Quenched Disorder and the Consolute Point

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9617943 Cannell This is a renewal project in which laser light scattering will be used to study the length scale and dynamics of order parameter fluctuations near the critical point of a model system involving isobutyric acid/water mixtures containing a dilute silica network. The critical point of this system lies below (in temperature) a region of metastable domain formation, much as the critical point of a random-field magnet lies below the metastable "frozen-domain" state. Unlike the case with magnets, a simple method of reaching the equilibrium state exists for the fluid mixture. (Leaving the gel containing the mixture in contact with a reservoir of the fluid mixture allows it to reach equilibrium.) This happy coincidence will permit experiments to be carried out on the equilibrium system near the critical point, something which is not feasible for random-field magnets. %%% This is a renewal project in which experiments will be done to study how very dilute porous materials affect certain phase transitions. The phase transition to be studied is the demixing of two liquids, and the porous material will be tenuous network of synthetic quartz (silica). The experiments will try to relate this system to what is already known about magnetic systems containing impurities that are fixed in position. For the fluid system, the silica network plays the role of the fixed impurities, and with no impurities it is already well known that the magnets and fluids are closely related. Although this is a very basic research project, a deeper understanding of how porous materials affect the demixing transition might prove helpful in situations such as contamination of ground water by organic liquids. ***