Fluid-like Behavior Research Articles

Interfacial behaviour of crayfish protein isolate

The interfacial behaviour of a crayfish protein isolate (CFPI) produced as by-product from the food industry has been studied at the air–water surface at two pH values (2 and 8). An analysis of the surface pressure and interfacial shear behaviour has been carried out as a function of CFPI content for the two mentioned pH values. The results indicate that CFPI shows higher surface pressure, smaller aggregates and higher interfacial viscoelasticity at pH 8 than at pH 2, being highly dependent on CFPI content. In fact, a transition from fluid-like behaviour to a gel-like behaviour have been obtained by increasing the protein content. These results are in agreement with the higher solubility and z-potential values and the longer emulsion stability found under alkaline conditions. Furthermore, usage of highly sensitive interfacial shear techniques, such as the magnetic rod interfacial stress rheometer or the double wall ring, both of them providing rather coincident results, has proven to be highly useful to study the viscoelastic properties of CFPI interfacial films at levels that cannot be detected by other methods.

The role of pressure anisotropy in the turbulent intracluster medium

In low-density plasma environments, such as the intracluster medium (ICM), the Larmour frequency is much larger than the ion-ion collision frequency. In such a case, the thermal pressure becomes anisotropic with respect to the magnetic field orientation and the evolution of the turbulent gas is more correctly described by a kinetic approach. A possible description of these collisionless scenarios is given by the so-called kinetic magnetohydrodynamic (KMHD) formalism, in which particles freely stream along the field lines, while moving with the field lines in the perpendicular direction. In this way a fluid-like behavior in the perpendicular plane is restored. In this work, we study fast growing magnetic fluctuations in the smallest scales which operate in the collisionless plasma that fills the ICM. In particular, we focus on the impact of a particular evolution of the pressure anisotropy and its implications for the turbulent dynamics of observables under the conditions prevailing in the ICM. We present results from numerical simulations and compare the results which those obtained using an MHD formalism.

On the viscoelastic characterization of the Jeffreys–Lomnitz law of creep

In 1958 Jeffreys proposed a power law of creep, generalizing the logarithmic law earlier introduced by Lomnitz, to broaden the geophysical applications to fluid-like materials including igneous rocks. This generalized law, however, can be applied also to solid-like viscoelastic materials. We revisit the Jeffreys-Lomnitz law of creep by allowing its power law exponent $\alpha$, usually limited to the range [0,1] to all negative values. This is consistent with the linear theory of viscoelasticity because the creep function still remains a Bernstein function, that is positive with a completely monotonic derivative, with a related spectrum of retardation times. The complete range $\alpha \le 1$ yields a continuous transition from a Hooke elastic solid with no creep ($\alpha \to -\infty$) to a Maxwell fluid with linear creep ($\alpha=1$) passing through the Lomnitz viscoelastic body with logarithmic creep ($\alpha=0$), which separates solid-like from fluid-like behaviors. Furthermore, we numerically compute the relaxation modulus and provide the analytical expression of the spectrum of retardation times corresponding to the Jeffreys-Lomnitz creep law extended to all $\alpha \le 1$.

On the rheology of dilative granular media: Bridging solid- and fluid-like behavior

A new rate-dependent plasticity model for dilative granular media is presented, aiming to bridge the seemingly disparate solid- and fluid-like behavioral regimes. Up to date, solid-like behavior is typically tackled with rate-independent plasticity models emanating from Mohr–Coulomb and Critical State plasticity theory. On the other hand, the fluid-like behavior of granular media is typically treated using constitutive theories amenable to viscous flow, e.g., Bingham fluid. In our proposed model, the material strength is composed of a dilation part and a rate-dependent residual strength. The dilatancy strength plays a key role during solid-like behavior but vanishes in the fluid-like regime. The residual strength, which in a classical plasticity model is considered constant and rate-independent, is postulated to evolve with strain rate. The main appeal of the model is its simplicity and its ability to reconcile the classic plasticity and rheology camps. The applicability and capability of the model are demonstrated by numerical simulation of granular flow problems, as well as a classical shear banding problem, where the performance of the continuum model is compared to discrete particle simulations and physical experiment. These results shed much-needed light onto the mechanics and physics of granular media at various shear rates.

