摘要:

Semiconducting tin dioxide particles were covered with insulating layer and its effect on electrorheological (ER) properties of the suspensions was examined under oscillatory and steady shear. When the particles were coated with titanium dioxide by hydrolyzing titanium tetraisopropoxide and heat‐treated at 600 °C, the suspension in a silicone oil showed a high yield stress at an electric field of 2.0 kV mm−1. However, since the titanium dioxide layer was semiconducting, the current density was about 0.2 mA cm−2and would not be applicable to practical device. Using aluminium ion, the titanium dioxide can be doped from a semiconducting to an insulating state. The particles covered with surface layer consisting of titanium dioxide and aluminum oxide provided excellent ER fluids in water‐free systems. The coating of semiconducting particles by hydrolysis of alkoxides is very useful for surface modification of particles to improve the ER performance of suspensions.

ISSN:0148-6055    

DOI:10.1122/1.550414

出版商:The Society of Rheology    

年代:1993

数据来源: AIP

摘要:

Two series of sulfonated poly(styrene‐co‐divinyl benzene)s (SSDs), different in degree of sulfonation and in average particle size, were synthesized. The electrorheological behavior of the suspensions of these SSDs dispersed in silicone oil was investigated. Shear stress induced by application of an electric field increased with increase in the degree of sulfonation and also in particle size. The sedimentation velocity of these suspensions increased monotonically with the degree of sulfonation and the average particle size. Another series of sulfonated poly(styrene‐co‐divinyl benzene), which had sulfonated surface layer and unsulfonated core, (SSDH), was separately prepared. Suspensions of SSDH showed electrorheological effect similar to those of SSD. The use of SSDH improved the stability of the suspension.

ISSN:0148-6055    

DOI:10.1122/1.550416

出版商:The Society of Rheology    

年代:1993

数据来源: AIP

摘要:

Electrorheological (ER) effect of dispersions of anhydrous spherical particles with conductive polymer core and nonconductive thin skin formed by chemical treatment was investigated in dielectric fluids. The ER effect was also studied to particles of aluminum for comparison. It was found that shear stress enhancement of both samples depended on what types of methods were used for observation of the ER effect. The ER effect of these dispersions was stronger under ac than dc electric fields in the rotary method, but stronger under dc than ac fields in the vibration method. This is in clear distinction from the behavior of traditional ER fluids containing hydrous particles, in which the ER effect is substantially the same under either ac or dc fields in both methods, and is tentatively related to the shear employed in the measurements.

ISSN:0148-6055    

DOI:10.1122/1.550465

出版商:The Society of Rheology    

年代:1993

数据来源: AIP

摘要:

The electrorheological (ER) properties of cellulose suspensions which include nonaqueous polar materials as active additives for ER effect were studied comparing with water‐activated suspension. The nonaqueous polar materials are alcohols, amides, and amines from the viewpoints of dielectric constant and vapor pressure. The ER properties of these suspensions were measured with a cylindrical rheometer at temperatures up to 120 °C. Also storage stability at 120 °C was investigated. The nonaqueous additives were effective to activate cellulose suspension: Especially at higher temperatures, the nonaqueous additives were more effective than water was. The shear stress of the water‐activated ER fluid decreased as the temperature increased. On the contrary the shear stress of the ER fluids, which contain the nonaqueous additives, increased as the temperature increased, and became greater than that of the water‐activated ER fluid at room temperature. Furthermore the nonaqueous additives had advantages of decreasing the electric power consumption and of improving thermal stability of shear stress after the storage for 250 h at 120 °C.

ISSN:0148-6055    

DOI:10.1122/1.550419

出版商:The Society of Rheology    

年代:1993

数据来源: AIP

摘要:

It is well known that dispersed particles in electrorheological fluid (ERF) form chain‐like clusters under an electric field. Many authors consider this cluster formation to be the origin of the electrically induced shear stress τe. If the shear rate γ̇ is increased, however, the clusters should be broken into shorter segments. Is this consistent with the experimental fact that τeis roughly independent of γ̇? To answer this question, we have studied the cluster formation under shear flow by simple theory and computer simulation, which are based on the force balance between the hydrodynamic resistance and electrostatic attraction among particles. The results show that, when γ̇ is increased, the length of clusters becomes shorter in proportion to γ̇−1/2, while the stress due to the clusters remains roughly constant. This indicates that the clusters are indeed the origin of the induced stress.

ISSN:0148-6055    

DOI:10.1122/1.550420

出版商:The Society of Rheology    

年代:1993

数据来源: AIP

摘要:

There are many rheological problems in the melt spinning process. They can be classified into two categories, i.e., the problems in shearing flow and those in extensional flow. The former is concerned with extrusion of molten PET (polyethyleneterephthalate) through spinneret orifices. Bagley’s plots showing the relationship of pressure drop toL/Dof orifice were done to obtain the end correlation in the capillary flow of PET. By using this end correction values, the relaxation time of molten PET was estimated to be around 2×10−3s under some assumptions. With regard to the problems in the extensional flow three typical and important examples were shown from both experimental and theoretical aspects. (1) Fine denier filament spinning for obtaining fibers with less than about 10 μm in diameter is a challengeable theme in the meaning of a conflict with extensional flow instability, so called draw resonance phenomenon. To solve this difficulty, it can be suggested that optimal spinneret orifice design will be required for instance. (2) High speed spinning is a process of stress‐induced crystallization of PET. Dependence of spinning behaviors such as neck‐like deformation and mechanical/structural properties on PET molecular weight was investigated. Crystallization of higher molecular weight PET was found to occur at lower spinning speed compared with that of lower one. (3) Air jet melt spinning for multifilament system was investigated both theoretically and experimentally. Computation results showed a good agreement with experimental ones in terms of the stretching speed in ejector. Birefringence values of as‐spun fibers can be estimated by using computed outputs.

