Rheological properties of materials

Particle size and shape have a strong effect on the rheological properties of materials as well, viscosity among them. 

Many of the rheological properties of materials are determined using stress-strain measurements. 

Specializes in rheological properties of materials but has recently expanded its product line to include surface characterization mechanisms. Provides dynamic contact angle fiber tensiometer, dynamic contact angle tensiometer, and contact angle tensiometer. 

In contrast to the mechanical and rheological properties of materials, which have defined physical meanings, no such definitions exist for the psychophysical assessment of equivalent textural properties of foods. To identify material properties, or combinations of these, which are able to model sensory assessments requires a mixture of theory and experimentation. Scientific studies of food texture began during the twentieth century by the analysis of the rheological properties of liquid or semi-solid foods. In particular Kokini14 combined theoretical and experimental approaches in order to identify appropriate rheological parameters from which to derive mathematical models for textural attributes of liquid and semi-solid foods, namely, thickness, smoothness and creaminess. 

There are three main rheological properties of materials viscous flow, plastic flow, and elastic deformation. The stress deformation behavior of elastic materials is represented by a straight line through the origin. However, in this case, the... 

In addition to the amoimt of plasticizer consmned by a filler it is important to analyze the potential for interaction between a filler and a polymer. Simple consmnption of the plasticizer by a filler affects only rheological properties of material but chemical interaction may affect numerous other properties relevant for plasticizer application in specific formulation. 

The central problem of rheology is to establish the relationship between applied forces and geometrical effects induced by these forces at a point. The mathematical description of the relationship is called the constitutive equation, or the rheological equation of state. It is a model of physical reality. The recent subject of rheology has tended to establish relationships between macroscopic rheological properties of material and its micro-level structure (Tanner 2009). 

We shall deal here with rheometiy, which concerns the techniques for characterizing the rheological properties of materials. The physical principles underlying the design of rheometers are presented. Stating them here is justified for several reasons ... 

There are stili several parts of the problem that cannot be dealt with at this level. First, the viscoelastic nature of the fiow must be considered as the deformation occurs over short times and may involve a significant extensional component. Second, the rheological properties of materials that are usually processed by means of compression molding are difficult... 

Blends of NBR with other rubbers or with thermoplastic or thermosetting resins have been known for several decades. Modification by blending is undertaken to reduce costs, to improve the rheological properties of material, or to confer specific physical or chemical properties to the end product. 

It is very important, from one hand, to accept a hypothesis about the material fracture properties before physical model building because general view of TF is going to change depending on mechanical model (brittle, elasto-plastic, visco-elasto-plastic, ete.) of the material. From the other hand, it is necessary to keep in mind that the material response to loads or actions is different depending on the accepted mechanical model because rheological properties of the material determine type of response in time. The most remarkable difference can be observed between brittle materials and materials with explicit plastic properties. 

Indeed, one often observes a more or less direct relationship between the rheological properties of melts and the mechanical strength of the condensed material. This is a commonplace statement in regard of, say, stiffness, since the equations relating the viscosity of heterogeneous materials with their composition... 

Organotitanates form regular adsorbed layers on the filler surfaces. This assures a high degree of dispersibility of the solid particles of the filler, removal of moisture and air from the surfaces, a material improvement of the rheological properties of filled compositions. Also, it is possible to use much greater percentages of cheap... 

All these quantities may depend on the content and behavior of a filler and to a certain extent on the prehistory of the material. This is a specific character of rheological properties of filled polymers. 

Some of these questions have strict and unambiguous answers, in a mathematical model, to other answers are derived from extensive empirical material. The present paper will discuss the problems formulated above, but concerning only rheological properties of filled polymer melts, leaving out the discussion of specific hydrodynamic effects occurring during their flow in channels of different geometrical form. 

The existence of yield stress Y at shear strains seems to be the most typical feature of rheological properties of highly filled polymers. A formal meaing of this term is quite obvious. It means that at stresses lower than Y the material behaves like a solid, i.e. it deforms only elastically, while at stresses higher than Y, like a liquid, i.e. it can flow. At a first approximation it may be assumed that the material is not deformed at all, if stresses are lower than Y. In this sense, filled polymers behave as visco-plastic media with a low-molecular and low-viscosity dispersion medium. This analogy is not random as will be stressed below when the values of the yield stress are compared for the systems with different dispersion media. The existence of yield stress in its physical meaning must be correlated with the strength of a structure formed by the interaction between the particles of a filler. 

The fact that the appearance of a wall slip at sufficiently high shear rates is a property inwardly inherent in filled polymers or an external manifestation of these properties may be discussed, but obviously, the role of this effect during the flow of compositions with a disperse filler is great. The wall slip, beginning in the region of high shear rates, was marked many times as the effect that must be taken into account in the analysis of rheological properties of filled polymer melts [24, 25], and the appearance of a slip is initiated in the entry (transitional) zone of the channel [26]. It is quite possible that in reality not a true wall slip takes place, but the formation of a low-viscosity wall layer depleted of a filler. This is most characteristic for the systems with low-viscosity binders. From the point of view of hydrodynamics, an exact mechanism of motion of a material near the wall is immaterial, since in any case it appears as a wall slip. 

Optical and electro-optical behavior of side-chain liquid crystalline polymers are described 350-351>. The effect of flexible siloxane spacers on the phase properties and electric field effects were determined. Rheological properties of siloxane containing liquid crystalline side-chain polymers were studied as a function of shear rate and temperature 352). The effect of cooling rate on the alignment of a siloxane based side-chain liquid crystalline copolymer was investigated 353). It was shown that the dielectric relaxation behavior of the polymers varied in a systematic manner with the rate at which the material was cooled from its isotropic phase. 

Interfacial rheologic properties of different crude oil-water systems were determined in wide temperature and shear rate ranges and in the presence of inorganic electrolytes, surfactants, alkaline materials, and polymers [1056]. 

The microphase separation and the rheological properties of these materials were subsequently studied. 

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