Oscillatory Experiments Research Articles

The nonlinear viscoelasticity of hyaluronic acid and its role in joint lubrication.

Hyaluronic acid solutions have been widely studied due to their relevance to the rheological behavior of synovial fluid and joint lubrication. Ambulatory joint motion is typically large oscillatory deflections; therefore, large amplitude oscillatory shear strain experiments are used to examine the relevant non-linear viscoelastic properties of these solutions. Using the sequence of physical processes method to analyze data provides time dependent viscoelastic moduli, which exhibit a clear physiologically relevant behavior to hyaluronic acids non-linear viscoelasticity. In particular, it is seen that during peak strain/acceleration, the time dependent elastic modulus peaks and the loss modulus is at a minimum. The hyaluronic acid can provide an immediate elastic response to sudden forces, acting like a shock absorber during sudden changes in direction of motion or maximum deflection. However, during peak rate, the elastic modulus is at a minimum and the loss modulus is at a maximum, which provides greater efficacy to hydrodynamic shear lubrication.

EFFECT OF FLOW IRREGULARITY ON OSCILLATORY BOUNDARY LAYER FLOW

The paper reports on new oscillatory flow tunnel experiments in which detailed measurements have been made of boundary layer velocities for full-scale regular and irregular oscillatory flows over sand-rough and gravel-rough fixed beds. The irregular flows were generated by amplitude modulation of the corresponding regular flows, to give same free-stream urms and same velocity and acceleration skewness. The experimental setup is described and initial results relating to flow structure, turbulence and bed shear stress are presented. Results presented for boundary layer development, turbulence intensity, turbulent stress and log-law-based estimates of bed shear stress suggest that the hydrodynamics within a flow half-cycle are largely independent of the previous flow half-cycle, at least close to the bed where the presented results have focused. Time-history effects are not entirely absent however, especially higher up from the bed. More detailed analysis is needed to elucidate further.

Hydrothermal effect and mechanical stress properties of carboxymethylcellulose based hydrogel food packaging.

The PVP-CMC hydrogel film is biodegradable, transparent, flexible, hygroscopic and breathable material which can be used as a food packaging material. The hygroscopic character of CMC and PVP plays a big role in the changing of their mechanical properties where load carrying capacity is one of important criteria for packaging materials. This paper reports about the hydrothermal effect on the mechanical and viscoelastic properties of neat CMC, and PVP-CMC (20:80) hydrogel films under the conditions of combined multiple stress factors such as temperature, time, load, frequency and humidity. The dry films were studied by transient and dynamic oscillatory experiments using dynamic mechanical analyser combined with relative humidity chamber (DMA-RH). The mechanical properties of PVP-CMC hydrogel film at room temperature (25 °C), in the range of 0-30%RH remain steady. The 20 wt% of PVP in PVP-CMC hydrogel increases the stiffness of CMC from 2940 to 3260 MPa at 25 °C and 10%RH.

Separation, preliminary characterization, and moisture-preserving activity of polysaccharides from Ulva fasciata

Sulfated polysaccharide (UFP31) extracted from the marine algae Ulva fasciata (UFP) was a heteropolysaccharide, and consisted of rhamnose, xylose, and glucose in a ratio of 1:0.46:0.27 with a (1→4)-linked glycosyl backbone. The rheology of UFP31 solution has been investigated by steady shear and small amplitude oscillatory experiments. The effects of concentration, temperature, and time were systematically investigated. Steady-shear rheological measurement in a range of shear rate (1–1000s−1) exhibited that UFP31 has a Newtonian behavior in diluted solutions (1.0%, 3.0%, and 5.0%, w/v), dilatant flow behavior at higher concentrations (7.0% and 9.0%, w/v). Specifically, UFP31 solution (7%, w/v) exhibited antithixotropic behavior. In small amplitude oscillatory experiments, both the storage modulus (G′) and the loss modulus (G”) of UFP31 solution (7%, w/v) increased with frequency swept but G′ increased more quickly. As a consequence, G′ tends to overcome G” at 2.7Hz. The capability of moisture-absorption and moisture-retention of the polysaccharide was also respectively examined gravimetrically in comparison with those of glycerol. It revealed that UFP31 exhibited a higher ability both in the moisture-absorption and moisture-retention test throughout the entire experiment. These results clearly establish the possibility that UFP31 could be employed as a new material of nature moisturizer.

