The ionization characteristics of monolayers of weak acids and bases

Betts, J. J.; Pethica, B. A.

doi:10.1039/tf9565201581

Cited by 161 publications

(88 citation statements)

References 3 publications

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“…The second explanation is that dipolar effects at the interface play an important role in determining the behavior of PE-C 2 H ( Figure 25B). 57 Both carboxylic acid and carboxylate groups have large dipole moments. Thus, there should exist a high electrostatic field gradient at the polymer-water interface.…”

Section: )mentioning

confidence: 99%

Acid-base behavior of carboxylic acid groups covalently attached at the surface of polyethylene: The usefulness of contact angle in following the ionization of surface functionality

Holmes‐Farley¹,

Reamey²,

McCarthy³

et al. 1985

Langmuir

309

245

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Oxidation of polyethylene with chromic acid/sulfuric acid generates a material (PE-C02H) having a high density of carboxylic acid and ketone functionalities in a thin surface layer on the polymer. This paper determines the extent of ionization of the surface and near-surface carboxylic acid groups of these materials in contact with water as a function of pH using three experimental techniques: measurement of attenuated total reflectance infrared (ATR-IR) spectra, measurement of contact angles, and direct potentiometric titration. On the basis of correlations between results obtained by these three techniques, we propose an equation relating the contact angle of an aqueous solution having a given value of pH and the extent of ionization (a;) of those carboxylic acid groups that are directly exposed to the solution. These carboxylic acid groups have broad titration curves and have C02H groups that are less acidic than soluble carboxylic acids. The initial ionization of these carboxylic acid groups occurs when the solution is approximately pH 6. The detailed structures of these oxidized polymer surface layers and the nature of the interactions between the carboxylic acid and carboxylate ions in them are still not completely defined. Salt effects on the extent of ionization a; at a particular value of pH are unexpectedly small and suggest that charge-charge interactions between carboxylate ions may not dominate the titration curves. This work demonstrates the usefulness of contact angle in following chemical changes occurring in organic functional groups on surfaces. Comparisons of wetting behavior of buffered and unbuffered solutions establishes the importance of using experimental protocols for measuring contact angles in which the reactive groups present in the interfacial region do not outnumber the reactive groups present in the small drop of dilute aqueous solution.

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Section: )mentioning

confidence: 99%

Acid-base behavior of carboxylic acid groups covalently attached at the surface of polyethylene: The usefulness of contact angle in following the ionization of surface functionality

Holmes‐Farley¹,

Reamey²,

McCarthy³

et al. 1985

Langmuir

309

245

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“…Adsorption mechanisms for BuNH2 and H20 appear quite different. Theoretical slopes for various models of surface coverage by BuNH~, assuming 25 .&2 for the area of butylamine molecule (Betts and Pethica, 1956) and 15.8 A2 for nitrogen, are itemized in Table 5. In Fig.…”

Section: Butylamine Adsorptionmentioning

confidence: 99%

Adsorption Studies on Kaolinites

Lloyd¹

1970

Clays and clay miner.

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Abstract--Adsorption studies have been performed on Georgia kaolins having a broad range of crystallinity~and particle size distributions (from 0.1/~ to 44/~) using N2 (78~ H20 (273~ and BuNH2 (298~ Using both vapor and liquid phase adsorption techniques, surface affinities of the adsorbates were determined.Modified FrenkeI-Halsey-Hill plots were used to compute the preferential adsorptivity of HzO vapor over N 2 (hydrophilicity index, H.|.) as a function of crystallinity index, C.I., and particle size. For amine adsorptivity, non-aqueous adsorption isotherms were obtained.Within any geographic deposit, crystallinity exhibits an inconsistent pattern with respect to particle size. A single generality is the tendency for crystallinity to increase toward the fine particle size range, D --* 0-2/.L. Adsorptivities of Nz, H~O, and BuNH~ show no dependence upon crystallinity within a given particle size range. However, F.H.H. compensated slopes, describing the preferential adsorptivity over N2, show a definite decrease as crystallinity increases. A striking anomaly occurs in the vicinity of 0.2 < C.I. < 0.7 where H.I. increases briefly then returns to the original trend. The rate of decrease of H.I. vs. C.I. is consistently steeper with increasing particle size. Adsorption of water vapor most likely occurs as a I : l configuration on each silica-alumina edge group, l : l on each basal silica, and l : 2 (hindered configuration) on each basal alumina group.The data suggest that amines adsorb preferentially and quantitatively on the edges, i.e. the Lewis and Bronsted acid sites, and follow a Langmuir pattern.

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“…Langmuir adsorption isotherms yield 32 ~2 per butylamine molecule as the effective adsorption area. This is slightly in excess of the minimum molecular cross sectional area, 25 A s (Betts and Pethica, 1956), for adsorption. Wettability of the kaolin surface, both the rate and extent, is strongly affected by amine adsorption (Kitahara and Williamson, 1964).…”

Section: Introductionmentioning

confidence: 99%

Adsorption Studies on Kaolinites — II Adsorption of Amines

Conley¹

1971

Clays and clay miner.

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Abstract-An investigation of the reaction between amines and hydrogen kaolinites having a broad range of crystallinites and particle sizes has been made. Aqueous and non-aqueous adsorption isotherms, conductivity titrations, rheological measurements and sediment volume studies give strong evidence that edge sites are dominantly involved in the reaction and basal surfaces remain essentially unaltered. The acid-base reaction produces a localized adduct rather than an ionized, protonated amine. The amine-hydrate adduct adsorbs with greatly modified geometry.

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The ionization characteristics of monolayers of weak acids and bases

Cited by 161 publications

References 3 publications

Acid-base behavior of carboxylic acid groups covalently attached at the surface of polyethylene: The usefulness of contact angle in following the ionization of surface functionality

Acid-base behavior of carboxylic acid groups covalently attached at the surface of polyethylene: The usefulness of contact angle in following the ionization of surface functionality

Adsorption Studies on Kaolinites

Adsorption Studies on Kaolinites — II Adsorption of Amines

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