Viscous Character Research Articles

Influence of aqueous medium on viscoelastic properties of carboxymethylcellulose sodium, hydroxypropyimethyl cellulose, and thermally pre-gelatinized starch gels

Neutral and semi-synthetic hydrophilic polymers are widely used in pharmaceutical technology to formulate controlled release drug delivery systems. The behaviour of the gel layer, formed around the hydrophilic matrices after water uptake, is of major importance for the drug release profiles. Rheological properties are related to the gel structure, interchain interactions and entanglements, and erosion and drug diffusion processes. Oscillatory test parameters were observed for highly concentrated Na carboxymethyl cellulose (NaCMC), hydroxypropylmethyl cellulose (HPMC), and thermally pre-gelatinized starch hydrogels obtained by the swelling of matrix tablets in a 0.1 mol/dm 3 HCl solution (pH 1.0) and a pH 6.8 phosphate buffer. The gel concentration range was 18–30% (w/w). The storage ( G′) and the loss ( G″) moduli, as well as the tangent of the phase angle (δ), were obtained under dynamic conditions of non-destructive oscillatory tests, in the frequence range 0.01–4.0 Hz. The pH and the ion type of the environment exert an influence on both the elastic and viscous behaviour of the NaCMC gels. The viscous character of the polyelectrolyte gel is pronounced in the phosphate buffer, while the elastic nature is dominating in the acid medium, as a result of the polymer neutralization. The sensitivity of neutral HPMC gels to pH changes is insignificant. No considerable differences of the functional parameters G′, G″ and tan δ, depending on the ionic strength, have been found. The visco-elastic behaviour of the pre-gelatinized starch gels is very similar to those of the neutralized NaCMC, regardless of the media used. This type of gel structure may determine a general kinetic pattern of drug release.

Rheological behavior of a lamellar lyotropic phase as a function of the substrate nature

Various rheological experiments were carried out on a lamellar phase system in order to analyze its structural organization using different geometries. The results showed a rheological behavior which depended on the chemical nature of the geometry. For stainless steel substrates, the rheological profile presented a liquid plastic behavior with a predominantly elastic character for low stresses. In the case of quartz, the rheological behavior was different, displaying a predominantly viscous and shear-thinning character. A detailed rheological analysis allowed us to conclude that there exists an inhomogeneous shear effect of the sample on quartz, probably induced by a local alignment effect of the lamellar layers in the vicinity of the quartz plates. X-ray analysis of the lamellar sample placed on either stainless steel or quartz showed a parallel alignment of the lamellar layers. However, on quartz substrates, this orientation was almost perfect in the vicinity of the plates and more marked than that observed on stainless steel substrates.

Viscoelastic Properties of Protein-Stabilized Emulsions: Effect of Protein-Surfactant Interactions.

Viscoelastic properties of whey protein isolate-stabilized emulsions have been investigated by determining storage and loss moduli of both fresh emulsions and heat-set emulsion gels. Gel strength increases with the increase of protein concentration in the system. The flocculated protein-covered oil droplets behave as active fillers and hence dramatically enhance the gel strength. The presence of water-soluble surfactant Tween 20 induces a dramatic reduction in emulsion gel strength, which is attributable to protein displacement from the oil-water interface. Oil droplets that are fully covered with Tween 20 do not adhere to protein gel matrix and do not contribute to gel strength. The presence of oil-soluble monopalmitin increases the viscous character of fresh emulsions and substantially reduces the modulus of heat-set emulsion gels. The viscoelastic properties of heat-set emulsion gels containing monopalmitin are only slightly frequency-dependent, and these gels can be classified as "strong gels".

