Spinodal concept

Lipson (1943, 1944), who had examined a copper-nickeMron ternary alloy. A few years ago, on an occasion in honour of Mats Hillert, Cahn (1991) mapped out in masterly fashion the history of the spinodal concept and its establishment as a widespread alternative mechanism to classical nucleation in phase transformations, specially of the solid-solid variety. An excellent, up-to-date account of the present status of the theory of spinodal decomposition and its relation to experiment and to other branches of physics is by Binder (1991). The Hillert/Cahn/Hilliard theory has also proved particularly useful to modern polymer physicists concerned with structure control in polymer blends, since that theory was first applied to these materials in 1979 (see outline by Kyu 1993). 

Within the pseudo-spinodal concept [11, 101] the diffusion coefficient of an off-critical mixture is still described in a similar way to the diffusion coefficient of the critical mixture. Only the critical temperature is now replaced by the temperature... 

It is not quite certain that the spinodal has a inecise experimental meaning. As pointed out recently K. Binder (unpublished), the nucleation processes have a low banier when we get close to the nominal spinodal line, and the onset of observable instabilities is probably (0 not sharp (it) dependent on the length of the observations. Bnt for many practical purposes, the spinodal concept is helpftil—particulafly so at the mean field level which we discuss here. 

Since the start of modern interpenetrating polymer network (IPN) research in the late sixties, the features of their two-phased morphologies, such as the size, shape, and dual phase continuity have been a central subject. Research in the 1970 s focused on the effect of chemical and physical properties on the morphology, as well as the development of new synthetic techniques. More recently, studies on the detailed processes of domain formation with the aid of new neutron scattering techniques and phase diagram concepts has attracted much attention. The best evidence points to the development first of domains via a nucleation and growth mechanism, followed by a modified spinodal decomposition mechanism. This paper will review recent morphological studies on IPN s and related materials. 

The concept of spinodal decomposition can be extended to multicomponent systems and allow the prediction of various morphologies, e.g., core-shell particles, dual-continuous phases, dual-dispersed phase, and more complex structures. Spinodal decomposition simulations, in contrast to cellular automata, do... 

From a thermodynamic point of view, phase diagrams may be constructed by changing the temperature (ii), pressure (12). or composition of a material. The present experiments are concerned with changes in composition at constant temperature and pressure, leading to a ternary phase diagram with polymer network I at one corner, monomer II at the second corner, and polymer network II at the third corner. According to classical concepts, at first there should be a mutual solution of monomer II in network I, followed by the binodal (nucleation and growth kinetics) and finally the spinodal (spinodal decomposition kinetics). 

Nevertheless, thermodynamics provides us with a simple concept which can help us to analyze the possible evolution, explosive or not, of a boiling or gas exsolution process. However, while the liquid spinodal curve of water is presumably well known, at least in its high-temperature part, the topology of spinodal curves of aqueous solutions is poorly known. The purpose of the next two sections is to fill in this gap for CO2 and NaCl aqueous solutions. 

PC/ABS blend is an injection moldable material widely used for automotive parts. These blends, developed in 1960, can be prepared by simple meltmixing of PC with ABS, without any compatibilizer. In this early stage of polymer blends technology, the phase diagram of polymer/polymer mixture, the spinodal decomposition, and the effect of the flow fields were not seriously considered. Nowadays, using these concepts, one can describe the processes that are behind the simple melt-mixing . 

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