The phase diagram composition-temperature of the AOT-water-decane system presents a line of critical points. This line has been approached along two paths which control the interactions between W/O droplets. The two parameters investigated are the temperature and the water over surfactant ratio. The critical behaviour has been followed by using light scattering. The data indicate a liquid-gas type behaviour and are in good agreement with the renormalization group theories for critical phenomena

2014 Nous présentons des résultats obtenus par diffusion de la lumière en différents points d'une ligne critique d'un système microémulsion quaternaire. Cette ligne débute par un point critique extreme. Les points critiques ont été approchés, soit en faisant varier la température à composition constante (chemin I), soit en faisant varier le rapport eau sur savon (X) à température constante (chemin II). Pour chaque point critique examiné, les valeurs des exposants critiques 03BD et 03B3 mesurées le long des deux chemins sont proches. Elles varient continûment des valeurs d'Ising à des valeurs très petites quand le point critique considéré s'approche du point critique extreme. Ce comportement critique complexe est analysé à l'aide des résultats du diagramme de phase. Abstract 2014 We present light scattering results obtained for a four-component microemulsion system in several distinct positions of a critical line. This line starts at a critical end point The critical points were approached either by raising the temperature at fixed composition (path I) or by increasing the water over surfactant ratio X at constant temperature (path II). For each critical point investigated, the critical exponents 03BD and 03B3 associated with the X variable (path II) are close to those obtained with the temperature (path I). They vary continuously from the Ising values to largely smaller ones as the critical end point is approached. This complex critical behaviour is discussed in relation with the phase diagram findings.

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