This paper reports on investigations of the thermal phase behaviour of
microemulsions of the water-oil-amphiphile type near their plait poin
ts. Upon approaching the plait point the correlation length in the hyd
rodynamic region is characterized by a critical exponent v = 0.58-0.63
, although th renormalized exponent of the three dimensional Ising mod
el, v = 0.71, has been anticipated for such systems.