摘要:

Steady flow and dynamic viscoelastic properties of concentrated aqueous disperse systems of colloidal silica spheres (diameter 8, 15, and 45 nm) have been measured in the deionized (salt‐free) state and in the presence of added salt NaCl. In the deionized state, the disperse system of the particle of 45 nm diameter shows high viscosity and typical so‐called yield stress, however, it shows Newtonian flow at extremely low shear rate. On the other hand, the system shows low viscosity and Newtonian flow in the ionized state. The transition from high viscosity to low viscosity state is very sharp. The deionized system shows nonlinear dynamic viscoelasticity even at strains as small as0.1∼0.2%.The disperse systems of smaller particle show Newtonian flow, irrespectively, at the deionized and the ionized states. The change in viscosity between the two states is very small. These results can be explained by the order‐disorder transition of colloidal systems, the effect of the particle size, and the Debye screening length.

ISSN:0148-6055    

DOI:10.1122/1.550019

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

From the rheologic point of view, the freezing, freeze‐drying, and pasteurization of a type of gazpacho (mixture of 86.0% tomato, 9.4% olive oil, 2.2% vinegar, 1.6% salt, and 0.8% garlic) are evaluated. Using a rotary viscometer, experimental data of shear stress versus shear rate and shear stress versus time were obtained. The values of the yield stress and the consistency index of the products are in the order: fresh, pasteurized, frozen, and freeze‐dried. The values of the yield stress vary between68.9×10−2and14.3×10−2 Paand those of the consistency index between15.0×10−2and6.0×10−2.The values of the flow behavior index vary between 0.53 for the fresh product and 0.67 for the freeze‐dried product in the outward run; in the return run, they vary between 0.54 for the fresh and pasteurized products and 0.66 for the freeze‐dried product. The values of the time‐dependent parameters of the two proposed equations indicate that the product which deviates most from the fresh product is the frozen product and the least deviant is the pasteurized product. The deviations of the values of these parameters, with respect to the fresh product, vary between −54 and −76% and between 16 and −30% for the two proposed models, respectively.

ISSN:0148-6055    

DOI:10.1122/1.550020

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

The generalized convective Maxwell fluid with variable coefficients (GCMFVC) is proposed and discussed. This model eliminates the drawbacks of the generalized convected Maxwell fluid (GCMF) in steady shear flow. The performance of the model proposed is compared with rheometic data of nine fluid samples reported in the literature. Quantitative predictions of the non‐Newtonian viscosity and primary normal stress difference are presented.

ISSN:0148-6055    

DOI:10.1122/1.550021

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

The outline of a model is presented to depict the entanglement states of polymers. Polymer melts are regarded in the model as composed of two components. Free macromolecular chains form the first component and the network of the entangled macromolecular chains the second. The state variables chosen to describe the internal structure of the polymer melt are: two conformational tensors (each describing one component) and another scalar that represents the relative proportion of each component (i.e., related to the entanglement density). The equations governing the time evolution of the state variables and the corresponding formula for the extra stress tensor are suggested with the help of recently developed diffusion‐convection equations. The model provides a convenient framework for the study of changes in the entanglement structure due both to different types of preparation of the polymers and to flow. Rheological data for two types of polyolefins either modified or unmodified are used to make preliminary assessment of the model.

ISSN:0148-6055    

DOI:10.1122/1.550061

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

The steady‐shear rheological properties of four submicron sterically stabilized silica dispersions differing in particle size were measured. The high‐ and low shear limiting viscosities were found to be a function of the volume fraction only and the volume fraction at which the viscosity diverges was found to beφm=0.63±0.02in the low shear limit andφm=0.71±0.02in the high shear limit, independent of particle size. The shear‐thinning behavior scales in the Peclet number. At higher volume fractions, the shear‐thinning transition shifts to a lower Peclet number. The time scale on which the shear‐thinning transition takes place is comparable to the time scale of short‐time self‐diffusion, that isDsshort/a2and relates to the structural changes in the dispersion which were observed in an earlier rheo‐optical study.