ISSN:0148-6055    

DOI:10.1122/1.550421

出版商:The Society of Rheology    

年代:1993

数据来源: AIP

摘要:

Dry spinning behavior of the segmented polyurethane‐urea elastometer/solvent binary system was studied theoretically and experimentally. Computer simulation was carried out by solving the partial differential equations numerically for discussing the structure and properties of as‐spun fibers. Spinning stress computed at the take‐up point was found to be useful for describing the segmental orientations and the aggregate structure of the hard segment in relation to the mechanical properties such as elastomeric character of the fibers. With increase of the spinning stress, orientation of the hard segment becomes higher. Orientation of the soft segment, however, is almost random regardless of spinning stress, resulting in the origin of the elastomeric character. Dependence of the spinning stress on the hydrogen bond concentration of urea group suggested that the aggregate structure of the hard segment was smaller when the fiber was spun at a higher spinning stress.

ISSN:0148-6055    

DOI:10.1122/1.550422

出版商:The Society of Rheology    

年代:1993

数据来源: AIP

摘要:

The flow behavior of oil‐in‐water emulsions is examined as a function of the volume fraction of dispersed drops, drop size, and viscosity ratio of internal to external phases. The results are interpreted in terms of internal circulation, deformation, and breakup of drops. At low volume fractions, the viscosity decreases with increasing shear rate and becomes constant at high shear rates. The Newtonian viscosity is independent of drop size. The viscosity in the pseudoplastic region increases with decreasing drop size. A change in drop size at constant volume fraction causes a horizontal shift in the viscosity versus shear rate curve. As the viscosity ratio decreases, the relative viscosity at a given volume fraction is reduced because hydrodynamic forces cause internal circulation which reduces the velocity perturbations outside drops. At high volume fractions where a network of thin liquid films is formed, the change in drop size leads to a vertical shift of the viscosity curve. The flow behavior in highly concentrated emulsions is governed by total interfacial area. When the deformation and breakup of drops occur at a high shear rates, the emulsions show pseudoplastic flow.

ISSN:0148-6055    

DOI:10.1122/1.550423

出版商:The Society of Rheology    

年代:1993

数据来源: AIP

摘要:

The mechanical properties of natural rubber composites filled with cellulose short fibers were investigated with respect to fiber concentration and fiber orientation. Strong anisotropy caused by the fiber orientation was observed in the mechanical properties at high fiber loading. The ultimate tensile strength in the longitudinal direction to the fiber orientation had a minimum atVf=12.5%, while the transverse strength decreased withVfvalues. The logarithmic elongation at break decreased linearly withVf, and the transverse elongation was higher than the longitudinal elongation. The modulus of the composite increased with fiber concentration, with semiempirical equationE=k/{1+[Vm/(1−Vm0.5)]} being valid for the transverse direction and the longitudinal direction at lower fiber loading. The longitudinal modulus was much higher than the transverse modulus. In order to improve adhesion between the fibers and matrix, polyallylacrylate was grafted on cellulose fibers, but grafting was ineffective on the mechanical properties of the composite. The dynamic viscoelastic properties of the natural rubber composite were also investigated. The dynamic modulus,E’, increased with increasing amounts of fiber concentration above the glass transition temperature. The loss modulus,E‘, had a peak at about −36 °C; which shifted to higher temperatures with increasing amounts of mixed fibers. The activation energy for glass transition of the composites was calculated at 198.6–228.6 kJ/mol, depending on fiber concentration for the longitudinal direction. The dynamic viscoelasticity in the transverse direction to the fiber orientation was not affected by filled fibers and the activation energy was 187.3 kJ/mol, approximately the same value as for the unfilled rubber vulcanizate.

ISSN:0148-6055    

DOI:10.1122/1.550424

出版商:The Society of Rheology    

年代:1993

数据来源: AIP

摘要:

Uniaxial and biaxial elongational flow behavior of low density polyethylene (LDPE)/polystyrene (PS) blends (LDPE/PS=2/1) with and without 5 wt. % styrene‐ethylene‐propylene block copolymer (SEP) was studied. In these blends, LDPE was the matrix phase and PS was the dispersed phase. Measurements of the uniaxial elongational viscosity η+(t,ε̇) and the biaxial elongational viscosity ηβ+(t,ε̇) were made using a Meissner‐type uniaxial elongational rheometer and a lubricated‐squeezing‐type equibiaxial rheometer, respectively. In the linear region, the relation between the transient shear viscosity η+(t) and the transient elongational viscosity, which were predicted by three‐dimensional linear Maxwell model, i.e.,EE+(t)=3η+(t) and ηB+(t)=6η+(t), did not hold well. This may be attributed to a volumetric resistance against the deformation perpendicular to the elongational direction because of the existence of PS particles. In the long‐time region, a difference of ηE+(t,ε̇) between blends with and without SEP was observed. In the case of uniaxial elongational flow, it may be presumed that a contribution of the deformation of PS domains to the elongational flow behavior has to be taken into account when the elongational strain is large.

ISSN:0148-6055    

DOI:10.1122/1.550425

出版商:The Society of Rheology    

年代:1993

数据来源: AIP