Viscoelastic Research Articles

Cyclic response and mechanical model of a rotational viscoelastic damper

This paper investigated the cyclic response of a new viscoelastic damper that utilized a rotational mechanism to enhance shear deformation in the viscoelastic material and increase its energy dissipation. Three damper prototypes were fabricated and subjected to displacement-controlled cyclic excitations with varying strain amplitudes and frequencies. For comparison, three conventional viscoelastic dampers, each containing an equivalent volume of viscoelastic material to the proposed damper, were also fabricated and tested. Results indicated that the proposed damper had up to three times larger loss factor and five times larger damping coefficient than the tested conventional viscoelastic damper. This study also presented two analytically driven equations to estimate the proposed damper's rotational stiffness and damping coefficient. A finite element model was proposed for simulating the damper in software, and its effectiveness was demonstrated.

Controlling the rheology of cellulose dissolved in 4–methylmorpholine N–oxide and tensile properties of precipitated cellulose films via mixture design

AbstractProperties which control the mechanical performance of regenerated or precipitated cellulose films are currently not well-known and a mechanistic understanding of the underlying phenomena should be established. Solution rheology is a crucial property for casting films and spinning fibres in terms of process runnability, and it can have a considerable effect on the mechanical properties of the prepared cellulose products. We hypothesized that the viscosity of cellulose dissolved in 4-methylmorpholine N-oxide (NMMO) and the mechanical properties of precipitated cellulose films could potentially be improved by controlling the molecular weight distribution of cellulose pulp, taking inspiration from traditional plastic industry. We evaluated the effects of pulp blends on the viscoelastic properties of dissolved cellulose-NMMO dopes and used the dopes to prepare cellulose films and determined their mechanical properties. Lastly, we employed the determined dope and film characteristics to build linear regression models for predicting dope rheology and mechanical performance of films. Mixture films with 2:1 and 1:2 ratios of pulps with both medium and high degree of polymerization showed in average 36% and 46% higher toughness than their unimodal versions. The model results demonstrated that film performance could be tailored by changing the pulp composition. These findings play an important role in optimizing the future processability of dissolved cellulose dopes for producing bio-based cellulose materials and could bring us a step closer to traditional plastic polymer disciplines by tailoring their performance based on pulp properties. Graphic abstract

Multimodal Photoacoustic/Elastography Imaging for the Detection of Acute Radiation Dermatitis in Breast Radiation Therapy

Purpose: This study evaluates whether photoacoustic (PA), sound touch elastography (STE), and viscoelasticity (VE) can distinguish between normal and abnormal post-radiotherapy breast skin and compare these methods with RTOG criteria at a 20 Gy threshold. Methods: Patients meeting inclusion and exclusion criteria underwent PA, STE, and VE on the same day. Collected data included radiation dose, molecular type, RTOG, Fitzpatrick skin type, pathology, neoadjuvant chemotherapy status, TNM classification, surgical procedures, primary breast cancer location, BMI, and age. A sample of 41 patients was determined using a two-sample t-test. Statistical tools like T-tests, variance analysis, rank sum tests, and chi-square tests, along with random forest analysis and ROC curves, were used to evaluate the radiation dose effects. Results: Data from 66 patients showed significant differences in parameters such as dermis and subcutaneous tissue oxygen saturation, dermal thickness, and skin elasticity (p-values < 0.05). However, minimum values of oxygen saturation and some photoacoustic measures were not significantly different. Notably, at a 20 Gy radiation threshold, significant variations in oxygen saturation, abnormal dermal thickness, and skin STE and VE were observed, proving more accurate than RTOG grading. Conclusion: The study confirms the effectiveness of PA and elastography imaging in differentiating normal from abnormal breast tissue and assessing radiation-induced changes, highlighting the potential of these imaging techniques.

