and design new gels with improved properties<br>

scholarly journals Capturing the Transient Microstructure of a Physically Assembled Gel Subjected to Temperature and Large Deformation

2021 ◽  
Author(s):  
Rosa Maria Badani Prado ◽  
Satish Mishra ◽  
Humayun Ahmad ◽  
Wesley R. Burghardt ◽  
Santanu Kundu
Keyword(s):  
Stress Relaxation ◽  
Relaxation Process ◽  
Triblock Copolymer ◽  
Large Strain ◽  
Real Life ◽  
Exponential Model ◽  
Complex Nature ◽  
Gelation Process ◽  
Oriented Structure ◽  
Step Strain

The microstructure of physically assembled gels depends on mechanical loading and environmental stimuli such as temperature. Here, we report the real-time change in the structure of physically assembled triblock copolymer gels that consist of 10 wt% and 20 wt% of poly(styrene)-poly(isoprene)-poly(styrene) [PS-PI-PS] triblock copolymer in mineral oil (i) during the gelation process with decreasing temperature, (ii) subjected to large oscillatory deformation, and (iii) during the stress-relaxation process after the application of a step-strain. The presence of loosely bounded PS-aggregates at temperatures higher than the rheologically determined gelation temperature (Tgel) captures the progressive gelation process spanning over a broad temperature range. However, the microstructure fully develops at temperatures sufficiently lower than Tgel. The microstructure orients in the stretching direction with the applied strain. In an oscillation strain cycle, such oriented structure has been observed at low-strain. But, at large-strain, because of strain-localization the oriented structure splits, and only a fraction of midblock participates in load-bearing. Both microstructure recovery and time-dependent moduli during the stress-relaxation process after the application of a step-strain have been captured using a stretched-exponential model. However, the microstructure recovery time has been found to be two orders of magnitude slower than the stress-relaxation time at room temperature, indicating a complex nature of stress-relaxation and microstructure recovery processes involving midblock relaxation, endblock pullout and reassociation. Due to their viscoelastic nature, these gels' mechanical responses are sensitive to strain, temperature, and rate of deformation. Therefore, insights into the microstructural information as a function of these parameters will assist these gels' real-life applications and design new gels with improved properties.

scholarly journals Stress Relaxation of Polymer Solutions under Large Strain: Application of Double-Step Strain

1974 ◽  
Vol 5 (3) ◽  
pp. 283-287 ◽  
Author(s):  
Kunihiro Osaki ◽  
Yoshiyuki Einaga ◽  
Michio Kurata ◽  
Nobuhiro Yamada ◽  
Mikio Tamura
Keyword(s):  
Stress Relaxation ◽  
Polymer Solutions ◽  
Large Strain ◽  
Double Step ◽  
Step Strain

STRESS RELAXATION OF MAGNETORHEOLOGICAL FLUIDS

2002 ◽  
Vol 16 (17n18) ◽  
pp. 2655-2661
Author(s):  
W. H. LI ◽  
G. CHEN ◽  
S. H. YEO ◽  
H. DU
Keyword(s):  
Stress Relaxation ◽  
Viscoelastic Model ◽  
Relaxation Modulus ◽  
Damping Function ◽  
Mr Fluids ◽  
Large Step ◽  
Linear Viscoelastic ◽  
Predicted Values ◽  
Two Parameters ◽  
Step Strain

In this paper, the experimental and modeling study and analysis of the stress relaxation characteristics of magnetorheological (MR) fluids under step shear are presented. The experiments are carried out using a rheometer with parallel-plate geometry. The applied strain varies from 0.01% to 100%, covering both the pre-yield and post-yield regimes. The effects of step strain, field strength, and temperature on the stress modulus are addressed. For small step strain ranges, the stress relaxation modulus G(t,γ) is independent of step strain, where MR fluids behave as linear viscoelastic solids. For large step strain ranges, the stress relaxation modulus decreases gradually with increasing step strain. Morever, the stress relaxation modulus G(t,γ) was found to obey time-strain factorability. That is, G(t,γ) can be represented as the product of a linear stress relaxation G(t) and a strain-dependent damping function h(γ). The linear stress relaxation modulus is represented as a three-parameter solid viscoelastic model, and the damping function h(γ) has a sigmoidal form with two parameters. The comparison between the experimental results and the model-predicted values indicates that this model can accurately describe the relaxation behavior of MR fluids under step strains.

