Acid-base interactions in wetting

Abstract

The study of the ionization of carboxylic acid groups at the interface between organic solids and water demonstrates broad similarities to the ionizations of these groups in homogeneous aqueous solution, but with important systematic differences. Creation of a charged group from a neutral one by protonation or deprotonation (whether -NH3+ from -NH2 or -CO2-from -CO2H) at the interface between surface-functionalized polyethylene and water is more difficult than that in homogeneous aqueous solution. This difference is probably related to the low effective dielectric constant of the interface (ε≃9) relative to water (ε≃80). It is not known to what extent this difference in ε (and in other properties of the interphase, considered as a thin solvent phase) is reflected in the stability of the organic ions relative to their neutral forms in the interphase and in solution, and to what extent in differences in the concentration of H+ and OH-in the interphase and in solution. Self-assembled monolayers (SAMs)-especially of terminally functionalized alkanethiols (HS(CH2)nX) adsorbed on gold-provide model systems with relatively well-ordered structures that are useful in establishing the fundamentals of ionization of protic acids and bases at the interface between organic solids and water. These systems, coupled with new analytical methods such as photoacoustic calorimetry (PAC) and contact angle titration, may make it possible to disentangle some of the complex puzzles presented by proton-transfer reactions in the environment of the organic solid-water interphase.

Effect of Substratum Surface Chemistry and Surface Energy on Attachment of Marine Bacteria and Algal Spores

“…It is known that carboxylic acid-terminated SAMs change their surface energy in response to the pH of the surrounding medium (18,26,40). These SAMs can be titrated, with the range and position of the pH-dependent change in AW varying with the surface concentration of COOH-containing thiolates.…”

Reactions and Reactivity in Self-Assembled Monolayers

“…[116] This is in contrast with the expectations that the smaller density of the charged groups in mixed monolayers would lead to the increase of the strength of acid groups. Other reasons that may be responsible for the shift of surface pK 1/2 values relative to their bulk counterparts include a low interfacial dielectric constant, [116,125,126] the presence of a low dielectric permittivity region surrounding the acidic/basic groups, and changes in the number of degrees of freedom for the immobilized species. [127] Formation of hydrogen bonds between adjacent acid or base groups in the monolayers may also have some effect on their ionization properties, [112] although this effect should decrease in mixed monolayers with alkanethiols.…”

Estimation of the Surface Energy and Acid-Base Properties of Wood by Means of Wetting Method

“…The aromatic rings present in are effectively hidden in the underlying layer away from any contact with water especially during the initial wetting. It is known that acidic conditions will enhance the hydrophobicity and basic conditions will enhance the hydrophilicity (Whitesides et al 1991). On the other hand, considerable evidence exists that water wetting in the perpendicular direction produce apparent hydrophobicity (Table 2).…”