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Rheological Properties (rheological + property)
Kinds of Rheological Properties Selected AbstractsEFFECT OF COMPOSITION OF GLUTHNIN SUBFRACTIONS ON RHEOLOGICAL PROPERTIES OF WHEATJOURNAL OF FOOD BIOCHEMISTRY, Issue 4 2000S. JOOD ABSTRACT Gluten extracted from defatted flours of cv. Aubaine (extra-strong), Hereward (strong) and Riband (weak) was separated into five different fractions (R2 to R6) by sequential centrifugation and addition of sodium chloride. A seven-minute mixing time was used to carry out fractionation on the basis of depolymerization of glutenin macropolymers (GMP). Depolymerization of GMP occurred at much higher rates in dough of the weak cultivar compared to the strong and extra-strong cultivars. Polypeptide compositions of different ghttenin fractions were determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis under reduced and non-reduced conditions, followed by densitometric scanning of stained patterns. The amount of HMW-glutenin subunits decreased and LMW-glutenin subunits increased correspondingly in each cultivar with the fractionation from R2 to R6. The rheological behavior of the fractions was analyzed by small deformation rheological tests (strain sweep and frequency tests). The high molecular weight fraction (R2) from extra-strong wheat had a higher vahte of G' and a lower tan , value as compared to strong and weak bread-making wheats. The moduli of HMW glutenin fractions (R2 and R3) were frequency independent and promoted the network properties, whereas moduli of LMW glutenin fractions were frequency dependent and gave rise to a plasticizing effect. Therefore, it was concluded from the present studies that HMW-glutenin subunits are not the only factors governing good bread-making quality but their proportions in relation to low molecular weight glutenin subunits is equally important in sinking a balance between viscous and elastic properties essential for bread making performance. [source] RHEOLOGICAL PROPERTIES OF CRYSTALLIZED HONEY PREPARED BY A NEW TYPE OF NUCLEIJOURNAL OF FOOD PROCESS ENGINEERING, Issue 4 2009YUE-WEN CHEN ABSTRACT Good spreadability is a highly desirable quality for crystallized honey used in product applications. In this study, we processed Taiwanese liquid litchi honey into crystallized honey by adding a new nuclei material, namely 0.1% (w/w) glucose powder, instead of the traditional 5,10% (w/w) natural nuclei. Rheological properties of the resulting product were determined during heating and cooling utilizing small amplitude oscillatory shear to assess spreadability. As the product was heated, it exhibited decreased consistency and improved fluidity (evidenced by decreasing storage modulus [G,] and loss modulus [G,] values) and three distinct regions within the G,curve ("softening,""crystalline plateau" and "melting"). As the product was cooled from 55 to 0C, moduli were lower than those obtained during heating, and the product did not exhibit the three G,curve regions across the temperature range. Therefore, we observed incomplete reversible crystallization and rheological properties during temperature migration. Flow properties of crystallized honey in the 0,25C temperature range could be successfully predicted using the Herschel,Bulkley model (R2 > 0.97). However, the product approached Newtonian flow behavior as temperatures neared the upper end of this range. Higher viscosity and lower yield stress were observed at temperatures below 15C. The crystallized honey developed for this study exhibited shear-thinning properties desirable in honey products intended to be spread. PRACTICAL APPLICATIONS Crystallized honey is traditionally prepared by introducing 5,10% natural nuclei into liquid honey. Our lab developed a new method that replaces the natural nuclei with glucose powder, which, at 0.1% (w/w), produces a good quality creamed honey that, in commercial production, offers the potential for significant production cost advantages. As crystallized honey is used in commercial/consumer applications as a spread, its dynamic rheology is of both academic and industrial interest. In this study, we discuss the physical properties of the crystallized honey developed using glucose powder to help better identify the factors and variables involved in honey spreadability and thus facilitate the development of better honey products with more desirable spreadability profiles. This study also provides a rheological properties and spreadability database for crystallized honey that reflects the range of temperature changes that can be expected to occur during