Macroscopic physics

Material Properties. The properties of materials are ultimately deterrnined by the physics of their microstmcture. For engineering appHcations, however, materials are characterized by various macroscopic physical and mechanical properties. Among the former, the thermal properties of materials, including melting temperature, thermal conductivity, specific heat, and coefficient of thermal expansion, are particularly important in welding. 

Group Contribution Methods. It has been shown that many macroscopic physical properties, ie, those derived from experimental measurements of bulk solutions or substances, can be related to specific constituents of individual molecules. These constituents, or functional groups, are usually composed of commonly found combinations of atoms. One procedure for correlating functional groups to a property is as foUows. (/) A set of... 

In its more advanced aspects, kinetic theory is based upon a description of the gas in terms of the probability of a particle having certain values of coordinates and velocity, at a given time. Particle interactions are developed by the ordinary laws of mechanics, and the results of these are averaged over the probability distribution. The probability distribution function that is used for a given macroscopic physical situation is determined by means of an equation, the Boltzmann transport equation, which describes the space, velocity, and time changes of the distribution function in terms of collisions between particles. This equation is usually solved to give the distribution function in terms of certain macroscopic functions thus, the macroscopic conditions imposed upon the gas are taken into account in the probability function description of the microscopic situation. 

The theoretical methods can be divided into two fundamental groups. The so-called continuum models are characterized by assuming that the medium is a structureless and polarizable dielectricum described only by macroscopic physical constants. On the other hand there are the so-called discrete models. The main advantage of... 

In Eq. (6) Ecav represents the energy necessary to create a cavity in the solvent continuum. Eel and Eydw depict the electrostatic and van-der-Waals interactions between solute and the solvent after the solute is brought into the cavity, respectively. The van-der-Waals interactions divide themselves into dispersion and repulsion interactions (Ed sp, Erep). Specific interactions between solute and solvent such as H-bridges and association can only be considered by additional assumptions because the solvent is characterized as a structureless and polarizable medium by macroscopic constants such as dielectric constant, surface tension and volume extension coefficient. The use of macroscopic physical constants in microscopic processes in progress is an approximation. Additional approximations are inherent to the continuum models since the choice of shape and size of the cavity is arbitrary. Entropic effects are considered neither in the continuum models nor in the supermolecule approximation. Despite these numerous approximations, continuum models were developed which produce suitabel estimations of solvation energies and effects (see Refs. 10-30 in 68)). 

Although they have the same bonding patterns, bromine and iodine differ from chlorine and fluorine in their macroscopic physical appearance and in their molecular behavior. As Figure 11-1 shows, at room temperature and pressure, fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid. 

As has been suggested in the previous section, explanations of solvent effects on the basis of the macroscopic physical properties of the solvent are not very successful. The alternative approach is to make use of the microscopic or chemical properties of the solvent and to consider the detailed interaction of solvent molecules with their own kind and with solute molecules. If a configuration in which one or more solvent molecules interacts with a solute molecule has a particularly low free energy, it is feasible to describe at least that part of the solute-solvent interaction as the formation of a molecular complex and to speak of an equilibrium between solvated and non-solvated molecules. Such a stabilization of a particular solute by solvation will shift any equilibrium involving that solute. For example, in the case of formation of carbonium ions from triphenylcarbinol, the equilibrium is shifted in favor of the carbonium ion by an acidic solvent that reacts with hydroxide ion and with water. The carbonium ion concentration in sulfuric acid is greater than it is in methanol-... 

Continuing with the mini-theme of computational materials chemistry is Chapter 3 by Professor Thomas M. Truskett and coworkers. As in the previous chapters, the authors quickly frame the problem in terms of mapping atomic (chemical) to macroscopic (physical) properties. The authors then focus our attention on condensed media phenomena, specifically those in glasses and liquids. In this chapter, three properties receive attention—structural order, free volume, and entropy. Order, whether it is in a man-made material or found in nature, may be considered by many as something that is easy to spot, but difficult to quantify yet quantifying order is indeed what Professor Truskett and his coauthors describe. Different types of order are presented, as are various metrics used for their quantification, all the while maintaining theoretical rigor but not at the expense of readability. The authors follow this section of their... 

Macroscopic physical phenomena in polar crystals, such as pyroelectricity, piezoelectricity, and optical activity, would appear to be useful for the assignment of absolute polarity of crystals, provided that one can explain such phenomena at the required level in terms of the atomic arrangement. It appears from the... 

Minerals are generally regarded as naturally oceurring erystalline phases defined on the basis of their maeroseopie physical properties [1], As phases, or more specifically bulk phases in the Gibbsian or classical equilibrium thermod5mamic sense, a mineral is said to be homogeneous with respect to its macroscopic physical properties and separable from other so-called phases (and external surroundings) by a physically distinct or discontinuous boundary. 

