Freezing and Melting of Water Confined in Silica Nanopores

Abstract

In nanosized pores, liquid water can be thermodynamically stable down to temperatures well below the limit of homogeneous nucleation of bulk water ( approximately 235 K). Studies of water in such pores therefore offer an opportunity to reveal the anomalous behavior of deeply supercooled water. Herein we focus on recent studies of the limits of freezing and melting of water in the cylindrical pores of ordered mesoporous silicas with pore diameters in the range of 2-10 nm, based on vapor sorption measurements, calorimetric studies, NMR spectroscopy and cryoporometry, and neutron diffraction studies.

Trinucleotide duplex formation inside a confined nanospace under supercooled conditions

“…Mesoporous silica pores thus provide a potentially useful confined nanospace for stabilizing short nucleotide duplexes. We also employ supercooled confined water [14][15][16][17] as part of our strategy to achieve efficient duplex formation.…”

Water thermoporosimetry as a tool of characterization of the textural parameters of mesoporous materials

“…Probably, in these cases, pores are not totally filled, even if the amount of water was sufficient, due to the lowest sorption capacity of the silica with the smallest pore size. The variation of pore area with l/m suggests that the layer of non-freezing water is not stable but varies not only with the temperature [40] but also with l/m and is the biggest for the highest water to silica mass ratio. Indeed, the amounts of non-freezing water calculated for all the samples at different moisture contents and collected in Table 2 confirm this supposition.…”

“…The existence of boundary layer of non-freezable water at silica pore walls is a common knowledge. It is also known that the arrangement and mobility of molecules in this layer is affected by SiOH groups at the pore walls [40]. During heating silica up to the temperature higher than 550°C, condensation of linked silanol groups takes place and siloxane bridges (Si-O-Si) are formed [31].…”

“…In case of water TPM, this factor was investigated by a few authors but only with partially filled pores. Schreiber et al [27] or Findenegg et al [40] observed that whereas melting scans exhibited only a single peak, two or three peaks appeared in the freezing scans, depending of the degree of pore filling. They attributed this behaviour to the existence of two or more distinct arrangements of solid and liquid in the pores.…”

“…In the latter case, the phase transition from liquid-to-solid state undergoes under normal pressure. It is known that pore filling in SBA-15 proceeds in layerby-layer mode [40]. Higher pressure exerted on the layers makes them ''ticker'' that lead to the situation that a bigger population of water layer experiences the interaction with silanol groups from pore walls.…”