Binary liquid mixtures in porous solids

Abstract

The technique of Nuclear Magnetic Resonance (NMR) cryoporometry has been used to study the behaviour of binary liquid mixtures of water and decane in porous sol-gel silicas. The pore volume occupied by each liquid was measured as the ratio of water to decane was altered. It was observed that the water preferentially absorbed onto the silica surface and so was able to displace the decane from the pores. Water displaced the decane first from the smallest pores with a higher surface to volume ratio. The addition of sufficient water to just overfill the silicas was seen to completely displace the decane already occupying the pores after twenty-four hours.2 List of Figures Figure 1 The cryoporometry melting curves of decane and water mixtures in 100Å Merck silica. The decane melting region is clearly separate from the water melting region. As the fraction of water increases the decane shifts from the pores into the bulk. Figure 2 The pore volume distributions for decane (top) and water (bottom) generated from the cryoporometry melting curves in Figure 1. It can be seen that water preferentially displaces decane from the smallest pores.

Nuclear magnetic resonance cryoporometry

“…The strengths of surface interaction of two liquids can be compared indirectly using NMR cryoporometry by observing preferential pore filling. The preferential filling of small pores by water over decane was observed in porous sol-gel silica (Alnaimi et al, 2004) where the polar water molecules had a stronger surface interaction; see figure 9. The two absorbates were distinguishable in the melting curve due to their distinctly different melting points.…”

Structural and dynamic studies of water in mesoporous silicas using neutron scattering and nuclear magnetic resonance

“…The findings have been published in a number of papers and reviews (Dore, 2000;Webber, Strange and Dore, 2001;Allen, Mallett and Strange, 2001;Alnaimi, Mitchell, Strange and Webber, 2004).…”

“…• Measurement of changes in the T 1 (longitudinal or spin-lattice) and T 2 (transverse or spin-spin) relaxation times (in the time domain) due to exchange of magnetisation between the liquid in the pore and the pore wall (Brownstein and Tarr, 1977;Halperin et al, 1991;Strange et al, 1996a;Stapf et al, 1996;Allen et al, 1998;Booth and Strange, 1998a,b;Allen et al, 2001;Levitz et al, 2003;Strange et al, 2003;Alnaimi et al, 2004). In low NMR static magnetic fields, this exchange of magnetisation tends to dominate the NMR relaxation of liquids in pores.…”

“…• Variation of the amplitude of the liquid component in the T 2 relaxation curve with temperature, and the interpretation of this in terms of the Gibbs-Thomson relationship -NMR cryoporometry (Strange et al, 1993;Overloop and van Gerven, 1993;Alnaimi et al, 1994;Hansen et al, 1996;Allen et al, 1998;Webber, 2000;Webber et al, 2001;Strange et al, 2003;Alnaimi et al, 2004).…”

A Perspective on Multi-scale Simulation: Toward Understanding Water-silica

“…Extensive efforts have been made to study absorption, diffusion, and penetration of water molecules on SiO 2 surfaces experimentally [7][8][9][10][11][12][13][14][15][16][17][18][19][20] and computationally [21][22][23][24][25][26][27][28][29][30][31][32][33]. These studies have yielded substantial data that enable understanding of the water-silica interaction at both macroscopic and microscopic levels.…”