scholarly journals Preparation and properties of hybrid materials for high-rise constructions

2018 ◽  
Vol 33 ◽  
pp. 02075 ◽  
Author(s):  
Tatyana Matseevich
Keyword(s):  
Stress Relaxation ◽  
Epoxy Resin ◽  
Relaxation Process ◽  
Hybrid Materials ◽  
Mechanical Performance ◽  
Mechanical Relaxation ◽  
Physical Parameters ◽  
Quasi Equilibrium ◽  
High Rise ◽  
Long Time

The theme of the research is important because it allows to use hybrid materials as finishing in the high-rise constructions. The aim of the study was the development of producing coloured hybrid materials based on liquid glass, a polyisocyanate, epoxy resin and 2.4-toluylenediisocyanate. The detailed study of the process of stress relaxation at different temperatures in the range of 20-100°C was provided. The study found that the obtained materials are subject to the simplified technology. The materials easy to turn different colors, and dyes (e.g. Sudan blue G) are the catalysts for the curing process of the polymeric precursors. The materials have improved mechanical relaxation properties, possess different color and presentable, can be easily combined with inorganic base (concrete, metal). The limit of compressive strength varies from 32 to 17.5 MPa at a temperature of 20 to 100°C. The values σ∞ are from 20.4 to 7.7 MPa within the temperature range from 20 to 100°C. The physical parameters of materials were evaluated basing on the data of stress relaxation: the initial stress σ0, which occurs at the end of the deformation to a predetermined value; quasi-equilibrium stress σ∞, which persists for a long time relaxation process. Obtained master curves provide prediction relaxation behavior for large durations of relaxation. The study obtained new results. So, the addition of epoxy resin in the composition of the precursor improves the properties of hybrid materials. By the method of IR spectroscopy identified chemical transformations in the course of obtaining the hybrid material. Evaluated mechanical performance of these materials is long-time. Applied modern physically-based memory functions, which perfectly describe the stress relaxation process.

Self-Assembly and Stress Relaxation in Acrylic Triblock Copolymer Gels

2007 ◽  
Vol 40 (4) ◽  
pp. 1218-1226 ◽  
Author(s):  
Michelle E. Seitz ◽  
Wesley R. Burghardt ◽  
K. T. Faber ◽  
Kenneth R. Shull
Keyword(s):  
Stress Relaxation ◽  
Self Assembly ◽  
Triblock Copolymer ◽  
Copolymer Gels

Nonseparable Behavior in Rubber Viscoelasticity

1989 ◽  
Vol 62 (1) ◽  
pp. 68-81 ◽  
Author(s):  
J. L. Sullivan ◽  
K. A. Mazich
Keyword(s):  
Stress Relaxation ◽  
Relaxation Spectrum ◽  
Loss Modulus ◽  
Large Strain ◽  
Viscoelastic Behavior ◽  
Strain Effects ◽  
Mixed Response ◽  
Strain Stress ◽  
Necessary And Sufficient ◽  
Solid Liquid

