Wetting and adsorption of acetylenic diol based nonionic surfactants on heterogeneous surfaces

The wetting and adsorption of acetylenic diol based surfactants on lampblack and phthalocyanine blue was studied to determine the mechanisms of wetting of heterogeneous surfaces. The TMDD series of reagents, commonly known as acetylenic diol based surfactants, are derivatives of 2,4,7,9-tetramethyl-5-decyne-4,7-diol. While studies of conventional nonionic surfactants have included alkyl ethoxylates and ethoxylated alkyl phenol surfactants, limited information is available for acetylenic diol based surfactants. The effect of the degree of ethoxylation of these surfactants on adsorption and wetting of pigments was studied. Although the Langmuir model could be used to fit adsorption data in many cases, further analysis of the data showed that the free energy of adsorption was a function of adsorption density. The change in free energy with adsorption density could be interpreted by considering a change in the orientation of the adsorbed molecules. At monolayer coverage, acetylenic diol based surfactants were found to have an area per molecule of 2–3 times that of similarly ethoxylated alkyl phenols. The area per molecule was found to increase linearly with increased ethoxylation within each family of surfactants. The surface tension of these surfactants at the liquid/air interface was also investigated to delineate the effects of ethoxylation on the adsorption mechanisms.