Physical Adsorption on Low-Energy Solids. III. Adsorption of Ethane, n-Butane, and n-Octane on Poly(tetrafluoroethylene)

Graham, Donald P.

doi:10.1021/j100782a052

Cited by 44 publications

(4 citation statements)

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“…Unlike the system benzene-PTFE, n-decane-PTFE gives zero contact angle at the boiling point in its vapor. It is interesting to note that Neumann et al [32] have reported that absorption of n-decane can take place on PTFE similar to that described earlier by Graham [33]. Boyes and Ponter [34] have described anomalous behavior of cyclohexane, a non-polar compound, on a PTFE surface which they suggested was also caused by an absorption process creating a surface modification.…”

Section: Discussionsupporting

confidence: 57%

The influence of environment on the drop size ? contact angle relationship

Ponter

Yekta-Fard

1985

Colloid & Polymer Sci

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Advancing contact angles are reported for the water-PTFE, water-copper, water-stainless steel, water-PMMA and n-decane-PTFE systems for a range of liquid drop sizes.The angles were determined at 25 ~ in an air or nitrogen-saturated atmosphere and compared with those measured at the boiling point in an environment only of its vapor.For water-PTFE and water-PMMA systems, a decrease in contact angle with decreasing drop size was observed in an air-saturated environment at 25 ~ confirming the data of Good and Koo. An increase in contact angle however occurred with decreasing drop size at the boiling point in the pure vapor atmosphere confirming the results of Boyes and Ponter. The introduction of nitrogen decreased the contact angle although the trend remained the same.

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Section: Discussionsupporting

confidence: 57%

The influence of environment on the drop size ? contact angle relationship

Ponter

Yekta-Fard

1985

Colloid & Polymer Sci

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“…Where interface curvature (J) is related to relative pressure (P/P°) by the Kelvin equation J = E~I n (P/P°) (1) and where the fluid-solid contact angle is known for the bulk fluid (of surface tension y and molar volume Vp, a pendular-ring isotherm may be constructed for spheres of a given radius R utilizing either the torus approxi-mation9 or the exact nodoid calculations.10 If the spheres are not of uniform diameter, as assumed previously where such corrections are a relatively small fraction of the total adsorption, the computation is more involved and must depend upon an accurate particle-size distribution. Rose11 has calculated the volume of the pendular-ring condensate held at sphere contacts when the spheres are of differing radii using the torus approximation.…”

Section: Resultsmentioning

confidence: 99%

“…Unfortunately, the proximity of the pendular-ring condensation and the measured isotherms while showing the controlling importance of capillary condensation at the same time prevents resolution of a true adsorption isotherm because of residual uncertainties in the calculations. Four areas of possible deficiency in pre-cision may exist in these calculations: (1) uncertainty in the particle-size distribution, (2) uncertainty in the coordination number, (3) variation in contact angle at pressures other than saturation vapor pressure, and (4) applicability of the Kelvin equation to small menisci. As noted in a previous discussion,8 the technique of depositing Teflon particles on supported films for electron microscopy could introduce a particle selection bias into the size distribution.…”

Section: Resultsmentioning

confidence: 99%

“…Although the true adsorption at high relative pressures cannot be resolved from these calculations, the following conclusions can be drawn from the study. (1) The major contribution to the measured isotherms at high relative pressures is the pendular-ring condensate. (2) The best calculations are not sufficiently accurate to permit a realistic estimate of the extent of true adsorption at high relative pressures.…”

Section: Resultsmentioning

confidence: 99%

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Pendular-ring condensation on Teflon powders

Wade¹,

Whalen²

1968

J. Phys. Chem.

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The wetting behavior of azeotropic systems at atmospheric and reduced pressures

Boyes¹,

Ponter²

1972

AIChE Journal

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Contact angles are reported for the azeotropic systems n-propanol-water and benzene-cyclohexane measured under distillation conditions at total reflux over a pressure range 50 to 760 torr on both copper and polytetrafluoroethylene surfaces. The influences of the solid surfaces, the surface tension positive and negative nature of the liquids, together with the changes accompanying the azeotropic shift with pressure on the wettability, have been established and shown to conform with wetting theory. ADRIAN P. BOYES and ANTHONY B. PONTER Deportment of Chemicol EngineeringUniversity of New BrunswickFredericton, Canada SCOPEThe wettability of binary liquids which form azeotropes and whose surface tensions are strongly dependent on concentration have been determined for a range of pressures in a cell in which the contact angles can be meawred at conditions which simulate total reflux in a distillation column. The object of the study was to establish if the wetting changes actually occurring were responsible for the large changes in efficiency of separation at concentrations near the azeotrope and at near-terminal compositions. No methods are available for predicting performance of columns in these regions and to date no interfacial properties have been reported for these conditions upon which the interfacial areas for transfer and so column efficiencies are dependent. CONCLUSIONS A N D SIGNIFICANCEWhen aqueous mixtures of n-propanol are distilled below the azeotropic composition, representing a surface tension positive system (that is, where the lighter component has the lower surface tension on copper which is a surface with a high surface free energy), a reduction in pressure has been shown to cause a decrease in wettability. Conversely, for n-propanol concentrations above the azeotrope, which is a surface tension negative system, an increase in wetting resulted when the pressure was reduced. With the low energy surface polytetrafluoroethylene for any propanol composition, the wetting was found to be independent of pressure and temnerature. For the benzene-cyclohexane system, however, the wetting behavior was not found to be analogous to that described when using n-nrouanol-water since an additional effect which was attributed to the cyclohexane being absorbed on the polytetrafluoroethylene surface was encountered.The azeotropic shift caused by varying the pressure was shown to result in binary mixtures which have compositions close to the azeotrope, changing from surface tension positive to negative in nature with accompanying differences in wetting behavior. The dependency, wetting on concentration, in particular near the azeotrope and at near-terminal values predicted by considering the relative contributions played by the vapor-liquid, liquid-solid, and vapor-solid interfaces, was in accord with the experimental findings.The data point conclusively to the controlling role played by wetting on column performance using these systems. They also illustrate that design of distillation columns for separation of azeotrop...

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Physical Adsorption on Low-Energy Solids. III. Adsorption of Ethane, n-Butane, and n-Octane on Poly(tetrafluoroethylene)

Cited by 44 publications

References 0 publications

The influence of environment on the drop size ? contact angle relationship

The influence of environment on the drop size ? contact angle relationship

Pendular-ring condensation on Teflon powders

The wetting behavior of azeotropic systems at atmospheric and reduced pressures

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