Low-frequency Shear Elasticity Research Articles

Low-Frequency Shear Elasticity of the Homological Series of Normal Hydrocarbons

Low-Frequency Shear Elasticity of the Homological Series of Normal Hydrocarbons

Correction for Zaccone et al., Explaining the low-frequency shear elasticity of confined liquids.

Correction for Zaccone et al., Explaining the low-frequency shear elasticity of confined liquids.

Signatures of nanoemulsion jamming and unjamming in stimulated-echo NMR.

The unjamming of elastic concentrated nanoemulsions into viscous dilute nanoemulsions, through dilution with the continuous phase, offers interesting opportunities for a pulsed-field gradient (PFG) NMR, particularly if the nanoemulsion is designed to take advantage of the nuclear specificity offered by NMR. Here, we make and study size-fractionated oil-in-water nanoemulsions using a perfluorinated copolymer silicone oil that is highly insoluble in the aqueous continuous phase. By studying these nanoemulsions using ^{19}F stimulated-echo PFG-NMR, we avoid any contribution from the aqueous continuous phase, which contains a nonfluorinated ionic surfactant. We find a dramatic change in the ^{19}F PFG-NMR decays at high field-gradient strengths as the droplet volume fraction, ϕ, is lowered through dilution. At high ϕ, observed decays as a function of field-gradient strength exhibit decay-to-plateau behavior indicating the jamming of nanodroplets, which contain ^{19}F probe molecules, in an elastic material reminiscent of a nanoporous solid. In contrast, at lower ϕ, only a simple decay is observed, indicating that the nanodroplets have unjammed and can diffuse over much larger distances. Through a comparison with bulk mechanical rheometry, we show that this dramatic change coincides with the loss of low-frequency shear elasticity of the nanoemulsion.

Collective Effects in Ionic Liquid [emim][Tf2N] and Ionic Paramagnetic Nitrate Solutions without Long-Range Structuring.

Mesoscopic shear elasticity has been revealed in ordinary liquids both experimentally by reinforcing the liquid/surface interfacial energy and theoretically by nonextensive models. The elastic effects are here examined in the frame of small molecules with strong electrostatic interactions such as room temperature ionic liquids [emim][Tf2N] and nitrate solutions exhibiting paramagnetic properties. We first show that these charged fluids also exhibit a nonzero low-frequency shear elasticity at the submillimeter scale, highlighting their resistance to shear stress. A neutron scattering study completes the dynamic mechanical analysis of the paramagnetic nitrate solution, evidencing that the magnetic properties do not induce the formation of a structure in the solution. We conclude that the elastic correlations contained in liquids usually considered as viscous away from any phase transition contribute in an effective way to collective effects under external stress whether mechanical or magnetic fields.

Highlighting Thermo-Elastic Effects in Confined Fluids.

The recent identification of a finite shear elasticity in mesoscopic fluids has motivated the search of other solid-like properties of liquids. We present an innovative thermal approach of liquids. We identify a dynamic thermo-elastic mesoscopic behavior by building the thermal image produced by different liquids upon applying a low frequency mechanical shear field. We selected three fluids: a low molecular weight polybutylacrylate (PBuA), polypropyleneglycol (PPG), and glycerol. We demonstrate that a part of the energy of the shear strain is converted in cold and hot shear bands varying synchronously with the applied shear field. This thermodynamic change suggests a coupling to shear elastic modes in agreement with the low frequency shear elasticity theoretically foreseen and experimentally demonstrated.

Low-Frequency Shear Elasticity of a Colloid Nanosuspension

The paper presents the experimental results of an acoustic impedance study of low-frequency (105 Hz) shear elasticity of a colloidal SiO2 suspension of differently sized particles in polyethylene siloxane liquid PES-2. The agreement of the experimental results obtained by different variants of the acoustic resonance method confirms that the low-frequency shear elasticity of colloidal nanoparticle suspensions is a bulk property.

Exploring “Dormant” Opto-Mechanical Properties of the Isotropic Phase of Liquid Crystals and Revealing Hidden Elasticity of (Ordinary) Liquids

There is little literature on the flow properties of the isotropic phase of liquid crystalline fluids. However, this phase is an ideal tool to bridge the physics of liquid crystals with those of (ordinary) fluids. Optical and mechanical studies are presented, demonstrating that away from any phase transition, the isotropic phase of liquid crystalline molecules (LCs) and liquid crystalline polymers (LCPs) can work as an optical oscillator in response to low-frequency mechanical excitation, establishing the elastic origin of the flow birefringence and “visualizing” the very existence of the elastic nature of the liquid state. Additionally, mimicking the excellent anchoring ability of liquid crystals, an alternative rheological protocol optimizing the fluid/substrate interfaces is presented to access the low-frequency shear elasticity in various one-component liquids and salt-free aqueous solutions.