Rheological investigation of heavy oil-in-water pickering emulsions for potential applications of fracturing fluids

Pickering emulsions as a kind of emulsified fracturing fluids can enhance the efficacy of shale fracturing. Investigation of the rheological properties of Pickering emulsions yields valuable insights for their in-situ fracturing applications. In this work, nano-clay particles and heavy crude oil were employed to form oil-in-water (O/W) Pickering emulsions. The impact of salinity, pH, and temperature on the rheological properties, including viscosity property and viscoelastic property, of Pickering emulsions were tested and analyzed. The results showed that the viscosity of heavy O/W Pickering emulsions were significantly affected by the change of salinity and pH values, with higher salinity or lower pH resulting in increased viscosity. Under ultra-high salinities (>5 wt% NaCl), the coalescence stability of Pickering emulsion strengthens and creaming stability declines. The massive formation of clay clusters leads to a reduction in the number of nano-clay particles used to generate the network, causing instability in the emulsion creaming. The heavy O/W Pickering emulsions exhibited high stability and high viscosity characteristics, which were mainly caused by the change of surface charge of nano-clay particles and the corresponding change of particle adsorption on droplet surface and particle-particle interactions. At a salinity of 2.5% NaCl and a pH of 4.6, the emulsion system remained stable at a temperature up to 120 °C, holding a viscosity reaching 74.1 mPa s at a shear rate of 6.81 s−1. Besides, heavy O/W Pickering emulsions were viscoelastic fluids, with both noticeable viscous property and elastic property at the same time. Elastic modulus (G′) and viscous modulus (G″) of the emulsion increased with increasing salinity and decreasing pH, enhancing great deformation capacity. Remarkably, the Pickering emulsions could maintain its viscoelastic behavior at varying temperature conditions. For the first time, rheological study of Pickering emulsions formed by nano-clay nanoparticles as a single emulsifier to heavy oil. Our study underscores the emulsifying ability of nano-clay particles to heavy crude oils, under a wide range of salinity and pH, yielding Pickering emulsions with exceptional stability and rheological properties. This novel emulsion system, possessing high resistance to temperature and salinity, holds promise for a high-performance fracturing fluid design.

Reduction in Floor Impact Noise Using Resilient Pads Composed of Machining Scraps.

Floor impact noise is a significant social concern to secure a quiescent living space for multi-story building residents in South Korea. The floating floor, consisting of a concrete structure on resilient pads, is a specifically designed system to minimize noise transmission. This floating structure employs polymeric pads as the resilient materials. In this study, we investigated the utilization of helically shaped machining scraps as a resilient material for an alternative approach to floor noise reduction. The dynamic elastic modulus and loss factor of the scrap pads were measured using the vibration test method. The scrap pads exhibited a low dynamic elastic modulus and a high loss factor compared to the polymeric pads. Heavyweight impact sound experiments in an actual building were conducted to evaluate the noise reduction performance. The proposed pads showed excellent performance on the reduction in the structure-borne vibration of the concrete slab and resulting sound generation. The analytical model was used to simulate the response of the floating floor structure, enabling a parametric study to examine the effects of the resilient layer viscoelastic properties. Both experimental and analytical evidence confirmed that the proposed scrap pads contribute to the development of sustainable solutions for the minimization of floor impact noise.

Application of a shear cell for the simulation of extrusion to test the structurability of raw materials

The required raw material properties and the mechanisms behind fibrous structure formation during high moisture extrusion cooking (HMEC) to produce plant-based meat analogues are not sufficiently understood. The implementation of new raw materials is therefore a labour-intensive, empirical endeavour. Hence, this research explores the potential of a high-pressure shear cell (HPSC) as a tool for rapid screening of raw materials for HMEC suitability. During these texturisation tests, material viscosity was monitored to gain deeper mechanistic insights. For that, hydrated pea protein isolate (PPI) and soy protein concentrate (SPC) were sheared at 5-40 s−1 in the HPSC with a cone-plate or plate-plate geometry under extrusion-like conditions at 140–160 °C and 20 bar. Fibrous structures were successfully generated with both tested plant proteins, but reproducibility was limited to trials with SPC. Monitoring of viscoelastic properties revealed an onsetting polymerisation, followed by a decrease in viscosity, indicating fracturing of the forming network as underlying structuring mechanism. The suggested fracturing of an emerging network aligns with an observed increase in fibrousness in the plate-plate geometry compared to the cone-plate geometry due to the radial shear rate gradient. Finally, this research showcased a high similarity of the process-structure response pattern for SPC between the applied HPSC process and HMEC. Yet, further modifications, such as increasing the mechanical energy input capacity, are required to effectively apply HPSC processing for the prediction of the structuring behaviour in HMEC for the broad range of existing raw materials.

