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

Webber, J. Beau W.; Dore, John C.

doi:10.1088/0953-8984/16/45/009

Cited by 71 publications

(84 citation statements)

References 71 publications

(130 reference statements)

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“…The relation between melting temperatures obtained on the basis of spin-echo measurements (this work, Webber 48,49 ) and by direct intensity measurements (Hansen 2 ) of the proton signal needs further discussion.…”

Section: Discussionmentioning

confidence: 92%

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Melting and freezing of water in cylindrical silica nanopores

Jähnert

Chávez

Schaumann

et al. 2008

Phys. Chem. Chem. Phys.

328

394

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Freezing and melting of H 2 O and D 2 O in the cylindrical pores of well-characterized MCM-41 silica materials (pore diameters from 2.5 to 4.4 nm) was studied by differential scanning calorimetry (DSC) and 1 H NMR cryoporometry. Well-resolved DSC melting and freezing peaks were obtained for pore diameters down to 3.0 nm, but not in 2.5 nm pores. The pore size dependence of the melting point depression DT m can be represented by the Gibbs-Thomson equation when the existence of a layer of nonfreezing water at the pore walls is taken into account. The DSC measurements also show that the hysteresis connected with the phase transition, and the melting enthalpy of water in the pores, both vanish near a pore diameter D* E 2.8 nm. It is concluded that D* represents a lower limit for firstorder melting/freezing in the pores. The NMR spin echo measurements show that a transition from low to high mobility of water molecules takes place in all MCM-41 materials, including the one with 2.5 nm pores, but the transition revealed by NMR occurs at a higher temperature than indicated by the DSC melting peaks. The disagreement between the NMR and DSC transition temperatures becomes more pronounced as the pore size decreases. This is attributed to the fact that with decreasing pore size an increasing fraction of the water molecules is situated in the first and second molecular layers next to the pore wall, and these molecules have slower dynamics than the molecules in the core of the pore.

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Section: Discussionmentioning

confidence: 92%

“…Also shown in Fig. 9 is a cryoporometry relation T c (D) proposed by Webber and Dore 48 for the melting of water in various sol-gel silicas. These authors employed the spin echo pulse sequence as in the present work but with a delay time t = 2 ms (instead of t = 0.5 ms used in the present work).…”

Section: Phase Transition As Observed By Nmr Cryoporometrymentioning

confidence: 95%

Melting and freezing of water in cylindrical silica nanopores

Jähnert

Chávez

Schaumann

et al. 2008

Phys. Chem. Chem. Phys.

328

394

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“…The spectral data indicated an increase in the thickness of the interfacial amorphous ice layer with increasing concentration of phloroglucinol. The amorphous nature of supercooled water and water-ice has been explored through simulations (Koga et al, 1998;Brovchenko and Oleinikova, 2006) and neutron diffraction experiments (Liu et al, 2006;Dore et al, 2002;Webber and Dore, 2004;Webber et al, 2007b;Webber and Dore, 2008;Seyed-Yazdi et al, submitted, b); see section 3.3 for additional discus-sion and references.…”

Section: Surface Interactions At the Solid-liquid Interfacementioning

confidence: 99%

Nuclear magnetic resonance cryoporometry

2008

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Nuclear Magnetic Resonance (NMR) cryoporometry is a technique for non-destructively determining pore size distributions in porous media through the observation of the depressed melting point of a confined liquid. It is suitable for measuring pore diameters in the range 2 nm -1 µm, depending on the absorbate. Whilst NMR cryoporometry is a pertabative measurement, the results are independent of spin interactions at the pore surface and so can offer direct measurements of pore volume as a function of pore diameter. Pore size distributions obtained with NMR cryoporometry have been shown to compare favourably with those from other methods such as gas adsorption, DSC thermoporosimetry, and SANS. The applications of NMR cryoporometry include studies of silica gels, bones, cements, rocks and many other porous materials. It is also possible to adapt the basic experiment to provide structural resolution in spatially dependent pore size distributions, or behavioural information about the confined liquid.

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“…Porous silica exists with various well-defined pore sizes, which allows the variation of the geometrical parameters in a controlled and straightforward manner. The solid substrate also enables the water/ice properties to be studied for complete and fractional-pore-filling, using a range of experimental and simulation techniques 3,4,5,6,7 .…”

Section: Introductionmentioning

confidence: 99%

Studies of water and ice in hydrophilic and hydrophobic mesoporous silicas: pore characterisation and phase transformations

Jelassi

Castricum

Bellissent-Funel

et al. 2010

Phys. Chem. Chem. Phys.

Self Cite

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A study has been made as a function of temperature of the phase transformation of water and ice in two samples of mesoporous silica gel with pore diameters of ∼50Å. One sample was modified by coating with a layer of trimethylchlorosilane, giving a predominantly hydrophobic internal surface, whereas the unmodified sample has a hydrophilic interface. The pore structure was characterised by nitrogen gas adsorption and NMR cryoporometry and the melting/freezing behaviour of water and ice in the pores was studied by DSC and neutron diffraction for cooling and heating cycles, covering a range of 200 to 300K. Measurements were made for several filling-factors in the range 0.2 to 0.9. The results show a systematic difference in the form of ice created in each of the samples. The non-modified sample gives similar results to previous studies with hydrophilic silicas, exhibiting a defective form of cubic ice superimposed on a more disordered pattern that changes with temperature and has been characterised as 'plastic' ice [Liu et al, 2006, Webber et al, 2007. The modified sample has similar general features but displays important variability in the ice transformation features, particularly for the case of the low filling-factor (f=0.2). The results exhibit a complex temperaturedependent variation of the crystalline and disordered components that are substantially altered for the different filling-factors. *

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

Cited by 71 publications

References 71 publications

Melting and freezing of water in cylindrical silica nanopores

Melting and freezing of water in cylindrical silica nanopores

Nuclear magnetic resonance cryoporometry

Studies of water and ice in hydrophilic and hydrophobic mesoporous silicas: pore characterisation and phase transformations

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