Viscous Character Research Articles

Tragacanth as an oral peptide and protein delivery carrier: Characterization and mucoadhesion

Biopolymers such as tragacanth, an anionic polysaccharide gum, can be alternative polymeric carrier for physiologically important peptides and proteins. Characterization of tragacanth is thus essential for providing a foundation for possible applications. Rheological studies colloidal solution of tragacanth at pH 3, 5 or 7 were carried out by means of steady shear and small amplitude oscillatory measurements. Tragacanth mucoadhesivity was also analyzed using an applicable rheological method and compared to chitosan, alginate and PVP. The particle size and zeta potential were measured by a zetasizer. Thermal properties of solutions were obtained using a differential scanning calorimetry. The solution exhibited shear-thinning characteristics. The value of the storage modulus (G′) and the loss modulus (G″) increased with an increase in angular frequency (Ω). In all cases, loss modulus values were higher than storage values (G″>G′) and viscous character was, therefore, dominant. Tragacanth and alginate showed a good mucoadhesion. Tragacanth upon dispersion created particles of a submicron size with a negative zeta potential (−7.98 to −11.92mV). These properties were pH dependant resulting in acid gel formation at pH 3.5. Tragacanth has thus a potential to be used as an excipient for peptide/protein delivery.

New controlled release material: aerated egg white gels induced by calcium ions

The aim of the research was to use low-mineral egg white albumin isolate to obtain aerated calcium ion-induced gels and to investigate their aptitude as matrices for active ingredients release. Aerated gels were prepared by adding calcium ions to pre-heated protein dispersions with simultaneous aeration. 20 mM calcium concentration was an optimal concentration at which the maximum viscosity and hardness of the gels were found. For higher concentrations of calcium ions (25–30 mM), aerated gels were characterized by lower values of the moduli and tangent of the phase angle was larger for aerated gels which indicated more viscous character than that of non-aerated gels. Increased ions concentration causes higher aggregation of protein matrix and less smooth microstructure of the interface between the gel and air. An increase in calcium concentration from 5 to 30 mM caused an increase in an average bubble size. The release of calcium ions from aerated gels was measured in an artificial stomach. It occurred by Fickian diffusion through the swelling matrix and it was faster for the gels with higher concentration of calcium. An increase in calcium concentration caused an increase in surface roughness of the aerated gels. There were linear correlations between the quadratic mean of the surface roughness and “n” coefficient from the Ritger and Peppas equation and between the maximum roughness size and “n”. The increased calcium concentration made the gel microstructure more particulate and the surface rougher, which enabled faster proteolysis of the gel in an artificial stomach and faster diffusion of calcium ions.

Anisotropy of Mechanical Properties and its Correlation with the Structure of the Stainless Steel 316L Produced by the SLM Method

Standard specimens made of austenitic stainless steel powder 316L were produced by the SLM method. Studies of the mechanical properties showed a strong dependence on the parameters of powder melting and the direction of specimens building. It is stated that the yield strength and tensile strength are higher than that of a stainless steel specimens obtained by traditional technology, and virtually independent of the direction of the specimens building. Impact strength and elongation, conversely, differ almost two times. The surface has a viscous character of destruction for all the specimens. Analysis of the structure by EBSD method revealed texture presence and coinciding major axis of grains with building direction. Comparison of strength properties and structure parameters allows associating the anisotropy of mechanical properties with the anisotropy of the structure. These results are important for taking into account the anisotropy of the mechanical properties while designing a particular item.

Herschel-Bulkley fluid flow within a pipe by taking into account viscous dissipation

The present numerical study deals with the analysis of thermal characteristics during the flow of an incompressible Herschel-Bulkley fluid of constant physical and rheological properties. The flow takes place within a pipe, of circular cross section, maintained at uniform wall temperature. Because of the viscous character of this kind of fluid, viscous dissipation is taken into account. The effect of this parameter is analyzed for various values of the fluid index flow and the Herschel-Bulkley number. The governing equations are resolved by means of the finite volume method and using the SIMPLER algorithm and the line by line method. The results reveal that heat transfer is significantly underestimated when viscous dissipation is neglected, particularly for shear-thinning fluids and for high values of the Herschel-Bulkley number. In addition, heat transfer is more important in the case of heating and the curves display a discontinuity, and negative values of Nusselt number are obtained.

