Two
hydrogen (H)-bond donors, phenol and l-threonine,
were added into the aqueous solutions containing crystalline micelles
of a poly(ε-caprolactone)-b-poly(ethylene oxide)
(PCL-b-PEO) block copolymer, respectively. Dynamic
light scattering (DLS) characterization showed that the micellar size
became smaller after addition of phenol. Transmission electron microscopy
(TEM) results revealed that the long crystalline cylindrical micelles
formed in the neat aqueous solution were fragmented into short cylinders
and even quasi-spherical micelles, as the phenol concentration increased.
By contrast, the spherical PCL-b-PEO crystalline
micelles could be transformed into short cylinders and then long cylinders
after addition of l-threonine. Reversible morphological transformation
was realized for the PCL-b-PEO crystalline micelles
by adding these two H-bond donors alternately. It is confirmed that
both phenol and l-threonine could form H-bonds with PEO.
We proposed that, the micellar corona was swollen by phenol, leading
to fragmentation of the micellar core, whereas the PEO blocks in the
micellar corona was dynamically cross-linked by l-threonine
beacuse of its multiple H-bond-donation groups, resulting in a smaller
reduced tethering density.
Crystallization-driven self-assembly of polyethylene-b-poly(tert-butylacrylate) (PE-b-PtBA) block copolymers (BCPs) in N,N-dimethyl formamide (DMF) was studied. It is found that all three PE-b-PtBA BCPs used in this work can self-assemble into one-dimensional crystalline cylindrical micelles. When the BCP solution is cooled to crystallization temperature (Tc) from 130 °C, the seed micelles may be produced via two competitive processes in the initial period: stepwise micellization/crystallization and simultaneous crystallization/micellization. Subsequently, the seed micelles can undergo growth driven by the epitaxial crystallization of the unimers. The lengths of both the seed micelles and the grown micelles are longer for the BCP with a longer PtBA block at a higher Tc. Quasi-living growth of the PE-b-PtBA crystalline cylindrical micelles is achieved at a higher Tc. A longer PtBA block evidently retards the attachment of unimers to the crystalline micelles, leading to a slower growth rate.
Due to their low cost and high efficiency, polymer/nanocrystal hybrid solar cells (HSCs) have attracted much attention in recent years. In this work, water-soluble hybrid materials consisting of amphiphilic block copolymers (ABCPs) and cadmium telluride nanocrystals (CdTe NCs) were used as the active layer to fabricate the HSCs via aqueous processing. The ABCPs composed of poly(3-hexylthiophene) (P3HT) and poly(acrylic acid) (PAA) self-assembled into ordered nanostructured micelles which then transformed to nanowires by comicellization with P3HT additives. Furthermore, after annealing, the hybrid materials formed an interpenetrating network which resulted in a maximum power conversion efficiency of 4.8% in the HSCs. The properties of the hybrid materials and the film morphology were studied and correlated to the device performance. The results illustrate how the inclusion of ABCPs for directed assembly and homo-P3HT for charge transport and light absorption improves device performance. The aqueous-processed HSCs based on the ABCPs and NCs offer an effective method for the fabrication of efficient solar cells.
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