Micron-Sized Structure in a Thin Glycerol Film Revealed by Fluorescent Probes

Abstract

We report on micrometer-sized structures in supercooled glycerol observed by imaging fluorescent probes at the temperatures close to, but above, the glass transition temperature (190 K). Two distinct heterogeneous patterns of the fluorescence intensity were detected, depending on how fast the sample was cooled down. In a slowly cooled sample, we observed a Swiss cheese-like pattern in which many micrometer-sized dark spots were nucleated in a bright background. A quickly cooled sample resulted in a spinodal decomposition pattern where many bright island-like features on micrometer scale were dispersed in a dark matrix. Similar patterns were seen earlier in triphenyl phosphite, another molecular liquid, which shows solid-like behavior at temperatures above its glass transition. Once the heterogeneous patterns are formed in the glycerol, they can persist for days, unless the samples are heated above 260 K for more than 10 h. Such heterogeneous patterns are ascribed to differential dye distributions in the glycerol film, pointing to long-lived and micrometer-scale density fluctuations in supercooled glycerol. The observation of such heterogeneity may provide additional understanding on how supercooled glycerol behaves before it turns into a glass.

Communication: Crystallite nucleation in supercooled glycerol near the glass transition

“…glycerol. 9,[12][13][14] We have evidence that a nucleation process takes place during aging at a temperature near T g . Nonetheless, crystallization strongly depends on the thermal history that the sample was submitted to.…”

“…Furthermore, the nanocrystallite theory may also help to understand the different patterns observed in supercooled glycerol with different thermal histories. 13 The nanocrystallite theory describes a developing morphology of the crystalline structures in supercooled liquids. Isolated nanocrystallites are first surrounded by liquid at the early stages, then grow and connect into a solid-like network.…”

“…Xia et al observed micrometer-sized structures in thin films of glycerol near the glass transition by fluorescence microscopy. 13 Later on, Möbius et al found that solidification appeared after glycerol aged at a temperature above its T g .…”

“…Hence, the structural origin of the solid-like structure developed in supercooled glycerol near T g becomes significantly important for a better understanding on previous experimental observations. 9,[12][13][14] To get more insight into the structural organization of the solid-like network and on the solid-like fraction of the sample, we performed neutron diffraction and inelastic neutron scattering.…”

Rattling the cage: Micro- to mesoscopic structure in liquids as simple as argon and as complicated as water

“…[31] In a few cases, the mesoscopic clustering extends to greater length scales and becomes visible. [32,33] In this short collaborative review, we show that through combining a number of spectroscopic probes and applying these to liquids of varying complexity, a better understanding of the macroscopic properties can be achieved. In section 2, the experimental techniques are introduced.…”