Minerals are generally regarded as crystalline phases formed as a result of geological processes. As a (bulk) crystalline phase in the classical sense, a mineral must satisfy the conditions of long-range structural order in three dimensions, and homogeneity with respect to its macroscopic physical and chemical properties. 

The opposition of the two concepts of time is particularly striking in the famous fundamental problem of statistical mechanics How can we understand the emergence of an irreversible evolution at the level of macroscopic physics (in particular, of thermodynamics) from the deterministic and reversible Newtonian laws of mechanics ... 

TNC. 12. P. Glansdorff and I. Prigogine, On a general evolution criterion in macroscopic physics, Physica 30, 351-374 (1964). 

All deposits of metals are made of grains whose structural-physical nature (1) can be divided into four types (1) columnar, (2) fine-grained, (3) fibrous, and (4) banded. In terms of their practical macroscopic physical properties, their main characteristics may be summarized as follows ... 

The first section of this book deals with current topics in network theory directed toward explaining the relationship between molecular architecture and macroscopic physical properties. The closely related questions of network formation and degradation are also discussed in this section. Deformation, fatigue, and fracture are discussed in the second section. The third section includes recent advances in cross-linking chemistry several chapters outline applications of new systems and detail the relationship between network structure and application properties. 

Symmetry restrictions exist for tensors describing macroscopic physical properties of all but triclinic crystals, and for tensors describing the local properties of atoms at sites with point-group symmetries higher than I. 

Attempts to throw light on the possible implications of cis/trans isomerism in chemical reactivity, complex formation, macroscopical physical properties, and biological activity are still at an early stage and several interesting results are likely to emerge. 

Let me try to rephrase the argument. We assume that the combination of a finite number of fundamental properties, via a combinatorial approach, leads to a discrete set of macroscopic physical possibilities. We also know empirically that the chemical elements occur in a discrete manner because there are no intermediate elements between, say, hydrogen and helium. The combinatorial approach can thus be taken as an explanation for the discreteness in the occurrence of elements and furthermore it justifies the fact that Mendeleev regarded the yet undiscovered elements like germanium as being physical possibilities rather than merely logical ones. 

Critical phenomena of gels have been studied mainly by dynamic light scattering technique, which is one of the most well-established methods to study these phenomena [18-20]. Recently, the critical phenomena of gels were also studied by friction measurement [85, 86] and by calorimetry [55, 56]. In the case of these methods, the divergence of the specific heat or dissipation of the friction coefficient could be monitored as a function of an external intensive variable, such as temperature. These phenomena might be more plausible to some readers than the divergence of the scattered intensity since they can observe the critical phenomena in terms of a macroscopic physical parameter. 

The question of determinateness presents itself as follows Let the initial (t = 0) values of all the macroscopically independent macroscopic variables be given the equations of macroscopic physics (thermal and hydro-dynamic equations, etc.) show that these variables evolve deterministically with t 0. Yet there are infinitely many different probability densities ( ")t = 0 which have the moments, etc., coinciding with the set of given initial macroscopic values. Each evolves (by Liouville s equation) differently, and hence may induce a different set of macroscopic expected values at / > 0. By what principle of natural selection is the class of probability densities so restricted as to restore macroscopic determinacy ... 

The central focus of Gibbs theory is the equilibrium state S, a quiescent limiting condition of a sufficiently large ( macroscopic ) physical system that exhibits characteristically simple responses to attempted changes of the control variables that specify the state. 

The importance of crosslinked polymers, since the discovery of cured phenolic formaldehyde resins and vulcanized rubber, has significantly grown. Simultaneously, the understanding of the mechanism of network formation, the chemical structure of crosslinked systems and the motional properties at the molecular level, which are responsible for the macroscopic physical and mechanical properties, did not accompany the rapid growth of their commercial production. The insolubility of polymer networks made impossible the structural analysis by NMR techniques, although some studies had been made on the swollen crosslinked polymers. 

There is at present available in the literature on polymers and on materials science a wealth of information regarding measurements of mechanical properties. These properties are dependent upon many relevant physical parameters and most measurements take this into account. There is also available a great deal of information regarding the relations between molecular structure and macroscopic physical properties and many calculations have been made. The bridge between these two extremes (the macro and the micro) is constructed primarily by the use of models of structure. 

For a Tg to occur in crosslinked systems, there must be sufficient molecular mobility to affect the macroscopic physical modulus of the material. As the effective molecular weight, between the crosslinks decreases with increasing crosslink density, the thermal activation required to induce sufficient molecular movement, seen by a Tg, is commensurably increased. 

The goal of this chapter is to understand the behavior of ionic liquids as solvents and their influence on reaction based on their chemical structure and microscopic environment. We will therefore provide only a basic overview of their macroscopic physical properties. An online database, compiled by a research team operating under the auspices of the International Union of Pure and Applied Chemists (IUPAC), is now available detailing the physical properties of many known IL species [52],... 

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