normal product storage and use. [source] RHEOLOGICAL PROPERTIES OF CHEMICALLY MODIFIED RICE STARCH MODEL SOLUTIONSJOURNAL OF FOOD PROCESS ENGINEERING, Issue 2 2006C.S. RAINA ABSTRACT Native rice starches have poor resistance to shear, and fair stability to retrogradation with soft texture, which can be altered through chemical modifications. Starch from broken pieces of rice of three rice cultivars (PUSA-44, PR-106 and PR-114) was chemically modified by etherification and esterification reactions by different combinations of modification reagents to investigate the effect of modification on the rheological properties of rice starches. The modification resulted in shear stable gel with apparent pseudoplastic characteristics. The viscosity of starches increased upon acetylation and dual modification as a result of increase in solubility. However, cross-linking had shown the reverse effect. The flow behavior index (n) and consistency coefficient (k) were significantly (P , 0.05) improved upon modification in acetylated and dual-modified starches. The effect of modification on the rheological properties was observed in similar pattern in all the three rice cultivars but varied significantly in variety PUSA-44 may be because of its relatively higher amylose content. [source] THERMAL AND RHEOLOGICAL PROPERTIES OF BRINE FROM FERMENTED AND SULFITE-PRESERVED CUCUMBERS,JOURNAL OF FOOD PROCESS ENGINEERING, Issue 4 2002O.O. FASINA ABSTRACT Pickling cucumbers may be temporarily preserved by fermentation in brine (6,8% NaCl) or without fermentation in salt-free, sulfite solution (300 ppm sulfite, pH 3.5). Brines obtained from preservation processes are often discarded. Due to environmental concerns, there is increasing consideration for further use of the brine solutions by recycling for use in bulk storage or filtration and incorporation into finished products. Thermal and rheological properties are fundamental to the reuse of the brine. The effect of temperature was determined on the rheological (5,45C) and thermal properties (5,75C) of brine. The properties of the brine samples were found to be significantly different (P < 0.05) from each other and from water. Salt content was the most important factor affecting the thermal and rheological properties of brine. At the same conditions, the values of the properties (thermal conductivity, specific heat, and thermal diffusivity, viscosity) were about 5 to 23% less than the corresponding values for water. [source] USE OF NONLINEAR DIFFERENTIAL VISCOELASTIC MODELS TO PREDICT THE RHEOLOGICAL PROPERTIES OF GLUTEN DOUGHJOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2001M. DHANASEKHARAN ABSTRACT Nonlinear viscoelastic models of the differential type, such as the Phan Thien Tanner model, White-Metzner model and Giesekus model were used to predict the steady shear, oscillatory shear and transient shear properties of gluten dough. The predictions were compared with new data and the experimental results of Wang and Kokini (1995b). The Phan-Thien Tanner model and the Giesekus model were used in eight modes to fit the relaxation modulus accurately. The White-Metzner model gave the best prediction for the steady shear properties as it used a Bird-Carreau dependence for the shear viscosity. The Phan-Thien Tanner model and the Giesekus model predicted the transient shear viscosity and the transient first normal stress coefficient better than the White-Metzner model. A consistent prediction of all the experimental data could not be obtained using a single model. [source] RHEOLOGICAL PROPERTIES OF NONCOHESIVE APPLE DISPERSION WITH HELICAL AND VANE IMPELLERS: EFFECT OF CONCENTRATION AND PARTICLE SIZEJOURNAL OF FOOD PROCESS ENGINEERING, Issue 5 2000DENIS CANTÚ-LOZANO ABSTRACT The proportionality constant, ks, between shear rate, ,, and agitation velocity, N, for a helical ribbon-screw (HRS) agitator was 17.8. Using the HRS agitator, values of consistency index K and the flow behavior index n of 14 apple pulp suspensions at seven different solids concentrations and two average particle diameters 0.71 mm and 1.21 mm were determined; in addition, values of the Casson viscosity ,c and yield stress ,OC were also calculated. The magnitudes of K increased and of n decreased with increase in pulp concentration. Experimental values of the vane yield stress, ,O,, measured with a six-blade vane increased with increase in pulp content. The values of ,OC obtained using the Casson model were close to the experimental values ,O,. The effect of particle size on the relative viscosity, ,r, was correlated with Peclet number. [source] RHEOLOGICAL PROPERTIES