Magnetic Properties of Adsorbed Vapors

Milligan, W. O.; Whitehurst, H.B.

doi:10.1021/j150501a009

Cited by 8 publications

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“…For the silica/water sample (this study) the activation energy of 15.3 kJ/mol obtained from the T 1 temperature dependency is similar to the value obtained for monomeric water molecules in solution . Milligan and Whitehurst concluded from magnetic susceptibility measurements that the separation of water molecules in the first monolayer on the surface does not permit hydrogen bonding. However, the temperature dependency of the T 1 values found in the study presented here suggests that a similar separation of water molecules may exist also in the water layers further from the silica surface.…”

Section: Discussionsupporting

confidence: 82%

Water Structure and Dynamics at a Silica Surface: Pake Doublets in ¹H NMR Spectra

Totland¹,

Steinkopf²,

Blokhus³

et al. 2011

Langmuir

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Detailed knowledge about the dynamics and structure of liquids in the vicinity of a solid surface is important in several fields of research. In this study a homogeneous model system of colloidal and nonporous silica particles with a narrow particle size distribution was used to examine such properties of adsorbed water and 1-heptanol. Doublet (1)H water resonances ("Pake doublets") indicate a preferred spatial orientation for the water molecules, as well as a lower molecular density in the surface-induced water structures compared to bulk water. These surface-induced structures are found to extend at least 8 nm from the silica surface. T(1) relaxation measurements at several temperatures indicate weaker H-bonding in the adsorbed water compared to bulk water. T(2) relaxation measurements at several temperatures reveal the presence of two water phases and give quantitative information on the mobility of water molecules and proton exchange processes. The presence of 1-heptanol changes the water characteristics, primarily in the water phase closer to the surface, where water molecules experience decreased translational and increased rotational freedom. In the absence of water, adsorbed 1-heptanol forms surface aggregates encompassing several molecular layers, where the first adsorbed layer shows severe restrictions in mobility and subsequent layers are more mobile.

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Section: Discussionsupporting

confidence: 82%

Water Structure and Dynamics at a Silica Surface: Pake Doublets in ¹H NMR Spectra

Totland¹,

Steinkopf²,

Blokhus³

et al. 2011

Langmuir

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“…The above hypothesis is offered as one possible explanation for the sorbed water entropy data. The density of the sorbed water (Anderson and Low, 1958), the large amounts of unfrozen water a t -5°C (Hemwall and Low, 1956), the nuclear magnetic resonance data on sorbed water (Pickett and Lemcoe, 1957), and the magnetic susceptibility of sorbed water (Milligan and Whitehurst, 1952) are all consistent with the concept that the sorbed phase has less structure than normal liquid water. I n fact, the author knows of no experimental data concerning the sorbed phase on clay that cannot be explained if the sorbed phase is interpreted as statistically more random than liquid water at the same temperature and pressure.…”

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confidence: 56%

Water Vapor Sorption on Kaolinite: Entropy of Adsorption

Martin

1959

Clays clay miner. (Natl. Conf. Clays Clay Miner.)

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Water vapor adsorption isotherms a t five temperatures between 0 and 40°C were obtained on Li and Na kaolinite. By a careful experimental technique, the error in the determination of weight of water adsorbed was reduced to +O.Ol mg/g and that of equilibrium vapor pressure was reduced to t0.0002 mm Hg. The data were used to calculate the integral and differential entropy of the adsorbed water phase. The differential entropy of adsorption (the partial molar entropy of water in the sorbate phase minus the molar entropy of normal liquid water) has large positive values a t low surface coverage. As more water is adsorbed, the differential entropy drops to a negative value approximately equal to that of a two-dimensional liquid which is about the same as the entropy for hypothetical ice a t this temperature and pressure. The water can hardly be treated as " ice " because the large negative entropy persists over a very smallp/po range and occurs a t a p/pO such that the surface is only about 70 percent covered. The integral entropy of adsorption (the molar entropy of water in the sorbate phase minus the molar entropy of normal liquid water) has positive values on both Li and Na kaolinite throughout the p/po range investigated; plpo = 0 to plpo = 0.5. These entropy data indicate that the water molecules in the adsorbed phase on Li or Na kaolinite possess greater randomness than the water molecules in normal liquid water from the dry clay up to at least p/po = 0.5. The difference between integralanddifferential entropies is explained as a " configurational entropy " that changes with the amount of the adsorbed phase. A hypothesis to explain the entropy data is proposed in which one builds inward from normal liquid water to the solid surface rather than the more conventional mechanisms which build outward from the solid surface. I n this way the entropy data can be explained in terms of what happens to the structure of normal liquid water when different sized ions or nonpolar molecules, or both, are added. Literature data for the low density and dielectric coefiicient of the sorbed phase plus the large amounts of-unfrozen water still present a t-5'C are frequently used as evidence for the quasi-solid structure of the sorbed phase. A consideration of the water molecules in the sorbed phase as more random than normal liquid water is a n equally plausible explanation. Nuclear magnetic resonance and magnetic susceptibility data which cannot be explained by an increase in water structure are in complete agreement with the entropy data and the proposed new working hypothesis. It is concluded that not only the present entropy data but also all literature data (known to the author) concerning the sorbed phase can be satisfactorily explained if one considers the water molecules in the sorbed phase as being more random, less structured, than normal liquid water.

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Adsorption and heat of adsorption of diethyl ether. acetone and acetic acid vapors on graphitized carbon black

1962

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Magnetic Properties of Adsorbed Vapors

Cited by 8 publications

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Water Structure and Dynamics at a Silica Surface: Pake Doublets in ¹H NMR Spectra

Water Structure and Dynamics at a Silica Surface: Pake Doublets in ¹H NMR Spectra

Water Vapor Sorption on Kaolinite: Entropy of Adsorption

Adsorption and heat of adsorption of diethyl ether. acetone and acetic acid vapors on graphitized carbon black

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Magnetic Properties of Adsorbed Vapors

Cited by 8 publications

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Water Structure and Dynamics at a Silica Surface: Pake Doublets in 1H NMR Spectra

Water Structure and Dynamics at a Silica Surface: Pake Doublets in 1H NMR Spectra

Water Vapor Sorption on Kaolinite: Entropy of Adsorption

Adsorption and heat of adsorption of diethyl ether. acetone and acetic acid vapors on graphitized carbon black

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Water Structure and Dynamics at a Silica Surface: Pake Doublets in ¹H NMR Spectra

Water Structure and Dynamics at a Silica Surface: Pake Doublets in ¹H NMR Spectra