In situ investigation of dynamical nanophase separation

The nanophase separation behavior of two semi-fluorinated isophthalic acid derivatives, F8H10-ISA and F12H11-ISA, at the liquid-solid interface is studied by in situ scanning tunneling microscopy. Two polymorphs of F8H10-ISA were observed at the interface. One polymorph, which is not stable in time, showed nanosegregation of the perfluorinated segments of the alkyl chains, while the second polymorph showed a completely interdigitating lamellar structure with solvent co-deposition. This co-deposition of solvent molecules is believed to induce extra stability in the monolayer which in turn aids the molecules in overcoming the repulsive interactions induced by the perfluorinated segment of the molecule. F12H11-ISA did not exhibit nanosegregation at the liquid-solid interface, despite the longer perfluorinated segment (increase by 4 carbon atoms) with respect to the non-fluorinated segment (increase by 1 carbon atom). Instead, clustering of the molecules into units consisting of eight molecules was observed. This is explained in terms of a compromise between opposing interactions arising from the chemical nature of the molecule. Whereas the perfluorinated-non-fluorinated segments tend to induce nanosegregation in the monolayer, the hydrogen-bonding network formed by the isophthalic acid groups in combination with solvent co-deposition tends to induce an interdigitated lamellar structure.