Surface tension contaminant detection

Most organic residues on assemblies are not detected by ionic contamination meters. However, such residues do change the surface tension of assemblies, thereby influencing the adhesion of subsequent coatings. This method determines the surface tension by iterative use of corresponding testing inks. 

By analogy with solid particle dispersions, adsorption isotherms can be determined as a function of the chemical potential of the solute. An indirect, but rapid and powerful, example is given by surface tension measurements, which can detect very low amounts of surface-active solute in the form of contaminant. This property is used to determine purity in easily hydrolysable surfactants such as SDS or sodium bis(2-ethylhexyOsulfosuccinate (AOT). A minimum in the surface tension near the CMC directly detects the presence of a surface-active contaminant such as dodecanol or octanol, which will desorb from the interface at high surfactant concentrations. This desorption is the origin of the a priori counter-intuitive increase of surface tension with surfactant content (16). 

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