Dilatation Modulus Research Articles

The sustained-release mechanism of citrus essential oil from cyclodextrin/cellulose-based Pickering emulsions

The design of functional delivery systems is crucial for achieving sustained flavor release in food products. In this study, we compared the stabilizing effects of β-cyclodextrin (CD)-based Pickering emulsions loaded with lemon essential oil (LEO) mediated by cellulose nanocrystals (CNC) and bacterial cellulose (BC). We also explored the potential mechanisms underlying the sustained flavor release in terms of emulsion properties, droplet micromorphology, and interfacial properties. CNC and BC mediation improved the overall stability of emulsions, primarily reflected by increased droplet dispersion and a slight reduction in droplet size (from 10.83 μm to 6.20 and 6.99 μm, respectively). High concentrations (0.12% and 0.24%) of BC mediation led to a sharp increase in emulsion viscosity (from 56.60 to 1872.57 and 6194.29 mPa s, respectively), and the strong network formed by BC in the continuous phase prevented droplet migration. In contrast, the distribution of CNC at the oil-water interface allowed droplets to possess a double-layer interfacial structure, effectively enhancing interfacial tension and interfacial dilatation modulus, and creating a greater barrier to LEO diffusion. These findings provide a scientific basis for the structural design of delivery systems to achieve regulated release of flavor factors.

Effect of Janus Nanoparticles on Foam Stability

The foam properties of different surfactants were evaluated by the stirring method. The synergistic foam stabilizing effect was formed by the combination of lauryl glucoside and hydrophilic nanoparticles, but the result was feeble. The blend of Janus nanoparticles and surfactants significantly improves foam stability, and the two have a strong synergistic effect on foam stability. The compound system has a specific temperature resistance. Kruss dynamic surface tensiometer and surface dilatation rheometer were used to measure the gas-liquid interface properties of the hydrophilic nanoparticles compound system, Janus nanoparticles compound system, and surfactant system, respectively. The effects of Janus nanoparticles on the surface tension and surface dilatation modulus of the compound system were analyzed, which were correlated with the stability of the foam.

Compressibility and porosity modulate the mechanical properties of giant gas vesicles

Gas vesicles used as contrast agents for noninvasive ultrasound imaging must be formulated to be stable, and their mechanical properties must be assessed. We report here the formation of perfluoro-n-butane microbubbles coated with surface-active proteins that are produced by filamentous fungi (hydrophobin HFBI from Trichoderma reesei). Using pendant drop and pipette aspiration techniques, we show that these giant gas vesicles behave like glassy polymersomes, and we discover novel gas extraction regimes. We develop a model to analyze the micropipette aspiration of these compressible gas vesicles and compare them to incompressible liquid-filled vesicles. We introduce a sealing parameter to characterize the leakage of gas under aspiration through the pores of the protein coating. Utilizing this model, we can determine the elastic dilatation modulus, surface viscosity, and porosity of the membrane. These results demonstrate the engineering potential of protein-coated bubbles for echogenic and therapeutic applications and extend the use of the pipette aspiration technique to compressible and porous systems.

ФИЗИЧЕСКАЯ СУТЬ СОПРОТИВЛЕНИЯ БЕТОНА И ЖЕЛЕЗОБЕТОНА ОТ ДИСЛОКАЦИЙ ДО ТРЕЩИН

The physical essence of resistance of concrete and reinforced concrete from dislocations, micro-cracks to macro-cracks and its experimental justification is investigated. For the "eight" structure of crystals of different materials (concrete and steel) a general model in the form of a sphere was developed. For it the summation of volume sectors, levels - radii from the matrix of sliding planes (including octahedral and pure shear) is written down. This uses an alternative to the theory of plasticity in the form of energy interpretation on the surface of the sphere and determining the integral of the mean square of the tangential stresses. It is important to obtain dislocations in the microcrack, angular and linear deformations, and displacements in a representative volume of the concrete cube. As the intensity increases, the deformation process proceeds already to the mainline cracks, where the double-concole elements of tension, compression, transverse shear and torsion (its internal parameters) are refined. Significant issues are the dilatation modulus and transverse coefficient, for which functions have been developed at the stages of the stress-strain state of concrete during the evolution of the transition from crack formation to main cracks. Concrete compression and tension diagrams for strain intensity or minimum pure shear use shear stresses. The fundamental difference of the stress diagram in the downward section is the use of the ultimate resistance of the concrete. Stress reduction in a material whose failure has a "tear-off" character is an unnatural phenomenon, and the limiting resistance of concrete at and reduction of prism strength at the i-th step is . The deformation pattern of concrete during the formation of earlier microcracks and then later main cracks is oriented along for compression or across the loading line for tensile force.