Theoretical and Experimental Comparisons for Damping Coefficients of a Short-Length Open-End Squeeze Film Damper

Squeeze film dampers (SFD) provide load isolation and attenuate rotor vibrations in high speed turbomachinery. Operating parameters such as whirl frequency, amplitude of journal motion, and value of external pressure supply determine the SFD dynamic force response and its dissipation of mechanical energy. Measurements of pressure fields and fluid film forces in a fully submerged open-end squeeze film damper are presented for tests with rotor speeds to 5000 cpm and low supply pressures. The damper has a clearance of 381 µm (0.015 in.) and the journal describes circular centered orbits of amplitudes ranging from 30 to 50 percent of the bearing clearance. Experimental film pressures depict a vapor cavitation (close to zero absolute pressure) zone increasing in extent as the whirl frequency increases. Estimated fluid film forces from the measured pressure profiles are found to be proportional to whirl speed and lubricant viscosity. Test cross-coupled damping coefficients (Crt) are smaller than predicted values based on the short-length bearing model with a π film cavitation assumption. The direct damping coefficients (Ctt) are larger than theoretical values, especially at low frequencies where the dynamic cavitation region has not grown to half the circumferential flow extent. The experiments demonstrate the viscous character of the fluid film forces in a SFD test apparatus where fluid inertia effects are minimal (squeeze film Reynolds number less than one). On the other hand, the extent of the cavitation zone appears to be dominant on the generation of fluid film forces.

Three‐dimensional finite element analysis of polymer rotational extrusion

AbstractA three‐dimensional finite element approach has been employed to model steady, creeping, isothermal helical flows and to study the effect of an imposed rotational field in a wire coating process and a tube extrusion process. It has been shown that the rotational field can affect process characteristics with an underlying viscous character, such as the velocity profile, pressure drop, viscous extrudate swelling, material pathlines, and deformation field. Significant pressure drop reduction may be achieved with implications on the process productivity, pressure drop reduction being most prevalent at low power‐law indices because of the increased nonlinearity in the shear‐thinning viscosity function. Extrudate swelling has been shown to be affected by the rotational field owing to the shear‐thinning nature of polymeric materials. Finally, it has been shown that significant material deformation may result from the imposition of the rotational field.

Rheology of Crosslinked Foams

Summary The rheology of foam fracturing fluids has been previously described as a yield-pseudoplastic fluid for a broad range of qualities, linear gel concentrations, and temperatures. With the increased use of foams for fracturing with higher proppant concentrations, crosslinking agents are often added. Because the viscous character of the external phase of the foam strongly influences the viscous properties of the foam, the viscosity of the foam will increase if the external phase is crosslinked. Rheological properties of 25%- to 75%-quality N2 foams containing borate-crosslinked guar were measured on the recirculating flow-loop viscometer at temperatures from 75 to 300°F. When polymer was crosslinked in the foam, viscosity increased by factors of 3 to 10 or more over foams that contained only linear gel. The fluid viscosity developed in a foam is a product of gas quality, external phase fluid viscosity, and crosslinking of the polymer in the external phase. The extent to which each of these factors is important depends upon both the quality and the concentration of the crosslinked polymer. Viscosity resulting from borate crosslinking is a stronger factor than either quality or linear polymer concentration. Borate crosslinking influence is greatest at low quality and at high polymer concentration.

EVALUATING RHEOLOGICAL PROPERTIES OF MOZZARELLA CHEESE BY THE SQUEEZING FLOW METHOD

ABSTRACTWe adapted the squeezing flow technique to make compression and relaxation tests on Mozzarella cheese at temperatures ranging from 30 to 60C during one month of refrigerated storage. The deformability modulus of the cheese decreased with aging and temperature but increased with deformation rate. The average decrease in the deformability modulus was 0.4 kPa/day and 0.5 kPa/C. Relaxation data also indicated a continuous increase in viscous character of Mozzarella with aging and temperature. Apparent relaxation time was less than 10 s. Relaxation parameters showed a strong temperature dependency in the range of 10‐60C. Lubricated squeezing flow data showed that the resistance of Mozzarella to flow decreased with aging and temperature indicating an increased meltability.

