Surface Segregation and Wetting from Polymer Mixtures
Coexisting binary polymer phases are characterised by very small interfacial energies even well below their critical solution temperature. By extension of Cahn’s ideas concerning critical point wetting, one expects that such low energies should readily lead to the exclusion of one of the phases from any interface which favours the other; this phenomenon has implications for practical surface-related effects, ranging from welding to wear properties. Using nuclear reaction analysis, we have now observed such complete wetting behaviour from two different classes of binary polymer mixtures. These are mixtures of statistical olefinic copolymers of structure -(C2H3(C2H5))x((CH2)4)1−x-, with differing x values, and an isotopic pair of deuterated and protonated polystyrene. In the former case we have been able to follow the growth with time t of the wetting layer thickness l; our results indicate l ~ logt.
KeywordsEntropy Ethyl Welding Toluene Polyethylene
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- 22.While there are no predictions for the case of wetting layer build-up for the precise situation corresponding to our geometry, there is a related theoretical study by Langer (Ann. Phys. (N.Y.), vol.65, p.53, 1971) which we recall in passing. This discusses how a series of one dimensional spinodal domains evolve with time. This situation bears some resemblance to our experiments in the following sense. Starting with an array of equidistant spinodal domains of the same width, every second domain grows while the domain adjacent to it shrinks, both with a logarithmic time dependence, while the interdomain region at the coexisting composition retains a constant width. This is very reminiscent of the time-evolution of the adjacent domains in the profiles in fig. 5, though the driving force for the growth of the wetting layer differs from that of the spinodal decomposition.Google Scholar