Self-Seeding in One Dimension: A Route to Uniform Fiber-like Nanostructures from Block Copolymers with a Crystallizable Core-Forming Block

Abstract

One-dimensional micelles formed by the self-assembly of crystalline-coil poly(ferrocenyldimethylsilane) (PFS) block copolymers exhibit self-seeding behavior when solutions of short micelle fragments are heated above a certain temperature and then cooled back to room temperature. In this process, a fraction of the fragments (the least crystalline fragments) dissolves at elevated temperature, but the dissolved polymer crystallizes onto the ends of the remaining seed fragments upon cooling. This process yields longer nanostructures (up to 1 μm) with uniform width (ca. 15 nm) and a narrow length distribution. In this paper, we describe a systematic investigation of factors that affect the self-seeding behavior of PFS block copolymer micelle fragments. For PI(1000)-PFS(50) (the subscripts refer to the number average degree of polymerization) in decane, these factors include the presence of a good solvent (THF) for PFS and the effect of annealing the fragments prior to the self-seeding experiments. THF promoted the dissolution of the micelle fragments, while preannealing improved their stability. We also extended our experiments to other PFS block copolymers with different corona-forming blocks. These included PI(637)-PFS(53) in decane, PFS(60)-PDMS(660) in decane (PDMS = polydimethylsiloxane), and PFS(30)-P2VP(300) in 2-propanol (P2VP = poly(2-vinylpyridine)). The most remarkable result of these experiments is our finding that the corona-forming chain plays an important role in affecting how the PFS chains crystallize in the core of the micelles and, subsequently, the range of temperatures over which the micelle fragments dissolve. Our results also show that self-seeding is a versatile approach to generate uniform PFS fiber-like nanostructures, and in principle, the method should be extendable to a wide variety of crystalline-coil block copolymers.

An investigation into the hexagonal phases formed in high-concentration dispersions of well-defined cylindrical block copolymer micelles

“…An alternative self-seeding method was employed to prepare the polydisperse micelles. [33] In this case, as-grown micelle solutions were heated to a certain temperature below the melting point of the PFS block and then cooled to room temperature. This process dissolves the smallest crystalline domains of the Table 1.…”

Monodisperse Cylindrical Micelles of Controlled Length with a Liquid‐Crystalline Perfluorinated Core by 1D “Self‐Seeding”

“…Based on the initial length of the seeds and the final length of micelles after annealing, we calculated the fraction of surviving fragments at each annealing temperature. As shown in Figure 2(d), in the range of 35−75 °C, the fraction of surviving seeds decreased exponentially with increasing temperature, a key characteristic of a self-seeding process [11,15] (see SI pages S6 for discussions).…”

“…Neither the solution concentration ( Figure S8, Table S3) nor the annealing time ( Figure S9 and Table S4) showed a significant effect on micelle length, as expected for a thermodynamical process. [15,18] After thermal annealing, the micelle length increased substantially in the initial 5 h after the sample was cooled to 23 o C and then remained constant after 8 h ( Figure S10 and Table S5). In addition, the central dark segment of the cylindrical micelles (inset image in Figure 2(b)), corresponding to surviving seeds, appeared to be significantly darker by TEM.…”

Uniform patchy and hollow rectangular platelet micelles from crystallizable polymer blends

“…To expand the generality of our approach to rectangular platelets that are dispersible in hydrophilic media we also explored the self-assembly of the blends derived from PFS 36 S6) gave rise to low dispersity platelet micelles (A w /A n < 1.01) with regular rectangular morphologies (Fig. 1).…”