Resonant Acoustic Rheometry for Real Time Assessment of Plasma Coagulation in Bleeding Patients.

Disordered hemostasis associated with life-threatening hemorrhage commonly afflicts patients in the emergency room, critical care unit, and perioperative settings. Rapid and sensitive hemostasis phenotyping is needed to guide administration of blood components and hemostatic adjuncts to reverse aberrant coagulofibrinolysis. Here, resonant acoustic rheometry (RAR), a technique that quantifies the viscoelastic properties of soft biomaterials, was applied to assess plasma coagulation in a cohort of bleeding patients with concomitant clinical coagulation assays and whole blood thromboelastography (TEG) as part of their routine care. RAR captured the dynamic characteristics of plasma coagulation that were coagulation activators-dependent. RAR coagulation parameters correlated with TEG reaction time and TEG functional fibrinogen, especially when stratified by comorbidities. A quadratic classifier trained on RAR parameters predicted transfusion of fresh frozen plasma and cryoprecipitate with high overall accuracy. These results demonstrate the potential of RAR as a bedside hemostasis assessment to guide transfusion in bleeding patients.

The impact of relative humidity on the nanoindentation relaxation in calcium silicate hydrates

Despite extensive research efforts, understanding the time-dependent behavior of concrete remains an enigma due to the complex nature of cement microstructure. In this study, the statistical nanoindentation was employed to investigate the influence of relative humidity (RH) on the relaxation behavior of calcium silicate hydrates (C-S-H) in a cement paste. Our experiments, performed at RH levels of 33 % and 86 %, revealed significant enhancements in both the indentation modulus and hardness of the C-S-H as RH increased. Remarkably, the internal water exerted a significant influence on the asymptotic relaxation behavior, displaying a clear power-law fashion. Further analysis identified the presence of short- and long-term viscoelastic behaviors within the C-S-H, distinguished by a transition observed within the initial seconds. These findings advance the understanding of nanoscale mechanisms driving concrete creep under different humidity conditions.

A viscoelastic harvester-absorber for energy generation and vibration control

Abstract A vibration energy harvester harnesses the oscillatory movement and&amp;#xD;converts it into electrical energy. On the other hand, a (dynamic) vibration absorber&amp;#xD;dissipates the mechanical energy of a host structure (primary system). The proposal for&amp;#xD;a harvester-absorber device (HAD), comprinsing a piezoelectric element (conventional&amp;#xD;harvester) bonded with a viscoelastic layer and a steel constrained layer, is based on the&amp;#xD;dual purpose of generating energy and at the same time reducing the vibratory response&amp;#xD;of the primary system. Introducing a viscoelastic dissipative layer in a conventional&amp;#xD;harvester, also offers the advantage of simultaneously reducing wear on the piezoelectric&amp;#xD;element, thereby extending its lifespan and preventing fatigue-related breakage. The&amp;#xD;paper presents a model of a harvester-absorber built from a bimorph piezoelectric&amp;#xD;beam, a layer of viscoelastic material (E-A-R C1002-01PSA) and a beam of steel, which&amp;#xD;acts as a constrained layer. A lumped parameter model is proposed for the theoretical&amp;#xD;description of the HAD which is successfully used to experimentally determine its&amp;#xD;parameters. After that, and using the equivalent stiffness concept, the HAD was&amp;#xD;coupled to a free-free beam with two masses at its ends to study its perfomance over a&amp;#xD;real host structure. The inertance of the composite system and voltage/force frequency&amp;#xD;response function of the HAD were obtained and compared with experimental results.&amp;#xD;The accuracy of the results justifies and validate the model which has the advantage&amp;#xD;of simplicity and can contribute to reducing wear and increasing the lifespan of brittle&amp;#xD;piezoelectric structures.

