Hydrogen-bonded molecular aggregates characterization

In summary, the infrared spectra of aprotic solvents are much simpler than those of protic solvents because of the absence of complications due to hydrogen bonding. On the other hand, the aprotic liquids are characterized by very high molecular dipole moments. As a result, dimers can be formed in which some of the molecules line up with their dipole vectors in an antiparallel fashion [30]. This can lead to the spectra being complicated by additional spectral features due to solvent aggregates. Nevertheless, the prominent band due to the polar group in these solvents can be used to probe solute-solvent interactions in non-aqueous media. This subject is discussed in more detail in the next section. 

Nonionic and ionic surfactant molecules adsorb on solid surface at water-insoluble solid-water interface such as silica gel-water and alumina-water interface through van der Waals, hydrophobic, hydrogen bonding, and polar/ionic interactions at low concentrations of surfactant. Then, at a relatively higher and specific concentration known as critical hemimicelle concentration (CHMC), the adsorption increases dramatically as hemimicelles form on the adsorbent involving forces that characterize hydrophobic, van der Waals, and polar/ionic forces. Hemimicelles are two-dimensional molecular aggregates whose structural and physicochemical behavior have not been studied as extensively as those of normal micelles and, consequently, they are not understood even at a very rudimentary level. 

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