The asymptotic critical regime in binary mixtures : can it be experimentally observed?

The lack of direct experimental evidence of the detection of the asymptotic critical behaviour in binary mixtures has led to the conjecture that the extent of the critical regime is exceedingly small in these systems. We address this problem from the theoretical side and find that: (i) the strong crossovers which affect the critical phenomena in mixtures are due to the competition between two different renormalization group fixed points; (ii) the crossover temperature is governed by a characteristic parameter which depends on the range of interactions as well as on purely thermodynamic quantities; and (iii) the extent of the asymptotic region is not necessarily small: specific systems and regimes allowing for the experimental observation of the true critical exponents are identified.