Induced collapse in the formation of alternating Langmuir-Blodgett films

Two compounds whose molecules have large dipole moments, stereoregular perfluorinated alkyl-methacrylate-co-methacrylic acid (A) and p-octadecylaminoazobenzene-p'-sulfamide (B), were used to assemble Langmuir-Blodgett polar films by the alternating method to achieve high polarization. According to estimates, the dipole moment of the dimeric unit of copolymer A is equal to about 4 D, the dipole moment of compound B, to 12 D. Unusually high (several units) transfer ratio was observed for the monolayer B when preparing the structures of (AB)n type. The monolayers were stable during their formation process. Upon the pause of a substrate when passing through the monolayer B, the monolayer area remained strictly constant. According to the model proposed, the monolayer looses its stability and locally collapses in the meniscus zone at the contact line of the monolayer B and substrate due to an increase in the electrostatic repulsion between the dipoles of molecules B. The validity of this model is confirmed by the data of small-angle X-ray diffraction and atomic force microscopy for various alternating Langmuir-Blodgett films.