SEARCH Articles Figures Tables X-9 shows plots of cos 6 versus 7l for various series of liquids on Teflon . Each line extrapolates to zero at a certain 7l value, which Zisman has called the critical surface tension 7 since various series extrapolated to about the same value, he proposed that 7 was a quantity characteristic of a given solid. For Teflon, the representative 7 was taken to be about 18 and was regarded as characteristic of a surface consisting of —CF2 — groups. [Publishers Imprint] [Publishers Imprint]