Amphiphilic
block copolymers can self-assemble into aggregates of a range of morphologies
when dispersed in water, and there is a growing interest in using them in
diverse applications such as in cosmetic products, shampoos, lotions, and as
improved drug carriers. To further advance the use of block copolymers it is
important to study their interactions with small amphiphiles. In the present
study we mixed a vesicle-forming and a micelle-forming polybutadiene-co-ethylene
oxide compounds (P2903-BdEO and P3017-BdEO, respectively), with the small
micelle-forming detergent, Triton X-100, and examined the effects of detergent
concentration and detergent-polymer contact time on the change in morphology
and type of structures formed. The analysis involved direct-imaging
cryo-transmission electron microscopy (cryo-TEM), light microscopy, dynamic
light scattering, and spectroscopy, and we obtained specific as well as global
structural information on assemblies ranging from a few nanometers to a few
microns in size. Coexistence of vesicles, threadlike micelles, and spherical
micelles is seen in the P2903-BdEO/Triton X-100 system, until vesicles
dissolution is completed, and spherical micelles are exclusively observed. In
the P3017-BdEO/Triton X-100 system large spherical polymer micelles transform
directly into smaller mixed micelles of uniform size. The results of both
systems show that addition of detergent into polymeric assemblies results in
the formation of structures of higher curvature. Furthermore, mixing large and
small amphiphiles can be used to yield unique structures, not obtainable in
single or double-component small amphiphile systems, as the short-armed
Y-branched threadlike micelles seen in the P2903-BdEO/Triton X-100 system. In
addition, we show that mixing between large block copolymers and small-molecule
detergent is instantaneous, and the assemblies seen immediately after mixing
are identical to those observed after long periods of time, indicating that
equilibrium is reached very quickly.
