Mixing behaviour of a conjugated molecular wire candidate and an insulating fatty acid within Langmuir–Blodgett films

The miscibility of a conjugated “molecular wire” candidate and an “insulating” fatty acid within a thin film has been comprehensively analyzed. Specifically, Langmuir and Langmuir–Blodgett films containing mixtures of 4-[4′-(4″-hexyloxyphenylethynyl)-phenylethynyl]-aniline (HBPEB amine) and behenic acid (BA) have been prepared, characterized, and their miscibility compared with that of mixtures of 4-[4′-(4″-hexyloxyphenylethynyl)-phenylethynyl]-benzoic acid (HBPEB acid) and BA studied previously. Surface pressure vs. area per molecule isotherms were recorded, with negligible excess areas per molecule at high surface pressures suggesting either complete miscibility or immiscibility of the two materials. The Langmuir films were transferred onto solid supports to fabricate Langmuir–Blodgett (LB) films which were characterized by SPM probe techniques. Scanning Polarization Force Microscopy (SPFM) undoubtedly shows good miscibility of the two materials in the films with no evidence of phase separation, in contrast with the HBPEB acid–BA system where phase separation occurs for HBPEB acid mole fractions over the 0.1–0.8 range.