Hard matter Polymers

Class III includes rigid macromolecules. They stay only in the solid states for reserving the integrity of chemical bonds. Examples of this class include metals, oxides, salts, ceramics, silicon glasses, diamond, graphite, and some conductive polymers without any solvent or melting point. The class of rigid macromolecules corresponds to the hard matter defined above. 

Polymer gels differ in various ways from hard solid polymer materials. The polymer chains in the gel are usually considered to be chemically or physically cross-linked and to form a three-dimensional network structure. For instance, polymer gel is usually a matter swollen with its good solvent, and the characteristics are diversified from a nearly solid polymer almost to a solution with very low polymer content but still maintaining its shape by itself. This extreme diversity in physical properties widens the function of the gel (see Fig. 2.4). 

Such transformations have been extensively studied in quenched steels, but they can also be found in nonferrous alloys, ceramics, minerals, and polymers. They have been studied mainly for technical reasons, since the transformed material often has useful mechanical properties (hard, stiff, high damping (internal friction), shape memory). Martensitic transformations can occur at rather low temperature ( 100 K) where diffusional jumps of atoms are definitely frozen, but also at much higher temperature. Since they occur without transport of matter, they are not of central interest to solid state kinetics. However, in view of the crystallographic as well as the elastic and even plastic implications, diffusionless transformations may inform us about the principles involved in the structural part of heterogeneous solid state reactions, and for this reason we will discuss them. 

Let s designate a force such as stirring or spreading a shear force. By shearing we mean forcing the molecules to slide past each other. No matter how hard we stir a pot of water or a jar of honey at constant temperature, the viscosity remains the same because both are Newtonian liquids. But what happens when we stir some polymer solutions It depends. Not all of the examples we discuss below are true solutions. So we ll use the broader term fluid. ... 

The study of phase transitions has played a central role in the study of condensed matter. Since the first applications of molecular simulations, which provided some of the first evidence in support of a freezing transition in hard-sphere systems, to contemporary research on complex systems, including polymers, proteins, or liquid crystals, to name a few, molecular simulations are increasingly providing a standard against which to measure the validity of theoretical predictions or phenomenological explanations of experimentally observed phenomena. 

Ferritins can store excess iron and release it when required for cellular processes. In addition, neuromelanin (NM), which is an organic polymer consisting of dihydroxyindole and benzothiazine units which are products of dopamine metabolism, is also present and is able to bind a number of metals, e.g., copper and iron. In oligodendrocytes, iron is bound to both H- and L-chain ferritin, in microglia to L-ferritin, while neurons contain mostly neuromelanin. In contrast, astrocytes contain hardly any ferritin. As to the movement of iron between different brain regions, this in the main remains unclear. It is thought that transferrin and ferritin may be important, since mRNA receptors for these iron proteins are detectable in grey matter and white matter, respectively. The fate of non-transferrin-bound iron, which may cross the BBB, remains unclear. 

Tonic interactions in macromolecules represent simultaneously one of the oldest and one of the most recent areas of activity in modem polymer science. While on the one hand polyelectrolyte solution studies have been pursued in a host of laboratories for decades, the study of the bulk properties of ionomers dates back hardly more than ten years ago— as a matter of fact the word ionomer came into common use only about a decade ago with the advent of the first commercial material of this type based on ethylene. Since that time, that aspect of the field has grown profoundly, both in regard to bulk investigations as well as studies in nonaqueous solutions, as is evidenced by the periodic symposia in the field, the recently initiated Gordon Conference, and the appearance of two books dealing primarily with bulk properties. 

---