Mixed monolayers phase segregation

A different situation has been observed using mixtures of thiolates with immiscible chains. AuNPs protected by mixed monolayers of different composition made of HS-C8-TEGME and HS-F8-PEG have been investigated by ESR spectroscopy using a radical probe sensitive to the hydrophobicity of the environment.223 The ESR spectral parameters of the probe in the monolayer are identical to those of the probe in a completely fluorinated medium when the ratio (Rcf) between alkyl and perfluoro-alkyl is lower than 2.5. Only at RCp > 2.5, the probe starts to experience the environment of alkyl chains. The experimental results support the phase segregation of perfluoroalkyl thiolates in patches on nanoparticles with a core size of 2.5 to 4.0 nm.223... 

Phase Transitions in Metal Oxide Catalysts- As alluded to above, several changes in solid structure can occur that can result in the loss of catalydcally active surface. For oxides on oxide supports, the individual solid phases may be active or a specific mixed oxide phase (such as a spinel or trirutile) may be more active than the segregated phases. Between these two extremes, many oxide catalysts are formed by monolayer epitaxy of an active surface oxide layer on a sympathetic support so that the support intimately but not directly promotes the formation of the active surface. 

In mixed monolayers with unsubstituted alkanethiols, containing up to 50% of the hydroxyalkanethiol, there is no indication of such H-bond formation. This is inconsistent with the phase-separation hypothesis, as hydroxy functions would surely form H-bonds with each other in domains, and Bertilsson and Liedberg concluded that the monolayers do not phase-segregate . On the other hand, mixed layers of alkanethiols of different chain lengths showed, however, that these layers are at least partially crystalline, while disorder was expected for homogeneous monolayers. Existence of at least partial phase-separation was inferred . ... 

All the strategies discussed so far suffer from a potential drawback, i.e., phase segregation. It has been reported that, in a mixed monolayer, the single components can be localized within domains, leading to a patchwork surface [85, 86]. This arrangement of the molecules often minimizes the overall energy of the system, thanks to the maximization of the attractive interaction between similar molecules within each domain. 

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