A review of exfoliated graphite

Exfoliated graphite (EG) refers to graphite that has a degree of separation of a substantial portion of the carbon layers in the graphite. Graphite nanoplatelet (GNP) is commonly prepared by mechanical agitation of EG. The EG exhibits clinginess, due to its cellular structure, but GNP does not. The clinginess allows the formation of EG compacts and flexible graphite sheet without a binder. The exfoliation typically involves intercalation, followed by heating. Upon heating, the intercalate vaporizes and/or decomposes into smaller molecules, thus causing expansion and cell formation. The sliding of the carbon layers relative to one another enables the cell wall to stretch. The exfoliation process is accompanied by intercalate desorption, so that only a small portion of the intercalate remains after exfoliation. The most widely used intercalate is sulfuric acid. The higher concentration of residue in unwashed EG causes the relative dielectric constant (50 Hz) of the EG to be 360 (higher than 120 for KOH-activated GNP), compared to the value of 38 for the water-washed case. An EG compact is obtained by the compression of EG at a pressure lower than that used for the fabrication of flexible graphite. Compared to flexible graphite, EG compacts are mechanically weak, but they exhibit viscous character, out-of-plane electrical/thermal conductivity and liquid permeability. The viscous character (flexural loss tangent up to 35 for the solid part of the compact) stems from the sliding of the carbon layers relative to one another, with the ease of the sliding enhanced by the exfoliation process.

Polymeric complexes obtained from the interaction of bovine serum albumin and κ-carrageenan

This study aimed to characterize and optimize the formation of polymeric complexes obtained from the interaction between bovine serum albumin (BSA) and κ-carrageenan, in different aqueous systems containing different pH values and various concentrations of polymer and NaCl. Response surface methodology was applied to optimize the process. The proposed polynomial model showed significant adjustment (R2 = 0.84), and the optimal conditions for the formation of carrageenan-BSA polymeric complexes were verified to be 6.40 mg of κ-carrageenan, 0.58 mol/L NaCl, and pH 6.30. The rheological analysis showed that the polymeric complex had a less viscous character than carrageenan. Scanning electron microscopy and X-ray diffractometry showed that the complex had a more well-differentiated morphology compared to the original biopolymers.

Thixotropic flow past a cylinder

We study the flow of a thixotropic fluid around a cylinder. The rheology of the fluid is described by means of a structural viscoplastic model based on the Bingham constitutive equation, regularised using the Papanastasiou regularisation. The yield stress is assumed to vary linearly with the structural parameter, which varies from zero (completely broken structure) to one (fully developed skeleton structure), following a first-order rate equation which accounts for material structure break-down and build-up. The results were obtained numerically using the Finite Element Method. Simulations were performed for a moderate Reynolds number of 45, so that flow recirculation is observed behind the cylinder, but vortex shedding does not occur. The effects of the Bingham number and of the thixotropy parameters are studied. The results show that the viscous character of the flow can be controlled within certain limits through these parameters, despite the fact that the Reynolds number is fixed.

Influence of both cation and alginate nature on the rheological behavior of transition metal alginate gels

The rheological properties of several ionotropic alginate hydrogels were investigated according to the nature of the divalent cation (Mn2+, Co2+, Cu2+) and the guluronic fraction of the alginate (HG and LG for “high G-content” and “low G-content”). Six hydrogels (Mn-LG, Mn-HG, Co-LG, Co-HG, Cu-LG and Cu-HG) were synthesized and studied by spectromechanical analyses. On one hand, Cu-HG, Cu-LG and Co-HG behaved as viscoelastic solids: the elastic contribution was higher than the dissipative component in all the frequency range studied (G′>G″). No flow zone (G″>G′) was detected even at very low values of the shearing frequency. On the other, Mn-HG, Mn-LG and Co-LG presented a spectromechanical behavior that resembled that observed classically for entangled polymers. Indeed, at high frequency, these latter materials could be compared to a viscoelastic solid but at low frequency, the flow zone was described and the viscous character became prevalent with finite relaxation time. Very good correlations with the microscopic structurations of the network were evidenced (rubbery vs. flow zone and fibrillar vs. complex morphology respectively).

