Thermodynamic functions of water and ice confined to 2nm radius pores

Abstract

The heat capacity C(p) of the liquid state of water confined to 2 nm radius pores in Vycor glass was measured by temperature modulation calorimetry in the temperature range of 253-360 K, with an accuracy of 0.5%. On nanoconfinement, C(p) of water increases, and the broad minimum in the C(p) against T plot shifts to higher temperature. The increase in the C(p) of water is attributed to an increase in the phonon and configurational contributions. The apparent heat capacity of the liquid and partially frozen state of confined water was measured by temperature scanning calorimetry in the range of 240-280 K with an accuracy of 2%, both on cooling or heating at 6 K h(-1) rate. The enthalpy, entropy, and free energy of nanoconfined liquid water have been determined. The apparent heat capacity remains higher than that of bulk ice at 240 K and it is concluded that freezing is incomplete at 240 K. This is attributed to the intergranular-water-ice equilibrium in the pores. The nanoconfined sample melts over a 240-268 K range. For 9.6 wt % nanoconfined water concentration ( approximately 50% of the maximum filling) at 280 K, the enthalpy of water is 81.6% of the bulk water value and the entropy is 88.5%. For 21.1 wt % (100% filling) the corresponding values are 90.7% and 95.0%. The enthalpy decrease on nanoconfinement is a reflection of the change in the H-bonded structure of water. The use of the Gibbs-Thomson equation for analyzing the data has been discussed and it is found that a distribution of pore size does not entirely explain our results.

Confinement effects on water structure in membrane lyotropic phases

“…At such mesoscopic scale, numerous studies have shown that the structure and the physical properties of confined liquids in cavities differ strikingly from the bulk system [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The experiments on the confinement of water or associated liquid such as alcohol in mesoporous materials (aerogels, controlled pore glass, MCM-41.…”

“…Numerous investigations have been devoted on the understanding of confined water and other liquids into mesoporous materials such as MCM-41, Vycor, clay and porous silicon [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. These studies have revealed effects of confinement which affect both the structure and dynamics of the confined system of which properties differ strictly from these-ones of bulk liquid [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Surfactant systems self assemble into a variety of structures which present particular organizations of the membranes and provide model system to host small or significant amounts of water for mimic confinement in biological objects [1,[19][20][21][22].…”

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].…”

Effect of pressure on thermal conductivity and pressure collapse of ice in a polymer-hydrogel and kinetic unfreezing at 1 GPa

“…29 Wilson et al 37 have already reviewed several aspects of premelting effects. They too noted that Dash and co-workers [38][39][40][41][42] discussed the presence of intergranular water and concluded that if the radius of curvature of the ice grains is 1 μm liquid water can be present down to ∼263 K. We also note that ice formed in nanopores of silica and other solids shows a melting endotherm that is broadened out on the low temperature side, [43][44][45] making it difficult to define the onset of bulk melting. The poorly defined onset temperature for melting of ice in 100% filled, 4 nm diameter pores of Vycor glass is ∼245 K (with a peak at 260 K) in Fig.…”