Gelation of Chicken Breast Muscle Actomyosin as Influenced by Weight Ratio of Actin to Myosin

Heat-induced gelation of reconstituted chicken breast muscle actomyosin was studied by monitoring the thermal stability and dynamic rheological properties at different weight ratios of actin (A) to myosin (M) (AM of 0:1, 1:15, and 1:1.3). Free myosin to actomyosin ratios were 0.2 and 2.4 for AM of 1:1.3 and 1:15, respectively. Addition of actin delayed the initial unfolding temperature of myosin and changed the enthalpy profile. This stabilizing effect was decreased with addition of pyrophosphate. Storage (G') and loss (G″) moduli of AM 1:1.3 sol at 30 o C were greater than those of myosin and AM 1:15 sols, but AM 1:1.3 had a higher loss tangent and lower G' at 80 o C. Pyrophosphate decreased G' of myosin and actomyosin solutions at 30 o C and increased viscous character after heating to 80 o C. Actin affected the denaturation of structural domains of myosin and possibly altered the gelation mechanism

Some Selected Physicochemical Properties of Buffalo Gourd (Cucurbita foetidissima HBK) Root Starch

AbstractThe starch granules of buffalo gourd contained 30.5% apparent amylose, showed a high swelling power and gelatinised over 57‐70.8°C with an enthalpy of 4.26cal·g−1. The starch pastes had a stable peak viscosity with a resistance to fragmentation intermediate to those of cassava and potato starches during holding at 95°C. The starch gels displayed a higher storage modulus (G′) than that of corn starch and a viscous character similar to that of potato starch. These properties differ from the maize‐like characteristics reported for this type of starch.

Necklace-like detachment of endothelial cell layer from arterial wall under low-calcium condition

The diversified morphological manifestations in various tissues and organs obtained by administration of differing amounts of calcium chelating agents were reported in previous papers (Yamaguchi et al 1981 a & b; 1982; 1990; 1993). In our recent research described here, administration of a moderate dose of Na2EDTA over the short term demonstrated necklace-like detachment from the arterial wall without disruption of the endothelial cell chain. Intercellular spaces in the media just beneath the detached endothelial cell layer was stained strongly with colloidal iron staining. Electron microscopic observation revealed that the detached endothelial cells showed a lot of elongated anchoring villi from the basal surface, usually seen at the luminal surface, adhered to the degenerative and thin flattened internal elastic lamellae. The alteration of the colloidal iron staining of the vascular wall under the low-calcium condition is suggested to be induced by loosening of the molecular structure of glycosaminoglycans (GAGs) as well as glycoproteins (GPs), comprising the important component of the intercellular matrix and elastic lamellae, which would induce a change in their pasty or viscous character. This would be an accelerative factor for detachment of endothelial cells. Moreover, the lack of the waving of the internal elastic lamellae, trapping of endothelial cytoplasmic processes among them, would play the decisive role in the total detachment of the endothelial cell layer. On the other hand, the low-calcium condition did not adversely influence the joining of endothelial cells. The pathognomatic mechanism will be discussed, with a comparison made to the angiolytic changes provoked by a large amount of Na2EDTA.

Viscous and elastic fingering instabilities in foam.

We investigate pattern formation in the immiscible displacement of foam from a confining geometry. The dominant length scales with the driving pressure gradient as for a Newtonian fluid, but depends surprisingly on the ratio of plate separation to bubble diameter. The pattern morphology exhibits a transition from a jagged, presumably elastic, character to a smooth, viscous character as the shear strain rate rises far above the natural internal relaxation time scale of the foam. These features may result from the two-dimensional nature of the flows and the unusual rheology of foams.

Theory of a dynamical coercive force in magnets with microscopic defects

The peculiar dynamical drag force F/sub c/ can arise at the domain wall motion in a magnet with microscopic defects, such that it cannot pin the domain wall in the usual way. The value of F/sub c/ is finite as the domain wall velocity v goes to zero. The reason for such behavior is the emission of bending waves of the domain wall. The calculations for different types of impurities as well as for both bulk ferromagnet and ultrathin magnetic layers are presented. In 3D ferromagnet the F/sub c/ value is finite at v/spl rarr/0 and this is interpreted as the dynamical coercive force. In the 2D case (e.g. in monolayer films) the drag force diverges at small velocities as F/sub c//spl prop/1/v/sup 1/2/. In the film with a finite thickness and very small v the force has a viscous character: F/sub c//spl prop/v. >

