Viscoelastic Ratio Research Articles

Analysis of short-term self-healing performance of asphalt mixture under a three-point bending fatigue test

To evaluate the self-healing performance of asphalt mixture under repeated loads, indoor three-point bending fatigue tests and self-healing tests were conducted on asphalt mixture AC-13. The stress control mode was selected to test the fatigue resistance of the mixture, and the dissipated energy recovery value and visco-elastic ratio were proposed to evaluate the self-healing performance of the mixture. The experimental results show that there is a good linear relationship between fatigue life and fatigue stress, and the damage degree to the mixture is exponentially related to the load times. The numerical dispersion of flexural tensile modulus is large, which is not suitable for evaluating the self-healing performance of the mixture. As the number of loading cycles increases, the hysteresis dissipated energy of the mixture gradually decreases and tends to stabilize. After the loading interval, due to the self-healing effect, the visco-elastic performance of the asphalt material is partially restored. The initial dissipated energy before and after interval can be used as an evaluation index for self-healing behavior, and there is a good linear relationship between the initial dissipated energy and the damage degree. Due to the deformation migration of the mixture during the initial loading stage before and after interval, the visco-elastic ratio has changed, and this change becomes more pronounced with the damage degree of the mixture, indicating that the self-healing ability of the mixture has also been improved.

Nonlinear dynamics of two electromechanical arms acting discontinuously on a balloon under the action of a sinusoidal excitation

Compression systems based electromechanical actuators require a good understanding of their dynamics for a better performance. This paper deals with the study of the nonlinear dynamics of an electromechanical system with two rotating arms subjected to a sinusoidal excitation for fluid compression purposes. The physical model integrating two balloons to be compressed by the arms alternately is presented and the mathematical equations traducing their dynamics are established. We emphasize on the influence of some control parameters namely the supply voltage, the discontinuity position and the viscoelastic ratio on the behaviour of the angular displacement of the arms. The study is also done by neglecting the inductance in the electrical part of the system. It is obtained that while the arms exhibit periodic motion during regular movement, compression of the balloons induces a shift to multi-periodic or chaotic dynamics, occasionally reverting to periodicity. Experimental and numerical simulation results demonstrate good agreement, with the R-system approximating more experimental outcomes than the RL-system. These findings hold significant implications for various environmental applications utilizing pump technology.

Evaluation of gelatin bloom strength on gelatin methacryloyl hydrogel properties

Gelatin methacryloyl (GelMA) hydrogels are widely used for a variety of tissue engineering applications. The properties of gelatin can affect the mechanical properties of gelatin gels; however, the role of gelatin properties such as bloom strength on GelMA hydrogels has not yet been explored. Bloom strength is a food industry standard for describing the quality of gelatin, where higher bloom strength is associated with higher gelatin molecular weight. Here, we evaluate the role of bloom strength on GelMA hydrogel mechanical properties. We determined that both bloom strength of gelatin and weight percent of GelMA influenced both stiffness and viscoelastic ratio; however, only bloom strength affected diffusivity, permeability, and pore size. With this library of GelMA hydrogels of varying properties, we then encapsulated Swan71 trophoblast spheroids in these hydrogel variants to assess how bloom strength affects trophoblast spheroid morphology. Overall, we observed a decreasing trend of spheroid area and Feret diameter as bloom strength increased. In identifying clear relationships between bloom strength, hydrogel mechanical properties, and trophoblast spheroid morphology, we demonstrate that bloom strength should considered when designing tissue engineered constructs.

Study on the Properties of Cellulose Acetate Composite Synergistically Toughened by Glycerol Triacetate and Modified Nano Titania

Glyceryl triacetate (GT) and nano titanium dioxide (TiO2) filler modified by titanate coupling agent were used to toughen cellulose diacetate to prepare CA/GT/nano TiO2@NZD-201 composites. The effects of glyceryl triacetate and modified titanium dioxide filler on the mechanical properties and rheological properties of cellulose acetate were studied. The rheological properties showed that glyceryl triacetate and modified nano TiO2 significantly increased the plasticity of the composite, reduced the complex viscosity, reduced the rigidity, and increased the viscoelastic ratio. The impact resistance of the composite was improved by 101% due to the addition of modified nano titanium dioxide.

