We found both nucleation-growth-type and spinodal-decomposition-type transformation from one liquid state to another in a "molecular liquid," triphenyl phosphite (TPP). Binodal and spinodal temperatures of this transition at ambient pressure were determined by the characteristics of morphological evolution, domain-growth kinetics, and rheological evolution. Furthermore, a distinct thermal signature of the glass transition of a second liquid was also detected in addition to that of an ordinary liquid. These findings strongly suggest the existence of a liquid-liquid transition; more precisely, a transformation of one supercooled liquid to a glassy state of another liquid, in TPP.

Contrary to the conventional wisdom that there is only one unique liquid state for any material, recent evidence suggests that there can be more than two liquid states even for a single-component substance. The transition between these liquid states is called a liquid-liquid phase transition. We report the detailed experimental investigation on the kinetics of the continuous spinodal-decomposition-type transformation of one liquid into another for triphenyl phosphite. From the analysis of the linear regime, we found that the correlation length, xi, of fluctuations of the relevant order parameter diverges as xi = xi(0)[(T(SD) - T)/T(SD)](-nu) (where xi(0) = 60 nm and nu = 0.5) while approaching the spinodal temperature, T(SD). This is an indication of a critical-like anomaly associated with the liquid-liquid transition. We also revealed that the order parameter governing the liquid-liquid transition must be of a nonconserved nature.

Even a single-component liquid may have more than two kinds of isotropic liquid states. The transition between these different states is called a liquidliquid transition (LLT). An LLT has been considered to be a rather rare phenomenon, in particular for molecular liquids. Very recently, however, we found an LLT in triphenyl phosphite, which may be the first experimental observation of an LLT for molecular liquids. Here we report convincing evidence of the second example of LLT for another molecular liquid, n-butanol. Despite large differences in the chemical structure and the molecular shape between triphenyl phosphite and n-butanol, the basic features of the transformation kinetics are strikingly similar. This suggests that an LLT may not be a rare phenomenon restricted to specific liquids, but may exist in various molecular liquids, which have a tendency to form long-lived locally favoured structures due to anisotropic interactions (e.g., hydrogen bonding).There are a number of experimental indications suggestive of the existence of liquid-liquid transition (LLT) for a variety of liquids covering atomic to molecular liquids [1][2][3][4][5][6][7][8]. Although there are rather clear examples of LLT for atomic liquids [2, 6],there was no direct experimental evidence for molecular liquids. LLT in water has been suggested on the basis of experimental evidence of polyamorphism [5] and numerical simulations [8], but its existence has not been confirmed experimentally yet. Recently, however, we found convincing experimental evidence for the existence of LLT in a molecular liquid, triphenyl phosphite (TPP) [9, 10] 1 . Both nucleation-growth-type and spinodal-decomposition-type phase transformations were directly observed with optical microscopy. In addition to the glass transition of a normal liquid, a distinct thermal signature of the glass transition of a second liquid was also detected. Namely, we confirmed the existence of two glass transitions for a single-component substance. We also 1 Polyamorphism in TPP was discovered by . Since then, there has been active debate on the nature of the newly discovered phase. On this issue, see [9,10] and the references therein.