Viscoelastic State Research Articles

Rheological and secondary structural characterization of rice flour-zein composites for noodles slit from gluten-free sheeted dough.

Rice flour-zein composites in a hydrated viscoelastic state were utilized to compensate for the role of wheat gluten in gluten-free sheeted dough. The use of zein above its glass transition temperature was able to form a viscoelastic protein network of non-wheat dough with rice flour. The mixing stability and development time of the rice dough were positively increased with increasing levels of zein. The protein secondary structural analysis by FTIR spectroscopy demonstrated that the rice doughs with high levels of zein showed significant increases in β-sheet structures whose intensity was almost doubled by the use of 10% zein. The use of zein at more than 5% (w/w) successfully produced gluten-free dough sheets that could be slit into thin and long noodle strands. In addition, the composites were effective in improving the rheological characteristics of gluten-free noodle strands by increasing their maximum force to extension, compared to wheat-based noodles.

Effect of aging time and salt on the viscosity behaviour of a Gemini cationic surfactant

ABSTRACTRheological properties of micellar solutions of a cationic Gemini surfactant, 2-hydroxypropyl-1,3-bis (dodecyldimethylammonium chloride), are studied as a function of aging time and salt addition. The results show that the self-aggregating behaviour in solution changes as a factor of time, probably due to intermolecular hydrogen bonds. The viscosity of the solution undergoes a series of visible changes so that the solution changes from a flow state to highly viscoelastic state, and finally, to a transparent solid, with a corresponding 4–6-fold increase in zero shear state viscosity. Rheology and freeze fracture transmission electron microscopy (FF-TEM) measurements show rod-like micelles at the beginning, which then change to wormlike micelles, and eventually to a quasi-gel-like network. Addition of an inorganic salt (NaCl) induces salting out, while the addition of an organic salt (NaSal) promotes micellar growth. At a fixed NaSal-to-surfactant molar ratio of 3:5, all solutions show Maxwell fluid behaviour and maximum zero-shear-rate viscosity; these trends can be attributed to the formation of a network structure between the cationic ions of the surfactant and Sal– as the surfactant concentration increases. Crystal analysis further confirms the presence of structures linked by intermolecular hydrogen bonds.

Viscous and viscoelastic stress states at the calving front of Antarctic ice shelves

ABSTRACTCalving mechanisms are still poorly understood and stress states in the vicinity of ice-shelf fronts are insufficiently known for the development of physically motivated calving laws that match observations. A calving model requires the knowledge of maximum tensile stresses. These stresses depend on different simulation approaches and material models. Therefore, this study compares results of a two-dimensional (2-D) continuum approach using finite elements with results of a one-dimensional (1-D) beam model elaborated in Reeh (1968). A purely viscous model, as well as a viscoelastic Maxwell model, is applied for the 2-D case. The maximum tensile stress usually appears at the top surface of an ice shelf. Its location and magnitude are predominantly influenced by the thickness of the ice shelf and the height of the freeboard, the traction-free part at the ice front. More precisely, doubling the thickness leads to twice the stress maximum, while doubling the freeboard, based on changes of the ice density, results in an increase of the stress maximum by 61%. Poisson's ratio controls the evolution of the maximum stress with time. The viscosity and Young's modulus define the characteristic time of the Maxwell model and thus the time to reach the maximum principal stress.

Residual stresses created during curing of a polymer matrix composite using a viscoelastic model

A modified viscoelastic constitutive model is proposed to predict cure-induced residual stresses in polymer matrix composites. The modifications rely on using the inverse of the Deborah number to describe regimes corresponding to a fully relaxed state, a viscoelastic state and an elastic state. The composite is only in a viscoelastic state for limited ranges of the Deborah number. By considering the evolution of the Deborah number during curing of the AS4/3501-6 composite, the composite is in a fully relaxed state when it is cured at high temperature and the degree of cure is lower than 0.73, and no further changes in the viscoelastic characteristics when the degree of cure is higher than 0.8. A 3D simulation of a composite laminate plate is used to predict the evolution of the residual stresses. The analysis reveals that the accurate simulation on the cure-induced residual stress should include the last two states of the entire cure process, and consider the stress relaxation, thermal deformation and chemical shrinkage.

