Objetivo A microscopic lattice gas model was formulated such that it captures a few dominant features of the cyanoadamantane crystal: the strong steric hindrance between specific orientations of neighbouring molecules, modelled by incorporating infinite repulsion terms into the hamiltonian. The order parameter of the model is nonconservative, with a high degeneracy of the ordered phases. The simplest version of the model is a spin 1 Ising like system on a square lattice. Spins -1 and +1 are equally favoured at low temperature. A hard condition reflecting steric hindrance was added to the model to prevent spins -1 and +1 being first neighbours. This last condition leads to an inhibited domain growth. The main consequences of the hard steric constraint are the following: a transient of weaker time dependence prior to the classical Lifshitz-Allen-Cahn growth law; a decrease in the amplitude and a slowing down of the absolute growth rate due to a lower driving force for the interface motion; a crossover to a much slower algebraic growth law showing up at low temperature (T). This slow algebraic growth ultimately leads to a freezing in of the system at T = O. This occurs because the hard condition imposes an activation energy on the domain wall migration and can lead to arbitrarily small exponents, strongly temperature dependent at low temperatures. Thermal quenches from the high temperature phase into the instable region close to but below the critical temperature have been simulated numerically. The classical behaviour was verified over more than two decades of time, indicating that the regime of domain coarsening is easily accessible in the present model. The static susceptibility increases in the same time interval by a power law, with exponent related to the dynamical exponent z. We have compared the above model with a similar model where the hard core repulsion is replaced by the more soft ferromagnetic interaction between nearest neighbours. Clearly, the hard core condition is responsible for the slow kinetics of the phase separation.The goal of the project is the study of the kinetics of a first order phase transition in a system with non-conserved order parameter. Contrary to demixing systems these kinetics are usually very fast which makes it difficult to study experimentally the instable and (pseudo-spinodal) metastable phases. In this domain recent theories predict very particular behaviour. The use of the 'glassy' crystal cyano-adamantane, a gel of orientational disorder, facilitates this study in an exceptional manner. The project will consist of two parts : The experimental part consists of a real time study (using X-ray scattering partly from a synchroton source) of the time evolution of the structure factor in order to explore the dynamic scaling laws as well as the eventual fractal character of the fluctuations; the theoretical part consists of the construction of suitable models, and their simulation by means of the Monte-Carlo method. The interactions taken into account include the steric hindrance between neighbouring molecules with particular orientations. Ámbito científico social scienceslaw Programa(s) FP2-SCIENCE - Programme plan (EEC) to stimulate the international cooperation and interchange needed by European research scientists (SCIENCE), 1988-1992 Tema(s) Data not available Convocatoria de propuestas Data not available Régimen de financiación CSC - Cost-sharing contracts Coordinador Université de Lille I (Université des Sciences et Technologies de Lille Flandres Artois) Aportación de la UE Sin datos Dirección UFR de Physique 59655 Villeneuve-d'Ascq Francia Ver en el mapa Coste total Sin datos Participantes (2) Ordenar alfabéticamente Ordenar por aportación de la UE Ampliar todo Contraer todo Danmarks Tekniske Universitet Dinamarca Aportación de la UE Sin datos Dirección 2800 Lyngby Ver en el mapa Coste total Sin datos UNIVERSITAIRE INSTELLING ANTWERPEN - UNIVERSITEIT ANTWERPEN Bélgica Aportación de la UE Sin datos Dirección 1,Universiteitsplein 1 Gebouw N. 2610 WILRIJK (ANTWERPEN) Ver en el mapa Coste total Sin datos