OF SET YOGURT AS INFLUENCED BY INCUBATION TEMPERATURE AND HOMOGENIZATIONJOURNAL OF FOOD QUALITY, Issue 5 2002R.R. SHAKER The effect of incubation temperature and homogenization on the rheological nature of yogurt curd during gelation was investigated in this study. Our results indicated that the optimum incubation temperature for acid development was 45C. The minimum viscosity was observed at 40C while the maximum viscosity was at 48C. Our results also indicated that incubation temperature affected yogurt viscosity during the gelation process while homogenization had no significant effect. Increasing the incubation temperature decreased the flow behavior index and increased the consistency coefficient; homogenization increased the flow behavior index and decreased the consistency coefficient as described by a power law model. [source] FLOW VELOCITY OF A BOLUS IN THE PHARYNX AND RHEOLOGICAL PROPERTIES OF AGAR AND GELATINJOURNAL OF TEXTURE STUDIES, Issue 2 2010HATSUE MORITAKA ABSTRACT The flow velocity through the human throat and rheological properties of 0.2,0.8% agar and 0.8,2.4% gelatin were investigated. The maximum flow velocity decreased with increasing concentrations of agar and gelatin, with marked changes from 0 to 0.4% in agar, and from 0 to 1.4% in gelatin, with no further changes at concentration higher than 0.4% in agar but changes at concentration up to 2.4% in gelatin. Although the hardness and adhesiveness increased with increasing concentrations of agar and gelatin, the cohesiveness decreased. In the sensory evaluation, agar and gelatin became difficult to swallow with increasing agar and gelatin concentration. PRACTICAL APPLICATIONS This research contributes to enhance the knowledge of the investigation area of the flow velocity of bolus in a pharynx. Moreover, this research is useful in order to make the foods for person with difficulties in chewing and swallowing. In fact, the results demonstrate the importance of measuring the flow velocity of bolus in the pharynx part not only the rheological properties of food. [source] MICROSTRUCTURAL AND RHEOLOGICAL PROPERTIES OF LOW-FAT STIRRED YOGHURTS MADE WITH SKIM MILK AND MULTIPLE EMULSIONSJOURNAL OF TEXTURE STUDIES, Issue 6 2009C. LOBATO-CALLEROS ABSTRACT This article focuses on the study of the dynamic rheological and structural properties developed in low-fat stirred yoghurts made with skim milk and multiple emulsions stabilized with carboxymethylcellulose (SYCMC) or amidated low methoxy pectin (SYALMP), in comparison with a full milk-fat stirred yoghurt control (SYMF). The SYALMP yoghurt exhibited greatest Tan,after 14 days of storage than the SYMF and SYCMC yoghurts. The SYALMP yoghurt presented the highest lacunarity value and was characterized by a structure composed of highly clusterized casein aggregates. In contrast, the SYCMC and SYMF yoghurts displayed lower lacunarity values and structures characterized by smaller casein clusters. Lower Tan,values were associated with lower lacunarity values. PRACTICAL APPLICATIONS Limited work has been done on stirred and set-style yoghurts, cheeses and, in general, dairy products, where milk-fat globules are substituted by skim milk combined with multiple emulsions containing polyunsaturated vegetable oils. As a result of this, multicomponent gels formation occurs (made up by milk proteins, polyunsaturated vegetable oils, emulsifiers, hydrocolloids and many possible other ingredients), which give rise to completely different structural arrangements that may display comparable mechanical-sensory properties with those exhibited by their full milk-fat counterparts, paving the way for the development of new healthier foods sensory and texturally acceptable to consumers. [source] RHEOLOGICAL PROPERTIES OF MOZZARELLA CHEESE DETERMINED BY CREEP/RECOVERY TESTS: EFFECT OF SAMPLING DIRECTION, TEST TEMPERATURE AND RIPENING TIMEJOURNAL OF TEXTURE STUDIES, Issue 3 2009MARÍA LAURA OLIVARES ABSTRACT The viscoelastic properties of mozzarella cheese using a creep/recovery test considering different sampling directions (parallel and perpendicular to protein fiber orientation), test temperatures (20, 30 and 40C) and ripening times (1, 8, 15, 29 and 36 days) were studied. Creep data were interpreted by a Burger model of four parameters. A semiempirical approach was proposed to obtain the contribution of each main compliance to the total deformation of the system. Creep tests at different temperatures allowed gaining a better understanding of changes that occur in the cheese matrix during heating and ripening. Sampling direction did not affect any of the parameters