Effect of organic intercalation on the viscoelastic behavior of clay

Clay is a soil component, a ceramic ware component, and a reinforcement in nanocomposites. Its viscoelastic behavior is relevant to vibration damping and slip rheology. The clay studied is hectorite, which is a trioctahedral magnesium-based smectite. Clay compacts with solid contents (50–53) vol% are studied in terms of the dynamic compressive properties at small static strains (3.1–3.5 %), low deformation amplitudes (5–8 μm), and low frequencies (0.2–10.0 Hz). The organic intercalation of hectorite (with basal spacing 12 A prior to intercalation) to form organoclay (nanoclay in the form of disteardimonium hectorite with basal spacing 29 A) increases both the loss tangent and the loss modulus of the solid part of the compact by up to about 27 %, while affecting the storage modulus negligibly. At 10.0 Hz, the organic intercalation increases the loss tangent of the solid part from 0.306 ± 0.009 to 0.366 ± 0.021 and increases the loss modulus of the solid part from (2.69 ± 0.08) × 104 to (3.44 ± 0.04) × 104 Pa. The organic intercalation affects the viscous behavior rather than the elastic behavior. The viscous behavior is attributed to the low-amplitude dynamic slippage at the interface between adjacent clay layers in a clay nanoplatelet and that between nanoplatelets in a clay particle. In case of organoclay, it is also due to the nanoscale viscous behavior of the organic component. The viscoelastic properties are essentially independent of the frequency. The viscous character of both unmodified clay and organoclay is weaker than that of carbon black or exfoliated graphite, but the elastic character of both unmodified clay and organoclay is stronger than that of carbon black or exfoliated graphite.

Viscoelastic behavior of the cell wall of exfoliated graphite

The cell wall (∼60-graphite-layer thick, average) in the cellular structure of exfoliated graphite compacts is viscoelastic, due to the shear between graphite layers. The viscous character decreases with increasing solid content (volume fraction), due to the increasing difficulty of shear, which becomes limited at solid contents above 4vol.%. The elastic character is essentially independent of the solid content, weakening slightly with increasing solid content. The viscous character is stronger under in-plane flexure than compression in the compaction direction, due to the preferred orientation of the graphite layers. At the lowest solid content of 1.0 vol.%, the loss-tangent/solid-content is 35 and 25 under flexure and compression respectively, the storage-modulus/solid-content is 125MPa and 46kPa under flexure and compression respectively, and the loss-modulus/solid-content is 45MPa and 13kPa under flexure and compression respectively. The viscous character is strong under both flexure and compression, whereas the elastic character is much stronger under flexure than compression. The loss-tangent/solid-content decreases with increasing solid content, leveling off at 0.9 at 15vol.% solid. The loss-modulus/solid-content also decreases with increasing solid content. The highest values of the loss-tangent/solid-content, storage-modulus/solid-content and loss-modulus/solid-content are greater for exfoliated graphite compacts than rubber or carbon black compacts.

Viscoelastic behavior of carbon black and its relationship with the aggregate size

The viscoelastic behavior of binderless carbon black compacts under dynamic compression (0.2–10.0Hz, static strain 1.0–2.5%, deformation amplitude 9.4–16μm and packing density 0.18–0.45g/cm3) is governed by the solid part of the compact, with the elastic character dominating the viscous character. The viscous character increases with increasing aggregate size, while the elastic character decreases. The interparticle movement in an aggregate contributes to the viscous deformation, while the connectivity among the aggregates contributes to the stiffness. The loss tangent of the solid part increases with increasing aggregate size up to 300nm, which is optimum for viscoelasticity. A larger specific surface area weakly correlates with a lower storage/loss modulus of the solid part. The particle size does not correlate with the viscoelastic behavior. Both viscous and elastic characters increase with increasing static strain, due to the tightening of the solid part. The loss tangent of the solid part is up to 1.2, compared to 21 and 0.67 for exfoliated graphite and rubber respectively. The storage and loss moduli of the solid part (up to 21 and 180kPa respectively) are below those of rubber, but are above or comparable to those of exfoliated graphite. Possible applications relate to mechanical isolation.