Magnetic resonance elastography of malignant tumors

Cancer biomechanical properties, including high stiffness, solid stress, and interstitial pressure, as well as altered micro-architecture, are drivers of tumorigenesis, invasiveness and resistance to treatment. Magnetic resonance elastography is an emergent non-invasive imaging method to assess the tumor mechanical properties in a spatially resolved fashion. Several MRE acquisition and reconstruction methods have been developed to assess tumors and surrounding tissues. It is increasingly recognized that the visco-elastic properties assessed with MRE are useful for characterizing malignant tumors and evaluating treatment response in various organs. Generally, malignant tumors, except brain tumors, have high stiffness and high visco-elastic ratio or fluidity. MRE transducers, acquisition sequences and reconstruction algorithms are continuously improved to increase depth penetration and spatial resolution, and limit artifacts at spatial discontinuities. Moreover, assessment of compression stiffening might provide new biomarkers of the altered physical traits of cancer. Increasing research and clinical validation will improve the efficacy of MRE for cancer characterization.

Linear Stability of Magneto Viscoelastic Walter’s B ′ Type with Heat and Mass Transfer

In this paper, the couple influence of axial magnetic field and the heat and mass transfer on two rotating cylinders of Walter’s B ′ viscoelastic fluids by using the potential flow theory of viscoelastic fluid has been investigated. The normal mode method is used to compute the growth rate of disturbance. The influence of gravity is ignored at the interface, while the effect of surface tension is present in the analysis. The effect of the parameters on the stability is studied. It is found that the rotation of the inner cylinder induces stability. Furthermore, the viscoelastic ratio of fluids has a stabilizing influence. The heat and mass transfer, magnetic permeability ratio, and Ohnesorge number have a stabilized influence, while viscosity ratio of fluids, density ratio of fluids, and axial magnetic field have destabilizing influence on the considered system.

On the examination of the viscous response of the brachial artery during flow-mediated dilation

In this study, mechanotransduction is investigated through a physics-based viscoelastic model describing the arterial diameter response during a brachial artery flow mediated dilation (BAFMD) test. The study is a significant extension of two earlier studies by the same group, where only the elastic response was considered. Experimental BAFMD responses were collected from 12 healthy volunteers. The arterial wall's elastic and viscous properties were treated as local variable quantities depending on the wall shear stress (WSS) sensed by mechanotransduction. The dimensionless parameters, arising from the model which serve as a quantitative assessment of the artery's physical state, were adjusted to replicate the experimental response. Among those dimensionless parameters, the viscoelastic ratio, which reflects the relative strength of the viscous response compared to its elastic counterpart, is of special relevance to this paper's main conclusion. Based on the results, it is concluded that the arterial wall's mechanical behavior is predominantly elastic, at least in the strict context of the BAFMD test. Recommendations for potential future research and applications are provided.

Size-dependent generalized thermo-viscoelastic response analysis of multi-layered viscoelastic laminated nanocomposite account for imperfect interfacial conditions