Determinants of Fluid-Like Behavior and Effective Viscosity in Cross-Linked Actin Networks

Determinants of Fluid-Like Behavior and Effective Viscosity in Cross-Linked Actin Networks

Rheological behaviour of reconstituted pyroclastic debris flow

An experimental study of the rheological behaviour of three natural pyroclastic soils with different depositional processes remixed with water was carried out with the help of a rotational rheometer and inclined plane tests. A homogeneous fluid-like behaviour is obtained only within a very narrow range of concentrations, typically not more than 10%. Below this range the material sedimentates rapidly; above this range it behaves like a solid. In the fluid-like range the typical rheological behaviour of these suspensions is that of a yield stress fluid exhibiting a static yield stress larger than its dynamic yield stress. This effect probably finds its origin in a ‘local' sedimentation effect: that is, the particles sedimentate just as necessary to form a structure more jammed than the structure during flow. As a result the flow of such materials is usually unstable: they will start to flow beyond a critical stress, but just beyond this value will reach a high shear rate associated with a high flowing velocity. The static and dynamic yield stresses of these materials increase widely from very low to very large values (several orders of magnitude). Inclined-plane tests were shown to provide reasonable although still approximate values for the static and dynamic yield stresses. These results suggest that in the field a small change in solid fraction will cause a slight decrease of the static yield stress, readily inducing a rapid flow that will stop only when the dynamic yield stress is reached, namely on a much smoother slope. This can explain the in situ observed post-failure behaviour of pyroclastic debris flows, which are able to flow over very long distances, even on smooth slopes.

Directed persistent motion maintains sheet integrity during multi-cellular spreading and migration

Multi-cellular migration plays an important role in physiological processes such as embryogenesis, cancer metastasis and tissue repair. Collective cell migration involves specific single cell motility behaviour that maintains the integrity of the monolayer and the fluid-like behavior of the sheet at long time scales. We have studied the dynamics of MCF-10A, MDA-MB-231 epithelial cell monolayers and that of a NIH-3t3 fibroblast monolayer. For the case where MCF-10A cell–cell interactions are so weak that single cells can detach from the monolayer, a collective cell front can be maintained by interplay between the directed persistent motion of the monolayer and the random motion of escaping single cells. The dynamics of the MCF-10A monolayer is contrasted with the MDA-MB-231 monolayer where single cells did not detach, with non-interacting NIH-3t3 fibroblast cells that are always random walkers, and with a MCF-10A monolayer treated with a calcium chelating agent that reduces intercellular interactions.

Solid Character of Membrane Ceramides: A Surface Rheology Study of Their Mixtures with Sphingomyelin

The compression and shear viscoelasticities of egg-ceramide and its mixtures with sphingomyelin were investigated using oscillatory surface rheology performed on Langmuir monolayers. We found high values for the compression and shear moduli for ceramide, compatible with a solid-state membrane, and extremely high surface viscosities when compared to typical fluid lipids. A fluidlike rheological behavior was found for sphingomyelin. Lateral mobilities, measured from particle tracking experiments, were correlated with the monolayer viscosities through the usual hydrodynamic relationships. In conclusion, ceramide increases the solid character of sphingomyelin-based membranes and decreases their fluidity, thus drastically decreasing the lateral mobilities of embedded objects. This mechanical behavior may involve important physiological consequences in biological membranes containing ceramides.

Irradiation behavior of the interaction product of U-Mo fuel particle dispersion in an Al matrix

Irradiation performance of U-Mo fuel particles dispersed in Al matrix is stable in terms of fuel swelling and is suitable for the conversion of research and test reactors from highly enriched uranium (HEU) to low enriched uranium (LEU). However, tests of the fuel at high temperatures and high burnups revealed obstacles caused by the interaction layers forming between the fuel particle and matrix. In some cases, fission gas filled pores grow and interconnect in the interdiffusion layer resulting in fuel plate failure. Postirradiation observations are made to examine the behavior of the interdiffusion layers. The interdiffusion layers show a fluid-like behavior characteristic of amorphous materials. In the amorphous interdiffusion layers, fission gas diffusivity is high and the material viscosity is low so that the fission gas pores readily form and grow. Based on the observations, a pore formation mechanism is proposed and potential remedies to suppress the pore growth are also introduced.