Characterization of concanavalin A-conjugated resistant starch acetate bioadhesive film for oral colon-targeting microcapsule delivery system

For the effectiveness of bioactive ingredient targeting delivery in the gastrointestinal tract (GIT), the concanavalin A (Con A)-conjugated RSA film was developed for the potential bioadhesive coating material for colon-targeting bioadhesive microcapsules which were designed by the method of extrusion–spheronization and film coating process. The Con A-conjugated RSA films with coupled Con A from 8 to 32μg/mg showed sufficient higher storage modulus (G′) and glass transition temperature (Tg). The G′ and Tg increased as immersion in simulated digestive fluids progressed which allowed the films transformed from a viscoelastic state to a glassy state and is benefit for the bioactive ingredients releasing. Through adjusting the amount of coupled Con A the brittleness time and brittlement of Con A-conjugated RSA film could be adjusted and controlled for matching the colon targeting and releasing performance. The in-vitro and in-vivo study demonstrated that the Con A-conjugated RSA film coated microcapsules have good colon targeting and bioadhensive properties which could not only target bioactive molecules to the colon but also increase the residence time of the microcapsules for 72h in the colon.

Virtual Uniaxial Creep Testing Method of Asphalt Mixture

AbstractThis paper presents a virtual uniaxial creep testing method. Different gradations were selected, and the X-ray CT was used to scan the asphalt specimens non-destructively in order to predict the deformation of asphalt mixture and verify the feasibility of the proposed method. Moreover, the finely distributed information of asphalt mixture microstructure, including aggregates, sand mastic and air voids, were captured. The 3D virtual specimen reflecting the real microscale distribution of asphalt mixture was created according to the developed 3D reconstruction theory and algorithm. Considering the Burgers visco-elastic consecutive relations of sand mastic, the visco-elastic state of sand mastic was transformed to the Prony parameters identified by finite element by using the Boltzmann superposition principle and Laplace theory. Finally, the virtual uniaxial creep testing was conducted. Results show that the predicted deformations agree well with the testing results. The proposed virtual uniaxial cre...

The Effects of Temperature on Clot Microstructure and Strength in Healthy Volunteers.

Anesthesia, critical illness, and trauma are known to alter thermoregulation, which can potentially affect coagulation and clinical outcome. This in vitro preclinical study explores the relationship between temperature change and hemostasis using a recently validated viscoelastic technique. We hypothesize that temperature change will cause significant alterations in the microstructural properties of clot. We used a novel viscoelastic technique to identify the gel point of the blood. The gel point identifies the transition of the blood from a viscoelastic liquid to a viscoelastic solid state. Furthermore, identification of the gel point provides 3 related biomarkers: the elastic modulus at the gel point, which is a measure of clot elasticity; the time to the gel point (TGP), which is a measure of the time required to form the clot; and the fractal dimension of the clot at the gel point, df, which quantifies the microstructure of the clot. The gel point measurements were performed in vitro on whole blood samples from 136 healthy volunteers over a temperature range of 27°C to 43°C. There was a significant negative correlation between increases in temperature, from 27°C to 43°C, and TGP (r = -0.641, P < 0.0005). Conversely, significant positive correlations were observed for both the elastic modulus at the gel point (r = 0.513, P = 0.0008) and df (r = 0.777, P < 0.0005) across the range of 27°C to 43°C. When temperature was reduced below 37°C, significant reductions in df and TGP occurred at ≤32°C (Bonferroni-corrected P = 0.0093) and ≤29°C (Bonferroni-corrected P = 0.0317), respectively. No significant changes were observed when temperature was increased to >37°C. This study demonstrates that the gel point technique can identify alterations in clot microstructure because of changes in temperature. This was demonstrated in slower-forming clots with less structural complexity as temperature is decreased. We also found that significant changes in clot microstructure occurred when the temperature was ≤32°C.

Risk of cardiovascular diseases in reproductive aging of women

Characteristics of reproductive age and association of clinical and endocrine changes in women of reproductive age from late to early menopause are presents in this article. We consider the theory of aging: the theory of evolution on genetically programmed aging, free-radical, mitochondrial, elevating, immunological theory, the hypothesis of the existence of the genetic program of self-destruction. The article focuses on the rigidity of the arterial wall that is directly related to the speed of the pulse wave, the definition of which is the standard measure of rigidity and can be used as a prognostic factor of death from cardiovascular diseases. Modern researchers consider the biomechanical properties of the vessels (the rate of viscoelastic state artery, pulse wave velocity) as one of the criteria of biological age, because, illustrating the close relationship with chronological age in conjunction with other criteria, they characterize a slow or rapid type of aging women. Menopause is accompanied by atherogenic changes in the lipid composition of the blood, namely, increased levels of LDL cholesterol and decreased levels of HDL cholesterol, and also an increase in the obesity prevalence, insulin resistance and diabetes, mostly type-2. Therefore, patients with hypertension in postmenopausal period often have a variety of the metabolic disorders that along with the increase in blood pressure potentially increases the risk of cardiovascular complications. Manifestation of the pre-climacteric syndrome, the duration of which in 35% of women more than 5 years, is worsens hypertension, and in patients with hypertension is more common it pathological course. Hot flushes development correlated with subclinical symptoms of cardiovascular diseases, which manifests endothelial dysfunction, calcification of the aorta, the increase in intima-media thickness of the carotid artery, increased levels of procoagulant factors dislipoproteinemia development. Numerous publications have a lot of results on the potential use of hormonal drugs for the prevention of aging processes in the vessel wall in order to maintain the normal state of the cardiovascular system of women.

