Linear Viscoelastic Regime Research Articles

A framework for 3D synthetic mesoscale models of hot mix asphalt for the finite element method

A versatile framework to create 3D mesoscale models of hot mix asphalt is presented. The mortar phase of a German standard hot mix asphalt is tested in the linear viscoelastic regime using a modified dynamic shear rheometry setup. The widely used generalised Maxwell-model is fit to master-curve data. Virtually any particle size distribution can be matched by a nested Voronoi tessellation algorithm, which is shown by generating geometrical models for three different types of hot mix asphalt. Several techniques to reduce the computational effort are introduced at the geometry and mesh levels. Representative volume elements for mixture SMA 8S are determined and used to predict the complex shear modulus and loss angle. An analysis of the reinforcing properties of the mineral aggregate phase is presented. The influence of the loading rate on the size of representative volume elements is investigated.

Applying rheological analysis to better understand the mechanism of acid conditioning on activated sludge dewatering

The pH value is a key parameter and affects sludge dewatering. Comprehensive understanding of the effects and mechanism of pH is important for sludge treatment process and sludge dewatering. The goal of this study was to evaluate the proposed mechanism of acid conditioning on sludge dewatering based on rheological analysis. At lower sludge pH, changes in floc structure, surface properties, and flocculation improved the performance of dewatering. Additionally, lower sludge pH caused the hydrolysis of EPS and intracellular materials, which released greater amounts of bound water. These changes resulted in altered rheological properties, weakening network strength and shrinking the linear viscoelastic regime, making the sludge system sensitive to shear. Thus, both the sludge dewatering rate and moisture reduction efficiency were improved by lowering the pH. These factors demonstrate that rheological analysis can understand the mechanism of acid conditioning on activated sludge dewatering better.

Evaluation of thermal hydrolysis efficiency of mechanically dewatered sewage sludge via rheological measurement

In this study, laboratory tests of both low temperature (60–90 °C) and high temperature (120–180 °C) thermal hydrolysis (LTHP and HTHP) were performed on mechanically dewatered high-solid sludges (at total solid of 14.2 wt% and 18.2 wt%) to evaluate the extent of organic solubilization through rheological measurements. The effects of treatment temperature and duration on organic solubilization and viscoelastic behavior of the sludge were comprehensively investigated. The results indicated that the organic solubilization contents including soluble chemical oxygen demand, soluble protein, and soluble polysaccharides increased logarithmically with the treatment time. Protein solubilized considerably faster than polysaccharides during thermal hydrolysis. The rheological curves exhibited the Payne effect in the amplitude sweep oscillation test. The elastic modulus in linear viscoelastic regime decreased logarithmically with treatment time. The viscoelastic behavior of sludge was well modeled by the Kaye–Bernstein–Kearsly–Zapas (KBKZ) model with paralleled Maxwell elements to describe the frequency dependence of elastic modulus and viscous modulus. With respect to the relaxation spectrum, the relaxation modulus first decreased with relaxation time and then increased. The relaxation modulus in each Maxwell element decreased with the treatment temperature and duration. Furthermore, in the HTHP, the influence of treatment temperature on enhancing organic solubilization and decreasing viscoelasticity exceeded the influence of treatment duration. In contrast, the treatment duration played a more important role than temperature in the LTHP. The content of organic matters was linearly related and logarithmically related to the elastic modulus in the LTHP and in the HTHP, respectively. The rheology analyses demonstrated that viscoelastic properties could be used as indicators to estimate the extent of organic matter solubilization in thermal hydrolysis process. The developed viscoelastic model provided insights for future research in numerically simulating the fluid dynamics of sludge.

Impact of gas injection on the apparent viscosity and viscoelastic property of waste activated sewage sludge

Gas injection is known to play a major role on the particle size of the sludge, the oxygen transfer rate, as well as the mixing efficiency of membrane bioreactors and aeration basins in the waste water treatment plants. The rheological characteristics of sludge are closely related to the particle size of the sludge floc. However, particle size of sludge floc depends partly on the shear induced in the sludge and partly on physico-chemical nature of the sludge.The objective of this work is to determine the impact of gas injection on both the apparent viscosity and viscoelastic property of sludge. The apparent viscosity of sludge was investigated by two methods: in-situ and after sparging. Viscosity curves obtained by in-situ measurement showed that the apparent viscosity decreases significantly from 4000 Pa s to 10 Pa s at low shear rate range (below 10 s−1) with an increase in gas flow rate (0.5LPM to 3LPM); however the after sparging flow curve analysis showed that the reduction in apparent viscosity throughout the shear rate range is negligible to be displayed. Torque and displacement data at low shear rate range revealed that the obtained lower apparent viscosity in the in-situ method is not the material characteristics, but the slippage effect due to a preferred location of the bubbles close to the bob, causing an inconsistent decrease of torque and increase of displacement at low shear rate range.In linear viscoelastic regime, the elastic and viscous modulus of sludge was reduced by 33% & 25%, respectively, due to gas injection because of induced shear. The amount of induced shear measured through two different tests (creep and time sweep) were the same. The impact of this induced shear on sludge structure was also verified by microscopic images.