studied. Finally, it was clearly observed that cheese matrix behaves as a quite different physicochemical system depending on temperature. Therefore, it is recommended to carry out the rheological tests at different temperatures to evaluate appropriately the viscoelastic properties of mozzarella cheese. PRACTICAL APPLICATIONS Mozzarella cheese must have certain characteristics to be used on pizzas and on other prepared foods that use the cheese in melted state. The protein chains in the mozzarella curds coalesce into large strands that are oriented in the direction of stretching. For this reason, mozzarella cheese has an anisotropic structure. Therefore, it is relevant to determine the effect of protein fiber orientation on the rheological properties. Valuable information may be obtained through the creep/recovery test of mozzarella cheese samples to study its rheological properties and to explain molecular mechanisms that occur during ripening or melting processes considering sampling direction. [source] EFFECT OF MINERAL FORTIFICATION ON RHEOLOGICAL PROPERTIES OF WHOLE WHEAT FLOURJOURNAL OF TEXTURE STUDIES, Issue 1 2009SAEED AKHTAR ABSTRACT This study was aimed to evaluate the rheological changes that take place in the dough as a result of addition of elemental iron, ferric sodium ethylenediaminetetraacetate, zinc sulphate and zinc oxide in various combinations to whole wheat flour (WWF), packaged in polypropylene woven bags and tin boxes and stored for a period of 60 days under ambient and controlled conditions of temperature and relative humidity. Water absorption (WA) capacity, dough development time (DDT) and dough stability time (DS) of the fortified WWF were measured by farinographic method, and peak viscosity was assessed by viscographic analyses. WA capacity and DDT of flours increased during storage. Fortification significantly (P < 0.05) affected WA, DDT, DS and viscographic characteristics of the flours. Packaging materials (P < 0.05) influenced WA, DDT and DS, while storage condition had only affected viscographic properties of the flours. PRACTICAL APPLICATIONS The success of any fortification program depends on the stability of micronutrients and food to which they are added. Exposure of the fortificants to any of the physical and chemical factors including heat, moisture, air, or light and acid or alkaline environments during food processing, packaging, distribution or storage affects their stability. The rheological properties of dough made from fortified flours determine the quality of the fortified end product. Changes in rheological properties as a result of the incorporation of fortificants in the flour, its storage under variable conditions and length of time might have an effect on quality, cost and nutrition of the product. [source] EFFECT OF COLD STORAGE ON CULTURE VIABILITY AND SOME RHEOLOGICAL PROPERTIES OF FERMENTED MILK PREPARED WITH YOGURT AND PROBIOTIC BACTERIAJOURNAL OF TEXTURE STUDIES, Issue 1 2008MARIA REGINA DAMIN ABSTRACT We examined the effect of storage time on culture viability and some rheological properties (yield stress, storage modulus, loss modulus, linear viscoelastic region, structural recuperation and firmness) of fermented milk made with Lactobacillus delbrueckii ssp. bulgaricus, Lactobacillus acidophilus (LA) and Bifidobacterium animalis ssp. lactis in coculture with Streptococcus thermophilus (ST). Acidification profiles and factors that affect viability (postfermentation acidification, acidity and dissolved oxygen) were also studied during 35 days at 4C. Fermented milk prepared with a coculture of ST and Bifidobacterium lactis gave the most constant rheological behavior and the best cell viability during cold storage; it was superior to ST plus LA for probiotic fermented milk production. PRACTICAL APPLICATIONS Probiotic cultures should grow quickly in milk, provide adequate sensory and rheological properties to the product, and remain viable during storage. Commercially, it is very common to use yogurt starter culture (i.e. Streptococcus thermophilus[ST] and Lactobacillus delbrueckii ssp. bulgaricus) in combination with the probiotic bacteria in order to reduce fermentation time. However, LB tends to post acidify fermented milk, which reduces the viability of the probiotic bacteria; thus, it is recommended to use starter cultures devoid of this species. We found that the technological properties and the viability of the probiotic bacterium Bifidobacterium animalis ssp. lactis BL O4 in coculture with ST make it suitable for probiotic fermented milk production; it produces rheological characteristics similar