ANTIFOAMS 121 The practical factors affecting the performance of silicone antifoams, in general, have been given (8-10) and will be elaborated upon elsewhere. Certain experimental aspects of the behavior of transient antifoams are now presented. SPECIALTY ANTIFOAMS: THE "TRANSIENT" ANTIFOAM Over the past 20 years, several specialty antifoams have evolved. They have been developed both on an ad-hoc basis, i.e., for specific foaming systems, or as generic specialty types. The most recent example of the latter type is the transient antifoam which is in contrast to practically all the antifoams described thus far which, in general, I I lOOO •ß 0.5% PALMOLIVE DISHWASHING LIQUID 2300 TEMPERATURE 100 - u ¸ 10 - TAf-1 300 ppm o• , TAr-l, 200 ppm 1 - - I I I 0 20 40 60 AGING TIME, hrs. Figure 8. ]•ffect of transient antifoam concentration on its performance in 0.5% Palmolive dishwashing liquid.

122 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS lead to lasting reduction of the foaming power of a given system. For certain process or product applications, the foam inhibition or control requirement may be only temporary and subsequent regeneration of foaming characteristics is either highly desirable or essential. For example, during handling of liquid surfactant systems such as shampoos or dishwashing liquids or in plant operations such as filling, temporary foam inhibition would significantly aid overall processing efficiency, but restoration of foaming power is essential thereafter. Transient antifoams have been developed with these applications in mind: after use and exerting their action they destroy themselves 1000 ß , , lOO lO ß ß 23øC TAr-1 ....... 400 ppm 0.5% PALMOLIVE DISHWASHING LIQUID ß 75øC 50øC I I I I 0 10 2o 3o AGING TIME, hrs Figure 9. Effect of aqueous aging temperature on the performance of the transient antifoam.