Importance of Interfacial Interactions to Access Shear Elasticity of Liquids and Understand Flow Induced Birefringence from Liquid Crystals to Worm-Like Micellar Solutions

This work points out the importance of the substrate boundary conditions to lower the dissipation in the dynamic measurement and access the closest dynamic characteristics of liquids, in particular to access the low frequency shear elasticity. The liquid/surface interface is a source of dissipation that enters and impacts the measurement. Examples of steady-state shear flows or flow birefringence are presented to highlight the non-universality of the behavior with respect to the nature of the substrate or the sheared thickness. Additionally the present development completes and extends the identification of low frequency shear elasticity made at sub-millimeter gaps in various one-component liquids to salt-free aqueous solutions (CTAB-water (Hexadecyl-TrimethylAmmonium Bromide)).

Hidden solidlike properties in the isotropic phase of the 8CB liquid crystal

Novel dynamic experiments have enabled the identification of a macroscopic solidlike response in the isotropic phase of a low molecular weight liquid crystal, 4,4'-n-octylcyanobiphenyl (8CB). This unknown property indicates that the low frequency shear elasticity identified in the isotropic phase of liquid crystal polymers is not reminiscent from the glass transition but reveals likely a generic property of the liquid state. The comparison to high molecular weight liquid crystals indicates, however, that the shear modulus is much enhanced when the liquid crystal moieties are attached to a polymer chain. The macroscopic length scales probed (0.050-0.100 mm) exclude wall-induced effects.

Identification of Shear Elasticity at Low Frequency in Liquid n-Heptadecane, Liquid Water and RT-Ionic Liquids [emim][Tf2N

By improving the boundary conditions between the sample and the substrate whereby the stress and the measurement are transmitted, novel dynamic experiments enable the detection of subtle properties as the identification of a no-zero low frequency shear elasticity in various liquids. This study is for the first time extended to molecular liquids as simple liquids (heptadecane), room temperature ionic liquids ([emim][Tf2N]) and water, confirming the generic character of the elastic properties identified at the sub-millimeter away from any phase transition.

Low-frequency shear elasticity of liquids

The shear modulus and mechanical loss tangent are measured for several liquids in the frequency region between 104 and 105 Hz. It is found that an increase in frequency is accompanied by a decrease in the shear modulus and an increase in the mechanical loss tangent.

Low-Frequency Shear Elasticity and Mechanical Losses in Ferroelastics

The features of acoustic property investigations carried out in different classes of ferroelastic crystals are considered. The special attention is given to elastic and anelastic properties of ferroelastics at low frequencies: the nonlinear hysteretic dependence of a strain on an external mechanical stress, a mechanical relaxation, a spontaneous twisting of samples below a Curie point, etc. Mechanisms of mechanical losses and nonlinear shear elasticity considering a rearrangement of lattice defects and their interactions are discussed.

The investigation of shear elasticity of liquids at low-frequent shear influence

In this paper shear properties of visco-elastic fluids have been investigated using an acoustic resonance method. The tested fluid is placed between the X-18° cut piezoquartz resonator and the solid cover-plate at rest. Piezoquatz performed tangential oscillations at resonance frequency (74 kHz). The liquid layer undergoes shear strain and shear standing waves are excited therein. The parameters of the resonance curve of the piezoquartz depend on the thickness of the liquid layer and allow finding visco-elastic parameters of the studied liquid. The solution of the problem of interaction of piezoquartz–liquid layer–cover-plate gives three methods of determination of the real shear modulus ( G) and the tangent of mechanical loss angle (tan θ). The first method is realized at smaller thickness of the liquid layer than the wavelength. Liquids of different classes have been studied using this method: polymer liquids, oils, glycols and alcohols. The second method is connected with the propagation of the shear wave in liquid layer, parameters of which determine G and tan θ. And the third method is based on the determination of the limiting shift of resonance frequencies at complete damping of the shear wave in thick layers of liquid. All these three methods give satisfactory agreement of results. The investigated low-frequency shear elasticity of liquids is a bulk property of liquids.

Shear viscoelastic properties of liquids and their boundary layers

An acoustical resonance method with piezoquartz vibrator was used in the experimental determination of shear elasticity modulus and a tangent of mechanical loss angle of studied liquids and their boundary layers. It has been shown that liquid has an earlier unknown low frequency (approx. 100 kHz) viscoelastic relaxation process. The experimental results of investigation of low frequency shear elasticity of different class of liquids and their solutions have been presented. An experimental research of shear properties in dependence on shear deformation rate has been carried out. The possibility of the discovery of anomalous high viscosity of liquids has also been considered.

The complex shear modulus of polymeric and small-molecule liquids

The complex shear moduli of some ordinary liquids and their dependence on the shear deformation angle have been measured by the resonance method at a frequency of 73.5 kHz. From the results obtained, it is concluded that liquids exhibit a low-frequency shear elasticity—a property unknown before—which is associated with collective interactions of liquid molecules.

The complex shear modulus of polymeric and small-molecule liquids

The complex shear moduli of some ordinary liquids and their dependence on the shear deformation angle have been measured by the resonance method at a frequency of 73.5 kHz. From the results obtained, it is concluded that liquids exhibit a low-frequency shear elasticity—a property unknown before—which is associated with collective interactions of liquid molecules.