Air Attack - Retardants, Rheology and Some New Options

The rheological properties of forest and brush land fire retardant solutions significantly affect their performance during and following aerial discharge and subsequent distribution within the fuel ladder. The degree of dispersion, the integrity of the retardant cloud, the magnitude of wind-induced drift, the continuity of coverage and retention on and penetration of the fuel complex are among diose performance related characteristics impacted. The viscous character of the solution during periods of extreme and relaxed shear and its elasticity are known to be important rheological properties. While applicable specifications and the technical literature document the importance of these factors, only the extremes (water-like and highly viscous and elastic fluids) have been available to the fire manager. A series of new fluid concentrate type retardants are now being evaluated jointly by the United States Forest Service and private industry. Upon simple dilution to use level concentration, these low viscosity fluids increase in viscosity and elasticity to one of three predetermined levels, i.e., low, medium or high as defined by the Federal Specifications. Selection of the proper rheology can, thus, be made by the fire manager dependent on the type and characteristics of the delivery platform, safe drop height relative to die terrain, atmospheric conditions, fuel characteristics and the management objective.

Mental Health in Family Members Living with Elders

We assessed the mental health conditions of 217 subjects who took care of elders at home, using our depression scale by the surveillance of the elders living at home in Ibaraki Prefecture. An analysis was made on how depression in the caretakers was related with each item of demographical results of the caretakers and the elders living together at home, and with ADL, depression, dementia, personality change and the personality trait of the elders. Our study revealed that depression, personality change and the viscous character of the elders are three factors associated with depression in the female caretakers. Furthermore, we pointed out the necessity of an education campaign to provide the caretakers with information on the elders' personality and personality change for maintenance of the good mental health of the caretakers living with the elders.

Alternatives to traditional epoxy embedding “kits”: Novel choices

Epoxy resin embedding “kits” invariably are offered as one epoxy resin coupled with the hardners dodecynyl succinic anhydride (DDSA), nadic methyl anhydride (NMA) and the amine catalyst 2,4,6-Tri(dimethylaminomethyl)phenol (DMP-30). This well-known mixture has been used widely for many years, perhaps in part because it is offered in the form of a convenient kit. Microscopists should be aware that packaged kits, eventhough they produce successful results, possess a never-changing high viscous character that could compromise optimum infiltration or damage delicate specimens. Past studies have shown clearly that the kit compnents DDSA and DMP-30 are particularly viscous compounds. Replacing DDSA with the less viscous nonenyl succinic anhydride (NSA), and substituting either dimethylaminoethanol (DMAE) or benzyldimethylamine (BDMA) as the catalyst of choice in place of DMP-30 will significantly reduce the viscosity of the overall mixture while producing easily manageable media that maintain fluidity longer, insure optimum infiltration, and ultimately produce results equal to those obtained with traditional kits.

Magnetization of lower crust and interpretation of regional magnetic anomalies: Example from Lofoten and Vesterålen, Norway

The interpretation of regional magnetic anomalies commonly observed over continental crust in both satellite and near‐surface magnetic data has remained enigmatic in its requirement for laterally extensive, thick, highly magnetic, and deep‐seated sources. Presented here are the results of a detailed field, analytical, and experimental study of the magnetic mineralogy and magnetic properties of rocks from Lofoten and Vesteralen, Norway, a province of deep‐seated origin with associated regional magnetic and gravity anomalies. These rocks have a bulk magnetic character of surprising uniformity, with susceptibilities, hysteresis, and Curie temperatures defined solely by coarse‐grained magnetite. Stable remanence is observed in samples from SW Lofoten but is not of significant magnitude. The thermal enhancement of magnetic susceptibility, the Hopkinson effect, is not important. Rocks from the deepest part of the section have the largest average susceptibilities, 6×10−2 (SI), and magnitudes of natural remanent magnetization (NRM), 5×10−4 A m2/kg. These values of susceptibility, together with the oft‐observed viscous character of the NRM, suggest that these granulite facies lithologies (particularly those of SW Lofoten) are perfect examples of lower crustal sources of typical regional magnetic anomalies. Furthermore, these intermediate‐pressure granulites define a unique magnetic petrology, especially for mafic compositions. At higher grades of metamorphism (high‐pressure granulites and eclogites) or lower grades (greenschist and amphibolite facies) such magnetite‐bearing assemblages will be unstable, and their high‐ or low‐grade equivalents will be only weakly magnetic. This evidence and these conclusions may be used to constrain models of lower crustal sources of regional magnetic anomalies over stable cratons. It portrays the lower crust as a highly magnetic unit, defined by metamorphic grade, with a Curie isotherm of 575°C (magnetite) and magnetization parallel to the ambient geomagnetic field (induced and viscous components).

