Single-component molecule systems

It is instructive to consider the approximate partition function for a single-component liquid system of N molecules that is the starting point of Flory s version of the theory... 

Just as it is not necessary for polymer chains to be linear, it is also not necessary for all repeat units to be the same. We have already mentioned molecules like proteins where a wide variety of different repeat units are present. Among synthetic polymers, those in which a single kind of repeat unit are involved are called homopolymers, and those containing more than one kind of repeat unit are copolymers. Note that these definitions are based on the repeat unit, not the monomer. An ordinary polyester is not a copolymer, even though two different monomers, acids and alcohols, are its monomers. By contrast, copolymers result when different monomers bond together in the same way to produce a chain in which each kind of monomer retains its respective substituents in the polymer molecule. The unmodified term copolymer is generally used to designate the case where two different repeat units are involved. Where three kinds of repeat units are present, the system is called a terpolymer where there are more than three, the system is called a multicomponent copolymer. The copolymers we discuss in this book will be primarily two-component molecules. We shall discuss copolymers in Chap. 7, so the present remarks are simply for purposes of orientation. 

Shear viscosity is a measure of the ahihty of one layer of molecules to move over an adjacent layer. Bulk viscosity will be mentioned in Section V.2. Since viscosity usually refers to shear viscosity, the term will he used in this way unless otherwise stated. Recommended techniques for measuring the viscosity of high-temperature melt are given below. Experimental data are available from the database mentioned in Section 1.2. Data on viscosities of slags (7 single component systems, 35 two-component... 

This section describes the phase change process for a single component on a molecular level, with both vaporization and condensation occurring simultaneously. Molecules escape from the liquid surface and enter the bulk vapor phase, whereas other molecules leave the bulk vapor phase by becoming attached to the liquid surface. Analytical expressions are developed for the absolute rates of condensation and vaporization in one-component systems. The net rate of phase change, which is defined as the difference between the absolute rates of vaporization and condensation, represents the rate of mass... 

Mixture of three different single-site molecules. In the previous examples we discussed two-state systems of L and H. These could be either a mixture of two components, or a mixture obtained by freezing-in an equilibrium between two states. We extend the discussion to three states, denoted by L, H, and T, with corresponding binding constants k, and kj. 

For multi-component systems it seems intuitive that single-component diffusion and adsorption data would enable one to predict which component would be selectively passed through a membrane. This is only the case where molecular sieving is observed for all other separations where the molecules interact with one another and with the zeolite framework their behavior is determined by these interactions. Differences in membrane properties such as quahty, microstructure, composition and modification can also play a large role in the observed separation characteristics. In many cases, these properties can be manipulated in order to tailor a membrane for a specific apphcation or separation. 

It is interesting to note that the only single component molecular metal known to date is Ni(tmdt)2, with ctrt —400 cm" (Tanaka et al., 2001). The possibility of obtaining such metals was predicted by theoretical work on the so-called two-hands systems by showing that electron transfer could be induced internally between two types of bands of the same component and that metal bis(dithiolene) molecules could lead to single-component molecular metals (Canadell, 1997). This is an example of internal doping. 

SOLVOLYSIS. A generalized conception of the relation between a solvent and a solute (i.e., a relation between two components of a single-phase homogeneous system) whereby new compounds arc produced, In most instances, the solvent molecule donates a proton to. or accepts a proton from a molecule of solute, or both, forming one or more different molecules. A particular case of special interest occurs when water is used as solvent, m which case die interaction between solute and solvent is called hydrolysis. 

---