Additional crystallization of the PCL segments therefore also took place during and after transfer

for the star-shaped block copolymers, which likely leads to a mica surface only partially covered

with adsorbed or crystallized polymer chains. At high surface pressures, dendritic and needlelike

crystals could be seen. These crystal structures are significantly different from those observed for

PCL homopolymers, which indicates that even though the PEO core did not crystallize, it

strongly influenced the crystallization of the PCL blocks in terms of crystal morphology. Many

variables have to be taken into consideration, such as molecular weight, PEO amount, film

thickness, water evaporation, residual water content, transfer pressure, and substrate affinity for

the polymer chains to fully investigate crystallization of PCL homopolymers and PCL-based

block copolymers in LB films. While this study gives some hint of the surface properties of these

interesting star-shaped block copolymers, complete understanding of the system will therefore

require further investigation.

4.2.4 PEO-b-PCL Linear Diblock Copolymers

 The PEO segment of the linear diblock copolymers (PEO2670, Mn = 2,670 g/mol) has a

molecular weight in the same range as the one of the PEO core of the star-shaped PEO-b-PCL

samples. Nevertheless, because of its linear architecture, this PEO segment has intrinsic surface

activity as shown in Figure 4-3, which should lead to the appearance of PEO phase transitions

not observable for the star-shaped samples in the low surface pressure region. The isotherms of

the four linear PEO-b-PCL diblock copolymers are presented in Figure 4-20. Compared to the

homopolymers PEO2670 and PCL2000 (PCL homopolymer with a molecular weight in the same

range as the PCL blocks of the linear diblock copolymers), higher surface pressures as high as 25

mN/m can be reached, similarly as for the star-shaped samples. As better shown in the

compressibility plot (Figure 4-21), three phase transitions that correspond to conformational

rearrangements of the polymer chains are clearly observed around 6.5, 10.5, and 13.5 mN/m. The