Nonlinear Viscoelasticity of Actin Transiently Cross-linked with Mutant α-Actinin-4

Filamentous actin and associated actin binding proteins play an essential role in governing the mechanical properties of eukaryotic cells. They can also play a critical role in disease; for example, mutations in α-actinin-4 (Actn4), a dynamic actin cross-linking protein, cause proteinuric disease in humans and mice. Amino acid substitutions strongly affect the binding affinity and protein structure of Actn4. To study the physical impact of such substitutions on the underlying cytoskeletal network, we examine the bulk mechanical behavior of in vitro actin networks cross-linked with wild-type and mutant Actn4. These networks exhibit a complex viscoelastic response and are characterized by fluid-like behavior at the longest timescales, a feature that can be quantitatively accounted for through a model governed by dynamic cross-linking. The elastic behavior of the network is highly nonlinear, becoming much stiffer with applied stress. This nonlinear elastic response is also highly sensitive to the mutations of Actn4. In particular, we observe that actin networks cross-linked with Actn4 bearing the disease-causing K255E mutation are more brittle, with a lower breaking stress in comparison to networks cross-linked with wild-type Actn4. Furthermore, a mutation that ablates the first actin binding site (ABS1) in Actn4 abrogates the network's ability to stress-stiffen is standard nomenclature. These changes in the mechanical properties of actin networks cross-linked with mutant Actn4 may represent physical determinants of the underlying disease mechanism in inherited focal segmental glomerulosclerosis.

Ellipsoidal capsules in simple shear flow: prolate versus oblate initial shapes

The large deformations of an initially-ellipsoidal capsule in a simple shear flow are studied by coupling a boundary integral method for the internal and external flows and a finite-element method for the capsule wall motion. Oblate and prolate spheroids are considered (initial aspect ratios: 0.5 and 2) in the case where the internal and external fluids have the same viscosity and the revolution axis of the initial spheroid lies in the shear plane. The influence of the membrane mechanical properties (mechanical law and ratio of shear to area dilatation moduli) on the capsule behaviour is investigated. Two regimes are found depending on the value of a capillary number comparing viscous and elastic forces. At low capillary numbers, the capsule tumbles, behaving mostly like a solid particle. At higher capillary numbers, the capsule has a fluid-like behaviour and oscillates in the shear flow while its membrane continuously rotates around its deformed shape. During the tumbling-to-swinging transition, the capsule transits through an almost circular profile in the shear plane for which a long axis can no longer be defined. The critical transition capillary number is found to depend mainly on the initial shape of the capsule and on its shear modulus, and weakly on the area dilatation modulus. Qualitatively, oblate and prolate capsules are found to behave similarly, particularly at large capillary numbers when the influence of the initial state fades out. However, the capillary number at which the transition occurs is significantly lower for oblate spheroids.

“Ridge” in Proton-Proton Scattering at 7 TeV

One of the most important experimental results for proton-proton scattering at the LHC is the observation of a so-called "ridge" structure in the two-particle correlation function versus the pseudorapidity difference Δη and the azimuthal angle difference Δφ. One finds a strong correlation around Δφ=0, extended over many units in Δη. We show that a hydrodynamical expansion based on flux tube initial conditions leads in a natural way to the observed structure. To get this result, we have to perform an event-by-event calculation, because the effect is due to statistical fluctuations of the initial conditions, together with a subsequent collective expansion. This is a strong point in favor of a fluidlike behavior even in pp scattering, where we have to deal with length scales of the order of 0.1 fm.

