RESEARCH
Solubilization Pegged as a Key to Detergency Effectiveness of surfactants is partly due to their ability to solubilize oily soils, Monsanto research shows Solubilization now appears to be an important mechanism in detergent action with oily soil systems (C&EX, Aug. 22, page 37). With the help of a new, radioactive tracer analytical technique, chemists at Monsanto's research and engineering division (Dayton, Ohio) find that more oily (or fatty) soil dissolves in a surfactant solution than was formerly thought. Also found: Solubilizing action seems to be the driving force behind this type of detergency. Pinpointing solubilization as a key mechanism is the latest result of Monsanto's long-term basic research program in detergency. According to Jay C. Harris, assistant director of research for surfactants, the question until now was: Is soil emulsified or solubilized when treated with detergents; or does some combination of the two occur? Results obtained with the tracer technique strongly support the solubilization concept, Mr. Harris claims. Other chemists working with him are Martin E. Ginn and Albert J. Blardinelli. Although the Monsanto research is aimed at drawing a mechanistic pic-
ture of detergency, data gathered can affect the very practical function of washing with detergents. Optimum detergents can't be formulated unless detergency mechanisms are fully understood. Monsanto feels that its group has made a lot of headway in that direction. What has been known so far, explains Mr. Harris, is that maximum detergency correlates with a phenomenon called critical micelle concentration ( c m c ) - a concentration at which individual surfactant molecules form an aggregate having regular dimensions. For any given surfactant, cmc is a constant. When a solution reaches cmc, surface tension is at a minimum, detergency rises steeply to a maximum. Since cmc is so significant in detergency. the Monsanto chemists used it as a starting point for their solubilization studies. Use Tagged Fats. The tracer analysis consists of washing a fatty soil tagged with carbon-14 from glass, then measuring remaining radioactivity. Either C 14 -labeled tristearin or triolein is in the fattv soil used. With tri-
stearin, C 14 is on a carboxyl group; triolein's tag is on glycerol. Although other substrates can be used besides glass (cloth, for example), the Monsanto team chose glass for convenience and because its chemical composition is known. The analysis is standardized for roughed (with Carborundum) microscope slides. Roughing the glass gives it 1.9 times the surface area of smooth specimens, also forms hemispheres which soil can adhere to. After the roughed slides are coated with known amounts of tagged soil, they're washed and remaining radioactivity measured. The solubilization technique will pick up concentrations of tagged soil (as fat) as low as 0.00()05
