Melting behavior of water in cylindrical pores: carbon nanotubes and silica glasses

Abstract

We report a study of the effects of confinement in multi-walled carbon nanotubes and mesoporous silica glasses (SBA-15) on the solid structure and melting of both H(2)O and D(2)O ice, using differential scanning calorimetry, dielectric relaxation spectroscopy, and neutron diffraction. Multi-walled nanotubes of 2.4, 3.9 and 10 nm are studied, and the SBA-15 studied has pores of mean diameter 3.9 nm; temperatures ranging from approximately 110 to 290 K were studied. We find that the melting point is depressed relative to the bulk water for all systems studied, with the depression being greater in the case of the silica mesopores. These results are shown to be consistent with molecular simulation studies of freezing in silica and carbon materials. The neutron diffraction data show that the cubic phase of ice is stabilized by the confinement in carbon nanotubes, as well as in silica mesopores, and persists up to temperatures of about 240 K, above which there is a transition to the hexagonal ice structure.

Model of waterlike fluid under confinement for hydrophobic and hydrophilic particle-plate interaction potentials

“…22 and Jelassi et al 27 show that for water confined in hydrophobic nanopores the liquid states persists to temperatures lower than in bulk and in hydrophilic confinement. These observations are confirmed by X-ray and neutron diffraction 27,28 .…”

Phase transitions of octamethylcyclotetrasiloxane confined inside aluminosilicate and silicate nanoporous matrices

“…One is the pore width H, the latter is the wettability parameter a w , a w ¼ q w e fw r 2 fwD e ff , which is the ratio of the fluid-wall to the fluid-fluid attractive interaction, where D is the inter-layer spacing in the solid and q w is the number of wall atoms per unit area. Our previous results [3,6,[30][31][32] indicate that the critical a w value for Lennard-Jones fluids in smooth-walled pores is about 1, and thus for alpha greater than 1, we have strongly attractive pores-like a wall of graphite, and then occurs an elevation in freezing temperature-while for values of alpha less than 1, we have weakly attractive pores-like a wall of silica, and then occurs a depression in freezing temperature. Our experimental evaluation of the effective wettability parameter a p based on the measurements of contact angle of OMCTS inside the silica pores has shown that the effective value of a in silica pores is about a p = 0.4 [24], and we can expect the depression of the melting temperature for OMCTS in the studied matrices.…”

“…For cylindrical pores with lower diameter, the confined phase at low temperature is an inhomogeneous phase with partially crystalline domains interspersed with amorphous regions [19]. For OMCTS in SBA-15 and Al-SBA-15 with pore size about 4 nm, we can expect that inside the pores below the melting temperature rather inhomogeneous phase will be formed, and at the solid phase, the crystal form can be partially deformed [30,31]. In such a case, the solid-solid transition observed in OMCTS bulk does not occur in the pores.…”

Structure and Dynamics of Water at Carbon-Based Interfaces

“…A variety of solid surfaces has been considered: silica pores (Vycor glass) [25,26], platinum [27], magnetite [28], zirconia [29], or pure carbon composites (graphite structure) in several geometries, from planar [30][31][32][33][34] to cylindrical [35][36][37]. At the experimental side, many authors have contributed to the study of water at hydrophobic interfaces using a wide variety of techniques such as scanning tunneling microscopy [38], environmental scanning electron microscopy and electron energy loss spectroscopy [39], ultrafast optical Kerr effect spectroscopy [40], atomic force spectroscopy [41], calorimetry [42], neutron diffraction [43][44][45][46] and electron cryomicroscopy [10].…”