Macroscopic level, solids

When we observe chemical reactions macroscopically, we encounter three common forms, or phases, of matter solids, liquids, and gases. At the macroscopic level, solids are hard and do not change their shapes easily. When a solid is placed in a container, it retains its own shape rather than assuming that of the container. Even a powdered solid demonstrates this trait because the individual particles still retain their shape, even though the collection of them may take on the shape of the container. 

In general, heterogeneities in structural materials are often the source of mechanical failure, but specific types also provide ways to disperse energy without failure. For example, some silks, at a microscopic and macroscopic level, are able to form structures such as spherulite inclusions that will develop into elongated cavities in the solid fibers (Akai, 1998 Frische et al., 1998 Robson, 1999 Tanaka et al., 2001). Interestingly, Isobe et al. (2000), in a significant but largely overlooked paper, showed that synthetic A/ i 4o produced spherulites that had the essential features of Alzheimer s amyloid senile plaques (Kaminsky et al., 2006). 

Matter (anything that has mass and occupies space) can exist in one of three states solid, liquid, or gas. At the macroscopic level, a solid has both a definite shape and a definite volume. At the microscopic level, the particles that make up a solid are very close together and many times are restricted to a very regular framework called a crystal lattice. Molecular motion (vibrations) exists, but it is slight. 

At the macroscopic level, a solid is a substance that has both a definite volume and a definite shape. At the microscopic level, solids may be one of two types amorphous or crystalline. Amorphous solids lack extensive ordering of the particles. There is a lack of regularity of the structure. There may be small regions of order separated by large areas of disordered particles. They resemble liquids more than solids in this characteristic. Amorphous solids have no distinct melting point. They simply become softer and softer as the temperature rises. Glass, rubber, and charcoal are examples of amorphous solids. 

Recent times have seen much discussion of the choice of hydrodynamic boundary conditions that can be employed in a description of the solid-liquid interface. For some time, the no-slip approximation was deemed acceptable and has constituted something of a dogma in many fields concerned with fluid mechanics. This assumption is based on observations made at a macroscopic level, where the mean free path of the hquid being considered is much smaller... 

On a familiar, macroscopic level, for example, water can be in three distinct states, a solid (ice), a liquid (ordinary water), or a gas (steam). There can be mechanical mixtures of the three states, as of water droplets falling or floating in the air, but the solid, liquid, and gas states are quite distinct. 

The concept of polymer free volume is illustrated in Figure 2.22, which shows polymer specific volume (cm3/g) as a function of temperature. At high temperatures the polymer is in the rubbery state. Because the polymer chains do not pack perfectly, some unoccupied space—free volume—exists between the polymer chains. This free volume is over and above the space normally present between molecules in a crystal lattice free volume in a rubbery polymer results from its amorphous structure. Although this free volume is only a few percent of the total volume, it is sufficient to allow some rotation of segments of the polymer backbone at high temperatures. In this sense a rubbery polymer, although solid at the macroscopic level, has some of the characteristics of a liquid. As the temperature of the polymer decreases, the free volume also decreases. At the glass transition temperature, the free volume is reduced to a point at which the... 

Of the three states, the gaseous state is by far the best understood. For this reason, as well as the importance that gases play in anesthesia, gases merit a detailed chapter of their own. In this chapter we will explore some of the properties of solids and liquids, with only a cursory examination of gases. We will explore the structure and properties of the states of matter, both at the macroscopic level as well as the molecular level. Finally, we will examine the energy changes that accompany changes of state. 

Both the molecular template and the self-assembly techniques presented above have limited control over the final shape of the solid, since this is generally obtained in the form of a powder, fibers, or thin films. It is possible, however, to control the shape and size of solids by combining the former techniques with techniques that restrict the volume in which the synthesis takes place. The final goal is to have control over the solids at the molecular as well as macroscopic level, in order to have in a single material properties emerging from several levels of scale. Such structures are referred to as hierarchical [2, 6]. 

The interfacial structure of a solid electrode depends on various factors. The interatomic distance varies with the exposed crystallographic face and with the interaction energy between the crystallites in a polycrystalline material there are breaks in the structure and onedimensional and two-dimensional defects, such as screw dislocations, etc. Adsorption of species can be facilitated or made more difficult, and at the macroscopic level we observe the average behaviour. 

When substances are heated and cooled, many students believe that the particles do likewise (Griffiths Preston, 1992 Lee et al., 1993). This belief correlates with the view that matter is continuous without space between particles. If a solid object contracts, students who believe that the particles are in contact have no way to explain this change other than to say the particles shrink because there is no free space between particles to diminish. From a students intuitive viewpoint, it is logical to say that particles expand and contract to explain the expansion and contraction seen at the macroscopic level. The scientific view insists that increased and decreased particle motion - kinetic particle jostling that is a function of energy content - accounts for expansion and contraction (Feynman, 1994). For the scientific view to be plausible, the student must see spaces between particles. 

The properties of solids are the complex result of the molecular features, the intermolecular arrangement, and forces between the molecules as weU as physical effects at the micro- and macroscopic level. This situation is summarized in Table 7.1 and will be briefly discussed. 

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