pseudoplateaus or inflection points characteristic of PEO aqueous dissolution. This absence is

also shown in the compressibility plot K versus surface pressure (Figure 4-14), where no peak


(local maximum) is observed below 11 mN/m (in compressibility plots versus surface pressure,

every phase transition in a Langmuir monolayer results in a local compressibility maximum).

This suggests that the PEO core of the star-shaped block copolymers is probably not adsorbed at

the interface but more likely already solvated in the water subphase in the vicinity of the

interface.

 9000
 1mNlm
 mNlm

 6mNlm

 9mN"
 10mNlm

 a 1mNlm



 0 20 40 60 80 100
 Number of E-caprolactone units


Figure 4-12. Plots of MMA versus number of e-caprolactone repeat units for different surface
 pressures from the isotherms of Star#3, Star#4, Star#5, and Star#6.

 25


 20 I PEO core extrapolated

 E 9+ PEO2000
 15




 10



 SArea per ethy-lene oxide~ unit (ii) 6


Figure 4-13. Isotherms of the PEO core extrapolated and PEO2000 normalized with respect to
 the number of ethylene oxide units.