Behaviors, rheological

The flow of polymer melts in extruders, injection molding machines, and pipes with the same cross section is mostly shear flow, which can be represented by the power law equation  

The current studies of whisker materials in China are focused mostly on the mechanical properties of polymer composite systems, and there is less research on rheology 

From Table 4.4 we can see that the introduction of filler material Increases the non-Newtonian property of melts, and 

Filler Ratio of Matrix to Filler Non-Newtonian Factor (n) Correlation Coefficients (R) 

The addition of fillers importantly influences melt viscosity and is mainly reflected in the following aspects. 

The following two sections discuss the effects of different solution properties and operational conditions on the stracture (especially, the diameter) of electros-pun polymer nanofibers. Many carbon, ceramic, metal and composite nanofibers are prepared from solutions that contain polymers, and hence the fundamental knowledge covered in the following sections also gives insight to the stractwe control of these nanofibers. 

Solution rheology has a significant influence on the diameter of electrospun nano-libers for example, McKee at al. studied the fiber formation process of electrospun linear and branched polyester and foimd that fiber diameter (D) increases with the zero shear rate viscosity ( / ) of the solution by  

In addition to polymer molecular weight and polymer concentration, mar other approaches can be used to adjust the viscosity of electrospinning solntions. For example, adding nanoparticle fillers and salt additives are two commonly used methods for adjusting the solution viscosity. These two approaches are discussed in sections 12.3.4 and 12.3.5, respectively. 

Besides viscosity, it also is found that viscoelasticity particularly relaxation time, plays a significant role in determining the electrospirmabihty of polymer solutions and the diameter of the resultant nanofibers. 

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Greases Mechanical and rheological behavior and its persistence Consistency and viscosity Mechanical stability Oxidation resistance... 

These normal stresses are more pronounced for polymers with a very broad molecular weight distribution. Viscosities and viscoelastic behavior decrease with increasing temperature. In some cases a marked viscosity decrease with time is observed in solutions stored at constant temperature and 2ero shear. The decrease may be due to changes in polymer conformation. The rheological behavior of pure polyacrylamides over wide concentration ranges has been reviewed (5). 

Although aH these models provide a description of the rheological behavior of very dry foams, they do not adequately describe the behavior of foams that have more fluid in them. The shear modulus of wet foams must ultimately go to zero as the volume fraction of the bubbles decreases. The foam only attains a solid-like behavior when the bubbles are packed at a sufficiently large volume fraction that they begin to deform. In fact, it is the additional energy of the bubbles caused by their deformation that must lead to the development of a shear modulus. However, exactly how this modulus develops, and its dependence on the volume fraction of gas, is not fuHy understood. 

Slurry Viscosity. Viscosities of magnesium hydroxide slurries are determined by the Brookfield Viscometer in which viscosity is measured using various combinations of spindles and spindle speeds, or other common methods of viscometry. Viscosity decreases with increasing rate of shear. Fluids, such as magnesium hydroxide slurry, that exhibit this type of rheological behavior are termed pseudoplastic. The viscosities obtained can be correlated with product or process parameters. Details of viscosity deterrnination for slurries are well covered in the Hterature (85,86). 

Viscous Hquids are classified based on their rheological behavior characterized by the relationship of shear stress with shear rate. Eor Newtonian Hquids, the viscosity represented by the ratio of shear stress to shear rate is independent of shear rate, whereas non-Newtonian Hquid viscosity changes with shear rate. Non-Newtonian Hquids are further divided into three categories time-independent, time-dependent, and viscoelastic. A detailed discussion of these rheologically complex Hquids is given elsewhere (see Rheological measurements). 

Flow Models. Many flow models have been proposed (10,12), which are useful for the treatment of experimental data or for describing flow behavior (Table 1). However, it is likely that no given model fits the rheological behavior of a material over an extended shear rate range. Nevertheless, these models are useful for summarizing rheological data and are frequently encountered in the Hterature. 

Dimensions. Most coUoids have aU three dimensions within the size range - 100 nm to 5 nm. If only two dimensions (fibriUar geometry) or one dimension (laminar geometry) exist in this range, unique properties of the high surface area portion of the material may stiU be observed and even dominate the overaU character of a system (21). The non-Newtonian rheological behavior of fibriUar and laminar clay suspensions, the reactivity of catalysts, and the critical magnetic properties of multifilamentary superconductors are examples of the numerous systems that are ultimately controUed by such coUoidal materials. 