Linking Metastatic Potential and Viscoelastic Properties of Breast Cancer Spheroids via Dynamic Compression and Relaxation in Microfluidics.

The growth and invasion of solid tumors are associated with changes in their viscoelastic properties, influenced by both internal cellular factors and physical forces in the tumor microenvironment. Due to the lack of a comprehensive investigation of tumor tissue viscoelasticity, the relationship between such physical properties and cancer malignancy remains poorly understood. Here, the viscoelastic properties of breast cancer spheroids, 3D (in vitro) tumor models, are studied in relation to their metastatic potentials by imposing controlled, dynamic compression within a microfluidic constriction, and subsequently monitoring the relaxation of the imposed deformation. By adopting a modified Maxwell model to extract viscoelastic properties from the compression data, the benign (MCF-10A) spheroids are found to have higher bulk elastic modulus and viscosity compared to malignant spheroids (MCF-7 and MDA-MB-231). The relaxation is characterized by two timescales, captured by a double exponential fitting function, which reveals a similar fast rebound for MCF-7 and MCF-10A. Both the malignant spheroids exhibit similar long-term relaxation and display residual deformation. However, they differ significantly in morphology, particularly in intercellular movements. These differences between malignant spheroids are demonstrated to be linked to their cytoskeletal organization, by microscopic imaging of F-actin within the spheroids, together with cell-cell adhesion strength.

Microstructure-mechanical property relationships of polymer nanocomposite reinforced with lyophilized montmorillonite/carbon nanotubes hybrid particles

Abstract Introducing multi-walled carbon nanotubes (MWCNT) and montmorillonite (MMT) simultaneously into a polymer can significantly enhance its properties. Meanwhile, choosing the best technique to homogeneously disperse these nanohybrid particles in polymers, without agglomerates, is still a challenge. In this study, a hybrid MMT/MWCNT, prepared by lyophilization process, is introduced in polylactide (PLA). Morphology of the resulting nanocomposites displays synergistic relationships of the MMT/MWCNT, facilitating dispersion in PLA. The analysis of transmission electron microscopy (TEM) specific particle densities of PLA0.5hyb, PLA1.0hyb, and PLA2.0hyb shows values of 77, 64, and 35 µm⁻2, respectively. This suggests that MMT platelets are significantly more exfoliated in PLA0.5hyb compared to the other nanocomposites. It also indicates that filler aggregation increases as the MMT/MWCNT concentration increases. Compared to neat PLA, elastic modulus of nanocomposites increased by up to 46 %, demonstrating the reinforcing effect of MMT/MWCNT hybrid nanofillers. The nanocomposites exhibit viscosity, plasticity and damage phenomena, which are significantly decreased because of the MMT/MWCNT incorporation, compared to neat PLA. Furthermore, the viscoelastic properties, analyzed by dynamic thermal-mechanical analysis, record about 27 % increase in the storage modulus of the nanocomposites compared to PLA, indicating the effectiveness of the hybrid MMT/MWCNT in increasing the resistance of PLA/MMT/MWCNT nanocomposite against thermomechanical aggression.

