Patterns Defects And Microstructures In Nonequilibrium Systems

Patterns, Defects and Microstructures in Nonequilibrium Systems

One of the most fascinating and intriguing aspects of natural phenomena is that complex systems may undergo symme try-breaking instabilities leading to pattern formation or coherent temporal behavior over macroscopic space and time scales. Therefore the understanding of why order may appear spontananeously in open systems far from equilibrium and which planforms are selected among a large manifold of possi bilities has become a major theme of research both theore- cally and experimentally. These studies, first related to fundamental questions, appear now to be of technological importance, especially for materials science problems. Effectively during the last years, the whole field of materials science experienced a complete renewal. By using techniques able to operate in strong nonequilibrium conditions and hence to escape from the constraints of equilibrium thermodynamics, totally new mate rials structures have been processed. Such techniques inclu de ion implantation, laser beam surface melting as well as electron beam heating. For example, ion implantation proces sing is able to create surfaces with compositions markedly different from the bulk, leading to materials having new electric, magnetic or chemical properties. In laser annea ling, after the tremendously rapid melting and recrystalliza tion of the sample surfaces, microstructures with superior resistance to friction, corrosion, ••• are frozen into place. Rapid solidification of alloys trigger the formation of quasi-crystalline structures. Ion beam mixing can modify the electrical properties of polymers or improve the adhesion of metallic films to ceramics.

Patterns, Defects and Microstructures in Nonequilibrium Systems

Patterns, Defects and Materials Instabilities

Understanding the origin of spatio-temporal order in open systems far from thermal equilibrium and the selection mechanisms of spatial struc tures and their symmetries is a major theme of present day research into the structures of continuous matter. The development of methods for pro ducing spatially ordered microstructures in solids by non-equilibrium methods opens the door to many technological applications. It is also be lieved that the key to laminar/turbulence transitions in fluids lies in the achievement of spatio-temporal order. Let us also emphasize the fact that the idea of self-organization in it self is at the origin of a reconceptualisation of science. Indeed, the appear ance of order which usually has been associated with equilibrium phase transitions appears to be characteristic of systems far from thermal equi librium. This phenomenon which was considered exceptional at first now the rule in driven systems. The chemical oscillations obtained appears to be in the Belousov-Zhabotinskii reaction were initially considered to be ther modynamically impossible and were rejected by a large number of chemists. Now these oscillations and related phenomena (waves, chaos, etc. ) are the subject of intensive research and new classes of chemical oscil lators have been recently discovered. Even living organisms have long been considered as the result of chance rather than necessity. Such points of view are now abandoned under the overwhelming influence of spatio-tem poral organization phenomena in various domains ranging from physics to biology via chemistry, nonlinear optics, and materials science .