Dynamic and shear stress rheological properties of guar galactomannans and its hydrolyzed derivatives

Guar galactomannan from seed of Cyamopsis tetragonolobus was hydrolyzed using acid (HCl), base [Ba(OH)2] and enzyme (mannanase) method to obtain depolymerized substances with possible functional applications as soluble dietary fiber. Rheological behavior of crude, purified, and depolymerized guar gum solutions was studied at 25°C, using shear stress and dynamic oscillatory measurements, performed with controlled stress rheometer Bohlin CVO (Malvern Instruments) fitted with cone-and-plate geometry. The various guar gums solutions with different viscosities exhibited shear-thinning behavior at high shear rate and Newtonian behavior at low shear rate. At low shear rate, sigma crude guar gum (SCGG), crude guar gum (CGG), acid hydrolyzed guar gum (AHGG) and enzyme hydrolyzed guar gum (EHGG) exhibited viscosities of 18.59, 1.346, 0.149 and 0.022Pas, respectively. Oscillatory experiments (G″, G′) of gums solutions showed typical behavior of weak viscoelastic gel. All investigated guar gums were further used for glucose bio-accessibility using a novel in vitro small intestinal model (SIM). All gums solutions resulted in 20% reduction in simulated glucose absorption, indicating a non-significant functionality difference between various guar gums. So, it can be concluded that hydrolyzed guar gums without disturbing their rheological and physiological behavior would be useful for incorporation in various food products as soluble dietary fiber.

Influence of silver paste rheology and screen parameters on the front side metallization of silicon solar cell

Four commercially available silver pastes for silicon solar cells front side metallization were examined and compared. Both rheological and printing experiments were used to correlate pastes properties and screens characteristics with printing results. Theoretical printability and spreading behavior were first characterized by means of rotational and oscillatory rheological experiments. Further on, the pastes were printed, dried, and fired in a standard solar cell process on an industrial line using a full factorial design of experiments. This methodology allows to study the effect of the paste, the screen, the aperture, and their interactions on the printing results. Especially, the finger aspect ratio, the finger cross section and its relative standard deviation, which are respectively linked to solar cell efficiency, silver consumption, and process stability, were systematically measured. This work allows finding general guidelines for process optimization. Finally, a confirmation test was carried out, leading to 19% efficiency on monocrystalline silicon solar cells in an industrial environment.

Effects of concentration and temperature on the rheological behavior of concentrated sodium lignosulfonate (NaLS) solutions

Abstract Concentrated sodium lignosulfonate (NaLS) solutions have wide industrial applications. Therefore, the viscoelastic properties of NaLS in concentrations of 55%–63% have been investigated between 5°C and 55°C by means of a dynamic rheological technique, namely, the oscillatory rheological experiments were conducted in a rheometer in the small amplitude oscillatory mode. All solutions showed “shear-thinning” behavior over frequency. The complex viscosity (η*) increased and the loss tangent (tanδ) decreased with increasing concentrations. Both the storage modulus (G′) and the loss modulus (G″) increased with increasing frequencies and concentrations. The change in viscoelastic behavior was probably caused by stronger aggregation effects. However, the effects of temperature on the viscoelastic properties are more complex. For 60% NaLS, G′, G″, and η* decreased, but tanδ increased with increasing temperatures. When the temperature exceeded 20°C, G′, G″, and η* increased, but tanδ decreased, and the relaxation times were increased as a function of temperature. The change in viscoelasticity as a function of temperature may also be related to intermolecular aggregation and the swelling of aggregates. The conductivity experiments indicated that the formation of a greater strength of network structures at higher levels of concentrations between 55% and 63% and temperatures between 20°C and 55°C was probably responsible for elasticity enhancement.

Rheological characterization of ferrous sulfate-containing water-in-oil-in-water (W1/O/W2) double emulsions

With use of response surface methodology (RSM), the W1/O/W2 emulsions containing ferrous sulfate as the inner phase were optimized in terms of stability (ES) and apparent viscosity (μ app ). Curvature display of the responses around their optimal settings was appropriately described using the quadratic polynomial regression model. The non-Newtonian behavior of the test W1/O/W2 emulsions was characterized using the power-law model and change from non-Newtonian to Newtonian (n≃1) was seen in the case of W1/O:W2 ratio equal 20: 80 when the level of Tween-80 was 1 v%. Results of the size distribution pattern showed 60% of the particles were less than 5 μm. Rheological properties of the test W1/O/W2 emulsions as the viscoelastic liquids were analyzed and the results of oscillatory experiments considering shear stress and frequency dependency of G′ and G″ moduli were discussed in terms of the internal microstructure of the emulsions.