Magnetorheological behavior of magnetoactive elastomers filled with bimodal iron and magnetite particles

Magnetoactive elastomers (MAE) based on soft silicone matrices, filled with various proportions of large diameter (approximately 50 μm) iron and small diameter (approximately 0.5 μm) magnetite particles are synthesized. Their rheological behavior in homogeneous magnetic fields up to 600 mT is studied in detail. The addition of small magnetite particles facilitates fabrication of uniformly distributed magnetic elastomer composites by preventing aggregation and sedimentation of large particles during curing. It is shown that using the proposed bimodal filler particles it is possible to tailor various magnetorheological (MR) properties which can be useful for different target applications. In particular, either absolute or relative magnetorheological effects can be tuned. The value of the damping factor as well as the range of deformation amplitudes for the linear viscoelastic regime can be chosen. The interdependencies between different MR properties of bimodal MAEs are considered. The results are discussed in the model framework of particle network formation under the simultaneous influence of external magnetic fields and mechanical deformation.

The electromechanical response of titanium dioxide/natural rubber composite

Natural rubber (NR) is one of interested dielectric elastomer. To study the effect of crosslink density on the electromechanical response (EMR), the crosslinked NR gels were prepared at various crosslinking ratio under UV radiation using MMMP and TMPTMP as photoinitiator and crosslinking agent, respectively. The crosslinking ratio (VTMPTMP/VNR) is 0.22, 0.44, 0.88, and 1.32%v/v for NR_CR01, NR_CR02, NR_CR03 and NR_CR04, respectively. To determine the electromechanical properties, the storage modulus (G′) at frequency of 0- 100 rad/s, 1% strain and electric field strength of 0 and 1500 V/mm were measured under linear viscoelastic regime. For crosslinked NR gels, G′ increased with increasing crosslink density which corresponding to rubber elasticity theory. When external electric field was applied, the G′ increased because the reorientation of polymer chain under electric field is dominated by the relaxation of dangling end in NR. Thus the EMR (Δ G′ = G′E - G′0) increased with increasing crosslink density. To enhance high EMR composite, 1%v/v of TiO2/NR composite was prepared. The G′ of TiO2/NR composite was higher than crosslinked NR because TiO2 acted as reinforcement particle. When external electric field was applied, G′ increased. TiO2 particles were polarized and tried to interact each other in soft NR gel, thus higher shear force was required to deform TiO2/NR composite. Thus TiO­2/NR can be a new class of smart actuation material which has high EMR and cost-effectiveness.

High Molecular Mobility and Viscoelasticity of Microphase-Separated Bottlebrush Diblock Copolymer Melts

We investigate the linear viscoelastic behavior of poly(styrene)-block-poly(ethylene oxide) (PS-b-PEO) AB diblock brush copolymer materials over a range of volume fractions and with side-chain lengths below entanglement molecular weight (PS Mn ∼ 3.5 kg/mol and PEO Mn ∼ 5 kg/mol). The high chain mobility of the brush architecture results in rapid microphase segregation of the brush copolymer segments, which occurred after mild thermal annealing. Master curves of the dynamic moduli were obtained by time–temperature superposition (tTS). The reduced degree of chain entanglements leads to a unique liquid-like rheology similar to that of bottlebrush (BB) homopolymers, even in the microphase-segregated state. The microphase-segregated domains were found to align at exceptionally low strain amplitudes (γ = 0.01) and mild processing temperatures as confirmed by small-angle X-ray scattering (SAXS). Domain/grain orientation occurred readily at strains within the linear viscoelastic regime (LVR) without noticeable ef...