Surface Dilatational Properties and Foam Performance of Surfactant-Nanoparticle Foaming System under Ultra-High Salinity

Abstract We have studied the surface dilatational properties of aqueous foaming dispersions containing mixtures of silica nanoparticles (Ludox CL) and sulfobetaine (LHSB) in Tahe formation water. The effects of temperature and pH on the surface dilatational modulus and time shift were studied by oscillating drop module (ODM). The ODM results show that the surface dilatational modulus of mixtures of CL and LHSB is large and increases with the decrease of surface area deformation, which results from hydrophobic interaction between adsorbed mixtures. Under test conditions, the Gibbs stability criterion E > σ/2 against foam coarsening is fulfilled. Results of Brewster angle microscopy (BAM) show that an uniform adsorption layer is established at the air-water interface. Temperature and pH-value influence the dilatation modulus of the surface by hydrophobic interaction or adsorption. Time shift has a similar variation trend. This is a surprising feature. It suggests that LHSB adsorbed on CL can respond to surface tension gradient. The time shift difference results from the response of LHSB at different adsorption sites. In addition, sand pack tests show that compared to LHSB, a finer foam was produced by the mixtures CL/LHSB due to the capillary-induced \snap-off". Thus, higher pressure difference and higher oil recovery could be achieved.

Study on enhanced oil recovery by multi-component foam flooding

To obtain a foam system with better stability and oil resistance, this paper starts with the mechanism of enhanced oil recovery by foam flooding and makes use of a combination of surfactants to make foam more stable. A foam system with strong stability can be obtained by combining anionic surfactants with nonionic surfactants. Based on this idea, a new type of multi-component foam flooding system (system 1) is developed. The main molecule is zwitterionic surfactant with a concentration of 0.7% fourteen alkyl sulfonated fluorobetaine (SFN). The auxiliary surfactants are present at a concentration of 0.3% of Sodium Dodecyl Sulfate (SDS), a concentration of 1.8% of potassium chloride (KCL) and a concentration of 3.0% of anhydrous ethanol (C2H6O). In addition, adding a 1000 mg/L solution of partially hydrolyzed polyacrylamide (HPAM) into the system can enhance the strength of the interfacial film, increase the surface dilatation modulus and extend the equilibration time, thereby enhancing the stability of the foam. The comparative evaluation experiment results show that the foaming capacity, foam stability and comprehensive performance of system 1 are better than those of other common foam systems under the condition of 30% Sor and a 1:1 ratio of gas to liquid. For system 1, the number of bubble films L (lamella number) is less than 7, the boundary between the foam and crude oil is clear, and the interaction is small. The foam of system 1 has good oil resistance. The results of oil displacement show that the oil recovery using system 1 increases by 16.8 percentage points after polymer flooding, which is 4–6 percentage points higher than that of an ordinary foam system. The results of the oilfield test show that the development effect of polymer flooding in the B block is poor. In January 2017, system 1 was injected into the reservoir. The 23 wells in the B block responded well, and the effective ratio reached 92%. Compared with the previous stage, the daily fluid production increased by 215 m3, the daily oil production increased by 141.0 t, the water cut decreased by 9.2 percentage points, and the reservoir effect was obvious. This result provides a new idea for the later development of high water cut reservoirs.

The effect of resonance on transient microbubble acoustic response: Experimental observations and numerical simulations.