Multi-layered viscoelastic laminated nanocomposites have been widely used as a kind of representative active/passive vibration isolator and high-efficient damper in the practical applications of nanoengineering, due to their high energy dissipation, wide damping band and lower cost, and such composite structures often serve in a non-isothermal environment. In this work, an analytical study is conducted to investigate the size-dependent generalized thermoviscoelastic responses of multi-layered viscoelastic laminated nanocomposites. Governing equations of each homogeneous viscoelastic layer, accounting for imperfect interfacial conditions, are formulated in the context of the size-dependent generalized thermo-viscoelasticity model. Solutions accounting for non-idealized interfacial and proper boundary conditions are first presented to characterize the thermomechanical coupling of multi-layered viscoelastic laminated nanocomposites. Transient results of temperature, displacement and stresses in time domain can be achieved via Laplace inversion. Then the transient solutions obtained are applied to a one-dimensional bi-layered medium. It is found that properly selecting the nonlocal parameter and viscoelastic material constants ratios can maximally improve the heat isolation and avoid the larger harmful thermal stresses, especially at surface coating of the nanocomposites. The strategy adopted in this work is expected to be beneficial to thermal management and vibration control in nanoengineering.

Optical force-based detection of splay and twist viscoelasticity of CCN47 across the Nematic-to-Smectic A transition

We measured the splay and twist elastic constant K and viscosity η of CCN47 by coupling optical forces with the nematic director and detecting the resulting deformation. This approach enables to separately induce each of the two distortions and allows to characterize the viscoelastic properties of both the nematic and the smectic A phase. We find that in the nematic phase far from the transition the splay elastic constant K1 is larger than that of twist K2, while its viscosity is smaller, ηsplay < ηtwist. Upon lowering the temperature, K1 and ηsplay continuously increase in the nematic and smectic phase. On the contrary, K2 and ηtwist exhibit an abrupt growth when approaching the N/SmA transition, confirming the expected critical behavior. The twist viscoelastic ratio remains approximately constant in the whole nematic phase, indicating that the critical exponents for K2 and ηtwist are similar.

Enhanced electro-optical response of nematic liquid crystal doped with functionalised silver nanoparticles in twisted nematic configuration

ABSTRACT The dipolar and surface plasmon properties of metallic nanoparticles, especially gold and silver NPs made them suitable candidates for doping with LC system, which provides faster switching time, low power consumption in the display devices. The doping of NPs in the LC system influences the physical properties such as dielectric anisotropy, optical anisotropy, elastic constants, viscosity, and conductivity. In this work, we report the effect of doping of hexane thiol functionalized silver nanoparticles (f-AgNps) of average diameter 3-5nm on the electro-optical switching properties of nematic LC 4-trans-pentyl-cyclohexyl cyanobenzene (5PCH) in the twisted nematic geometry. The threshold as well as switching voltages have also reducedin the nanocomposites of 5PCH compared to pure 5PCH. The steepness of the V-T graph necessary for better multiplexing performance and high contrast has increased by 230% in the 0.025 wt% of f-AgNPs doped 5PCH compared to pure 5PCH. The ion current for 0.025 wt% f-AgNPs doped nanocomposites of 5PCH has reduced by 60% compared to pure 5PCH. We have observed faster switching time in f-AgNPs nanocomposites compared to pure 5PCH due to the decrease of visco-elastic ratio. The total response time of 0.05 wt% f-AgNPs nanocomposites is reduced by 19% compared to pure 5PCH.

Dynamic response evaluation of liquid crystal with negative dielectric anisotropy

ABSTRACT Rotational viscosity coefficient is an important material parameter affecting the dynamic response of liquid crystals. We evaluated the dynamic response of two series of mixed liquid crystals SCL17V33L00 and SCL17V28L00 with negative dielectric anisotropy on the basis of the accurate measurement of rotational viscosity. At the temperature of 25°C, 30°C and 35°C, the parallel and vertical dielectric constants of them were calculated from the dual-cell capacitance model and liquid crystal cell capacitance model. Then, the bend and splay elastic constants of them were determined by analysing the Fréedericksz transition threshold voltage in the vertically aligned nematic cell and comparing the liquid crystal layer capacitance–voltage curve through the finite-differential iteration method with experimental curve. At last, the rotational viscosity coefficients γ 1 of them were obtained by performing dynamic response simulation using Visual Fortran software. As the temperature increases, the rotational viscosity coefficient of them decreases. Although the rotational viscosity coefficient of the second mixed liquid crystal was relatively large under the same temperature, the viscoelastic ratio coefficient was small, and the figure-of-merit was large, thereby resulting in a relatively fast dynamic response.