Gelation and dough‐forming properties of canary seed protein concentrate in comparison with commercial soy protein concentrate and vital wheat gluten

AbstractBackground and ObjectivesIn this study, a lab‐scale process was developed to aqueously de‐oil canary seed (yellow and brown‐seeded) flour and derive a protein concentrate. The protein concentrates prepared were evaluated for their gelation and bread dough‐forming properties.FindingsThe aqueous process successfully reduced the oil content in both yellow‐seed and brown‐seed roller‐milled flour. The protein concentrate prepared from yellow‐seed flour and brown‐seed flour had 74.9% and 68.6% purity (dry weight basis), respectively. Proteins showed high resistance to thermal denaturation (peak denaturation at 107°C). It was found that the least gelation concentration of both protein concentrates was 16% (w/w). There were no significant differences in viscoelastic properties and water holding capacity between the protein gels of these two canary seed types and the addition of salt did not noticeably improve these properties. Compared to canary seed, commercial soy protein showed better gelation properties. Both yellow and brown canary seed protein showed a good potential for improving bread dough strength when incorporated into a low‐gluten‐strength wheat flour and was comparable to commercial vital wheat gluten at 1%–3% (w/w) inclusion levels.ConclusionsThe new canary seed protein ingredients prepared by the solvent‐free aqueous‐based process hold good potential for application in food formulation based on their gelation and bread dough‐forming properties.Significance and NoveltyThe gelation and dough‐forming properties of canary seed were not previously studied; therefore, this study provides an insight into those properties for potential food applications for canary seed proteins, which is important for canary seed market diversification as a novel protein source.

Progress on the Sound Absorption of Viscoelastic Damping Porous Polymer Composites.

Porous polymer composites (PPC) have developed rapidly recently, which are widely used in various industrial fields. Viscoelastic damping is an important behavior of porous polymer composites, and it can determine the sound absorption for noise reduction applications. This review has mainly covered the viscoelastic damping and sound absorption of porous polymer composites. Different fabrication approaches of porous polymer composites are gathered. The mechanism of viscoelastic damping behavior is described, and also the sound absorption properties. Followed by the introduction of enhanced sound absorption of viscoelastic damping porous polymer composites, including the incorporation of fillers, microstructures modification, combination with nanofibrous materials, and multilayer configuration, etc. The incorporated fillers can effectively adjust the interfacial area in composites, and obtain desired bonding conditions. Microstructures modification is an effective tool to improve the morphologies of both polymer matrix and fillers, which can be achieved by chemical treatment and surface coating. The combination with lightweight nanofibrous layer can increase the low frequency absorption. The configuration of multilayer composites can improve both acoustical and mechanical properties for engineering applications. It is hoped that this comprehensive review is benefit for the promising development of porous polymer composites in related fields.

Thermomechanical properties of bat and human red blood cells—Implications for hibernation

Hibernation is a widespread and highly efficient mechanism to save energy in mammals. However, one major challenge of hibernation is maintaining blood circulation at low body temperatures, which strongly depends on the viscoelastic properties of red blood cells (RBCs). Here, we examined at physiologically relevant timescales the thermomechanical properties of hundreds of thousands of individual RBCs from the hibernating common noctule bat (Nyctalus noctula), the nonhibernating Egyptian fruit bat (Rousettus aegyptiacus), and humans (Homo sapiens). We exposed RBCs to temperatures encountered during normothermia and hibernation and found a significant increase in elasticity and viscosity with decreasing temperatures. Our data demonstrate that temperature adjustment of RBCs is mainly driven by membrane properties and not the cytosol while viscous dissipation in the membrane of both bat species exceeds the one in humans by a factor of 15. Finally, our results show that RBCs from both bat species reveal a transition to a more viscous-like state when temperature decreases. This process on a minute timescale has an effect size that is comparable with fluctuations in RBC viscoelasticity over the course of the year, implying that environmental factors, such as diets, have a lower impact on the capability of RBCs to respond to different temperatures than general physical properties of the cell membrane. In summary, our findings suggest membrane viscoelasticity as a promising target for identifying mechanisms that could be manipulated to ensure blood circulation at low body temperatures in humans, which may be one first step toward safe synthetic torpor in medicine and space flight.