to those of yogurt. [source] DETERMINATION OF ULTRASONIC-BASED RHEOLOGICAL PROPERTIES OF DOUGH DURING FERMENTATION,JOURNAL OF TEXTURE STUDIES, Issue 1 2004SUYONG LEE ABSTRACT An ultrasonic technique was used to study the changes of the rheological properties of dough during fermentation at 37C and compared with the extensional properties of fermented dough obtained from tensile tests carried out in a Universal Testing Maching. The velocity and attenuation of a longitudinal wave (P-wave) propagated through the dough samples were measured and analyzed to obtain the viscoelastic moduli of the dough; the storage modulus M' and the loss modulus M". These moduli include both the bulk and the shear moduli. A wavelet analysis also was used to determine the effect of frequency on the ultrasonic-based viscoelastic moduli and the effect of the fermentation process on the ultrasonic velocity dispersion. A decrease in ultrasonic velocity was observed with increasing fermentation times. Ultrasonic waves were strongly attenuated in the dough subjected to long fermentation times and fermentation had a large influence on the viscoelastic moduli of the dough. The ultrasonic velocity increased with increasing frequency, clearly showing the viscoelastic nature of the fermented dough. The analysis also showed significant ultrasonic velocity dispersion upon fermentation. Ultrasonic measurements yielded results that agreed with those obtained from conventional rheology commonly used to characterize the extensional properties of dough. Both tests clearly showed the loss of elasticity by the dough samples upon fermentation. [source] RHEOLOGICAL PROPERTIES, WHEY SEPARATION, AND MICROSTRUCTURE IN SET-STYLE YOGURT: EFFECTS OF HEATING TEMPERATURE AND INCUBATION TEMPERATUREJOURNAL OF TEXTURE STUDIES, Issue 5-6 2003WON-JAE LEE The effects of heat treatment and incubation temperature on the rheological and microstructural properties of yogurt were studied. A central composite experimental design and response surface methodology were used for data analysis. The rheological properties were determined by dynamic low amplitude oscillation and the amount of spontaneous whey separation was quantified by the volumetric flask test. Confocal scanning laser microscopy was used to examine the gel structure. The storage moduli of yogurts increased with an increase in heating temperature and a decrease in incubation temperature. The maximum loss tangent value during gelation, permeability, and amount of spontaneous whey separation of yogurts increased with a decrease in heating temperature and with an increase in incubation temperature. These parameters indicated an increased possibility for rearrangements, which was confirmed by presence of large pores in the gel network. Second order polynomial models successfully predicted the effects of heating temperature and incubation temperature on the rheological properties, permeability, and whey separation of yogurts. Whey separation was negatively correlated with storage modulus (r= -0.66), and was positively correlated with the maximum loss tangent (r= 0.63) and permeability (r= 0.78). This study demonstrates that weak yogurt gels, which have high loss tangent values, favor rearrangements in the network and the resulting network has larger pores (high permeability) and exhibits greater whey separation. [source] RHEOLOGICAL PROPERTIES OF HOT PEPPER-SOYBEAN PASTEJOURNAL OF TEXTURE STUDIES, Issue 4 2001B. YOO Rheological properties of fermented hot pepper-soybean paste (HPSP) were evaluated at different total solid contents (TS, 43.6-54.7%) and temperatures (10-40C). HPSP samples at 20C are highly shear thinning fluids (n=0.25-0.33) with large magnitudes of Casson yield stresses (106-573 Pa). Consistency index (K) and apparent viscosity (,a,20) increased with increase in TS. Apparent viscosity of HPSP obeyed the Arrhenius temperature relationship. The magnitudes of activation energy (7.6-20.4 kJ/mole) for HPSP increased with increase in TS. A single equation, combining the effects of temperature and concentration on ,a,20, was used to describe flow behavior of HPSP. The time-dependent model of Weltman was found to be most applicable (R2= 0.97-0.99) for HPSP. Storage (G') and loss (G") moduli increased with increase in TS, while complex viscosity (,*) decreased. Magnitudes of G'were higher than those of G" over the entire range of frequencies (,). [source] Nanoparticle Coating for Advanced Optical, Mechanical and Rheological Properties,ADVANCED FUNCTIONAL MATERIALS, Issue 16 2007F. Hakim Abstract Primary titania nanoparticles were coated with ultrathin alumina