We
report a first-order like sharp surface wettability transition
with varying film thickness dependent morphology in cast films of
an amphiphilic triblock copolymer. Films composed of poly(2-(<i>N</i>-ethylperfluorooctanesulfonamido) ethyl methyl acrylate),
poly(FOSM), and poly(<i>N</i>,<i>N</i>′-dimethyl
acrylamide), poly(DMA), with thickness (<i>h</i>) in the
transition-range, 200 < <i>h</i> < 300 nm, exhibited
an abrupt hydrophobic to hydrophilic dynamic water contact angle transition.
After an induction time, <i>t</i><sub><i>i</i></sub> ≈ 40 to 180 s, water contact angle varied as θ<sub>c</sub> ≈ 116° to 40° with an ultrafast contact
angle decay time constant, dθcdt ≈ −18°/s.
This behavior
is a result of competing heterogeneous and antagonistic effects of
bumpy poly(DMA) wetting domains against a nonwetting planar poly(FOSM)
background, with a “jump percolation” wetting transition
when the poly(DMA) domain density reaches unity. Outside of this film
thickness range, relatively shallow decreasing water contact angle
gradients were observed with a monotonically increasing poly(DMA)
domain area coverage with increasing film thickness in the overall
range of 40 nm (hydrophobic, θ<sub>c</sub> ≈ 118°)
< <i>h</i> < 500 nm (hydrophilic, θ<sub>c</sub> ≈ 8°). The optical diffuse reflectance properties of
these rough surfaces exhibit an onset of diffuse reflectance maxima
correlated to the transition morphology film thickness