A large number of acoustic signals from single lipid-shelled Definity® (Lantheus Medical Imaging, N. Billerica, MA) microbubbles have been measured using a calibrated microacoustic system, and a unique transient characteristic of resonance has been identified in the onset of scatter. Comparison of the numerically obtained response of microbubbles with acoustic measurements provides good agreement for a soft shell that is characterized by small area dilatation modulus and strain softening behavior, and identifies time to maximum radial excursion and scatter as a robust marker of resonance during transient response. As the sound amplitude increases a two-population pattern emerges in the time delay vs the fundamental acoustic scatter plots, consisting of an initial part pertaining to microbubbles with less than resonant rest radii, which corresponds to the weaker second harmonic resonance, and the dominant resonant envelope pertaining to microbubbles with resonant and greater than resonant rest radii, which corresponds to the primary and subharmonic resonances. Consequently, a wider resonant spectrum is observed. It is a result of the strain softening nature of soft lipid shells, based on which the microbubble sizes corresponding to the above resonances decrease as the sound amplitude increases. This bares an impact on the selection of an optimal microbubble size pertaining to subharmonic imaging.

Static response and stability of coated microbubbles—multiplicity of solutions and parameter estimation

The static response of a coated microbubble subject to an external pressure distribution is investigated, in order to identify different response patterns with varying viscoelastic properties of the shell. Theoretical and numerical analysis of the axisymmetric response of a microbubble is performed via the static force balance, in order to obtain the radial and tangential (polar) displacements of a shell subject to a uniform or point load. The stretching and bending stiffnesses of the shell, along with the compressibility of the internal gas, comprise the resistance to deformation of the microbubble. The finite element methodology, with B-splines as basis functions, is employed for the solution of the nonlinear static problem while Newton’s iterations provide the converged solution. The Jacobian matrix provides necessary information regarding stability of the emerging static configurations. The buckling instability of a uniformly loaded shell results in a subcritical bifurcation that is characterized by symmetric/asymmetric shapes for the parameter range pertaining to polymeric/phospholipid shells. As the relative importance of bending stiffness with respect to stretching decreases symmetric shapes determine the primary buckling instability. Strain softening shell behavior conforms to this pattern due to the increase of the effective area dilatation modulus during compression. Increasing the resistance to compression forces the asymmetric and symmetric solution families to terminate at larger bubble volumes. When a point load is considered the force deformation curve is characterized by a transition from a linear Reissner-type to a nonlinear Pogorelov-type response, followed by a regime where resistance to compression dominates. Identifying these regimes in atomic force microscopy measurements can be used for estimating the area dilatation and bending modulus of the shell.

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.

Nonlinear radial oscillations of encapsulated microbubbles subject to ultrasound: The effect of membrane constitutive law

The nonlinear radial oscillations of bubbles that are encapsulated in an elastic shell are investigated numerically subject to three different constitutive laws describing the viscoelastic properties of the shell: the Mooney-Rivlin (MR), the Skalak (SK), and the Kelvin-Voigt (KV) models are used in order to describe strain-softening, strain-hardening and small displacement (Hookean) behavior of the shell material, respectively. Due to the isotropic nature of the acoustic disturbances, the area dilatation modulus is the important parameter. When the membrane is strain softening (MR) the resonance frequency decreases with increasing sound amplitude, whereas the opposite happens when the membrane is strain hardening (SK). As the amplitude of the acoustic disturbance increases the total scattering cross section of a microbubble with a SK membrane tends to decrease, whereas that of a KV or a MR membrane tends to increase. The importance of strain-softening behavior in the abrupt onset of volume pulsations, that is often observed with small insonated microbubbles at moderately large sound amplitudes, is discussed.