Analysis of Complex Modal Characteristics of Fractional Derivative Viscoelastic Rotating Beams

For the transverse vibration problem of a fractional derivative viscoelastic rotating beam, the differential equation of the system is obtained based on the Euler–Bernoulli beam theory and Hamilton principle. Then, introducing dimensionless quantities to differential equations and boundary conditions, the generalized complex eigenvalue equations of the system are obtained by the differential quadrature method. The effects of the slenderness ratio, the viscoelastic ratio, the hub radius‐beam length ratio, and dimensionless hub speed and fractional order on the vibration characteristics of fractional derivative viscoelastic rotating beams are discussed by numerical examples. Numerical calculations show that when the dimensionless hub speed is constant, the real part of complex frequency increases with the increase of the fractional order, and the higher‐order growth trend is more obvious. Through the study of displacement response at different points on the beam, it can be seen that the closer to the free end, the larger the response amplitude. And, the amplitude of response has been attenuated, which is also consistent with the vibration law of free vibration considering damping.

Rheological behavior of composites made from linear medium-density polyethylene and hemp fibers treated by surface-initiated catalytic polymerization

This work presents different rheological methods to determine the effect of fiber surface treatment on their interaction with a polymer matrix. In particular, surface-initiated catalytic polymerization was investigated on hemp fibers to improve their adhesion with linear medium-density polyethylene (LMDPE). The selected rheological tests (creep-recovery (solid state), small and large amplitude oscillation shear, and transient rheology (melt state)) were used to compare the treated and untreated fiber composites with the neat matrix. The results showed a significant improvement of the treated hemp composite (LPHC) creep modulus with respect to its untreated counterpart (LNHC) leading to a reduction of the creep strain, especially as temperature increases. The transient viscosity was modeled using a modified Kohlrausch-Williams-Watt (KWW) equation showing an increase in the transient viscosity ( $$ {\eta}_0^{+} $$ ) and relaxation time (τ) with fiber addition and surface treatment. These results were confirmed by large amplitude oscillatory shear (LAOS) through the reduction of the relative third harmonic (I3/1), intrinsic nonlinearity parameter (Q0), and nonlinear viscoelastic ratio (NRL). The results clearly show that catalytic polymerization is a good surface modification technique to increase the compatibility between natural fibers and polymer matrices as to improve all their final properties.

A surface wave elastography technique for measuring tissue viscoelastic properties

A surface wave elastography method is proposed to study the viscoelastic properties of skin by measuring the surface wave speed and attenuation on the skin. Experiments were carried out on porcine skin tissues. The surface wave speed is measured by the change of phase with distance. The wave attenuation is measured by the decay of wave amplitude with distance. The change of viscoelastic properties with temperature was studied at room and body temperatures. The wave speed was 1.83m/s at 22°C but reduced to 1.52m/s at 33°C. The viscoelastic ratio was almost constant from 22°C to 33°C. Fresh and decayed tissues were studied. The wave speed of the decayed tissue increased from 1.83m/s of fresh state to 2.73m/s. The viscoelastic ratio was 0.412/mm at the decayed state compared to 0.215/mm at the fresh state. More tissue samples are needed to study these viscoelastic parameters according to specific applications.

Separation of Storage and Loss Modulus of Polyelectrolyte Multilayers on a Nanoscale: A Dynamic AFM Study

Atomic force microscopy (AFM) is used to carry out rheology measurements on the nanoscale and to determine the mechanical properties of poly(l-lysine) (PLL)/hyaluronic acid (HA) multilayer films. Storage (G') and loss modulus (G″) of the films are calculated and compared with the values obtained from quartz crystal microbalance with dissipation monitoring measurements (QCM-D). A predominant elastic behavior independently of the applied frequencies (5-100 Hz) is observed for native HA/PLL films consisting of 36 double layer. If the layers are cross-linked, the value of G' increases by 2 orders of magnitude, while the loss modulus becomes negligible, making these films a purely elastic chemical gel. The values of G' and G'' extracted from QCM-D measurements on native films are much higher, due to the different frequency regime of the applied shear stress. However, the viscoelastic ratio from the two methods is the same and proves the elastic dominated response of the multilayer in both frequency regimes.