films using Atomic Layer Deposition (ALD). The deposited films were highly uniform and conformal with an average growth rate of 0.2,nm per coating cycle. The alumina films eliminated the surface photocatalytic activity of titania nanoparticles, while maintained their original extinction efficiency of ultraviolet light. Deposited films provided a physical barrier that effectively prevented the titania surface from oxidizing organic material whereas conserving its bulk optical properties. Parts fabricated from coated powders by pressureless sintering had a 13,% increase in surface hardness over parts similarly fabricated from uncoated particles. Owing to its homogeneous distribution, the secondary alumina phase suppressed excessive grain growth. Alumina films completely reacted during sintering to form aluminum titanate composites, as verified by XRD. Coated particles showed a pseudoplastic behavior at low shear rates due to modified colloidal forces. This behavior became similar to the Newtonian flow of uncoated nanoparticle slurries as the shear rate increased. Suspensions of coated particles also showed a decreased viscosity relative to the viscosity of uncoated particle suspensions. [source] Functional, Nutritional, and Rheological Properties of Protein Powders from Arrowtooth Flounder and their Application in MayonnaiseJOURNAL OF FOOD SCIENCE, Issue 2 2005Subramaniam Sathivel ABSTRACT: Arrowtooth flounder soluble protein powder (AFSP) and arrowtooth flounder insoluble protein powder (AFISP) were evaluated for their functional, nutritional, and rheological properties. AFSP and AFISP contained 80% and 79% protein and 5.9% and 14.9% fat, respectively. Yield of AFSP (8.6%) was less than AFISP (13.1%). AFSP and AFISP had desirable essential amino acid and mineral contents. Emulsion stability of AFSP was greater than AFISP. Fat and water absorptions (mL/g protein) were 5.2 and 1.8 for AFSP, respectively, and 3.3 and 4.2 for AFISP Mayonnaises made from AFSP had greater emulsion stability than mayonnaise made from AFISP. Mayonnaises from both AFSP and AFISP possessed pseudoplastic and viscoelastic characteristics. [source] Effect of Ultra-high-pressure Homogenization on Structure and on Rheological Properties of Soy Protein-stabilized EmulsionsJOURNAL OF FOOD SCIENCE, Issue 9 2002J. Floury ABSTRACT: An ultra high-pressure homogenizer (20 to 350 MPa) was used to realize fine food emulsions stabilized by soy proteins. The first aim of the work was to understand how dynamic high-pressure processing affects soybean globulin conformation. Then, the effect of homogenizing pressure on the emulsions structure and rheology was investigated. High-pressure homogenization caused denaturation of proteins due to strong mechanical forces and high temperatures encountered in the valve. Droplet sizes of emulsions were greatly reduced with high-pressure homogenization and Newtonian liquid emulsions were converted into shear-thinning emulsion gels by homogenization at pressures above 250 MPa. Hydrophobic interactions between proteins were supposed to cause the gel-like network structure of emulsions. [source] Effect of Slurry Rheological Properties on the Coating of Ceramic Honeycombs with Yttria-Stabilized-Zirconia WashcoatsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2000Christos Agrafiotis Recently, a novel automotive catalyst design, based on the use of palladium supported on yttria-stabilized zirconia (YSZ), was proposed. In the present work, the coating of cordierite honeycomb samples with YSZ slurries for the preparation of such washcoats was investigated. The loading percentage, homogeneity, and reproducibility were found to depend strongly on the slurry viscosity. Parameters such as the slurry-solids content, pH, type of powder used, and use and quantity of the dispersants were optimized for the preparation of stable, low-viscosity YSZ slurries, adjustments that could lead to an efficient coating process for honeycomb structures. [source] Effects of Ammonium Chloride on the Rheological Properties and Sedimentation Behavior of Aqueous Silica SuspensionsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2000J. Jiyou Guo The influence of ammonium chloride (NH4Cl) on the rheological properties and sedimentation behavior of aqueous silica (SiO2) suspensions of varying solids volume fraction (,s) was studied. SiO2 suspensions with low NH4Cl concentration (,0.05M, pH 5.2) exhibited Newtonian behavior and a constant settling velocity (U). The volume fraction dependence was well described by the Richardson,Zaki form, U=U0(1 ,,s)n, where n= 4.63 and U0= 1.0419 × 10,5 cm/s. At