Supercooled water confined in a metal-organic framework

Abstract

Within the so-called "no-man's land" between about 150 and 235 K, crystallization of bulk water is inevitable. The glasslike freezing and a liquid-to-liquid transition of water, predicted to occur in this region, can be investigated by confining water in nanometersized pores. Here we report the molecular dynamics of water within the pores of a metalorganic framework using dielectric spectroscopy. The detected temperature-dependent dynamics of supercooled water matches that of bulk water as reported outside the borders of the no-man's land. In confinement, a different type of water is formed, nevertheless still undergoing a glass transition with considerable molecular cooperativity. Two different length scales seem to exist in water: A smaller one, of the order of 2 nm, being the cooperativity length scale governing glassy freezing, and a larger one (> 2 nm), characterizing the minimum size of the hydrogen-bonded network needed to create "real" water with its unique dynamic properties.

Nuclear Magnetic Resonance and Broadband Dielectric Spectroscopy Studies on the Dynamics of Ethylene Glycol in Mesoporous Silica

“…In Figure , we compare the dielectric loss spectra ε″(ν) of EG in large, medium-sized, and small pores at 190 K. To determine the pore-size dependencies of P1–P4, we fit the BDS data of EG in the studied silica confinements to eq . In accordance with previous studies on confined liquids, − we find that such a superposition of CC processes describes the results for all diameters and temperatures. In Figure , the individual processes are indicated for EG in large pores.…”

“…It should, however, not be left unmentioned that when cross terms are not negligible, reorganization of molecular aggregates can lead to pronounced additional contributions, as was reported for hydrogen-bonded bulk liquids. − Following previous BDS approaches to confined liquids, − we analyze the dielectric permittivity ε̂(ω) of confined EG by fitting to a conductivity term and a sum of Cole–Cole (CC) functions Here, ε ∞ is the high-frequency limit of the permittivity, ε 0 is the vacuum permittivity, and σ dc denotes the dc conductivity. Moreover, the CC processes are described by their relaxation strengths Δε n , relaxation times τ CC, n , and width parameters 0 < α n ≤ 1.…”

“…Numerous studies are focused on confined water. − In an important line of research, it was exploited that the melting temperature of water decreases when the confinement size is reduced, as described by the Gibbs–Thomson relation, until crystallization is fully suppressed. − Thus, severe geometrical restriction provides access to the properties of deeply cooled liquid water, which are of fundamental importance for an understanding of the anomalies of water, , but commonly masked by rapid crystallization. However, despite large research efforts, − structures and dynamics of confined waters remain controversial subjects to this day.…”

Salt Enrichment and Dynamics in the Interface of Supercooled Aqueous Droplets

“…1−15 In a broader context, the unique physical chemistry in small-volume cold systems has been demonstrated by the formation of new ice structures that cannot been seen in the bulk. [1][2][3][4][5][6][7][8][9][10][11][12]16 Cold nano-and microdroplets have been studied through experiment and simulation in relation to crystallization and to their thermodynamic and structural properties. [17][18][19][20][21][22][23][24][25][26][27][28][29]29,30 These cold nanoscopic systems have a surprisingly complex internal structure that varies with temperature and size, as revealed by computer simulations of the TIP4P/2005 model of water, 31−33 which we now summarize in the context of the present study.…”

High cubicity of D2O ice inside spherical nanopores of MIL-101(Cr) framework: a neutron diffraction study

“…[56][57][58] The extended H-bonding network may form large crystalline ice. Although the formation of a single crystal extending into the neighboring pore may not be guaranteed, the slow H-bonding dynamics [59][60][61] may make it possible to form a crystal with extended correlation length.…”