Biomedical Engineering Reference
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(a)
(b)
Figure 6. Advancing (closed symbol) and receding (open symbol) contact angles of surfactant solu-
tions on (a) Teflon AF coated and (b) OTS coated, etched aluminum. Pure liquid contact angles are
given as open circles (advancing) and ' × 's (receding). Lines show the model prediction of contact an-
gles (using Eqs (10b) and (10d) for Wenzel and Cassie mode wetting, respectively) using parameters
found for aqueous solutions of SDS on Teflon AF. Standard deviations are generally of the same order
as symbol size, and are not shown.
on OTS coated aluminum compared to Teflon AF coated aluminum. All of this is
expected since the OTS coated silicon (Fig. 4b) shows lower intrinsic contact angle
compared to Teflon AF coated silicon (Fig. 4a). Surfactant solution contact angles
are still well predicted by the modified Cassie model, and are still higher than cor-
responding non-aqueous pure liquid contact angles. It seems, however, that OTS
coated aluminum shows a state of partial penetration for the highest concentrations
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