Viscoelastic Behavior of Silica Particle Compacts under Dynamic Compression

Theviscoelastic behavior of model sandy soils in the form of silica particle compacts under dynamic compression (0.2-10.0 Hz) is reported. The solid content ranges from 24 to 28% by volume, as controlled by compaction. Both viscous and elastic characters are largely governed by the solid part of the compact. The elastic character stems from the stiffness of the silica, while the viscous character stems from the interparticle movement. The elastic character of the solid part (the storage modulus and solid content) is essentially independent of the degree of compaction, indicating validity of the rule of mixtures. The viscous character of the solid part (the loss tangent and solid content) decreases with increasing degree of compaction, indicating decreasing ease of interparticle movement as the degree of compaction increases. The loss modulus and solid content is essentially independent of the degree of compaction. All quantities decrease with increasing frequency. A low degree of compaction is recommended for fast decay of the vibration amplitude; no particular degree of compaction is recommended for mechanical energy dissipation. DOI: 10.1061/(ASCE)MT.1943-5533.0000831. © 2014 American Society of Civil Engineers. Author keywords: Soil compression; Viscoelasticity; Dynamic properties; Mechanical properties; Compression tests; Vibration damping; Silica; Particles.

Rheological behavior of an acrylamide-based terpolymer with p-vinylbenzyl-terminated octylphenoxy poly(ethylene oxide)

A comb-like associating terpolymer PAOE was synthesized from acrylamide (AM), sodium 2-aciylamido-2-methylpropane sulphonate (NaAMPS) and a novel macromonomer: p-vinylbenzyl-terminated octylphenoxy poly(ethylene oxide) (VOE, degree of polymerization: 4—using aqueous free-radical copolymerization technique. The polymer chains were still comparatively extended in the brine solutions at low polymer concentrations. This leaded to the formation of continuous network structures via the intermolecular hydrophobic associations of the octylphenyl groups in despite of the addition of NaCl. As a result, PAOE predominantly exhibited significant elastic characters in brine solutions at 0.5–9 g/dL NaCl, as well as in aqueous solutions. The viscous and elastic character decreased slightly with increasing temperature from 25 to 45°C for the PAOE brine solution with 0.5 g/dL NaCl. The PAOE aqueous and brine solutions displayed obvious shear thickening behavior upon consecutive steady shear cycles. The brine solution also showed the excellent thickening properties, salt-thickening behaviors twice, and resistance to salt.

Effects of swelling on the viscoelastic properties of polyester films made from glycerol and glutaric acid

AbstractViscoelastic properties have been determined for poly(glycerol‐co‐glutaric acid) films synthesized from Lewis acid‐catalyzed polyesterifications. The polymers were prepared by synthesizing polymer gels that were subsequently cured at 125°C to form polymer films. The polymers were evaluated for the extent of reaction before and after curing by Fourier transform infrared spectroscopy. They were subsequently immersed in dimethylsulfoxide, tetrahydrofuran, water, methanol, and hexane for 24 h. The amounts of solvent absorbed were monitored and recorded. Dependent up the solvent used, the polymers were able to absorb 9.5–261% of its weight. The effects of the solvent absorption on the viscoelastic properties of the polyester films were evaluated by determining their elastic modulus (G′), viscous modulus (G″), tan δG″/G′, and complex viscosity (η*) by performing oscillatory frequency sweep experiments. The elastic modulus (G′) and viscous modulus (G″) were both higher for the dry polymers than the solvent‐absorbed polymers. However, the polymer films were all higher in elastic (G′) character than viscous (G″) character. Therefore, tan δG″/G′ < 1 before and after immersion in solvents. Values for η* decreased with angular frequency for all of the polyesters tested in this study. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Friction response of ZDDP thermal film and tribofilm

An original dynamic tribotest was used to study the friction response of two kinds of tribological surface: zinc-dialkyl-dithio-phosphate (ZDDP) thermal film and ZDDP tribofilm. This apparatus allows friction to be determined with no need for measuring tangential force. A velocity dependent friction contribution was found in each case in addition to a velocity independent one, showing the viscous character of such films. Furthermore, during test on ZDDP thermal film, the viscous damping represents 18% of the total dissipated energy as it is 16% for ZDDP tribofilm.

A quasi-lumped model for the peripheral distortion of the arterial pulse

As blood circulates through the arterial tree, the flow and pressure pulse distort. Principal factors to this distortion are reflections form arterial bifurcations and the viscous character of the flow of the blood. Both of them are expounded in the literature and included in our analysis. The nonlinearities of inertial effects are usually taken into account in numerical simulations, based on Navier-Stokes like equations. Nevertheless, there isn't any qualitative, analytical formula, which examines the role of blood's inertia on the distortion of the pulse. We derive such an analytical nonlinear formula. It emanates from a generalized Bernoulli's equation for an an-harmonic, linear, viscoelastic, Maxwell fluid flow in a linear, viscoelastic, Kelvin-Voigt, thin, cylindrical vessel. We report that close to the heart, convection effects related to the change in the magnitude of the velocity of blood dominate the alteration of the shape of the pressure pulse, while at remote sites of the vascular tree, convection of vorticity, related to the change in the direction of the velocity of blood with respect to a mean axial flow, prevails. A quantitative comparison between the an-harmonic theory and related pressure measurements is also performed.