Block (Star) Arrangement. The known star polymers, like their linear counterparts, exhibit microphase separation. In general, they exhibit higher viscosities in the melt than their analogous linear materials. Their rheological behavior is reminiscent of network materials rather than linear block copolymers (58). Although they have been used as compatibiUzers in polymer blends, they are not as effective at property enhancements as linear diblocks... 

An indication of whether block or copolymer architecture is AB, ABA, or ( AB ) n often be seen in its rheological behavior. For example,... 

For fast-setthug slurries, ensuring conveyance is usually the key design issue while pressure drop is somewhat less important. For nonsettling slurries conveyance is not an issue, because the particles do not separate from the liquid. Here, viscous and rheological behavior, which control pressure drop, take on critical importance. 

M. Schoen. Computer simulations of the rheological behavior of confined films. Mol Simul 77 369-419, 1996. 

The structure formation in an ER fluid was simulated [99]. The characteristic parameter is the ratio of the Brownian force to the dipolar force. Over a wide range of this ratio there is rapid chain formation followed by aggregation of chains into thick columns with a body-centered tetragonal structure observed. Above a threshold of the intensity of an external ahgn-ing field, condensation of the particles happens [100]. This effect has also been studied for MR fluids [101]. The rheological behavior of ER fluids [102] depends on the structure formed chainlike, shear-string, or liquid. Coexistence in dipolar fluids in a field [103], for a Stockmayer fluid in an applied field [104], and the structure of soft-sphere dipolar fluids were investigated [105], and ferroelectric phases were found [106]. An island of vapor-liquid coexistence was found for dipolar hard spherocylinders [107]. It exists between a phase where the particles form chains of dipoles in a nose-to-tail... 

This chapter reports the results of studies on the physical, dynamic mechanical, and rheological behavior of zinc oxide neutralized m-EPDM, particularly in the presence of stearic acid and zinc stearate, with special reference to the effects of precipitated silica filler. 

The rheological behavior of the blends and composites was totally different. Addition of LCP reduced the... 

The paper contains a review with original theoretical and experimental data on the basis of the rheological behavior of gas-containing systems — thermoplastic melts — during extrusion. 

The above considerations illustrate the difficulties of trying to formulate equations descriptive of rheological behavior of polymer melts with gas bubbles. An optimistic approach to the solution of this task is contained in [60, 61]. The content of these works is revealed by their titles On the Use of the Theory of Viscoelasticity for Describing of the Behaviour of Porous Material and for the Calculation of construction... 

Linear novolac resins prepared by reacting para-alkylphenols with paraformaldehyde are of interest for adhesive tackifiers. As expected for step-growth polymerization, the molecular weights and viscosities of such oligomers prepared in one exemplary study increased as the ratio of formaldehyde to para-nonylphenol was increased from 0.32 to 1.00.21 As is usually the case, however, these reactions were not carried out to full conversion, and the measured Mn of an oligomer prepared with an equimolar phenol-to-formaldehyde ratio was 1400 g/mol. Plots of apparent shear viscosity versus shear rate of these p-nonylphenol novolac resins showed non-Newtonian rheological behavior. 

Dispersants will further disperss soil in the washing process avoiding its redeposition on fibers. Dispersants are frequently used in production of paints to avoid precipitation of pigments and to control the rheological behavior. 

The effects of different surfactants on the rheological behavior of cement-water dispersions were studied by a rotational-type viscometer. The type of... 

The rheological behavior of xylans has rarely been investigated [4,114,115]. The water-insoluble hemicellulose from the viscose process (containing > 85% xylan) was reported to form thixotropic aqueous dispersions of high... 

The rheological behavior of storage XGs was characterized by steady and dynamic shear rheometry [104,266]. Tamarind seed XG [266] showed a marked dependence of zero-shear viscosity on concentration in the semi-dilute region, which was similar to that of other stiff neutral polysaccharides, and ascribed to hyper-entanglements. In a later paper [292], the flow properties of XGs from different plant species, namely, suspension-cultured tobacco cells, apple pomace, and tamarind seed, were compared. The three XGs differed in composition and structural features (as mentioned in the former section) and... 

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