Elasticity of the spinal cord, pia, and denticulate ligament in the dog.

The longitudinal elasticities of the dog spinal cord, pia, and denticulate ligaments were obtained by measuring the load-elongation curves. Both pia and denticulate ligaments were moderately elastic, but the spinal cord substance showed an upward curve, which indicated a predominantly viscous character. In situ, the spinal cord and pia were moderately strained. A 40-mm segment of the cord with dorsal and ventral roots severed and denticulate ligaments removed became 1 mm shorter when the cord and pia were transected at both ends. It was estimated that the cord and pia in situ were stressed by a force of 2 to 3 gm, the denticulate ligaments with 3 to 5 gm, and the dura with 50 to 70 gm. The elastic moduli of the spinal cord substance were 1.68 X 10(5) dynes/sq cm for loading between 5 and 10 gm and 1.19 X 10(5) dynes/sq cm between 30 and 35 gm.

Isolation of sialic acid from casein and reclamation of residual casein.

Crystalline sialic acid was isolated in 50 to 60% yields from a commercial grade of dry isoelectric casein by Warren's hydrolysis procedure. One part of casein was heated at 80 C/60 min in ten parts of .18 N sulfuric acid (pH 1.5). A crude sialic acid preparation (7.8%) was obtained from the hydrolysate after addition of calcium hydroxide to remove protein at pH 4.6 and sulfate as calcium sulfate at pH 7.0 followed by concentration and lyophilization of the soluble material. Highly purified sialic acid (95%) was obtained by chromatography on Dowex-1 X 8 with a gradient of 0 to 2 M sodium acetate. The sialic acid positive fraction was passed through Duolite C20H followed by lyophilization. Slow evaporation of a concentrated solution of this material produced typical crystals of N-acetylneuraminic acid. The study also included an examination of the properties of the residual sialic acid-free casein. Electrophoretic patterns, solubility properties, rennet sensitivity, and viscous character revealed that the residual casein was remarkably similar to intact casein. However, the calcium sensitivity of this modified protein was increased in the presence of .1 M calcium chloride.

Dislocation Description of Twin Dynamic Behaviour

AbstractRelationships are obtained which allow to describe the characteristics of the twin as functions of time and medium constants for dynamic external loads within the framework of the dislocation theory. The case of large velocities is considered when the drag force arising in the dislocation motion is of the viscous friction character and, yet, the relativistic effects may be neglected. Two problems in the dynamic behaviour of the twin are solved, namely the escape of the elastic twin from an unloaded crystal due to the surface tension force and passage across the crystal by the twin in a uniform stress field. The obtained results are compared with experimental data for iron, calcite, and cadmium. It is shown that in the considered case of large velocities the twin motion velocity should be weakly (at least, not exponentially) dependent on temperature. This result is in agreement with available experimental data.

Determination of dislocation damping in copper single crystals with stress pulse method

Dislocation damping in copper single crystals was determined by the stress pulse method. For this purpose very short stress pulses were used, maximum length 30 μs, by which loading conditions of a metallic matrix in the frontal region of a propagating brittle crack were simulated. At loading by these very short stress waves, strain rates\(\dot \gamma \) above 104 s−1 are achieved, however, the strain rate during loading is not constant. Therefore a technique was elaborated that enables to compare the measured results of mechanical characteristics with very short stress pulses (\(\dot \gamma \) ≠ ≠ const.) with results obtained on a device with a constant strain rate of the specimen. With the use of the dependence τ = τ(\(\dot \gamma \)) the existence of damping mechanisms of a viscous character was proved and the damping coefficientB determined. These results agree with theoretical assumptions in [10,20] about the probable mechanical behaviour in the region of the propagating brittle crack.