Abstract New large-strain rubber viscoelasticity results for a filled and an unfilled IIR vulcanizate and previously published results for two NR gum vulcanizates have been discussed. The data show that the “mixed” response functions of large-strain stress relaxation, and the incremental storage and relaxation moduli do not demonstrate factorizability of time and strain effects. This is a consequence of the elastic and relaxation contributions in each of the mixed functions being different. The incremental dynamic data also show that the loss modulus for the filled IIR and unfilled NR vulcanizates (unavailable for the unfilled IIR) are separable functions of time and strain. This directly shows that the relaxation spectra for the filled IIR and unfilled NR vulcanizates are independent of strain for the deformations studied. In fact, it is argued that a necessary and sufficient condition for the relaxation spectrum to be independent of strain is that the loss modulus is a factorizable function of time and strain effects. The quantitative success of the Generalized Solid-Liquid (GSL) model in representing the viscoelastic behavior of the gum NR vulcanizate has been reviewed. Although the GSL model applies only to unfilled vulcanizates, it has also been successfully used to qualitatively interpret the results for the filled IIR compounds. Both successes are attributed to the physical assumptions intrinsic to the GSL model; more specifically, 1) the relaxation spectrum is independent of the state of strain, and 2) the deformational dependences of elastic and relaxation contributions to the overall response of the system need not be the same. Physical arguments justifying these assumptions have been covered. It has also been shown with the aid of the GSL model, that a material might exist which demonstrates factorizability in stress relaxation and incremental loss modulus behaviors but nonfactorizability in the incremental storage and relaxation moduli.

Study on Nonlinear Viscoelastic Properties of Asphalt Mixture Based on Stress Relaxation Test

2014 ◽  
Vol 563 ◽  
pp. 48-52
Author(s):  
Lei Chen ◽  
Zhi Xin Yu ◽  
Wei Ping Cui ◽  
Li Juan Qin
Keyword(s):  
Stress Relaxation ◽  
Asphalt Mixture ◽  
Viscoelastic Behavior ◽  
Exponential Model ◽  
Relaxation Test ◽  
Asphalt Binders ◽  
Stress Relaxation Test ◽  
Nonlinear Viscoelastic ◽  
Low Temperature Cracking ◽  
Relaxation Experiments

Development of normal stress in the direction perpendicular to the asphalt mixture is an important feature of the nonlinear viscoelastic behavior of asphalt binders. In this paper, this phenomenon was studied with the help of stress-relaxation experiments in torsion.  Results indicate that stress relaxation test by controlling strain could be used to evaluate the stress relaxation ability of asphalt mixture. With the aging degree of asphalt mixtures increased, the low temperature cracking resistance got worse; the higher the temperature is, the faster the stress relaxed; the smaller the initial strain, the worse the stress relaxation ability also. The viscoelasticity of asphalt mixture could be simulated by exponential model fractional and the experiments well supported the modeling results.

scholarly journals Modeling Step—Strain Relaxation and Cyclic Deformations of Elastomers

2002 ◽  
Vol 75 (2) ◽  
pp. 333-345
Author(s):  
A. R. Johnson ◽  
T. Chen ◽  
J. L. Mead
Keyword(s):  
Least Squares Method ◽  
Large Strain ◽  
Strain Relaxation ◽  
Nonlinear Least Squares ◽  
Friction Stress ◽  
Maxwell Model ◽  
Constitutive Theory ◽  
Relaxation Data ◽  
Nonlinear Least Squares Method ◽  
Step Strain

Abstract Data for step—strain relaxation and cyclic compressive deformations of highly viscous short elastomer cylinders are modeled using a large strain rubber viscoelastic constitutive theory with a rate—independent friction stress term added. In the tests, both small and large amplitude cyclic compressive strains, in the range of 1% to 10%, were superimposed on steady state compressed strains, in the range of 5% to 20%, for frequencies of 1 and 10 Hz. The elastomer cylinders were conditioned prior to each test to soften them. The constants in the viscoelastic—friction constitutive theory are determined by employing a nonlinear least-squares method to fit the analytical stresses for a Maxwell model, which includes friction, to measured relaxation stresses obtained from a 20% step—strain compression test. The simulation of the relaxation data with the nonlinear model is successful at compressive strains of 5%, 10%, 15%, and 20%. Simulations of hysteresis stresses for enforced cyclic compressive strains of 20%±5% are made with the model calibrated by the relaxation data. The predicted hysteresis stresses are lower than the measured stresses.

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