Non-linear extensions to shell models of ultrasound contrast agents: theory and experiment

The standard UCA models, characterized by the area dilatation modulus and viscosity of the encapsulating membrane, are extended in order to account for deviations from linear material behaviour and for non-spherical pulsations. The former effect is captured by introducing a parameter that measures the degree of membrane softness, whereas the latter is modelled by introducing a bending elasticity. Lipid shells exhibit the phenomenon of 'thresholding behavior' where excursions in the relative area dilatation are measured only beyond a critical sound amplitude. Treating the lipid shell as strain softening reproduces this non-linear behaviour which can be further optimized by controlling the shell softness parameter. Such a tuning can be used to estimate the degree of softness for the contrast agent BR-14. Stability analysis allowing for shape distortions provides an estimate for the bending elasticity that reproduces the experimentally observed threshold for growth of surface modes. Phase diagrams are constructed for BR-14, based on high-speed optical observations and stability analysis. Both experiment and numerical analysis exhibit a smaller variation between the stability threshold of subsequent shape modes in the case of UCA's, as compared to free bubbles. Numerical simulations reproduce the experimentally observed saturation of growing shape modes for pre-stressed UCA's.

Stability and simulations of pulsating contrast agents

The encapsulating membrane of ultrasound contrast agents, UCA's, is treated as a viscoelastic thin shell whose deviation from linear Hookean behavior is modeled as a strain softening or strain hardening effect via a parameter measuring the degree of membrane softness. As the amplitude of sound increases it controls the shift in resonance frequency until it hits the forcing frequency in which case an abrupt increase in the microbubble response takes place. Only strain softening shells exhibit this behavior. Deviations from sphericity are modeled via an additional parameter, namely the scalar bending modulus. This parameter controls static buckling of the shell, the onset of parametric instability and dynamic buckling. In this fashion phase diagrams can be constructed for a specific UCA that map regions of subharmonic growth of shape modes. Stability analysis and numerical simulations are employed in order to capture the onset, growth and break-up or saturation of shape modes. The above two parameters are added to the area dilatation modulus and viscosity of the membrane in order to construct a model that can be used to design new agents that behave optimally in different diagnostic or therapeutic modalities.

Effect of constitutive laws for two-dimensional membranes on flow-induced capsule deformation

Three constitutive laws (Skalak et al.'s law extended to area-compressible interfaces, Hooke's law and the Mooney–Rivlin law) commonly used to describe the mechanics of thin membranes are presented and compared. A small-deformation analysis of the tension–deformation relation for uniaxial extension and for isotropic dilatation allows us to establish a correspondence between the individual material parameters of the laws. A large-deformation analysis indicates that the Mooney–Rivlin law is strain softening, whereas the Skalak et al. law is strain hardening for any value of the membrane dilatation modulus. The large deformation of a capsule suspended in hyperbolic pure straining flow is then computed for several membrane constitutive laws. A capsule with a Mooney–Rivlin membrane bursts through the process of continuous elongation, whereas a capsule with a Skalak et al. membrane always reaches a steady state in the range of parameters considered. The small-deformation analysis of a spherical capsule embedded in a linear shear flow is modified to account for the effect of the membrane dilatation modulus.

Mechanisms of aortic valve incompetence: Finite-element modeling of Marfan syndrome

Objectives: Progressive aortic root dilatation and an increased aortic root elastic modulus have been documented in persons with Marfan syndrome. To examine the effect of aortic root dilatation and increased elastic modulus on leaflet stress, strain, and coaptation, we used a finite-element model. Methods: The normal model incorporated the geometry, tissue thickness, and anisotropic elastic moduli of normal human roots and valves. Four Marfan models were evaluated, in which the diameter of the aortic root was dilated by 5%, 15%, 30%, and 50%. Aortic root elastic modulus in the 4 Marfan models was doubled. Under diastolic pressure, regional stresses and strains were evaluated, and the percentage of leaflet coaptation was calculated. Results: Root dilatation and stiffening significantly increased regional leaflet stress and strain compared with normal levels. Stress increases ranged from 80% to 360% and strain increases ranged from 60% to 200% in the 50% dilated Marfan model. Leaflet stresses and strains were disproportionately high at the attachment edge and coaptation area. Leaflet coaptation was decreased by approximately 20% in the 50% root dilatation model. Conclusions: Increasing root dilatation and root elastic modulus to simulate Marfan syndrome significantly increases leaflet stress and strain and reduces coaptation in an otherwise normal aortic valve. These alterations may influence the decision to use valve-sparing aortic root replacement procedures in patients with Marfan syndrome.J Thorac Cardiovasc Surg 2001;122:946-54