Reduced serum content and increased matrix stiffness promote the cardiac myofibroblast transition in 3D collagen matrices

The fibroblast-myofibroblast transition is an important event in the development of cardiac fibrosis and scar formation initiated after myocardial ischemia. The goals of the present study were to better understand the contribution of environmental factors to this transition and determine whether myofibroblasts provide equally important feedback to the surrounding environment. The influence of matrix stiffness and serum concentration on the myofibroblast transition was assessed by measuring message levels of a panel of cardiac fibroblast phenotype markers using quantitative reverse transcriptase polymerase chain reaction. Cell-mediated gel compaction measured the influence of environmental factors on cardiac fibroblast contractility. Immunohistochemistry characterized alpha-smooth muscle actin expression and cell morphology, while static and dynamic compression testing evaluated the effect of the cell response on the mechanical properties of the cell-seeded collagen hydrogels. Both reduced serum content and increased matrix stiffness contributed to the myofibroblast transition, as indicated by contractile compaction of the gels, increased message levels of col3α1 and alpha-smooth muscle actin, and a less stellate morphology. However, the effects of serum and matrix stiffness were not additive. Mechanical testing indicated that reduced serum content increased the initial elastic modulus of cell-seeded gels and that gels lost their viscous character with time. The results suggest that reduced serum and increased matrix stiffness promote the myofibroblast phenotype in the myocardium. This transition both enhances and is promoted by matrix stiffness, indicating the presence of positive feedback that may contribute to the pathogenesis of cardiac fibrosis.

Structures and N 2-sorption properties of carbonaceous films prepared by high-powered sputtering of d-phenylalanine

Amino acid-based carbonaceous films were prepared by the radio-frequency (rf) sputtering of d-phenylalanine under the rf power density from 0.18 to 0.53 W/cm 2. As the rf power was increased, the deposition rate tended to increase, especially for 120-W sputtering. The surface of carbonaceous films prepared by high rf power have rugged surfaces following their storage in a vacuum box. The carbonization of the sputtered films progressed with rf power; the oxygen and nitrogen content in the films decreased as rf power increased, as well as the content of CH moieties decreased. Increasing the rf sputtering power enhanced the N 2-sorption capability and the viscous character of the carbonaceous films. The quartz crystal resonators coated with the carbonaceous films by the highest rf sputtering power had superior resonance signals toward the N 2 sorption-desorption measurement with suppressed noise.

Fission-to-spallation ratio and fission dynamics manifestation

Fission of highly excited nuclei is affected by the viscous character of the system motion in deformation coordinates as is reported for very heavy nuclei with Z ⩾ 90. The long-time-scale fission was proved for such systems formed in heavy-ion-induced reactions. The overdamped diabatic motion may influence also fission of the spallation-residue products in reactions with protons at intermediate energy. In the present work, the experimental results on fission-to-spallation ratio are analyzed and the evidences for the long-time-scale fission are found in the fission excitation functions for medium-mass targets with Z = 70–75.

Fluorous imidazolium room-temperature ionic liquids based on HFPO trimer

Imidazole substituted with a polyfluoropolyether chain based on HFPO trimer combined with various polyfluoroalkyl triflates produced novel highly fluorous ionic liquids. Their metathesis with four different anions generated a final set of 20 fluorous ionic liquids of waxy or viscous liquid character, which are all soluble in perfluorinated solvents. Two model reactions using selected ionic liquid, the opening of a THF ring with benzoyl chloride under Friedel–Crafts conditions and substitution of benzyl chloride with sodium azide, led to decomposition of the ionic liquid. However, Diels–Alder reaction of 2,3-dimethylbuta-1,3-diene with dimethyl acetylenedicarboxylate in a fluorous ionic liquid resulted in a reasonable enhancing of the reaction rate with smooth recycle of the fluorous solvent. The fluorophilicity of these fluorous ionic liquids ranges from more than 10 for water, toluene or dichloromethane to less than 0.2 for acetonitrile or methanol.