higher NH4Cl concentrations (0.07,2.0M, pH 5.2), suspensions exhibited shear thinning and more complicated sedimentation behavior due to their aggregated nature. For all suspensions studied, however, the apparent suspension viscosity, characteristic cluster size, and initial settling velocity were greatest at ,0.5M NH4Cl and exhibited a similar dependence on salt concentration. Above 0.5M NH4Cl, considerable restabilization was observed. This behavior cannot be explained by traditional DLVO theory. [source] Effect of Surface-Active Substances on the Rheological Properties of Silicon Carbide Suspensions in ParaffinJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2000Reinhard Lenk In this paper, the possibility of stabilization of SiC suspensions in paraffin (hot-molding slips) was investigated from the colloid science point of view. By considering the surface properties of finely dispersed silicon carbide, surface-active agents (fatty amine and alkylsuccinimide) which are suitable for surface modification by chemical adsorption on SiC were selected. Adsorption of fatty amines and alkylsuccinimide was carried out in model experiments in chloroform. Increasing the length of the carbon,hydrogen chain caused the adsorption to decrease, and the adsorption area of one molecule in the saturated adsorption layer to increase. The stabilizing effect of surface-active agents resulted in improved flow behavior of hot-molding slips. The efficiency of surface-active agents increased with increased adsorption layer thickness. In highly concentrated SiC hot-molding slips, a combination of alkylsuccinimide and fatty amine proved to be very efficient. This synergistic effect of long- and short-chained surface-active agents is discussed in terms of an adsorption layer model. [source] Synthesis and Rheological Properties of Polylactide/Poly(ethylene glycol) Multiblock CopolymersMACROMOLECULAR BIOSCIENCE, Issue 11 2005Feng Li Abstract Summary: Ring-opening polymerization of D,L -lactide was carried out in the presence of poly(ethylene glycol), using Zn powder as catalyst. The hydroxyl-capped PLA-PEG-PLA triblock copolymers were coupled with adipoyl chloride at different molar ratios under mild conditions. N -Dimethylaminopyridine (DMAP) was used as catalyst of the coupling reaction. The resulting PLA/PEG multiblock copolymers were characterized by various analytical techniques such as IR, 1H NMR, SEC, and DSC. Sol-gel transition properties of the multiblock copolymers were investigated by mechanical rheology. The data showed that the sol-gel transition temperature and the transition modulus increased with increasing molecular weight and the solution concentration of the multiblock copolymers. Variation of storage modulus (G,) and loss modulus (G,) as a function of temperature for a 20% sample of MB3. [source] Influence of Short-Chain Branching of Polyethylenes on the Temperature Dependence of Rheological Properties in ShearMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 22 2007Florian J. Stadler Abstract This contribution describes the influence of short-chain branching on the temperature dependence of rheological properties of polyethylene (PE) melts in shear. The materials investigated are linear and short-chain branched, metallocene-catalyzed PEs of narrow molecular mass distribution. The linear viscoelastic properties are determined by dynamic-mechanical analysis. Short-chain branching (SCB) leads to an increase of the flow activation energy. The activation energy was found to increase linearly with rising weight comonomer content. [source] Effect of Reaction Conditions and Catalyst Design on the Rheological Properties of Polyolefins Produced in Gas-Phase Olefin Polymerization ReactorsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 9 2008P. Pladis Abstract A model is developed to predict the viscoelastic behavior of polyolefins produced in catalytic polymerization reactors. The approach is based on the solution of different sub-models (e.g., a kinetic model, a single particle model, a macroscopic reactor model and a rheological model). From the calculated rheological curve, the polymer melt index is determined. The ability of the proposed model to predict the viscoelastic behavior of linear polymer melts quantitatively is examined for the operation of a catalytic olefin polymerization cascade-loop reactor process. In addition, the transient rheological properties of polyolefins produced in a Ziegler-Natta gas-phase olefin polymerization fluidized-bed reactor are calculated. [source] Evolution of Culture Broth Rheological Properties during Propagation of the