3.3 Conclusions

 In this work, the A/W interfacial behavior of two dendrimer-like block copolymers based

on polystyrene and poly(tert-butylacrylate) (Dendl) or poly(acrylic acid) (Dend2) and their LB

film morphologies on hydrophilic mica substrates were investigated. Dend1 formed

thermodynamically stable Langmuir monolayers and self-assembled into circular surface

micelles up to 24 mN/m with a very low aggregation number (~ 3), likely resulting from the high

PtBA wt % and from the peculiar dendrimer-like architecture. At 24 mN/m, the PtBA segments

desorbed and aggregated on top of the water surface, and all the monolayers formed beyond this

threshold were metastable and relaxed down to 24 mN/m. Poly(acrylic acid) is surface active

only under acidic pH conditions below its pKa value (~ 5.5), and a preliminary study on a PAA

homopolymer (PAA250K, Mn = 250,000 g/mol) showed that it is able to form stable monolayers

up to ~ 3.5 mN/m before dissolving in the water subphase. Because of its small PS wt %, Dend2

similarly did not form stable Langmuir monolayers under high pH conditions, and therefore its

self-assembly at the A/W interface was investigated only under acidic conditions. The isotherm

indicated the presence of a pseudoplateau at 5 mN/m characteristic of a phase transition that

corresponds to a pancake-to-brush transition, with the progressive aqueous dissolution of the

PAA segments underneath the anchoring PS cores. For pressures below the pseudoplateau,

Dend2 molecules also aggregated into circular surface micelles with a very low aggregation

number (~ 5). This study confirmed that various parameters such as for instance polymer

architecture, chain length/polarity, surface density, or even subphase pH can all strongly

influence the self-assembly of block copolymers at the A/W interface. Therefore, while this

work gave some hint of the interesting interfacial properties of these two novel PS-b-PtBA and

PS-b-PAA dendrimer-like copolymers, additional investigations with other samples with