Dynamic insights into thermal shock response of double-layer cylinders with FGM main layer and viscoelastic holder via generalized Green-Naghdi theory

This study investigates the dynamic thermoelastic response of a hollow cylinder composed of two distinct layers: a Functionally Graded Material (FGM) as the primary layer and an isotropic viscoelastic material as the supporting layer. Utilizing a power function, the material properties of the FGM layer are determined, while the viscoelastic layer follows the Kelvin-Voigt model. The research employs the generalized Green-Naghdi theory to formulate the heat transfer equation, capturing the energy dissipation and thermoelastic wave propagation within this novel configuration. Highly coupled equations governing both layers are derived, incorporating appropriate boundary and continuity conditions. The Chebyshev collocation element (CCE) method is utilized for the spatial solution, significantly reducing the computational effort by requiring only two higher-order elements. The Newmark time marching approach is employed to solve the resulting ordinary differential equations (ODEs). The model's accuracy is validated against existing literature, and parametric studies are conducted to evaluate the impact of thermal shock on the FGM layer. It has been observed that the presence of the viscoelastic barrier effectively impedes the full penetration of stress waves, thereby reducing the potential for shock-induced damage.

Influence of Gamma irradiation on shape memory polymer nano-composite for satellite deployment mechanism

This research investigates the impact of gamma irradiation on epoxy-MWCNT nanocomposites for satellite deployment mechanisms. Nanocomposites, enhanced with surfactants, were meticulously prepared and subjected to controlled gamma irradiation (250–1000 kGy) utilizing the Cobalt-60 facility Industrial Mega Gamma-1 at NCRRT in Egypt. Surface tension measurements explored surfactant effects on epoxy-MWCNT composites in acetone. Acetone reduced tension from 26.7 to be 24.2 (mN/m). Surfactants (Tween 80, SDS) effectively lowered tension (24.4 mN/m), while surfactant-free systems had higher tension (25.1 mN/m). Cationic surfactant (CTAB) slightly increased tension (25.4 mN/m) but aided MWCNT dispersion. Nonionic and anionic surfactants showed superior dispersing power, aligning with MWCNTs and enhancing dispersion. Thermogravimetric analysis (TGA) unveiled alterations in the thermal stability of epoxy-MWCNT nanocomposites induced by radiation, particularly evident at elevated doses (500 and 1000 kGy). Notably, surfactant-modified specimens exhibited discernible effects on various thermal stability parameters. DMA analysis revealed radiation-induced changes in viscoelastic properties. Unirradiated epoxy exhibited a Tg of 58 °C, while 250 kGy irradiation enhanced crosslinking (Tg: 64 °C). Higher doses (500 kGy, 1000 kGy) caused marginal Tg changes. Surfactant-modified samples showed varied effects, with Tween 80 emphasizing its role in phase separation. Results highlighted radiation’s influence on stiffness and energy dissipation. Shape memory behavior indicated increased recovery time with higher doses, except at 250 kGy. Epoxy-MWCNT exhibited a stable recovery time, suggesting a MWCNT stabilizing effect. Fixation rates consistently reached 100%, indicating improved shape recovery influenced by MWCNTs and surfactants. This study provides insights into optimizing nanocomposites for satellite deployment applications.

State-of-the-art Review of Springback Behavior of Polymers

The spring-in and spring-back behavior of polymers is intricate and influenced by various process parameters and mechanisms, including interply slip, anisotropic thermal expansion, and crystallization, all of which can lead to residual stresses. Composite materials made of metal and polymer are being investigated by researchers as a promising alternative to monometallic materials due to their superior properties. However, the number of studies related to metal/polymer/metal laminates on the same topics is relatively limited. A comprehensive review study was carried out with a focus on research works that were conducted with the consideration of different process parameters, such as radius of die and punch, friction, and force applied by blank holder, in order to observe their impact on the springback behavior of polymers. Springback on polymer components depends on the accuracy of appropriate materials and the consideration of appropriate experimental strategies. However, due to their viscoelastic properties, polymers demonstrate distinctive springback behavior. Furthermore, when subjected to deformation, polymers experience a combination of elastic and viscous responses, resulting in immediate elastic recovery and time-dependent viscoelastic relaxation. This intricate behavior presents difficulties in precisely forecasting and managing springback. To enhance the control and optimization of springback in polymer-based manufacturing processes, it is essential to improve the understanding of polymer behavior under diverse loading conditions and to refine simulation techniques accordingly. This review focuses on springback prediction models specific to polymers.

