Star#4, and Star#3 overlap in this region suggests that all the PCL chains have collapsed and

crystallized above the interface, and that the sharp pressure increase arises mainly from

interactions between the hydrated PEO cores. Therefore, PCL crystallization probably takes

place for these four stars with the PEO core still hydrated in the water subphase, with the PCL

chains stretching and crystallizing away from the interface. The isotherms of Star#2 and Star#1

shift toward smaller mean molecular areas because of the water solubility behavior mentioned

before. A cartoon of the polymer chains' conformations as the Langmuir monolayers are

compressed is proposed in Figure 4-18. It should be mentioned that the experiments discussed

here do not provide enough information to fully understand the aggregation of the star-shaped

PEO-b-PCL block copolymers. For instance, eventual phase separation between the different

blocks leading to the formation of various surface micelles could not be directly determined from

surface pressure measurements.

 O e-caprolactone repeat unit

 *ethylene oxide repeat unit


 High MMLA reon~l~ ~N


air


Figure 4-18. Proposed conformations modeling the adsorption of the star-shaped block
 copolymers at the A/W interface versus surface pressure.


Intermediate MMLA region
 (12mN/mc<x<1mN/m)




 Low MMLA region
 (x>15mN/m)