SELF-ASSEMBLY AND COMPLEX PHASE BEHAVIOUR IN THE AMMONIUM PENTADECAFLUOROOCTANOATE / WATER / AMMONIUM CHLORIDE SYSTEM.
AUTOR(ES)
Mariétte Sueli Baggio Brandão
FONTE
IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia
DATA DE PUBLICAÇÃO
199609
RESUMO
The ammonium pentadecafluorooctanoate in heavy water system (APFO/\ pot.2\ H\ ind.2\ O) exhibits exceptional phase behaviour stemming from strong tendency of the surfactant to form disc-like micelles which are stable over a wide concentration and temperature intervals. An understanding of this phase behaviour requires exposing the factors which govern the stability of these disc-like micelles. To this end the effect of salt on the phase behaviour and the structure of the micelles has been studied. The ternary phase diagram has been established in part. It reveals the occurrence of a cloud point \ \"curve\" with an upper consolute temperature, in the dilute regime of surfactant concentration. This represents coexistence of a dilute F and a concentrated I\ \ micellar solution. Small angle X-ray scattering experiments carried out in the ternary system above the cloud point curve reveal that the dilute solution is comprised mainly of long rod-like micelles (for weight fractions of APFO Wa ^ou= 0.05) whilst the concentrated micellar solution is formed by disc-like micelles (for Wa >0.20). It is found that with increasing surfactant concentration a gradual change from rod-to-disc micelles occurs at the concentration interval 0.05