Tidal Heating of Earth-like Exoplanets around M Stars: Thermal, Magnetic, and Orbital Evolutions.

The internal thermal and magnetic evolution of rocky exoplanets is critical to their habitability. We focus on the thermal-orbital evolution of Earth-mass planets around low-mass M stars whose radiative habitable zone overlaps with the “tidal zone,” where tidal dissipation is expected to be a significant heat source in the interior. We develop a thermal-orbital evolution model calibrated to Earth that couples tidal dissipation, with a temperature-dependent Maxwell rheology, to orbital circularization and migration. We illustrate thermal-orbital steady states where surface heat flow is balanced by tidal dissipation and cooling can be stalled for billions of years until circularization occurs. Orbital energy dissipated as tidal heat in the interior drives both inward migration and circularization, with a circularization time that is inversely proportional to the dissipation rate. We identify a peak in the internal dissipation rate as the mantle passes through a viscoelastic state at mantle temperatures near 1800 K. Planets orbiting a 0.1 solar-mass star within 0.07 AU circularize before 10 Gyr, independent of initial eccentricity. Once circular, these planets cool monotonically and maintain dynamos similar to that of Earth. Planets forced into eccentric orbits can experience a super-cooling of the core and rapid core solidification, inhibiting dynamo action for planets in the habitable zone. We find that tidal heating is insignificant in the habitable zone around 0.45 (or larger) solar-mass stars because tidal dissipation is a stronger function of orbital distance than stellar mass, and the habitable zone is farther from larger stars. Suppression of the planetary magnetic field exposes the atmosphere to stellar wind erosion and the surface to harmful radiation. In addition to weak magnetic fields, massive melt eruption rates and prolonged magma oceans may render eccentric planets in the habitable zone of low-mass stars inhospitable for life. Key Words: Tidal dissipation—Thermal history—Planetary interiors—Magnetic field. Astrobiology 15, 739–760.

Viscoelastic potential-induced changes in acoustically thin films explored by quartz crystal microbalance with motional resistance monitoring

Viscoelastic properties of intrinsically conducting polymers depend on different factors, among them polymer structure, ionic and solvent population and film thickness. During a voltammetric cycle, electrochemical reactions involve changes of these factors. Consequently, the viscoelastic properties are expected to be changed. Electrochemical quartz crystal microbalance with motional resistance monitoring were employed to calculate the instantaneous resonant frequency/motional resistance ratio (dfr/dRm)during the electrochemical processes of acoustically thin films of poly(o-toluidine). dfr/dRm is defined as the energy dissipation factor and shows values around ∼10HzΩ−1 for a net liquid-loading effect on resonator electrode. Therefore, as this value is larger the film deposited on resonator electrode is expected to be more rigid. The experimental results showed in this work points to this assumption. Viscoelastic state of acoustically thin films of poly(o-toluidine) were investigated through redox reactions, in different electrolytes and scan rates potential perturbations. Finally, viscoelastic changes of a relaxed POT and packed POT was compared. The viscoelastic aspects of poly(o-toluidine) here investigated can help to understand and adjust the signal transduction of (bio) sensors or for composite supercapacitors where the mechanical properties of the different organic layers can limit the performances of the electrochemical system.

Structure-Sensitive Maxima in the Absorption Spectra of Polymers in the Terahertz Frequency Range

The basic sizes characterizing the morphology of a few practically important synthetic organic polymers in the glassy and viscoelastic states are confronted with the maxima of the absorption spectra in the terahertz frequency range. These sizes are determined using the X-ray diffraction technique. The absorption spectra of these polymers have been measured by the method of terahertz time-domain spectroscopy in the temperature range from helium to room temperatures.