Smart viscoelastic and self-healing characteristics of graphene nano-gels

Readily synthesizable nano-graphene and poly ethylene glycol based stable gels have been synthesized employing an easy refluxing method, and exhaustive rheological and viscoelastic characterizations have been performed to understand the nature of such complex gel systems. The gels exhibit shear thinning response with pronounced yield stress values which is indicative of a microstructure, where the graphene nanoflakes intercalate (possible due to the refluxing) with the polymer chains and form a pseudo spring damper network. Experimentations on the thixotropic behavior of the gels indicate that the presence of the G nanoflakes leads to immensely augmented structural stability capable of withstanding severe impact shears. Further information about the localized interactions of the G nanoflakes with the polymer chains is revealed from the amplitude and frequency sweep analyses in both linear and non-linear viscoelastic regimes. Massively enhanced cross over amplitude values are recorded and several smart effects such as enhanced elastic behavior at increasing forcing frequencies are registered. Structural resonance induced disruption of the elastic behavior is observed for the gels for a given range of frequency and the proposition of resonance has been justified mathematically. It is observed that, post this resonance bandwidth, the gels are able to self-heal and regain their original elastic behavior back without any external intervention. More detailed information on the viscoelastic nature of the gels has been obtained from creep and recovery compliance tests and justifications for the spring damper microstructure has been obtained. Smart features such as enhanced stress relaxation behavior with increasing strain have been observed and the same explained, based on the proposed microstructure. The viscoelastic response of the gels has been mathematically modeled and it has been revealed that such complex gels can be accommodated as modified Burger's viscoelastic systems with predominant elastic/plastic behavior. The present gels show promise in microscale actuators, vibration isolation, and damping in devices and prosthetics, as active fluids in automotive suspensions, controlled motion arrestors, and so on.

The effect of pressure on the viscosity of two different nanocomposites based on a PS matrix: A case of piezorheological complexity

The pressure dependence of viscosity of two nanocomposites with a polystyrene (PS) matrix that contains, respectively, multiwalled carbon nanotubes (MWCNTs) and graphene, was investigated. Two procedures were used: (a) Pressure-volume-temperature (PVT) results to obtain the pressure coefficient β0 for Newtonian viscosity and (b) measurements in a pressure chamber in a capillary rheometer, to obtain the pressure coefficient at constant shear rate, β′ and the pressure coefficient at constant shear stress, β″. PVT results revealed that the most significant differences between the samples concerned the variation of the glass transition with pressure, dTg/dP, which was concomitant with the number of polymer chains fixed on the surface of the nanofillers. Pressure chamber results showed that the pressure coefficient β″ was similar for PS and the nanocomposites, at the shear rates involved in processing. For the first time, the piezorheological complexity of nanocomposites was analyzed, together with the thermorheological complexity. PS/MWCNT nanocomposite was thermorheologically complex in the linear viscoelastic regime, but thermorheologically and piezorheologically simple in the shear thinning flow region. Nevertheless, PS/graphene nanocomposite was thermorheologically and piezorheologically complex in the linear viscoelastic regime and the shear thinning regime. This was due to the high capacity of graphene 2D platelets to retain polymer chains anchored to its surface.

Modeling and Simulation of Mucus Flow in Human Bronchial Epithelial Cell Cultures - Part I: Idealized Axisymmetric Swirling Flow.

A multi-mode nonlinear constitutive model for mucus is constructed directly from micro- and macro-rheology experimental data on cell culture mucus, and a numerical algorithm is developed for the culture geometry and idealized cilia driving conditions. This study investigates the roles that mucus rheology, wall effects, and HBE culture geometry play in the development of flow profiles and the shape of the air-mucus interface. Simulations show that viscoelasticity captures normal stress generation in shear leading to a peak in the air-mucus interface at the middle of the culture and a depression at the walls. Linear and nonlinear viscoelastic regimes can be observed in cultures by varying the hurricane radius and mean rotational velocity. The advection-diffusion of a drug concentration dropped at the surface of the mucus flow is simulated as a function of Peclet number.

Experimental investigation and modeling of mechanical behaviors of polyurea over wide ranges of strain rates and temperatures

Theoretical and experimental studies on the compressive mechanical behavior of two formulations of polyurea under uniaxial stress state and quasi-one dimensional strain state are conducted over the temperature range of −40°C–+20 °C and the strain rate range of 0.001/s–12000/s. The stress–strain behavior of polyurea samples is established at different strain rates and temperatures, and key mechanical properties of the materials are determined. The experimental results show the significant sensitivity of compressive stress–strain curves of polyurea to strain rate and temperature within and beyond linear viscoelastic regime. In addition, the mechanical properties of PU605 (Versalink P-650 reacted with 105% molar equivalent Isonate 143L) are compared to those of PU105 (Versalink P-1000 reacted with 105% molar equivalent Isonate 143L). Based on the experimental results with confined pressure, a calculation method is presented which is available to study the bulk modulus of polyurea. Finally, a visco-hyperelastic constitutive model is developed to describe the nonlinear mechanical behavior of polyurea over a wide range of strain rates and temperatures.

