Model and Experimental Study of Surfactant Solutions and Pure Liquids Contact Angles on Complex Surfaces - Drops and Bubbles in Contact with Solid Surfaces - page 199

(a)

(b)

Figure 7. Advancing (closed symbol) contact angles of surfactant solutions and pure liquids on (a)
Teflon AF coated and (b) naturally saturated hydrocarbon chemistry AKD. Pure liquid contact angles
are given as open circles (advancing). Lines show the model prediction of contact angles (using Eqs
(10b) and (10d) for Wenzel and Cassie mode wetting, respectively) using parameters found for aque-
ous solutions of SDS on Teflon AF. Standard deviations are generally of the same order as symbol
size, and are not shown.

is possible to fit the high concentration data on Fig. 7a with the modified Wenzel
equation using r

2 . 85 (see
Table 1). Further, since uncoated AKD is seen not to be wetting in the Wenzel mode
for high concentration surfactants, it is unlikely that Teflon AF coated AKD (with
a higher intrinsic contact angle) would wet in the Wenzel mode. The Wenzel mode
predictions for r

≈ 5. This is incongruous with the measured value of r =

≈ 5 are therefore not shown on Fig. 7a. Multiple Cassie mode