Experimental evidence for crossover to mean-field tricritical behavior in a concentrated salt solution

We have discovered a mean-field multicritical point on the critical locus i n an aqueous solution of 3-methylpyridine and sodium bromide. Light-scatter ing measurements indicate Ising-like asymptotic critical behavior at the lo wer salt concentrations. However, the temperature range of Ising critical b ehavior shrinks with increasing salt concentration and the critical behavio r becomes mean-field-like at a concentration of about 17% mass fraction of NaBr. Emergence of a new characteristic length scale diverging at this poin t and a simultaneous pronounced increase in the background scattering sugge sts mean-field tricritical behavior associated with the formation of a micr oheterogeneous phase due to clustering of ions and molecules.