Blends With a Small Surface Energy Difference Afs

Blends With a Small Surface Energy Difference Afs 

At least three of the studied blends [16,145] h86 (N86=1520)/d75 (N75=1625, deuteration extent e=0.4),d75/h66 (N66=2030) and h66/d52 (N52=1510 as well as e=0.34) may be described by a rather small Afs driving surface segregation. In an extreme case of the lowest Afs magnitude the enrichment-depletion effect is expected, as observed for the h66/d52 blend (see the next section). Here we characterize this class of mixtures with the results obtained for the h86/d75 blend. Surface excess z has been determined [145] as a function of bulk concentration at two different temperatures the corresponding (f) values are denoted as open circles (O) in the h86/d75 phase diagram (see inset to Fig. 21a). Surface segregation of the h86 component with a local concentration ( (z) has been stud- 

This Cahn construction (Fig. 22) suggests that for the h86/d75 blend the wetting point Tw ( 72 °C) may be located close to the critical point Tc (=97 °C). Similar conclusions are suggested by the Cahn analysis made for the h66/d52 and d75/h66 blends. Our very recent experiments [215], studying the growth of the surface excess layer from coexistence composition, seem to confirm these findings. 

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