Solid-state rheological properties

At service temperature and frequency, the solid-state rheological properties of a TPE and a conventional rubber are similar, although at large strains the former will generally have some permanent set, while the latter will not. Only by changing the temperature and/or the frequency do substantial differences between the two emerge. If the temperature is lowered or the frequency raised, the qualitative response of the two materials is still very similar. Both materials become more resistant to stress until a temperature is reached that corresponds to the Eg of the soft segment in a TPE or the rubbery matrix in a conventional... 

Rheological studies explore the flow of a material as an external force acts upon it. This flow depends not only on the magnitude and directionality of the external force, but also on the molecular composition and structure of the material that experiences the force. In this chapter, we will focus on the flow behavior of molten polymers, as it relates to their molecular structure. It is important to note that the molecular characteristics that determine a molten polymer s behavior also define the polymer s solid state behavior. Therefore, many of the concepts introduced in this chapter will reappear in Chapter 8, Solid State Properties of Polymers., ... 

Blends of ethylene-vinyl acetate (EVA) copolymer with metallocene-catalysed elastomeric ethylene-alpha-olefin copolymer were investigated and were found to be immiscible in the melt and solid state but mechanically compatible. The morphology (SEM), thermal (DSC), rheological (viscosity), mechanical (including tensile, shear thinning and elastic behaviour) and optical properties of EVA-rich and ethylene-alpha-olefin copolymer-rich blends were studied and the results are discussed in terms of processibility in film applications. 24 refs. 

Electrorheological (ER) fluids are materials whose rheological properties (viscosity, yield stress, shear modulus, etc.) can be readily controlled using an external electric field. For example, in some cases, they can switch from a liquid-like material to a solid-like material within a millisecond with the aid of an electric field, by means of the so-called ER effect.1617 The unique feature of the ER effect is that ER fluids can reversibly and continuously change from a liquid state to a solid state. ER fluid research is focused mainly on the automotive and robotics industry as electrical and mechanical interfaces for applications such as clutches, brakes, damping devices, fuel injection, and hydraulic valves. However, more recently, there is growing... 

This chapter deals almost exclusively with neat, or pure, diblock copolymer melts. Polymer blends are discussed in Chapter 9, micellar solutions in Chapter 12, and stabilized suspensions in Chapter 6. In the following, Section 13.2 briefly reviews the thermodynamics of block copolymers, and Section 13.3 describes the rheological properties and flow alignment of lamellae, cylinders, and sphere-forming mesophases of block copolymers. More thorough reviews of the thermodynamics and dynamics of block copolymers in the liquid state have been written by Bates and Fredrickson (1990 Fredrickson and Bates 1996). The processing of block copolymers and mechanical properties of the solid-state structures formed by them are covered in Folkes (1985). Biological applications are discussed in Alexandridis (1996). 

In amorphous state, solid polymers retain the disorder characteristic for liquids, except that the molecular movement in amorphous solid state is restrained. The movement of one molecule versus the other is absent, and some typical liquid properties such as flow are absent. At low stress, polymers display elastic properties, reverting to a certain extent to the initial shape in a relaxation process. However, they can be irreversibly deformed upon application of appropriate force. The deformation and flow of polymers is very important for practical purposes and is studied by a branch of science known as rheology (see e.g. [1]). The combination of mechanical force and increased temperature are commonly applied for polymer molding for their practical applications. The polymers that can be made to soften and take a desired shape by the application of heat and pressure are known as thermoplasts, and most linear polymers have thermoplastic properties. 

The attention paid to the polymer solid state is minimized in favour of the melt and in this chapter the static properties of the polymer are considered, i.e. properties in the absence of an external stress as is required for a consideration of the rheological properties. This is addressed in detail in Chapter 3. The treatment of the melt as the basic system for processing introduces a simplification both in the physics and in the chemistry of the system. In the treatment of melts, the polymer chain experiences a mean field of other nearby chains. This is not the situation in dilute or semi-dilute solutions, where density fluctuations in expanded chains must be addressed. In a similar way the chemical reactions which occur on processing in the melt may be treated through a set of homogeneous reactions, unlike the highly heterogeneous and diffusion-controlled chemical reactions in the solid state. 

This result may, by a similar argument, be extended to the interpenetration of chains as random coils in the amorphous solid state. These results will be of importance when the rheological properties of the melt through to the developing solid are considered in Chapters 2 and 3. 

The two main rheological properties of a suspension are the yield stress and the viscosity. Yield stress determines when the system becomes a fluid state and when is in a solid state, whereas viscosity determines the ability to flow. In this section, we start with the viscosity measurement. Although one can extract the yield stress from the complete viscosity-shear rate curve, it is helpful to measure the yield stress directly as well. The dynamic and transient measurements are also important for concentrated suspensions. However, because these two types of measurements can be blended into the measurements of the two main rheological properties with some modifications to the measuring instrument, we refer to their measurements only briefly when it is relevant to the discussion. 

ATER-SOLUBLE POLYMERS (WSPs) are an important class of industrial polymers. They have many applications in solution and in the solid state. In solution, they are widely used as thickeners to control the rheology of various water-based formulations, such as latex paints, drilling muds, foods, cosmetics, and building materials. Chemically modified natural polysaccharides such as starch, cellulose, and guar are a large class of commercial water-soluble polymers. The appropriate chemical modification of these polysaccharides can lead to the modified solution properties needed for specific applications. 

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