On the abundance and general nature of the liquid–liquid phase transition in molecular systems

Abstract

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.

Microscopic identification of the order parameter governing liquid–liquid transition in a molecular liquid

“…Each scenario captures a certain feature of the glacial phase, but fails in explaining all of the experimental results in a consistent manner. Similar situations are often seen in other candidates of LLTs, such as l-butanol [LLT (13) vs. microcrystallization (40)(41)(42)(43)], confined water [LLT (5) vs. other phenomena (44)(45)(46)], and aqueous solutions [LLT (6, 7) vs. microcrystallization (8,28,47,48)]. For TPP, however, some pieces of experimental evidence supportive of the LLT scenario rather than the microcrystallization scenario have recently been reported (11,12).…”

“…This means that there can be more than two liquid states for a single-component substance. Despite its counterintuitive nature, there have recently been many pieces of experimental and numerical evidence for the existence of LLT, for various liquids such as water (1)(2)(3)(4)(5), aqueous solutions (6)(7)(8), triphenyl phosphite (9-12), l-butanol (13), phosphorus (14), silicon (15,16), germanium (17), and Y 2 O 3 -Al 2 O 3 (18,19). This suggests that the LLT may be rather universally observed for various types of liquids.…”

Glass formation and glass transition in supercooled liquids, with insights from study of related phenomena in crystals

“…It is a puzzle that there are so few cases of systems with liquid-liquid transitions above T g . Kurita and Tanaka [72] have shown that Kivelson's "glacial phase" of tri-phenyl phosphite, TPP is such a case and anticipate [73], as do we [48], that there should be many others but have so far only identified t-butanol as additional. The LL transition for TPP is indeed associated with rapid crystallization, as is the case with other polyamorphic transitions [22,24].…”

Heating-induced glass-glass and glass-liquid transformations in computer simulations of water

“…We note that glass polymorphism is not particular to water. Experiments indicate that other materials, such as silicon, 57,58 germanium, 59, 60 silica, 61 aluminium-oxide yitrium-oxide mixtures, 62 n-butanol, 63,64 triphenyl phosphite, 65,66 and water-glycerol solutions, 67 also exhibit glass polymorphism, with low and high-density amorphous forms. Hence, characterizing water glass polymorphism may help to understand polyamorphism in other substances as well.…”