Mixed monolayers cooperativity

In another study by Kunitake, the amphiphile 45 was used to bind dipeptides at the air-water interface [75]. Using mixed monolayers of45 and a dioctadecyl glycylglycinamide amphiphile, a Langmuir isotherm for the binding of Gly-Leu was produced. The result was a cooperative binding event between the two... 

Since a SAM is a densely packed system where cooperative phenomena may occur, the overall strength of the next-neighbor interactions is difficult to foresee. For this reason, it is not possible to ensure that a feeding solution made of two, or more, thiols in any well-defined molar ratio will produce mixed monolayers with the same composition. The experimental parameters and conditions may be changed to a certain extent to tune the composition of the resulting monolayer. For instance, the solvent may be chosen to favor a polar thiol over an apolar one.40 43 44... 

The association of the acidic phospholipid PI with the cationic linear polysoap PVPC6 is cooperative in both mixed spread monolayers and mixed swollen multibilayers. This association has a condensation effect on the spread mixed monolayers on one hand and affects the properties of the interbilayer structural water of swollen mixed multibilayers on the other hand. Namely the increase in the degree of... 

SAMs consisting of a mixture of non-fimctionalised aUcanethiols and co-functionalised alkanethiols provide the chance to study isolated functionalised sites in SAMs. In these mixed SAMs the non-functionalised alkanethiols serve as dummy molecules to dilute the fimctionalised compounds and to isolate the active sites in order to minimise their interactions. These mixed SAMs play an important role, e.g. in the development of biorecognition surfaces [137-139). One obstacle in producing mixed monolayers is the different rate of adsorption of the non-functionalised and the end-fimctionalised thiols. Consequently, the final composition of the mixed SAMs not only depends on the initial ratio of the two thiols but also on their individual as well as cooperative adsorption and desorption kinetics [140]. Another problem is the tendency for similar molecules to aggregate into islands on the surface (Fig. 15) [141,142[. Therefore, the final SAM composition caimot be predicted easily. 

Figure 6. Cooperativity of the PI and PVPC6 association in mixed multibilayers and spread monolayers. Effect of this association on multibilayer structural water.

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