![Octane is a non-polar liquid. Its interaction with the glass substrate is purely dispersive giving rise to the octane/water interfacial tension. Water is a polar liq-uid . Its interactions with the glass substrate may be broken down into two compo-nents: dispersive and non-dispersive. The dispersive (London) interactions are those generated by instantaneous (non-permanent) dipole interactions . The non-dispersive interactions include the permanent dipole interactions (Keesom and Debye interactions), hydrogen bonding and acid-base interactions. The latter two generate a surface charge on the glass substrate. The dissociation of silanol (SiOH) groups at the glass surface may be represented by the following reaction: The surface charge generated by these acid-base interactions increases the glass/water interfacial energy. The dispersive component of the surface tension of water is almost equa l to the surface tension of octane: y = 21.8 mJ/m [5] and Yo = 21.6 mJ/m [6], where the subscript "w" stands for water and the subscript](https://images.tandf.co.uk/common/jackets/crclarge/978906764/9789067643764.jpg "Octane is a non-polar liquid. Its interaction with the glass substrate is purely dispersive giving rise to the octane/water interfacial tension. Water is a polar liq-uid . Its interactions with the glass substrate may be broken down into two compo-nents: dispersive and non-dispersive. The dispersive (London) interactions are those generated by instantaneous (non-permanent) dipole interactions . The non-dispersive interactions include the permanent dipole interactions (Keesom and Debye interactions), hydrogen bonding and acid-base interactions. The latter two generate a surface charge on the glass substrate. The dissociation of silanol (SiOH) groups at the glass surface may be represented by the following reaction: The surface charge generated by these acid-base interactions increases the glass/water interfacial energy. The dispersive component of the surface tension of water is almost equa l to the surface tension of octane: y = 21.8 mJ/m [5] and Yo = 21.6 mJ/m [6], where the subscript \"w\" stands for water and the subscript")
ABSTRACT
The non-dispersive (dipolar, hydrogen bond, and acid-base) interactions between a clean glass surface and water can give a simple estimate of the hydroxyl group density at the glass surface, providing a measure of the density of SiOH reactive sites at the glass surface. If we assume the non-dispersive interaction between glass and water to be dominated by hydrogen bonding and acid-base interactions, we may consider that at the point of zero charge of the glass substrate the non-dispersive interaction energy to be dominated by hydrogen bonding. At this point, the surface energy per unit area can be divided by the energy per hydrogen bond to obtain the number of hydrogen bonds per unit area. Taking the -OH bond energy between water and the glass surface as 24 kJ/mol [8] gives the following expression for the -OH group density, expressed as the number of hydroxyl bonds per square nanometer:
(9)
where 9 is the contact angle of sessile water drop under octane at the point of zero charge. The above equations relating wettability measurements to the nondispersive interaction between the glass surface and water are valid if organic contamination is absent from the glass surface.
