Viscoelastic liquids, blending

The liquid-in-liquid systems can be divided into three categories those in which both liquids are Newtonian, those in which both phases are viscoelastic, and systems comprising one Newtonian and one viscoelastic liquid. The first of these categories covers emulsions, E, the second polymer blends, B, and the third undefined class of systems is usually used as models, M, to gain an insight into the effects of elasticity on the flow and morphology. Some polymer blends may also be classified as M. 

While the Choi and Schowalter [113] theory is fundamental in understanding the rheological behavior of Newtonian emulsions under steady-state flow, the Palierne equation [126], Eq. (2.23), and its numerous modifleations is the preferred model for the dynamic behavior of viscoelastic liquids under small oscillatory deformation. Thus, the linear viscoelastic behavior of such blends as PS with PMMA, PDMS with PEG, and PS with PEMA (poly(ethyl methacrylate))at <0.15 followed Palierne s equation [129]. From the single model parameter, R = R/vu, the extracted interfacial tension coefficient was in good agreement with the value measured directly. However, the theory (developed for dilute emulsions) fails at concentrations above the percolation limit, 0 > (p rc 0.19 0.09. 

Graebling, D., Muller, R., and Palierne, J.F. (1993) Linear viscoelastic behavior of some incompatible polymer blends in the melt interpretation of data with a model of emulsion of viscoelastic liquids. Macromolecules. 26 (2), 320-329. 

The concentration dependence of blends viscosity (at constant T and additivity rule. In rj = S<(>j In Hj, as showing a positive deviation, PDB, negative, NDB, or mixed, PNDB or NPDB. Treating blends as emulsions of viscoelastic liquids, leads to prediction of PDB (found in 60% of blends). The mechanism that explains NDB is the interlayer slip, caused by the thermod3mamically... 

Where, d is the particle diameter, v is the interfacial tension, and (T is the stress applied on the particle. The capillary number describes the balance between two simultaneous stresses such as the deforming and restoring stresses acting simultaneously on the droplet. However, this treatment is applicable to Newtonian liquids. Anyway, the general trend is expected to be applicable for viscoelastic material. In the case of viscoelastic polymer blend the deviation is expected as it is no more Newtonian fluid. The strategy for getting microfibrills is to have a elastomer as the matrix... 

Many of the new plastics, blends, and material systems require special, enhanced processing features or techniques to be successfully injection molded. The associated materials evolution has resulted in new plastics or grades, many of which are more viscoelastic. That is, they exhibit greater melt elasticity. The advanced molding technology has started to address the coupling of viscoelastic material responses with the process parameters. This requires an understanding of plastics as viscoelastic fluids, rather than as purely viscous liquids, as is commonly held... 

This formula is crude, and it does not account for differences in shear rates between the droplet and the medium (which are large when the viscosity ratio differs greatly from unity). Nevertheless, because of the shear-rate-dependence of, Eq. (9-22) can predict a.minimum in droplet size as a function of shear rate that is observed in some cases (Sundararaj and Macosko 1995 Plochocki et al. 1990 Favis and Chalifoux 1987). Viscoelastic forces have indeed been shown to suppress the breakup of thin liquid filaments that would otherwise rapidly occur via Rayleigh s instability (Goldin et al. 1969 Hoyt and Taylor 1977 Bousfield et al. 1986). Elongated filaments, for example, are observed in polymer blends (Sondergaard... 

In the range of frequencies low enough that the interfacial terms become important, one can usually assume that both components of the blend are in their terminal regimes, and thus behave as Newtonian liquids. Following this reasoning, Gramespacher and Meissner (1992) divided the linear viscoelastic response of a blend of polystyrene (PS) and poly(methylmethacrylate) (PMMA) into bulk and interfacial terms, as in Eq. (9-35). The interfacial contributions were taken from the Choi-Schowalter theory for Newtonian liquids. Eq. f9-37h with ju, T], and Xj from Table 9-1. while the bulk contributions were obtained from Eq. (9-41), With these expressions for G ui and Gramespacher and... 

This book is concerned mainly with the study of the viscoelastic response of isotropic macromolecular systems to mechanical force fields. Owing to diverse influences on the viscoelastic behavior in multiphase systems (e.g., changes in morphology and interfaces by action of the force fields, interactions between phases, etc.), it is difficult to relate the measured rheological functions to the intrinsic physical properties of the systems and, as a result, the viscoelastic behavior of polymer blends and liquid crystals is not addressed in this book. 

Dynamic mechanical properties of all pure components and blends were measured as a function of percent strain and indicated a linear viscoelastic region up to approximately 30-35 percent. Therefore, all rheological experiments were conducted at a strain rate of 20 percent. In cases where thermal degradation occurred (as seen in time sweep), the heating chamber was continuously purged with liquid nitrogen. Frequency sweeps, and in some cases frequency-temperature sweeps, were performed on all pure components and blends. 

The linear viscoelastic properties in the melt state of highly grafted polymers on spherical silica nanoparticles are probed using linear dynamic oscillatory measurements and linear stress relaxation measurements. While the pure silica tethered polymer nanocomposite exhibits solid-like response, the addition of a matched molecular weight free matrix homopolymer chains to this hybrid material, initially lowers the modulus and later changes the viscoelastic response to that of a liquid. These results are consistent with the breakdown of the ordered mesoscale structure, characteristic of the pure hybrid and the high hybrid concentration blends, by the addition of homopolymers with matched molecular weights. 

Blending of free homopolymer molecules to the polymer tethered silica hybrid systematically alters the viscoelastic response and most clearly observed in the low-frequency response of G and The low frequency plateau value of G decreases with increasing homopolymer content and liquid-like behavior is observed for the blend with 20% silica hybrid material. This is also manifested as a low-frequency Newtonian type behavior for the complex viscosity, p, which becomes independent of frequency for the 20 % silica hybrid blend. On the other hand, the viscosity for the blends with higher hybrid concentration demonstrated a strong power-law behavior at low frequencies, consistent with the solid-like modulus behavior described in Figure 3a. 

By contrast with polymer blends (see Part 7.5.1.), emulsions are prepared by carefully designing the interface system and by sequential addition of ingredients. Both elements are essential when 96 vol% of one liquid must be dispersed in 4 vol% of another. If, due to interactions of emulsifiers, the continuous phase becomes viscoelastic, the emulsion has high consistency or a body. There is gradual passage of structures, from rotating doublets in dilute systems, to entrapment of the dispersed phase in a continuous network of interacting interfaces. Consequently, emulsions can show Newtonian character as well as a complex thixotropic and viscoelastic one [Nielsen, 1977]. 

E. Shiva Kumar, C. Das, K. Banik, and G. Mennig. Viscoelastic properties of in situ composite based on ethylene acrylic elastomer (AEM) and liquid crystalline polymer (LCP) blend. Compos. Sci. Tech., 67(6) 1202-1209, May 2007. 

Shivakumar E, Das C, Segal E, Narkis M. Viscoelastic properties of ternary in situ elastomer composites based on fluorocarbon, acrylic elastomers and thermotropic liquid crystalline polymer blends. Polymer 2(X)5 46(10) 3363-71. 

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