ISSN:0148-6055    

DOI:10.1122/1.550062

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

Sensory perception of mechanical attributes by humans is frequently based on information generated during deformation of the assessed object with the relatively soft fingertips or the tongue. The mechanical sensitivity of a testing system, in which the machines own deformability is considerable relative to that of the specimen, depends on the deformation pattern of both machine and specimen as well as the applied force. The mechanical sensitivity of such a system is constant and force independent if both have the same compressibility. If the machine is compressible and the specimen yielding the sensitivity can be larger than unity, depending on the relative rigidity of the machine and the magnitude of the applied force. There are also situations where the mechanical sensitivity is negative which means that the resistance of the machine‐specimen array decreases while that of the tested object increases. Under most circumstances, however, compressibility of the machine increases the mechanical sensitivity of the system within the range between zero and unity, as demonstrated with experimental data of a human finger and a variety of foods.

ISSN:0148-6055    

DOI:10.1122/1.550022

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

The viscoelastic properties of 30 wt% solutions of styrene(S)‐butadiene(B) radial (star) block copolymers in dibutyl phthalate (DBP) have been measured to investigate the effect of temperature. Block structure used was(S—B—)mand(B—S—)n,wheremandnare about 5. The solvent, dibutyl phthalate (DBP), is a good solvent for the PS block and a poor solvent for the PB block. The temperature dependences of the storage modulusG′and loss modulusG″for the solutions exhibit a rheological transition atTc=66∼68°C.On raising the temperature,G′decreases remarkably at the temperatures and correspondinglyG″jumps up almost discontinuously. On lowering the temperature,G′andG″show the apparent hysteresis behavior caused by slow kinetics of phase separation and values ofG′andG″return to the original levels. When the temperature is lower than the transition temperatureTc,the measuredG′is higher thanG″,and whenT>Tc,G″>G′.These results suggest that the rheological transition atTcis associated with phase transition between a liquid with domain structures and a homogeneous solution. The rheological transition temperature coincides with the temperature at which differential scanning calorimetry (DSC) heating curves for the samples show an endothermic peak. According to the rheological behavior investigated in this study, it was found that the samples re‐form the original domain structure after 50 min at 60°C.

ISSN:0148-6055    

DOI:10.1122/1.550023

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

Linear viscoelastic dynamic moduli of two‐phase PP/PA6 blends in the molten state have been measured as a function of frequency in a cone and plate rheometer. With respect to the PP and PA6 components, blends are characterized by high values of the storage modulus at low frequencies and long relaxation times. A parallel has been drawn between these results and morphological observations of sheared specimens showing that the time required for deformed dispersed domains to revert to their spherical shape is of the same order of magnitude as mechanical relaxation times. A model for undiluted emulsions of Newtonian liquids has been used to account for the variations of dynamic moduli in the terminal zone. In this frequency range, the rheological behavior is directly related to a few physically significant parameters such as zero‐shear viscosity of phases, dispersed particle size, and surface tension between phases.

ISSN:0148-6055    

DOI:10.1122/1.550024

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

Constitutive relations are formulated for a class of incompressible viscoelastic fluids for which internal structural changes occur at a rate that is influenced by the history of the strain. For the materials considered, the contribution to the stress at timetmade by the strain at an earlier time τ is a function of that strain, the true elapsed timet−τ,and a quantityσ(t,τ)that can be interpreted as the elapsed time measured by a clock whose rate of advance, because it is tied to the rate of structural change, is affected by the history of the strain. The functional relating∂σ(t,τ)/∂tto the history of the strain up to timetis assumed to have the same domain and a structure similar to that relating stress to strain history. The present theory reduces to the theory of BKZ fluids in the (extreme) special case in whichσ(t,τ)≡t−τ,in other words, in which∂σ(t,τ)/∂t≡1.It is shown that there is a sense in which constitutive relations recently found to account well for observed discrepancies between experimental observations and predictions of the BKZ theory can be considered first‐order approximations to the relations formulated here.

ISSN:0148-6055    

DOI:10.1122/1.550025

出版商:The Society of Rheology    

年代:1989

数据来源: AIP

摘要:

Experiments measuring the birefringence following the inception of a steady shearing flow were conducted on a series of concentrated polyisoprene solutions. The steady‐state shear stress was also measured in a mechanical rheometer. The data obtained from the two experiments confirmed that the birefringence and stress were linearly related (stress‐optical law) over a range of shear rates that extended far into the non‐Newtonian region. Interesting nonlinear effects were also observed during the transient response at high shear rates. Both the shear stress and the first normal stress pass through maximums before reaching their steady‐state values. A maximum in the normal stress is not predicted by the original Doi‐Edwards model but a modification of their theory which includes chain stretching is in qualitative agreement with our results.

ISSN:0148-6055    

DOI:10.1122/1.550026

出版商:The Society of Rheology    

年代:1989

数据来源: AIP