Measuring average rheological quantities of cell monolayers in the linear viscoelastic regime

During the last decades, the rheology of cells has been studied almost entirely in single cells. While cell-to-cell variation is typically very large and most studies were carried out in the nonlinear viscoelastic regime, we quantify average linear viscoelastic cell properties like storage and loss moduli and normal stress in monolayers of different cell types showing that murine 3T6 fibroblasts, human fibroblasts, and HeLa cells differ considerably in their storage modulus. To this end, we modified a commercial rheometer to set up a parallel-disk configuration at gap widths of a few micrometers and optically detected the cell concentration in the gap. This enables studying the linear viscoelastic behavior of the cells and permits quantifying the impact of drugs affecting the cytoskeleton or the extracellular matrix connection. Thus, due to its high-content approach, without the need of treating the samples in the rheometer, this envisions the use of this method as a fast diagnostic tool. The method also allows for quantitatively studying of the impact of pre-stress on the storage and loss moduli of the cells.

Viscoelastic properties of cellular polypropylene ferroelectrets

Viscoelastic properties of cellular polypropylene ferroelectrets (PP FEs) were studied at low frequencies (0.3–33 Hz) by dynamic mechanical analysis and at high frequencies (250 kHz) by laser Doppler vibrometry. Relaxation behavior of the in-plane Young's modulus (Y11′ ∼ 1500 MPa at room temperature) was observed and attributed to the viscoelastic response of polypropylene matrix. The out-of-plane Young's modulus is very small (Y33′ ≈ 0.1 MPa) at low frequencies, frequency- and stress-dependent, evidencing nonlinear viscoelastic response of PP FEs. The high-frequency mechanical response of PP FEs is shown to be linear viscoelastic with Y33′ ≈ 0.8 MPa. It is described by thickness vibration mode and modeled as a damped harmonic oscillator with one degree of freedom. Frequency dependence of Y33* in the large dynamic strain regime is described by the broad Cole-Cole relaxation with a mean frequency in kHz range attributed to the dynamics of the air flow between partially closed air-filled voids in PP FEs. Switching-off the relaxation contribution causes dynamic crossover from the nonlinear viscoelastic regime at low frequencies to the linear viscoelastic regime at high frequencies. In the small strain regime, contribution of the air flow seems to be insignificant and the power-law response, attributed to the mechanics of polypropylene cell walls and closed air voids, dominates in a broad frequency range. Mechanical relaxation caused by the air flow mechanism takes place in the sound and ultrasound frequency range (10 Hz–1 MHz) and, therefore, should be taken into account in ultrasonic applications of the PP FEs deal with strong exciting or receiving signals.

Blood linear viscoelasticity by small amplitude oscillatory flow

Blood is a complex fluid with non-Newtonian characteristics and consists primarily of a concentrated suspension of red blood cells (RBCs) characterized by high deformability and aggregability. The majority of both research and clinical investigations on blood rheology is based on steady shear measurements aimed at determining blood viscosity as a function of shear rate. On the other hand, investigations of blood rheology in the linear viscoelastic regime are sparse in the literature and currently limited. In principle, small amplitude oscillatory flow is best suited to study blood microstructure and rheology under quasi-static conditions, which are relevant in a range of applications, from blood storage to blood aggregability testing. Here, we present the first systematic experimental investigation of blood rheological behavior in the linear viscoelastic regime, by performing oscillatory shear measurements by conventional bulk rheology. The storage (G′) and loss (G″) moduli of whole human blood have been measured over an extended range of frequencies [0.1–30 rad/s]. Data show that G″ predominates over G′ across the entire tested range of frequency. By comparing steady and oscillatory shear viscosity, it was found that the Cox-Merz rule is followed to a good approximation, with higher deviations at small shear rate/frequencies. The effects of RBC volume fraction and of aggregating media (i.e., dextran solution at two different concentrations) have been also investigated. Overall, our results are consistent with the behavior of a weakly attractive suspension, where RBCs form reversible aggregates that can be broken by the action of flow.