The dynamic performance of a shear thickening fluid viscous damper

This paper presents a study of the rheological properties of shear thickening fluids (STF) and the performance of a viscous damper filled with an STF by performing a cyclic loading test. In the rheological test, the STF samples were prepared by blending nanoscale fumed silica powder with polypropylene glycol fluid in different weight fractions. Using a strain-controlled rheometer with a cone and plate tool, both steady and oscillatory state experiments were performed and the rheological properties of the STF were observed. Experimental results showed an abrupt increase in complex viscosity beyond a critical dynamic shear strain rate . In this study, a hydraulic steel tube was filled with an STF to develop an innovative passive damper device. The STF-filled damper performance test showed that the area and shape of hysteresis loops can vary with different loading conditions. The analytical models studied and a numerical approach showed that STF-filled dampers are potentially useful in practical engineering applications.

Rheological Properties of Aloe Vera (Aloe barbadensis Miller) Juice Concentrates

AbstractFlow characteristics of aloe vera juice concentrates (1.5–5.5°Brix) were determined over a range of temperatures (15–55C) by using coaxial cylinder geometry. Aloe vera juice exhibited non‐Newtonian fluid behavior which was well described by power law model. Functional groups were characterized by Fourier‐transform infrared (FTIR) spectroscopy indicating the presence of O‐acetyl and shifting of –CH bonds. Effect of test temperatures at different shear rates on viscosity was evaluated using Arrhenius‐type equation and the activation energy values were evaluated which ranged between 12.148 and 53.073 kJ/mol. Effect of concentration was evaluated using power type and exponential type equations. An expression for combined effect of temperature and concentration was developed. Small amplitude oscillation sweep measurement was also carried out and the frequency sweep test exhibited viscoelastic nature of juice.Practical ApplicationsAloe vera is commercially very important crop and is being used in food, medicines and cosmetics. Rheological properties are important parameters and are used to assess the functional and structural properties of food products. In this study, the flow and deformation characteristics of aloe vera juice concentrates were evaluated as a function of temperature and concentration. An expression for the combined effect of concentration and temperature on the viscosity was evaluated. Oscillatory sweep experiments can be used to assess the viscoelastic properties, which are useful to develop the products of desired functionalities. The changes in functional groups due to concentration can be assessed using FTIR spectroscopy analysis.

Synthesis and aqueous solution properties of hydrophobically modified polyacrylamide

ABSTRACTHydrophobically modified polyacrylamide (HMPAM) is synthesized by a free radical micellar polymerization method with low amounts of anionic long‐chain alkyl, sodium 9‐(and 10)‐acrylamidostearate (NaAAS), which is derived from a renewable resource material, oleic acid. In this progress, the molar ratio of Sodium dodecyl sulfate (SDS) to NaAAS is adjusted, so polymers with different lengths of the hydrophobic blocks (NH = 3 and NH = 6) are obtained. The copolymers are characterized by 1H NMR, and the polymer weight and polydispersity are determined by gel permeation chromatography. The solution behaviors of the copolymers are studied as functions of concentrations, pH, and added electrolytes by steady‐flow and oscillatory experiments. The viscosities of these HMPAMs increase enormously above the critical concentration (c*). The sample with longer hydrophobic blocks exhibits better thickening effect. The rheological behaviors of aqueous solutions of HMPAMs are also investigated at different pH and brine environments. Low pH or the presence of brine promotes the intramolecular associating of hydrophobes for the both copolymers in semidilute solutions. The introduction of ionizable carboxylic group on the long hydrophobic side chain significantly influences the aggregation behaviors of the copolymers, leading to unique solution behaviors of the poly(AAm/NaAAS) copolymers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40754.

The quasilinear large-amplitude viscoelastic regime and its significance in the rheological characterization of soft matter

We present a novel approach for using large-amplitude oscillatory shear flow experiments (LAOS) to determine—in a simple, direct, and robust manner—the mechanical behavior of materials that possess a microstructure and may exhibit solidlike, liquidlike, viscoelastic, viscoplastic, and/or thixotropic behavior. As the stress amplitude and frequency are independently varied, two classes of motion are observed: (i) structure-changing motions, characterized by a nonsinusoidal response, when the stress amplitude is large enough to cause microstructural changes and the frequency is of the order of the reciprocal of the time scale of microstructural changes; and (ii) constant-structure motions, characterized by a sinusoidal response, when either the stress amplitude is not large enough to cause microstructural changes or the stress amplitude is large enough to cause microstructural changes but the frequency is much larger than the reciprocal of the time scale of microstructural changes. For a commercial hair gel, we confirm experimentally the existence of these two classes of motions, which was theoretically predicted by de Souza Mendes and Thompson [Rheol. Acta 52(7), 673–694 (2013)]. In contrast to the presently available LAOS analyses, which focus on the structure-changing motions, our methodology—quasilinear LAOS or QL-LAOS—relies for the most part on data obtained from constant-structure motions. This fact simplifies dramatically the experiments and the analysis and provides material functions the physical meanings of which are quite evident.

