Contact angle hysteresis near a first-order wetting transition

We examine the contact angle hysteresis for n-octane droplets on a n-hexade cyltrichlorosilane-coated silicon wafer in the vicinity of a first-order we tting transition with wetting temperature T-w = 49.5 degreesC. A pinning tr ansition is observed at T-p = 46.8 degreesC for the receding contact angle. Above this temperature, the contact line for receding droplets is pinned; consequently, the receding contact angle theta (r), = 0 degrees. We use con tact angle data to quantify the substrate surface energy difference, Delta sigma (T) = sigma (sv)(T) - sigma (sl)(T), and the relative surface heterog eneity, h(0)/sigma (iv), as a function of temperature T where sigma (ij) is the surface energy between phases i and j.