Determination of Surface Tension of Surfactant Solutions from a Regulatory Perspective

Determining the surface tension of surfactant solutions sounds simple, and the state of the art for decades has been Pendant Drop Tensiometry (Drop Shape Analysis). According to DIN/EN/ISO standards and OECD guidelines, the only legally existing methods in the field of surfactants are the ring/plate methods, basically from the pre-computer era. For many technical surfactants and especially for surface-active polymers, these vintage methods have serious technical shortcomings caused by an inherently uncontrolled surface age. This will be demonstrated by discussing the surface tension results of two associative thickeners. Normalization activities have been initiated to „legalize“ the current state of the art, Pendant Drop Tensiometry, also in the field of surfactants.