Peptide-Nanofiber-Supported Palladium Nanoparticles as an Efficient Catalyst for the Removal of N-Terminus Protecting Groups.

Sonication-induced tryptophan- and tyrosine-based peptide bolaamphiphile nanofibers have been used to synthesize and stabilize Pd nanoparticles under physiological conditions. The peptide bolaamphiphile self-assembly process has been thoroughly studied by using several spectroscopic and microscopic techniques. The stiffness of the soft hydrogel matrix was measured by an oscillatory rheological experiment. FTIR and circular dichroism (CD) experiments revealed a hydrogen-bonded β-sheet conformation of peptide bolaamphiphile molecules in a gel-phase medium. The π-π stacking interactions also played a crucial role in the self-assembly process, which was confirmed by fluorescence spectroscopy. Electron (SEM and TEM) and atomic force microscopy (AFM) studies showed that the peptide bolaamphiphile molecules self-assemble into nanofibrillar structures. Pd nanoparticles were synthesized in the hydrogel matrix in which redox-active tryptophan and tyrosine residues reduce the metal ions to metal nanoparticles. The size of the Pd nanoparticles are in the range of 3-9 nm, and are stabilized by peptide nanofibers. The peptide-nanofiber-supported Pd nanoparticles have shown effective catalytic activity for the removal of N-terminus protecting groups of amino acids and peptides.

Rheological properties of hydrolyzed polyacrylamide/sodium oleate mixed system in the presence of different inorganic salts

Abstract The effects of inorganic salts NaCl, KCl, CaCl2 and MnCl2 with the same anions but different cations on the rheological properties of hydrolyzed polyacrylamide/sodium oleate (HPAM/C17H33COONa) mixed system were investigated systemically by steady-flow and oscillatory experiments at different concentrations of inorganic salts and temperatures, respectively. The results of steady-flow measurements indicate that for all of the systems, the steady-shear viscosities (η) decrease obviously with the addition of inorganic salts and show shear-thinning property at higher shear rate and the data fit power-law equation. In oscillatory experiments, all of the systems show elastic behaviors which also depend strongly on the concentrations of the inorganic salts. The storage moduli (G'), loss moduli (G″), the complex viscosities (η⁎) and η all decreased as the inorganic salts concentrations increased. The order of effectiveness of cations in decreasing the viscosity and the activation energy of HPAM/C17H33COONa mixed system is Na+>K+> 1 2 Ca2+> 1 2 Mn2+.

The effect of pulsed IR-light on the rheological parameters of blood in vitro.

In this study we attempted to assess the effect of light of 855 nm wavelength (IR-light) on the rheological parameters of blood in vitro. As an anticoagulant, heparin was used. The source of IR-light was an applicator connected to the special generator--Viofor JPS®. The blood samples were irradiated for 30 min. During the irradiation the energy density was growing at twelve-second intervals starting from 1.06 J/cm2 to 8.46 J/cm2, then the energy density dropped to the initial value; the process was repeated cyclically. The study of blood viscosity was carried out with a Contraves LS40 oscillatory-rotational rheometer, with a decreasing shearing rate from 100 to 0.01 s⁻¹ over 5 min (flow curve) and applying constant frequency oscillations f=0.5 Hz with decreasing shear amplitude ˙γ0 (viscoelasticity measurements). The analysis of the results of rotational measurements was based on the assessment of hematocrit, plasma viscosity, whole blood viscosity at four selected shear rates and on the basis of the numerical values of parameters from Quemada's rheological model: k0 (indicating red cell aggregability), k∞ (indicating red cell rigidity) and ˙γc (the value of the shear rate for which the rouleaux formation begins). In oscillatory experiments we estimated viscous and elastic components of the complex blood viscosity in the same groups of patients. We observed a decrease of the viscous component of complex viscosity (η') at ˙γ0=0.2 s⁻¹, while other rheological parameters, k0, k∞, and relative blood viscosity at selected shear rates showed only a weak tendency towards smaller values after irradiation. The IR-light effect on the rheological properties of blood in vitro turned out to be rather neutral in the studied group of patients.

