Viscoelastic behavior concentration effects

The rheological properties of a fluid interface may be characterized by four parameters surface shear viscosity and elasticity, and surface dilational viscosity and elasticity. When polymer monolayers are present at such interfaces, viscoelastic behavior has been observed (1,2), but theoretical progress has been slow. The adsorption of amphiphilic polymers at the interface in liquid emulsions stabilizes the particles mainly through osmotic pressure developed upon close approach. This has become known as steric stabilization (3,4.5). In this paper, the dynamic behavior of amphiphilic, hydrophobically modified hydroxyethyl celluloses (HM-HEC), was studied. In previous studies HM-HEC s were found to greatly reduce liquid/liquid interfacial tensions even at very low polymer concentrations, and were extremely effective emulsifiers for organic liquids in water (6). 

The effects attributed to entangling interactions, e.g., the plateau region in stress relaxation, appear most prominently at high concentrations and in melts. It is important, however, to distinguish this interaction from other types which are present at lower polymer concentrations. To make the separation properly, it is necessary to examine viscoelastic behavior at all levels of concentration, beginning at infinite dilution. 

Absorption of a solute liquid or vapor into a polymer film can profoundly affect the viscoelastic behavior of the polymer. The magnitude of this effect depends on the nature of the solute/polymer interactions and on the amount of solute absorbed. The solute/polymer interactions can range fttun simple dispersion to hydrogen-bonding and other specific interactions. The extent of absorption can be described by the partition coefficient, AT, which quantifies the thermcxlynamic distribution of the solute between two phases (K = coiKentration in polymer divided by die concentration in the liquid or vapor phase in contact with the polymer). It has long been known that acoustic wave devices can be used to probe solubility and partition coefficients (53,67). Due to the relevance of these topics to chemical sensors, more comprehensive discussions of these interaction mechanisms and the significance of the partition coefficient are included in Chapter 5. 

Brona et al [18] have tested the relationship between alginate concentration, scaffold stiffness and viscoelastic behavior mimics that of the NP. The effect of variations in scaffold stiffness had been investigated on the expression of ECM molecules specific to NP. The sample discs were prepared of various concentrations of alginate (1 6%) by two different methods i.e. diffusion and in situ gelation. They found that the alginate can mimic the viscoelastic properties of the NP and capable of preserving the biosynthetic phenotype of NP cells. 

Pokrovskii [112] demonstrated theoretically that concentrated suspensions of solid ellipsoidal bodies in a Newtonian fluid give rise to a viscoelastic behavior. He showed that for such suspensions it is possible to use the concept of transverse viscosity which expresses the effect of normal stresses and found that the transverse viscosity increases with velocity gradient. 

This chapter deals with viscoelastic behavior in the liquid state, particular emphasis being placed upon those aspects associated with the flow properties of polymer melts and concentrated solutions. The time-dependent response of polymers in the glassy state and near the glass transition, one variety of viscoelasticity, was discussed in Chapter 2. The concern in this chapter is the response at long times and for temperatures well above the glass transition. The elastic behavior of polymer networks well above the glass transition was discussed in Chapter 1. The conditions here are similar, and elastic effects may be very important in polymeric liquids, but steady-state flow can now also occur because the chains are not linked together to form a network. All the molecules have finite sizes, and, for flexible-chain polymers, the materials of interest in this chapter, the molecules have random-coil conformations at equilibrium (see Chapters 1 and 7). 

There are various types of carbon nanofillers which include carbon black, multi walled carbon nanotubes (MWCNTs), and single walled carbon nanotubes (SWCNTs) [27]. In this section the effect of these nano fillers on viscoelastic behavior is thoroughly discussed. The physicomechanical properties of conductive carbon black (CCB) filled ethylene acrylic elastomer (AEM) vulcanizates have been reported by B.P. Sahoo et al. They have discussed thoroughly about the effect carbon black concentration on the viscoelastic behavior of CCB-AEM nanocomposites with respect to temperature variation. Figure 10a, b represents the variation of storage modulus and loss modulus with temperature. It is observed that the value of storage modulus (E ) increased with increase in filler loading in the... 

In this chapter we review the solution properties of K-carrageenan and its interaction with starch and non-starch polysaccharides in aqueous media. We stress the importance of the sol-gel transition and gelation mechanism of K-carrageenan p>articularly the effect of temperature, polysaccharide concentration and external counterions on the transition and the interaction of K-carrageenan with other pwlysaccharides. Given the economic importance of K-carrageenan, we also discuss its viscoelastic behavior and microstructure as well as actual and potential applications in foods. 

In this contribution, a brirf review of selected results was presented on the elastic and viscoelastic behavior of amorphous polymer nanocomposites. The ovei-view was done in a simplified manner, in order to support its miderstaudability. Below the matrix Tg, a nanocomposite behaves like a two component system due to the low-entropy/low-mobility state of polymer matrix. Above the mati-ix Tg, the polymer chains near the nano-filler surface become perturbed in respect to their dynamics. These changes occurring on the molecular level cause severe effects observable on micro- and macroscopic levels. Due to the extensive nanofiller surface area, the filler nanoparticles are able to cause these effects even at a very low filler concentration. Interestingly, the immobilization phenomenon in polymers filled with high specific surface area fillers has already been addressed in the 60s by DiBenedetto [40], Lipatov [44,56] and others [39,43,45]. The cited authors interpreted the results properly although very poor computer simulation possibilities were available at that time. 

In the preparation and processing of ionomers, plasticizers may be added to reduce viscosity at elevated temperatures and to permit easier processing. These plasticizers have an effect, as well, on the mechanical properties, both in the rubbery state and in the glassy state these effects depend on the composition of the ionomer, the polar or nonpolar nature of the plasticizer and on the concentration. Many studies have been carried out on plasticized ionomers and on the influence of plasticizer on viscoelastic and relaxation behavior and a review of this subject has been given 119]. However, there is still relatively little information on effects of plasticizer type and concentration on specific mechanical properties of ionomers in the glassy state or solid state. 

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