High-Definition Imaging of Carotid Artery Wall Dynamics

The carotid artery (CA) is central to cardiovascular research, because of the clinical relevance of CA plaques as culprits of stroke and the accessibility of the CA for cardiovascular screening. The viscoelastic state of this artery, essential for clinical evaluation, can be assessed by observing arterial deformation in response to the pressure changes throughout the cardiac cycle. Ultrasound imaging has proven to be an excellent tool to monitor these dynamic deformation processes. We describe how a new technique called high-frame-rate ultrasound imaging captures the tissue deformation dynamics throughout the cardiac cycle in unprecedented detail. Local tissue motion exhibits distinct features of sub-micrometer displacements on a sub-millisecond time scale. We present a high-definition motion analysis technique based on plane wave ultrasound imaging able to capture these features. We validated this method by screening a group of healthy volunteers and compared the results with those for two patients known to have atherosclerosis to illustrate the potential utility of this technique.

Mechanisms for three kinds of limiting shear stresses appearing in the traction modes of viscous, viscoelastic, and glassy states of lubricants

We present that the tractional flow of a lubricant shows three kinds of limiting shear stresses at which the shear stresses take place independently of the shear rates in its viscous, viscoelastic, and glassy states. We propose three models on the mechanisms for the limiting shear stresses, based on the data of Brillouin spectra and viscosity of viscoelastic liquids previously reported by us and based on the data of the deformation of glassy polymers referred from others. The Brillouin spectra of a viscoelastic lubricant measured at up to 5 GPa at 25 and 80 °C show that we could not observe a frequency dispersion in sound waves below 0.8 GPa at 80 °C, while we can observe the frequency dispersion above 0.1 MPa at 25 °C owing to the viscosity of the lubricant. This result predicts the viscous limiting shear stress in the viscous state owing to the disappearance of meso-structures by heating and shearing under pressure. The viscosity of a polymer measured around the glass transition temperature (Tg) shows that Tg determined by the viscosity measurement is 27 K lower than that determined by calorimetry. This result predicts the elastic limiting shear stress in the viscoelastic state near the glass transition pressure (Pg) owing to the shear thinning effect by shearing a lubricant film. In addition, there is the plastic limiting shear stress in the glassy state owing to the yield stress at which the tractional flow of a glassy lubricant behaves as a plastic solid.

A Numerical–Analytical Method for Solving Problems of Linear Viscoelasticity

A numerical method for solving problems of the linear viascoelasticity of an anisotropic body is proposed. The method does not require deriving explicit analytical expressions for the creep and relaxation kernels. The approximate solution of the integral equations is based on using experimental data preliminarily smoothed with filling in data gaps. The results of numerical analysis of the viscoelastic stress state of an orthotropic plate with an elliptic hole are presented

The Effect of the Physical State of Binders on High-Shear Wet Granulation and Granule Properties: A Mechanistic Approach to Understand the High-Shear Wet Granulation Process. Part IV. The Impact of Rheological State and Tip-speeds

The purpose of this study is to provide a mechanistic understanding concerning the effect of tip-speed on a granulation at various binder rheological states; the in situ rheological state of a binder was controlled by exposing a granulation blend to 96% relative humidity. This approach allowed us to investigate the impact of tip-speed on granule consolidation coupled with the in situ binder state, which was not possible using a conventional granulation approach. Experimentally, the rheological state of binders was characterized using a rheometer. Granule size and granule porosity were measured by Qicpic instrument and Mercury Intrusion Porosimetry, respectively. For the granulations containing binders at viscous state (PVP K17 and PVP K29/32), the granule size increased significantly with mixing time and the growth rate increased with tip-speed until 5.8 m/s; when binders were at viscoelastic state, tip-speed had no impact on granulation. Furthermore, the granule porosity was higher for granulation with binders at viscoelastic state (HPC and PVP K90), whereas it was lower for granulation with binders at viscous state. In addition, the impeller tip-speed had minimal impact on the porosity of the final granules. Finally, Ennis' model was used for interpreting results, providing mechanistic insights on granulation.

Molecular mechanisms of cellular mechanosensing

Mechanical forces direct a host of cellular and tissue processes. Although much emphasis has been placed on cell-adhesion complexes as force sensors, the forces must nevertheless be transmitted through the cortical cytoskeleton. Yet how the actin cortex senses and transmits forces and how cytoskeletal proteins interact in response to the forces is poorly understood. Here, by combining molecular and mechanical experimental perturbations with theoretical multi-scale modeling, we decipher cortical mechanosensing from molecular to cellular scales. We show that forces are shared between myosin II and different actin crosslinkers, with myosin having potentiating or inhibitory effects on certain crosslinkers. Different types of cell deformations elicit distinct responses, with myosin and α-actinin responding to dilation, and filamin mainly reacting to shear. Our observations show that the accumulation kinetics of each protein may be explained by its molecular mechanisms, and that protein accumulation and the cell's viscoelastic state can explain cell contraction against mechanical load.

