Dimensional Control of Block Copolymer Nanofibers with a π‐Conjugated Core: Crystallization‐Driven Solution Self‐Assembly of Amphiphilic Poly(3‐hexylthiophene)‐b‐poly(2‐vinylpyridine)

Abstract

With the aim of accessing colloidally stable, fiberlike, π-conjugated nanostructures of controlled length, we have studied the solution self-assembly of two asymmetric crystalline-coil, regioregular poly(3-hexylthiophene)-b-poly(2-vinylpyridine) (P3HT-b-P2VP) diblock copolymers, P3HT23-b-P2VP115 (block ratio=1:5) and P3HT44-b-P2VP115 (block ratio=ca. 1:3). The self-assembly studies were performed under a variety of solvent conditions that were selective for the P2VP block. The block copolymers were prepared by using Cu-catalyzed azide-alkyne cycloaddition reactions of azide-terminated P2VP and alkyne end-functionalized P3HT homopolymers. When the block copolymers were self-assembled in a solution of a 50% (v/v) mixture of THF (a good solvent for both blocks) and an alcohol (a selective solvent for the P2VP block) by means of the slow evaporation of the common solvent; fiberlike micelles with a P3HT core and a P2VP corona were observed by transmission electron microscopy (TEM). The average lengths of the micelles were found to increase as the length of the hydrocarbon chain increased in the P2VP-selective alcoholic solvent (MeOH<iPrOH<nBuOH). Very long (>3 μm) fiberlike micelles were prepared by the dialysis of solutions of the block copolymers in THF against iPrOH. Furthermore the widths of the fibers were dependent on the degree of polymerization of the chain-extended P3HT blocks. The crystallinity and π-conjugated nature of the P3HT core in the fiberlike micelles was confirmed by a combination of UV/Vis spectroscopy, photoluminescence (PL) measurements, and wide-angle X-ray scattering (WAXS). Intense sonication (iPrOH, 1 h, 0 °C) of the fiberlike micelles formed by P3HT23-b-P2VP115 resulted in small (ca. 25 nm long) stublike fragments that were subsequently used as initiators in seeded growth experiments. Addition of P3HT23-b-P2VP115 unimers to the seeds allowed the preparation of fiberlike micelles with narrow length distributions (L(w)/L(n) < 1.11) and lengths from about 100-300 nm, that were dependent on the unimer-to-seed micelle ratio.

A design strategy for the hierarchical fabrication of colloidal hybrid mesostructures

“…Although the specific proof of concept example described here involved PFS 30 -b-P2VP 300 as the micelle forming polymer, the fabrication protocol should in principle apply to any BCP that forms elongated core-crystalline micelles and to any substrate to which the corona chains of the seed crystallites can attach. For example, we have recently shown that CDSA can be extended to BCP micelles with a conjugated crystalline polythiophene core 22,37 Electron microscopy. Bright-field transmission electron microscopy (TEM) images were taken using a Hitachi H-7000 instrument.…”

“…Many BCPs consisting of a long soluble block attached to a shorter crystallizable block 21 are potential candidates for this approach. While CDSA has been reported for BCPs with poly (3-hexylthiophene) 22 , polylactide 23 , polycaprolactone 24 and polyethylene 25 as the crystallizable block, one has the greatest control over this kind of seeded growth for polyferrocenylsilane (PFS) BCPs. Under appropriately chosen self-assembly conditions, all of the added unimer of a PFS BCP grow off the ends of the crystallite seeds in the sample, and uniform elongated structures can be formed [26][27][28][29][30][31] .…”

Interfacial Crystallization‐Driven Assembly of Conjugated Polymers/Quantum Dots into Coaxial Hybrid Nanowires: Elucidation of Conjugated Polymer Arrangements by Electron Tomography

“…[ 7,28,41 ] Herein, chloroform and acetonitrile were used as a good solvent for P3HT-b -P2VP and a selective solvent for P2VP, respectively. [ 23 ] A series of optical micrographs presented in Figure 1 a (see also Figure S1, Supporting Information) shows the progression of the formation of self-aggregates through the color change of solution (0.1 mg mL −1 of CP).…”

Hybrid Photovoltaics – from Fundamentals towards Application

“…insulating blocks as for example PMMA (P3HT-b-PMMA), [224] or poly(2-vinylpyridine) (P3HT-b-P2VP, [225][226][227][228][229] or P4VP (P3HT-b-P4VP), [230][231][232] or PEO (P3HT-b-PEO), [233][234][235][236][237][238][239][240][241][242] or polylactides (P3HT-b-PLA), [243] or polyacrylic acids (P3HT-b-PAA). [244,245] Also more special block copolymer with P3HT block were reported as for example azobenzene liquid crystalline mesogen, 6-(4-((4-methoxyphenyl)diazenyl)phenoxy)hexyl methacrylate (MMAZO) incorporated into a block copolymer with P3HT.…”