Mixed monolayers for the design of structured surfaces to induce oriented 3-D crystallization

Mixed monolayers containing two different amphiphiles C19H39CONHCH2CH2CO2H (A) and C19H39CONH2 (B) were designed in order to form a two-dimensional (2-D) crystalline solid solution in which the A-type molecules form domains within the sea of B-type molecules. A ''continuous'' 2-D arrangement of the aliphatic chains was expected, driven by the amide hydrogen bonding requirement; a tendency for the formation of the embeded A-type domains should be provided by the interactions between the -CH2CH2CO2H head group moieties. The mixed monolayers served to promote the oriented nucleation of silver propionate 3-D crystals attached at the monolayer-solution interface. Only the A-type domains induced silver propionate crystallization whereas the B-type domains were essentially inert. The mixed A + B monolayers were found to be efficient nucleators down to a 1:10 molar ratio, providing proof for the existence of A-type domains. Additional information such as the structure and ion-binding properties of the mixed monolayers was furnished by specular X-ray reflectivity and grazing incidence X-ray diffraction using synchrotron radiation.