Is adhesion between amorphous polymers sensitive to the bulk glass transition?

Two bulk samples of one and the same or of different amorphous polymers were brought into contact and held for a chosen period of time at a constant healing temperature (T) over the interval of T from below the bulk glass transition temperature (Tgbulk) by ~50 °C to above Tgbulk by ~10 °C. As formed adhesive joints were shear-fractured in tension at room temperature, and lap-shear strength (σ) was measured as a function of T. It has been found that σ develops with T as logσ ~ 1/T both at symmetric and asymmetric interfaces of polystyrene, poly (methyl methacrylate) and poly (2,6-dimethyl-1,4-phenylene oxide). This behaviour implies that there is no discontinuity in the evolution of σ when going through Tgbulk, and that this process is controlled by one and the same diffusion mechanism both below and above Tgbulk. The results obtained indicate that the contact layer of the polymers investigated is in the viscoelastic state at T well below Tgbulk and support the concept of a decrease in the Tg of a near-surface layer with respect to Tgbulk.

Viscoelastic deformation of lunar impact basins: Implications for heterogeneity in the deep crustal paleo‐thermal state and radioactive element concentration

Diverse geological characteristics found for the three major lunar provinces (i.e., the Feldspathic Highlands Terrane (FHT), the South Pole‐Aitken Terrane (SPAT), and the Procerallum KREEP Terrane (PKT)) strongly suggest their distinctly different thermal histories. Quantitative differences among these provinces in their early thermal histories and crustal radioactive element concentrations, however, are highly unknown. One of the few observables that retain a record of the ancient lunar thermal structure is the viscoelastic state of impact basins. This study investigates the long‐term evolution of basin structures using global lunar gravity field data obtained by Kaguya tracking and derives constraints for (1) the paleo‐thermal state of impact basins and for (2) crustal column‐averaged radioactive element concentrations for each province. Our calculation results indicate that impact basins in the central anorthositic region of the FHT (i.e., the FHT‐An) require a very cold interior ( dT ∕ dr ≤ 20 K km − 1 on the surface). This result strongly suggests that the deep portion of the thick farside highlands crust is highly depleted in radioactive elements (Th ≤ 0.5 ppm), indicating that the Th‐rich SPA basin floor crust is clearly different from the lower crust underneath the FHT‐An and cannot be accounted for by simple exposure of the lower crust. Our analysis also indicates that the observed basin structure allows as high as ∼ 6 ppm of column‐averaged Th concentration in the crust inside the PKT. These results indicate that radioactive element concentrations deep in the crust probably vary greatly region by region, similarly to those observed on the surface.

The Molecular Landscape of Mechanosensing by the Cell Cortex

Mechanical forces direct a host of cellular and tissue processes. While much emphasis is placed on cell adhesion complexes as force sensors, these forces must be transmitted through the cortical cytoskeleton. However, how the cortex senses and transmits forces and how cytoskeletal proteins interact in response to these forces are poorly understood. Here, by combining molecular and mechanical experimental perturbations with theoretical multi-scale modeling, we decipher cortical mechanosensing from molecular to cellular scales. Forces are shared between myosin II and different actin crosslinkers with myosin having potentiating or inhibitory effects on certain crosslinkers. Furthermore, different types of cell deformations elicit distinct responses: myosin and α-actinin respond to dilation while filamin mainly reacts to shear. The kinetics of each protein's accumulation may be explained by its molecular mechanisms. Finally, protein accumulation, along with the cell's viscoelastic state, can also explain the monotonic or oscillatory contraction against mechanical load in different mutant strains.

Bidirectional actuation of a thermoplastic polyurethane elastomer

Herein, we report on how to teach a thermoplastic polyurethane elastomer completely stress-free, bidirectional motion. Briefly spoken, we applied training, consisting of extensive tensile deformation in the specimen's viscoelastic state, initiating deformation-induced crystallization. Once unloaded, thermo-reversible specimen expansion and contraction could be detected. Following the microstructural evolution of such a trained specimen by in situ wide-angle X-ray scattering gave evidence for progressive growth of oriented crystallites during cooling. Upon heating, crystallite melting resulted in structural disorder. Beyond this, modification of the training method was used to introduce a geometrically more complex crystalline order. Here, actuation in the form of a decrease and an increase in sample thickness and specimen twisting and untwisting were witnessed. The novel semi-crystalline polymer actuator highlights an enormous potential for realizing versatile reversible shape changes in elastomers.