Viscous and elastic properties of polylactide melts filled with silica particles: Effect of particle size and concentration

Mixing of inorganic particle into polymer material is widely used to tailor polymer with desired physical properties and processibility, in which the size and concentration of the former play a critical role in polymer processing. In this study, rigid spherical silica particle with varying size (average diameter of 7 nm, 40 nm, and 9 μm) were used to reinforce polylactide (PLA) by melt compounding. The dependence of rheological properties of PLA/silica composites on the silica size and concentration were examined by dynamical mechanical and creep-recovery experiments. Our results demonstrate that mixing of silica particles into PLA matrix could increase the thermal stability of PLA. Oscillatory shear tests in the linear viscoelastic regime revealed a strong concentration-dependent behavior for the storage, loss moduli, and complex viscosity of the PLA/silica composites by the addition of nanosilica, while these properties were slightly affected by the addition of microsilica at low frequency range. A linear relationship between the silica concentration and the logarithmic form of zero shear viscosity (logη0) of the composites is found when the concentration is below the rheological percolation threshold, whereas the growth rate is inversely influenced by the silica particle size. Creep-recovery experiments indicated that the elastic properties of PLA were more sensitive by the addition of silica than the viscous properties. Even for microsilica, a remarkable enhancement of the elastic properties was found at low silica concentration. A model based on the radius of gyration of polymer matrix Rg and the mean distance between particles D is proposed to describe the interactions between polymer matrix and particles. When D is larger than 2Rg, the particles-polymer interactions are suggested to be responsible for the rheological properties. On the other side, when D is smaller than Rg, a silica network structure will be formed and the rheological properties of the composites are dominated by the interactions of particle–particle and particle-polymer.

Calcium binding and calcium-induced gelation of sodium alginate modified by low molecular-weight polyuronate

The functions of low molecular-weight Mw polyuronate on the calcium binding and calcium-induced gelation of normal sodium alginate (ALG) have been investigated. Mannuronate- and guluronate-rich fractions were prepared from ALG at two different Mw for each. In the mixtures of ALG and each alginate fraction, changes in the relative viscosity of dilute solutions and rheological properties of the gels were examined after calcium addition. In dilute solutions, the mannuronate-rich fractions did not substantially alter the calcium binding behavior of ALG regardless of Mw. On the contrary, the guluronate-rich fractions changed the calcium binding behavior of ALG, and more calcium was required for increase in the relative viscosity relating to the formation of egg-box dimers and subsequent aggregations. These results were more evident when Mw of guluronate-rich fractions was lower. Gel rheology was also different between the mannuronate- and the guluronate-rich fractions. In the gels, both fractions decreased the storage modulus in the linear viscoelastic regime with increased yield strain, but these effects of the guluronate-rich fractions were greater than the mannuronate-rich fractions when compared at equivalent Mw. These functions of the guluronate-rich fractions were quite different from those of low-methoxyl pectin fraction. By using well-characterized polyuronate samples, calcium-induced gelation for the mixture of ALG and each low Mw polyuronate was compared on the molecular level.

Characterising skeletal muscle under large strain using eccentric and Fourier Transform-rheology

Characterising the passive anisotropic properties of soft tissues has been largely limited to the linear viscoelastic regime and shear loading is rarely done in the large deformation regime, despite the physiological significance of such properties. This paper demonstrates the use of eccentric rheology, which allows the anisotropy of skeletal muscle to be investigated. The large amplitude oscillatory strain properties of skeletal muscle were also investigated using Fourier Transform-rheology. Histology was used to qualitatively assess the microstructure changes induced by large strain. Results showed that skeletal muscle was strongly anisotropic in the linear regime. The storage and loss moduli were found to be significantly different (p<0.05) between the three fibre alignment groups; for the group tested with fibres perpendicular to plane of shear was 12.3±1.3kPa and 3.0±0.35kPa, parallel to shear direction was 10.6±1.2kPa and 2.4±0.23kPa, and perpendicular to shear direction was 5.5±0.90kPa and 1.3±0.21kPa. The appearance and growth of higher order harmonics at large strain was different in the three testing directions indicating that the anisotropy of muscle affects skeletal muscle behaviour in the nonlinear regime. Histological analysis showed an increasing destruction of extracellular matrix and the rearrangement of fibres with increasing strain indicating mechanical damage at strains of larger than 10%. These microstructural changes could contribute to the complex nonlinear behaviour in skeletal muscle. This paper demonstrates a method of characterising the anisotropic properties in skeletal muscle under large strain whilst giving meaningful information on the physical response of tissue at various strains.

