Self-Assembly of Synthetic and Biological Polymeric Systems of ...

4.3.1.- Relevant aspects
I. For E12S10 dilute solutions, the coexistence of spherical micelles with vesicular structures
has been observed. In addition, the spontaneous formation of vesicles by
poly(oxystyrene)-poly(oxyethylene) block copolymers is reported for the first time, as
confirmed by light scattering, polarized light microscopy, and transmission and cryo-
scanning electron microscopy data.
II. In dilute solution, the self-assembly of copolymer E10S10E10 leads to the formation of
elongated micelles as supported by light scattering and transmission electron techniques.
III. In the case of copolymer E137S18E137, typical spherical micelles are observed. Tube inversion
and rheological measurements were used to define the sol- soft- and gel-hard boundaries
of this copolymer.
IV. E12S10 and E10S10E10 copolymers did not form gels in the concentration range analysed.
However, only certain concentrations of copolymer E10S10E10 were analysed by rheometry.
From experimental data, an upturn in the low-frequency range of the stress moduli was
observed, denoting the existence of an emerging slow process, which was assigned to the
formation of an elastic network.
V. Block copolymers E12S10, E10S10E10 and E137S18E137 showed spontaneous adsorption at the
air-water interface, which slowed down when the hydrophobicity of the molecule was
increased. In contrast, at the chloroform/water interface no measurable effect is observed
for copolymer E12S10 due to the slow diffusion of its chains to the interface in combination
with a low bulk concentration; this slow diffusion is associated with the fact that
chloroform is a good solvent for both E and S blocks.
VI. Copolymer E137S18E137 displays an adsorption isotherm with the four classical regions
representing the pancake, mushroom, brush and condensed states; the presence of a
pseudo-plateau is attributed to the pancake-to-brush transition as E chains submerge into
the aqueous sub-phase. On the other hand, for E12S10 and E10S10E10 copolymers only two
regions are observed in their adsorption isotherms as a consequence of their low
molecular weights, short S and E block lengths, and much larger S/E ratio. This involves the
disappearance of the pseudo-plateau region due to the decrease in the fractional
interfacial area occupied by EO segments.
VII. According to AFM images, circular micelles are observed on Langmuir-Blodgett films of the
copolymers obtained at two surface transfer pressures. A decrease in micelle size and an
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