Effects of acoustic vibration on nano and sub-micron powders fluidization

Fluidization of nano and sub-micron powders with and without acoustic vibration was investigated. The effects of sound pressure level and frequency were studied. Loudspeakers located under the distributor plate were used as the sound source to disintegrate larger agglomerates concentrated at the bottom of the bed. Nanoparticles showed fluid-like behavior similar to Geldart's A group and application of sound vibration improved their fluidization quality. Submicron particles were hard to fluidize and their fluidization quality was partially improved by sound excitation. Bed compaction, caused by rearranging of the agglomerates, was observed for submicron particles at low gas velocities while the bed was fixed. Nanoparticles did not experience any bed compaction. Sound vibration led to a decrease in minimum fluidization velocity and an increase in bed pressure drop and bed expansion for both types of particles. The fluidization quality of both particles increased at low frequencies, while the reverse was observed at higher frequencies. Fluidization of these particles was improved by increasing sound pressure level. There was a critical sound pressure level of 110 dB, below which the effect of sound vibration was insignificant. A novel technique was employed to find the apparent minimum fluidization velocity from pressure drop signals.

Bioslurry as a Fuel. 4. Preparation of Bioslurry Fuels from Biochar and the Bio-oil-Rich Fractions after Bio-oil/Biodiesel Extraction

In this study, bio-oil is extracted using biodiesel to produce two fractions: a biodiesel-rich fraction (also referred as biodiesel/bio-oil blend) and a bio-oil-rich fraction. The results show that the compounds (mainly phenolic) extracted from bio-oil into the biodiesel-rich fraction reduce the surface tension of the biodiesel/bio-oil blends. The bio-oil-rich fraction is mixed with ground biochar to produce a bioslurry fuel. It is found that the bioslurry fuels with 10 and 20% biochar loading prepared from the bio-oil-rich fraction of biodiesel extraction at a biodiesel/bio-oil blend ratio of 0.67 have similar fuel properties (e.g., density, surface tension, volumetric energy density, and stability) in comparison to those prepared using the original whole bio-oil. The slurry fuels exhibit non-Newtonian with pseudo-plastic characteristics and good pumpability, desirable for fuel handling. The viscoelastic behavior of the slurry fuels also shows dominantly fluid-like behavior in the linear viscoelastic reg...

Sliding Instabilities and Hypervelocity Gouging

Hypervelocity gouging occurs in material systems with high sliding speeds and has been observed in rocket sleds, light-gas guns, and railguns. Gouging takes the form of teardrop-shaped craters on the rail surface and usually occurs above a threshold speed that is material-pair dependent. The best predictive tools developed for gouging rely on semiempirical relationships that relate material hardness to shock pressure and hydrocodes that model the fluid-like behavior of materials under high stresses and strain rates. A parallel field of research is explosive welding. In explosive welding, the interface between two sliding surfaces impacted at high speeds undergoes a transition between flat bonded surfaces to a wavy interface. The onset of these interface waves, like hypervelocity gouging, is primarily dependent on the relative sliding speed of the materials, with other operating conditions being second order. Of particular interest is the fact that gouging and explosive welding waves occur at similar speeds for similar material pairs. This paper explores the parallels between these two fields of research and assesses the applicability of the respective predictive tools in determining the onset of gouging/interface waves.

Reproduction of thermal pressurization and fluidization of clay-rich fault gouges by high-velocity friction experiments and implications for seismic slip in natural faults

