An investigation of the morphology of Langmuir films based on molecular polyimide brushes containing magnetite nanoparticles

Abstract

Molecular brushes having a polyimide (PI) backbone with degree of polycondensation n = 33 and polymethylmethacrylate (PMMA) side chains with two different degrees of polymerization (m = 63 and m = 114) were synthesized by the method of controlled atom transfer radical polymerization. Hydrophobic magnetite nanoparticles of a size of 18 ± 2 nm were prepared. Langmuir monolayers on the basis of the polyimide brushes and composite monolayers, containing magnetite nanoparticles with a hydrophobic surface, were formed at the water/air interface. It is found that, in the condensed state of the monolayer at the surface pressure values from 25 to 40 mN/m, the limiting surface area A 0 per side chain of a brush grows with an increase in the length of PMMA side chains of polymer brushes almost by a factor of 2: from A 0 = 744 ± 64 A2 for PI-graft-PMMA-63 to A 0 = 1644 ± 50 A2 for PI-graft-PMMA-114. Increasing the magnetite solution aliquot mixed with the polymer brush solution at the ratios from 1 : 2 and 1 : 1 to 2 : 1 leads to a rise in the limiting surface area values A 0 to 1072 ± 59 A2 for the first two ratios to 2534 ± 79 A2 for the third one. The obtained monolayers were transferred onto mica by the Langmuir-Schaeffer method at different surface pressure values (0.5, 10, and 25 mN/m). With the use of the method of atomic force microscopy, it is shown that a four- to sixfold increase in the mean roughness of a composite film surface due to the inclusion of magnetite nanoparticles into the polymer brush monolayer is typical of all samples.