On a New Method to Determine the Yield Stress in Lubricating Grease

An experimental study using both a controlled stress and a controlled strain rheometer has been undertaken to characterize lubricating grease in shear, creep, stress relaxation, and oscillatory flow, with a main focus on determining the yield stress. The yield stress was examined using a cone–plate and parallel-plate system with smooth and rough surfaces. Clear discrepancies were observed in the yield stress values obtained using different techniques where oscillatory strain sweep measurements seem to be the best choice. This technique is less sensitive to wall slip, shows good reproducibility, and is relatively easy to perform. The method also shows that the yield stress is a function of the imposed frequency and therefore of the time domain. At lower values of shear—that is, in the linear viscoelastic regime—there is no structural breakdown and the rheology of the grease can be described by the Maxwell model where the stress and the strain are almost proportional to each other. Based on this observation, a novel method to determine the yield stress is proposed: “The yield stress can be determined from the point where this linearity no longer applies.” This method is compared to those that are commonly used. The yield stress was found to depend exponentially on temperature and linearly on frequency.

Hysteresis of the viscoelastic properties and the normal force in magnetically and mechanically soft magnetoactive elastomers: Effects of filler composition, strain amplitude and magnetic field

Hysteresis in dynamic modulus, loss factor and normal forces of magnetoactive elastomers (MAEs) comprising various proportions of small (3–5 μm) and large (50–60 μm) ferromagnetic particles are experimentally studied using dynamic torsion performed at a fixed oscillation frequency in varying DC magnetic fields. It is shown that hysteresis is a characteristic feature of MAEs observed both under increasing/decreasing magnetic field strength and increasing/decreasing strain amplitude. This hysteresis is attributed to the specific rearrangement of the magnetic filler network under simultaneously applied magnetic field and shear deformation. Rheological properties of the magnetic filler network formed in the magnetic field and, therefore, the rheological properties of MAEs depend strongly on the filler composition and the magnetic field magnitude. Larger magnetic particles and higher magnetic fields provide stronger magnetic networks. Both factors result in the extension of the linear viscoelastic regime to larger strain amplitudes and lead to higher values of shear storage and loss moduli. It is found that the hysteresis width maximises at an intermediate magnetic field where it is attributed to the balance between elastic and magnetic particle interactions. This is apparently where the most significant restructuring of the magnetic network occurs. The hysteresis width decreases with increasing fraction of large particles in the magnetic filler. The loss factor grows significantly when the magnetic network is physically broken by large strains γ > 1%. A huge (more than one order of magnitude) increase of normal force at maximum magnetic field strengths is observed. It is predicted that any physical quantity depending on the internal structuring of the magnetic filler should demonstrate hysteresis either with a changing magnetic field and constant deformation amplitude or under variable deformation in a constant magnetic field.

Strain amplitude dependence of shear modulus in heavy oils: Rheometer versus tension/compression technique

Although heavy oils are an enormous resource and a common seismic monitoring target, their geophysical properties remain poorly understood. The shear modulus is of particular interest, because under the right conditions, these oils can transmit S-waves. However, there is a large uncertainty on how to measure the shear modulus of heavy oils. The use of the rheometer, common in chemical engineering applications, has been proposed as a good alternative to tension/compression techniques. Rheometers are an attractive alternative for measuring the shear modulus because of their widespread use and availability. In order to test the validity of the rheometer as a method to measure the shear modulus of heavy oils for geophysical applications, we tested two samples using techniques familiar to geophysics (tension/compression and ultrasonic) and compared the results with the rheometer measurements. We noticed a difference in the measured shear modulus between the two techniques. The samples showed a solid-like behavior when tested in the tension/compression equipment while behaving liquid-like in the rheometer. Both measurements were done in the linear regime (in which there is no change in modulus with amplitude), indicative of the potential presence of two linear viscoelastic regimes (LVRs) at different amplitudes. We developed a model that explains the presence of the two LVRs for heavy oils with a large content of resins and asphaltenes and at temperatures that allows the formation of large aggregates. We analyzed the presence of the two LVRs in terms of the weak interaction that appeared between aggregates when subjected to small-amplitude strains, resulting in a solid-like behavior; those weak interactions were not present when the sample was subjected to larger strains resulting in a liquid-like behavior.