Multifractional microablative laser combined with spacially modulated ablative (SMA) technology for facial skin rejuvenation.

Due to the increasing demand for aesthetic procedures, especially facial aesthetic surgery, a new laser technology has been developed for facial skin rejuvenation and wrinkle treatment. The aim of this study was to objectively and subjectively assess the clinical efficacy and safety of Erbium:YAG laser combined with Spatially Modulated Ablation (Er:YAG + SMA) on facial skin rejuvenation. Patients with Fitzpatrick skin type's I-IV were prospectively included. Inclusion criteria consisted of having wrinkles and irregular skin texture. All patients underwent two Er:YAG + SMA sessions (1 month apart) to stimulate tissue regeneration. Er:YAG laser emits wavelength at 2,940 nm and when combined with SMA, a resonance effect is produced in the dermis to promote tissue regeneration. Facial skin elasticity and firmness were objectively assessed by Cutometer at baseline and month 6 (M6). Aesthetic improvement was qualitatively assessed using digital photographs. Patient satisfaction with regard to their facial appearance was self-assessed using the validated FACE-Q scale and the patient-perceived age VAS scale at baseline, M1, and M6. Side effects were investigated after each session. Thirty-four patients were included, 50% (18 patients) had Fitzpatrick skin type III and 41% (14 patients) were smokers. Skin elasticity indices were significantly improved: from 0.335 ± 0.015 at baseline to 0.387 ± 0.021 at M6 (P = 0.05*) for R5 (net elasticity). Skin firmness was assessed through R7 (biological elasticity) and R6 (viscoelastic ratio) at baseline and M6: a significant increase from 0.235 ± 0.01 to 0.2709 ± 0.009 (P < 0.03**) and decrease from 0.486 ± 0.022 to 0.3918 ± 0.023 (P < 0.006***) were respectively observed. A negative value for R6 corresponded to an improved skin condition. The FACE-Q scores were significantly increased from 39.4 ± 6.7 at baseline to 45.4 ± 9.1 at M1 (P < 0.006***) and 50.4 ± 9.8 at M6 (P < 0.0001***), reflecting wrinkle reduction and enhanced rejuvenation. According to the age appraisal VAS scale, results showed that patients felt younger by -2.92 years at M1 (P < 0.0001***) and -4.13 years (P < 0.0001***) at M6. No adverse reaction was reported. The Er:YAG + SMA technology offers an effective and safe treatment alternative for facial skin rejuvenation. It reduces the recovery time compared to conventional lasers such as carbon dioxide laser. Lasers Surg. Med. 49:78-83, 2017. © 2016 Wiley Periodicals, Inc.

Effects of silica nanoparticles on copper nanowire dispersions in aqueous PVA solutions

In this study, the effects of adding silica nanoparticles to PVA/CuNW suspensions were investigated rheologically, in particular, by small and large amplitude oscillatory shear (SAOS and LAOS) test. Interesting, the SAOS test showed the complex viscosities of CuNW/silica based PVA matrix were smaller than those of PVA/CuNW without silica. These phenomena show that nano-sized silica affects the dispersion of CuNW in aqueous PVA, which suggests small particles can prevent CuNW aggregation. Nonlinearity (third relative intensity ≡ I 3/1) was calculated from LAOS test results using Fourier Transform rheology (FT-rheology) and nonlinear linear viscoelastic ratio (NLR) value was calculated using the nonlinear parameter Q and complex modulus G*. Nonlinearity (I 3/1) results showed more CuNW aggregation in PVA/CuNW without silica than in PVA/CuNW with silica. NLR (= [Q 0(ϕ)/Q 0(0)]/[G*(ϕ)/G*(0)]) results revealed an optimum concentration ratio of silica to CuNW to achieve a well-dispersed state. Degree of dispersion was assessed through the simple optical method. SAOS and LAOS test, and dried film morphologies showed nano-sized silica can improve CuNW dispersion in aqueous PVA solutions.