Entomopathogenic Nematode Steinernemacarpocapsae, in Submerged Monoxenic CultureBIOTECHNOLOGY PROGRESS, Issue 2 2003Norberto Chavarría-Hernández This article presents the evolution of culture broth rheological properties during monoxenic cultures of Steinernema carpocapsaein cylindrical bottles agitated orbitally. Rheological properties were evaluated in simple-shear flow conditions and were well-modeled by the Ostwald-de Waele model. Rheological properties varied from slightly dilatant, n= 1.2 (,), to moderately pseudoplastic flow behavior, n= 0.6 (,). Nematode concentrations increased from 750 ± 190 to 130 900 ± 6900 nematodes/mL, and the apparent viscosity (,a) evolved from 4.5 ± 0.7 to 46.6 ± 3.2 mPa·s during the fermentations. Rheological behavior did not appear to be strongly influenced by nematode number and/or its stage of development; however, the release of substances from the decomposition of nematode cadavers appeared to be of great importance. Among the different developmental stages of the nematodes, only juveniles of the first stage (J1) were highly susceptible to the shearing conditions tested (shear stress, ,r,, from 0.9 to 3.5 Pa during periods of 80,100 min), resulting in the viability loss of 85% of J1 nematodes. [source] Rheological Properties of Fractal Deformation in Multilayer FoldsACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2009Guiting HOU Abstract: The fractal dimensions of folds are related to layer thickness and viscosity of the multilayer. This paper discusses how the thickness, viscosity, and anisotropic degree affect the rheological deformation of fractal folds in multilayers. The number of layers, their thicknesses, viscosities, and anisotropic degree of multilayers cooperate to affect the rheological deformation of folds, which is not controlled by a single rheological factor. A greater anisotropic degree of multilayers is favorable to develop the more complex and disharmonious fractal folds. [source] Rheological properties of magnetic fluids and their microstructural backgroundGAMM - MITTEILUNGEN, Issue 1 2007S. Odenbach Abstract Beyond the changes exerted by magnetic fields on the flows and properties of suspensions of magnetic nanoparticles, the change of their viscous behavior attracts ongoing research interest since nearly four decades. Within this contribution we'll review the general rheological features of ferrofluids and will present theoretical explanations on microstructural basis providing an insight in the mechanisms leading to a magnetic field dependence of ferrofluid's rheology. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Rheological properties and biocompatibility of endodontic sealersINTERNATIONAL ENDODONTIC JOURNAL, Issue 8 2003A. E. Kaplan No abstract is available for this article. [source] Mexican Queso Chihuahua: rheology of fresh cheese,INTERNATIONAL JOURNAL OF DAIRY TECHNOLOGY, Issue 1 2007DIANE L VAN HEKKEN Rheological properties of fresh Queso Chihuahua made from raw milk (RM) or pasteurized milk (PM) were characterized using texture profile, torsion and small amplitude oscillatory shear analyses. Although the rheological properties varied significantly among the different brands with overlapping ranges for the individual RM and PM cheese brands, overall the PM cheeses were harder, chewier and more cohesive but had lower viscoelastic values than the RM cheeses. Establishing the rheological properties of Mexican Queso Chihuahua increases our understanding of the quality traits of Hispanic-style cheeses and provides a foundation for maintaining the traditional texture of the cheese. [source] Physicochemical properties of low-fat and full-fat Cheddar cheesesINTERNATIONAL JOURNAL OF DAIRY TECHNOLOGY, Issue 3 2006E KÜÇÜKÖNER Low-fat (6% fat) and full-fat (32% fat) Cheddar cheese was manufactured and aged up to 6,9 months at 5°C. The objective was to study the impact of fat on the physicochemical properties of Cheddar cheese. Total soluble nitrogen (TSN) and protein nitrogen (TPSN) in aqueous extracts were determined by the Kjeldahl method. The peptide content of each cheese was determined with reverse phase chromatography (RPC). Low-fat Cheddar (LFC) had a markedly higher peptide content than full-fat Cheddar (FFC). The overall peptide quantity increased with age with a marked increase in hydrophobic peptide content. Rheological properties were determined using an Instron Universal Testing Machine. LFC had significantly higher stress values, indicating hard and rubbery texture, than FFC. Furthermore, LFC had lower strain values, indicating crumbliness. [source] | |||||||||||||||||||||||||