Seismic Stability Evaluation of Landfill Veneer Cover Systems Using Modified Pseudo-Dynamic Method

ABSTRACT This study evaluates the seismic stability of veneer cover systems, addressing the sliding failure (SF) and uplifted-floating failure (UF) caused by retained water. The modified pseudo-dynamic (MPD) method, considering hydrostatic, hydrodynamic, and seismic forces, is employed. Comparison of the results with the literature under the pseudo-static (PS) and pseudo-dynamic (PD) loading conditions highlight the precision of the MPD method. Consideration of the visco-elastic behavior and soil damping in the analysis enhances the accuracy of the MPD method. Design charts are proposed for the determination of the allowable thickness of cover soil, which is cost-effective, ensuring seismic safety against SF and UF modes.

Minimum effective plyometric training volume in sedentary individuals: Impact on lower limb viscoelastic properties and functional performance in a randomised controlled trial

ABSTRACT Sedentary lifestyles reduce muscle mass, strength, power, and alter viscoelastic properties. Plyometric jump training (PJT) shows promise in countering these effects, but the optimal training volume for individuals with low athletic performance remains unclear. This study aimed to determine the minimal PJT volume required to improve muscle and tendon viscoelastic properties, strength, and power in sedentary individuals. A double-blind randomised controlled trial included 44 participants divided into three groups: Control Group (CG) (n = 16), Reduced Volume Training Group (RVTG) (n = 16), and Training Group (TG) (n = 12). The four-week PJT programme involved three weekly sessions with gradual volume increments; RVTG performed 50% less volume than TG. Baseline and follow-up assessments included the isokinetic standing up (SU) and sitting down (SD) phases at 15 cm/s and 5 cm/s, and myotonometer measurements. In the SU phase at 15 cm/s, significant differences were found (p = 0.01) with higher values in TG (10.0 ± 3.3 N/kg) compared to CG and RVTG. At 5 cm/s, differences in SD were observed (p = 0.002). For Achilles tendon properties in RVTG: stiffness (p = 0.04), decrement (p = 0.01), and relaxation (p = 0.02). A PJT volume of 2,414 jumps improved muscle strength, while 1,207 jumps altered tendon properties.

Effect of shear rate, temperature, and salts on the viscosity and viscoelasticity of semi‐dilute and entangled xanthan gum

AbstractXanthan gum, a naturally‐occurring, high‐molecular‐weight, anionic polyelectrolyte, exhibits significant drag‐reducing properties at low concentrations in water, suggesting promising applications in geothermal networks. The flow behavior of xanthan solutions are explored, specifically at concentrations in the semi‐dilute (1000 ppm by mass) and entangled (4000 ppm) regimes as well as in both water and various salt solutions across a temperature range of 5–85°C. The viscosity and viscoelastic properties of xanthan solutions examine relationships between polyelectrolyte concentration, temperature, and salt concentration. Viscosity decreases by two orders of magnitude in 4000 ppm xanthan solutions in deionized water and with 50 mM NaCl (in the high salt limit) as the temperature increases from 5 to 85°C. Next, the addition of salts affects viscosity differently in the two concentration regimes. Specifically, at 25°C, the zero‐shear rate viscosity upon salt addition decreases by 63% for 1000 ppm solutions (from 0.54 to 0.2 Pa s) but increases by 280% for 4000 ppm solutions (from 28 to 107 Pa s). At 1000 ppm, salt ions cause chain collapse, reducing viscosity; At 4000 ppm, entanglements led to structural changes, resulting in higher viscosity. Furthermore, three salts commonly found in geothermal waters, namely NaCl, Na2CO3, and NaHCO3, exhibited similar changes in viscosity and shear thinning behavior in the entangled regime across temperatures from 5 to 85°C.