Characterization of Compatibilizing Effect of Organoclay in Poly(lactic acid) and Natural Rubber Blends by FT-Rheology

The compatibilizing effect of organoclay in immiscible poly(lactic acid) (PLA) and natural rubber (NR) blends was investigated through small-amplitude oscillatory shear (SAOS) and large-amplitude oscillatory shear (LAOS) tests by varying clay concentrations, mixing conditions, and types of clay. A quantified nonlinear parameter (I3/1) from FT-rheology and complex moduli (|G*|) were used to analyze the structural development of the PLA/NR blends in response to added clays. The nonlinear–linear viscoelastic ratio (NLR ≡ normalized nonlinear viscoelastic property/normalized linear viscoelastic property) was also introduced to describe morphological changes in the blends. Observation of the TEM images revealed that the drop size of natural rubber decreased as the clay content increased from 0.5 to 3 wt %. However, the NR size did not change above 3 wt % of the clay. The NLR value increased up to 3 wt % and then reached a plateau. The drop size reduction due to increased mixing rates was reflected in the NLR v...

Influence of carbon nanotubes localization and transfer on electrical conductivity in PA66/(PS/PPE)/CNTs nanocomposites

The localization and transfer of carbon nanotubes (CNTs) in PA66/(PS/PPE)/CNTs nanocomposites were investigated using several methods including TEM/EDS techniques, surface energy and wetting coefficient calculations, electrical conductivity measurements, and rheological analysis. The CNTs were found to be dispersed preferentially in the polyamide 66 (PA66) phase and not in the miscible polystyrene (PS)/poly(phenylene ether) (PPE) blend phase because CNTs have a higher affinity for PA66. The electrical conductivity of the PA66/(PS/PPE)/CNTs nanocomposites significantly increased compared to the PA66/CNTs nanocomposites at the same CNT loading. The nanocomposites were prepared with three different compounding procedures. The nanocomposites prepared with sequence III (premixing PS/PPE and CNTs, and then blending the (PS/PPE)/CNTs with PA66) yielded a better CNT dispersion that resulted in a higher electrical conductivity. The CNT dispersion was determined by TEM and rheological analysis. Additionally, the nonlinear-linear viscoelastic ratio (NLR) was used to quantify the degree of CNT dispersion. Because the CNTs initially dispersed in the unfavorable PS/PPE phase were transferred as individual rods into the preferred PA66 phase during the second step of compounding sequence III, the nanocomposite prepared with sequence III had a higher NLR value, that is, a better CNT dispersion compared to the other nanocomposite prepared with different compounding sequences.

A study of viscoelasticity index for evaluating muscle hypotonicity during static stretching.

Static stretching is widely used as a preventative treatment for musculoskeletal disabilities by providing muscle hypotonicity, which results from changes in muscle tissue structure. However, the quantitative evaluation of hypotonicity during stretching has had limited success owing to the confounding factor of mechanical stress relaxation. To resolve this problem, we propose a new evaluation method for hypotonicity based on a viscoelastic muscle model using fractional calculus, which is known to be effective for biomaterials. We made continuous measurements of rectus skin indentation during static stretching as an indicator of reaction force in the rectus femoris muscle. The viscoelastic ratio and modulus were computed from the indentation trace. Both viscoelastic parameters decreased significantly between the early and final phases of stretching. The results suggest that our method is useful for quantitative evaluation of muscle hypotonicity during stretching.