Comicellization and complex formation

The complex formation by polymer-surfactant interaction has been extensively studied, as well for ionic and non-ionic polymers as for the different surfactant types, for example anionic, cationic and non-ionic low molecular weight surfactants. The driving forces for these complex formations are in general electrostatic or hydrophobic-hydrophobic interactions between polymer and siufactant. These concepts have been extended to block copolymer systems mainly to those containing a water-soluble PEO block, such as PPO-PEO, PS-PEO, PEO-PMAA, PMMA-PEO in the presence of anionic or cationic surfactants [258]. 

This concept has been extended to the complex formation between an ionomer block copolymer and either an homopolymer or a copolymer of opposite charges. In addition to these so-called polyion complexes (PIC), it should be mentioned that similar complexes can be formed by hydrogen bonds instead of electrostatic interactions as outlined in Section 7.3.10. 

Also mixed micelles could be obtained by comicellization of PPO-PEO-based copolymers in the presence of a non-ionic (EO)s low molecular weight surfactant [264] or by combination of PEO-PPO diblocks and PEO-PPO-PEO triblocks [265]. This topic will not be reviewed further and the following will mainly be focused on supramolecular assemblies formed through specific interactions between a given block copolymer and either a homopolymer or another block copolymers. 

At a pH between 3 and 5 no micellization takes place, the different species being molecu-larly dispersed. In the pH range of 6-8, micellization starts again with a core of the PMAA/ PDEAEMA complex and a fringe of PEO, whereas at higher pH, above 8, there is only formation of PDEAEMA core micelles stabilized by PEO in the presence of molecularly dispersed neutralized PMAA. 

A similar situation was described by Tenhu and co-workers [267] for a PEO-PMANa diblock copolymer in presence of poly(methacryl oxyethyltrimethylammonium chloride) as cationic homopolymer. 

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The different concepts of comicellization and complex formation are schematically indicated in Figure 7.8 and will be discussed in the following exclusively for aqueous micellar systems. 

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