Specific solvent strength definition

Various scales of solvent strength (polarity) and selectivity have been used to classify stationary phases. Classification based on polarity had to be abandoned because of the lack of a working definition. There is no substance that is uniquely polar and suitable to probe the polarity of other substances. Selectivity is defined as the relative capacity of a stationary phase for specific intermolecular interactions, such as dispersion, induction, orientation, and hydrogen-bond formation. Early attempts at a systematic definition of selectivity scales were based on the system of phase constants introduced by Rohrschneider and... 

Adhesives are nonmetaUic substances used to join two surfaces by means of surface adherence (adhesion) and inherent strength (cohesion), DIN 16920. This definition of adhesives does not cover water glass adhesives, adhesive ceramics, or adhesive mortars. The substances used as adhesives are polymers that go through a liquid phase at least once (reactive adhesives) or more than once (hotmelts, thermally activated adhesives). The liquid phase can also be achieved by dissolution in suitable solvents (nonreactive adhesives). In dispersion adhesives, the polymer molecules are dispersed (finely distributed) in a liquid - usually water - whereby the polymer molecules themselves are not dissolved. Fig. 6. These adhesives are also known as water-based or aqueous adhesives. It must be remembered that solvents are contained in these adhesives in addition to the water. Genuine aqueous adhesives contain less than 5% solvents in the liquid phase. The dispersions crnitain, in contrast to the solute adhesive molecules, additional substances, disposal of which requires specific additional measures. Since the dispersions represent stable systems in water, the water-resistance of such adhesives is reduced. Their thermal and water resistance can be increased by additional crosslinking (usually with isocyanates). 

Two species combine to form a complex in water if the sum of the intermolecular forces between them more than olfsets the sum of the loss of favorable interactions with solvent and any unfavorable interactions that develop between solutes during complex formation. Collectively the interactions between non-bonded species are referred to as cohesive forces, defined as those forces lost when the species are transferred to infinite separation in the gas phase. While it is common to classify chemical forces as covalent or non-covalent, the interactions are fundamentally the same only the magnitude of the interactions varies. Cohesive, non-specific forces are weak compared to covalent interactions typically we consider cohesive forces as those forces with strengths less than 1% of covalent bond strengths. We will see, however, that this definition is somewhat arbitrary and in fact a continuum of interaction energies exists. 

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