Micellization of PEO/PS Block Copolymers at the Air/Water Interface:  A Simple Model for Predicting the Size and Aggregation Number of Circular Surface Micelles

Abstract

Isotherms of monolayers of poly(ethylene oxide) (PEO) and polystyrene (PS) triblock copolymers spread at the air/water interface were obtained by film balance technique. In a low concentration regime, the PEO segments surrounding the PS cores behave the same way as in monolayers of PEO homopolymers. Langmuir-Blodgett (LB) films prepared by transferring the monolayers onto mica at various surface pressures were analyzed by atomic force microscopy (AFM). The results reveal that these block copolymers form micelles at the air/water interface. Within the micelles, the PS blocks act as anchoring structures at the interface. In several cases, aggregation patterns were modified by the dewetting processes that occur in Langmuir-Blodgett films transferred to solid substrates. High transfer surface pressures and metastable states favored these changes in morphology. A flowerlike surface micelle model is proposed to explain the organization of the surface circular micelles. The model can be generalized and applied to diblock copolymers as well. The model permits prediction of the aggregation number and the size of circular surface micelles formed by PEO/PS block copolymers at the air/water interface.

Controlled Interfacial Assembly and Transfer of Brushlike Copolymer Films

“…In the so‐called gaseous regime, the low surface density corresponds to a large area per molecule, and the film exhibits a low surface pressure. This small but finite surface pressure indicates that the copolymer remains at the interface, consistent with the known surface activity of PEO homopolymers 21–24. With increasing density at the surface due to molecular crowding, a pseudoplateau appears at an area of approximately 15 nm 2 molecule −1 , caused by insertion of PEO segments into the aqueous subphase.…”

Nanostructure of PEO–polyurethane–PEO triblock copolymer micelles in water

“…In previous work, it was found that a fourth polymer with a PEO weight fraction of 0.96 would not form a micelle over the entire pH range from 8 to 2 with or without ionic salts present [2]. A decrease in aggregation number with PEO content has been observed by others [44][45][46] although the variation of aggregation numbers with composition are somewhat more complex than observed for the small number of samples investigated here. This suppression of micellization was attributed to the solubility of the PEO combined with the high fraction of PEO in the polymer.…”

Direct imaging of the surface distribution of immobilized cleavable polyethylene oxide‐polybutadiene‐polyethylene oxide triblock surfactants by atomic force microscopy

“…Thus, volume exclusion by the PEO side‐chains cannot be responsible for bare spots that ranged in size from several nm to ~50 nm (accounting for tip radius effects). The patterns may be due to the adsorption of triblocks from lamellar, worm‐like, or circular micellar conformations caused by the relatively large hydrophobic PBD centerblock and short PEO chains . Phase separation may also occur during self‐assembly; indeed, the surface features are morphologically similar to those observed in spin‐cast thin films of diblock copolymers .…”