Biodegradation behavior of bacterial-based polyhydroxyalkanoate (PHA) and DDGS composites

The extensive use of plastics in agriculture has increased the need for development and implementation of polymer materials that can degrade in soils under natural conditions. The biodegradation behavior in soil of polyhydroxyalkanoate (PHA) composites with 10 wt% distiller's dried grains with solubles (DDGS) was characterized and compared to pure PHA over 24 weeks. Injection-molded samples were measured for degradation weight loss every 4 weeks, and the effects of degradation times on morphological, thermomechanical, and viscoelastic properties were evaluated by scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), and small-amplitude oscillatory shear flow experiments. Incorporation of DDGS had a strong effect on biodegradation rate, mechanical properties, and production cost. Material weight loss increased linearly with increasing biodegradation time for both neat PHA and the PHA/DDGS 90/10 composites. Weight loss after 24 weeks was approximately six times greater for the PHA/DDGS 90/10 composites than for unaltered PHA under identical conditions. Rough surface morphology was observed in early biodegradation stages (≥8 weeks). With increasing biodegradation time, the composite surface eroded and was covered with well-defined pits that were evenly distributed, giving an areolate structure. Zero shear viscosity, Tg, gelation temperature, and cold crystallization temperature of the composites decreased linearly with increasing biodegradation time. Addition of DDGS to PHA establishes mechanical and biodegradation properties that can be utilized in sustainable plastics designed to end their lifecycle as organic matter in soil. Our results provide information that will guide development of PHA composites that fulfill application requirements then degrade harmlessly in soil.

Rheological Characterization of Starch Gelatinization: Effects of plasticizer/starch ratio and clay content in corn-starch/glycerol thermoplastic starch (TPS)

ABSTRACTThis work presents a systematic rheological study of the gelatinization process of corn-starch plasticized with glycerol, showing the effects of the glycerol/starch ratio, water/starch ratio, and clay (montmorillonite) content. Gelatinization temperatures at different heating rates in rheological oscillatory temperature-sweep experiments were determined for different corn-starch/glycerol/clay formulations. The influences of the different formulation variables on the gelatinization processes and on the gel properties are analyzed. Some hypotheses postulating how the different intermolecular interactions present in the composites are responsible for these effects are discussed.

Multifunctional lipid-coated polymer nanogels crosslinked by photo-triggered Michael-type addition

Novel, multifunctional lipid-coated polymer nanogels crosslinked by photo-triggered Michael-type addition were prepared via the use of liposome templates. The photo-sensitive gelation and temporal control of the crosslinking reaction were confirmed by oscillatory rheology experiments of bulk hydrogels, and the production of nanogels was confirmed via dynamic light scattering and transmission electron microscopy. The surface functionality of the lipid-coated nanogels was demonstrated by surface modification with a reactive fluorescent dye. These multifunctional lipid-coated nanogels, given the mild preparation conditions, ease of size control, and versatility of the chemical linkages used as cross-links, have significant potential for use in polymeric nanoparticulate drug delivery systems.

Effect of surfactant on the viscoelastic behavior of semidilute solution of two different families of water-soluble copolymers prepared by solution polymerization

The interactions between hydrophobically modified polyacrylamides (HMPAM) and the anionic surfactant SDS (sodium dodecyl sulfate) and/or the cationic surfactant DTAB (dodecyltrimethylammonium bromide) were studied in aqueous solution using steady flows and oscillatory rheological experiments. The structure of the HMPAM used consisted of a telechelic polymer (with hydrophobic groups at the chain ends) and a multisticker polymer (with hydrophobic groups along the polymer chain). The multisticker polymer was prepared with acrylamide and N-hexadecylacrylamide (HDAM), whereas the telechelic polymer was prepared with acrylamide and a hydrophobic initiator that was derived from 4,4′-azobis(4-cyanopentanoic acid) (ACVA) and contained a long linear chain of 16 carbon atoms (ACVA16). In both polymers, the rheological behavior depended strongly on the amount of surfactant added. For the telechelic and multisticker polymers, the terminal relaxation time TR exhibited a maximum when the surfactant concentration was augmented (SDS or DTAB). An increase or decrease in the plateau modulus G0 was observed, depending on the structure of the polymer (telechelic or multisticker).

Ageing Effect on Steady Rheological Behavior in Oilfield Water of Water-Soluble, Hydrophobically Associating Polymer

The effect of ageing time on the macromolecular composition and conformation on intermolecular entanglement and crosslinking was investigated for a water-soluble, hydrophobically associating polymer (WSHAP), by steady-flow and oscillatory experiments at reservoir temperature (65 °C). The measurement of rheological properties was carried out with changing sample properties such as shear stress, shear rate and storage time. Moreover, for the investigated samples, the mathematical interpretation of relationship between the modulusGand the shear rate γ according to the Ostwald de Waele (power law) model, was carried out. Energy of viscous flow (Ea) has also been determined and discussed.