Piecewise constant optimal controls and minimal acoustic transmission

The existence of completely piecewise constant optimal controls in the wide bandwidth, normal incidence, minimal acoustic transmission problem [MIN(γ2)] for layers of viscoelastic materials is examined numerically. It has been found that such solutions exist if the Hamiltonian is linear in the controls and the dynamic compressibility is defined in terms of fractional derivatives which approximate a generalized Maxwell model of the dilatation modulus. The low‐frequency dynamic compressibility and the low‐ to high‐frequency step of the compressibility in the relaxation region are assumed to be the controls. Calculations are presented that show the resulting optimal, multilayered structures. For shallow slopes of the compressibility the optimal controls are partially continuous (singular). As the slope increases, the controls become piecewise constant. Piecewise constant optimal controls are the exception. Their appearance seems to be restricted to relatively simple definitions of the control functions. Their occurrence may also be limited to the MIN(γ2) problem in the set of three basic problems defined by transmission, reflection, and absorption.

Analytic expressions for resonant and anti-resonant frequencies in a composite viscoelastic material

General analytic representations for resonances and anti-resonances in the effective dilatation modulus and effective density have been found. These are valid in the Rayleigh regime k1a < 1, where k1 is the compressional wavenumber in the host medium and a is the radius of the spherical inclusion. The resonance frequency with respect to the dilatation modulus can assume values that are real or purely imaginary which correspond to the cases of an underdamped and overdamped system, respectively. A similar situation holds true for the case of the anti-resonance frequency. The effective density shows resonant and anti-resonant behavior analogous to the effective dilatation modulus. All these frequencies are shown to be functions of the weighted ratio of the Lamé constants of the host and inclusion media. Some specific examples will be considered.

Effective dynamic properties of composite viscoelastic materials

General expressions for the dilatation modulus and density of composite viscoelastic materials are derived within the framework of a theory that is an extension of the self-consistent field approach. The dynamic dependence of these parameters is found up to values of wavenumber in the host medium times void radius equal to two. For various void concentrations and damping constants, the effective modulus shows regions of high stiffness and resonant compliance. The effective density shows single-peaked behavior for various concentrations and damping constants. In the long wavelength limit the effective modulus and density agree with the results of other investigators.

The effective dynamic moduli and density for composite viscoelastic materials

By extending the self‐consistent field technique of Chaban [Sov. Phys.‐Acoust. 10, 298 (1965) and 11, 81 (1965)] we have derived general expressions for the dilatation modulus and density of composite viscoelastic materials. The range of validity extends to values of wavenumber times void radius equal to two, corresponding to the truncation of the partial wave analysis. The effective modulus exhibits resonance behavior in the neighborhood of [k1a] equal to 0.27 for various void volume concentrations and for a range of damping constants. This corresponds quite closely to the resonance that Meyer, Brendel, and Tamm [J. Acoust. Soc. Am. 30, 1116 (1958)] calculated. The moduli exhibit other resonances and stiffness regimes as well. The effective density exhibits sharp double peaks in the region of k1a approximately 0.43 and 0.46 for a range of concentrations and damping constants. For large values of k1a approaching two, the ratio of the effective density to the density of the host material approaches unity. The density, in the long wavelength limit (or static approximation) shows some disagreement with that obtained by Chaban, while the effective moduli in this limit is quite similar to Chaban's to first order.

Optimal distribution of density and dilatation modulus in inhomogeneous layers

The extremals of the minimal layer thickness problem for reflectance modification, given monochromatic waves at normal incidence and real material parameters, are analyzed. The structures of sublayer sequences leading to minimal total layer thickness, when both the density and the dilatation modulus are allowed to vary independently are presented. It is found that there exist two different sublayer sequences. Both are periodic with unit cells of four layers. Minimal sequences for the corresponding one-parameter problems are obtained as limiting cases.