Title: The relationship of structure to properties in surfactants. IV. Effectiveness in surface or interfacial tension reduction
Abstract: Equations have been derived for the effectiveness with which a surfactant above its Krafft point depresses the surface or interfacial tension of a solvent. The effectiveness, defined as the interfacial tension reduction (or interfacial pressure, πeme) attained at the critical micelle concentration, is shown to depend upon: (1) the maximum surface excess concentration of the surfactant, (2) its critical micelle concentration, and (3) the efficiency, log (1/C)π=20, with which it can depress the interfacial tension by 20 dynes/cm, and is related to the difference in the free energy changes involved in the transfer of the surfactant molecule to the micelle or to the air/liquid (or liquid/liquid) interface at π = 20. For both nonionic and 1:1 ionic surfactants, πeme is only slightly affected by change in the length of the hydrophobic group. Other structural changes in the hydrophobic group or in the counterion, however, can cause marked changes in the effectiveness. In polyoxyethylenated nonionics, πeme reaches a maximum at about four oxyethylene units, and then decreases with increase in the number of these units above six due to the increase in the cross-sectional area of the molecule at the interface.
Publication Year: 1976
Publication Date: 1976-08-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 111
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