Abstract We examine the frictional properties and microstructures of clay-rich fault gouges subjected to thermal pressurization and fluidization, generated in high-velocity friction experiments under dry and wet conditions. In the dry tests, slip weakening occurs by thermal pressurization, which is marked by a fault-gouge expansion associated with a water-phase transition from liquid to vapour. The water is derived from dehydration of clay minerals by frictional heating. The resulting microstructure in the gouge layer is a random distribution of spherical clay–clast aggregates in the matrix, and mixing of different gouge constituents without shear surfaces. In the wet tests, slip weakening is caused by pore-fluid pressurization resulting from shear-enhanced compaction of the water-saturated gouge and frictional heating. Compared to the dry tests, the wet tests show smaller dynamic stress drops and slip weakening distance. The steady-state shear stress in the wet tests is almost independent of normal stress, suggesting a fluid-like behaviour of the fault gouge during high-velocity shearing. The microstructures after the wet tests show that the foliated zone is accompanied by grain-size segregation in the gouge layer. The grain-size segregation is attributed to the Brazil-nut effect resulting from the difference in dispersive pressure in the granular-fluid shear flow at high shear rates, indicating a fluidization of fault gouge. Our results obtained at seismic slip rates imply that the propagation of an earthquake rupture can be enhanced by fluid pressurization and frictional heat, potentially leaving characteristic microstructures resulting from water vaporization by frictional heating or flow sorting at high slip rates.

Path integral molecular dynamics simulation of quasi-free rotational motion of CO doped in a large para-hydrogen cluster

Path integral molecular dynamics simulation is used to study the rotational motion of a CO molecule doped in a large para-hydrogen (p-H2) cluster. The quasi-free rotational motion of CO in a p-H2 cluster with a reduced rotational constant is derived from the imaginary-time orientational correlation functions, and is in good agreement with recent experimental observations. We attribute the reduced rotational constant to the low-viscous fluid-like behavior of the host p-H2 cluster.

Finite-size effects in dynamics of zero-range processes

The finite-size effects prominent in zero-range processes exhibiting a condensation transition are studied by using continuous-time Monte Carlo simulations. We observe that, well above the thermodynamic critical point, both static and dynamic properties display fluidlike behavior up to a density ρc(L), which is the finite-size counterpart of the critical density ρc=ρc(L→∞). We determine this density from the crossover behavior of the average size of the largest cluster. We then show that several dynamical characteristics undergo a qualitative change at this density. In particular, the size distribution of the largest cluster at the moment of relocation, the persistence properties of the largest cluster, and the correlations in its motion are studied.

Start-up flow of a viscoelastic fluid in a pipe with a fractional Maxwell’s model

Unidirectional start-up flow of a viscoelastic fluid in a pipe with a fractional Maxwell’s model is studied. The flow starting from rest is driven by a constant pressure gradient in an infinite long straight pipe. By employing the method of variable separations and Heaviside operational calculus, we obtain the exact solution, from which the flow characteristics are investigated. It is found that the start-up motion of a fractional Maxwell’s fluid with parameters α and β, tends to be at rest as time goes to infinity, except the case of β=1. This observation, which also can be predicted from the mechanics analogue of fractional Maxwell’s model, agrees with the classical work of Friedrich and it indicates that a fractional Maxwell’s fluid presents solid-like behavior if β≠1 and fluid-like behavior if β=1. For an arbitrary viscoelastic model, a conjecture is proposed to give an intuitive way judging whether it presents fluid-like or solid-like behavior. Also oscillations may occur before the fluid tends to the asymptotic behavior stated above, which is a common phenomenon for viscoelastic fluids.

Surface Properties of Monolayers of Amphiphilic Poly(ethylene oxide)-Poly(styrene oxide) Block Copolymers

The surface properties of poly(styrene oxide)-poly(ethylene oxide) block copolymers EO12SO10, EO10SO10EO10, and EO137SO18EO137 at the air−water (a/w) and chloroform−water (c/w) interfaces have been analyzed by Tracker drop tensiometry, Langmuir film balance, and atomic force microscopy (AFM). The kinetic adsorptions for the block copolymer solutions at both interfaces were determined by the pendant drop technique. At the a/w, the polymer adsorption is reduced as the polymer hydrophobicity increases. Measurements of the interfacial rheological behavior of the copolymers showed that the adsorption layers at the a/w interface manifest obvious solid-like properties in the whole accessible frequency range, whereas a viscous fluid-like behavior is displayed at the c/w interface. The differences observed in the monolayer isotherms obtained for the three copolymers arose from their different hydrophobic/hydrophilic block ratios and block lengths. In this regard, copolymer EO137SO18EO137 displays an adsorption iso...