Fiber-like (1D) core-crystalline micelles of uniform length can be obtained in protocols involving multiple steps from block copolymers (BCPs) in which crystallization of the core-forming polymer drives the self-assembly. Here we report a systematic study that shows that adding small amounts (<5 w/w%) of a homopolymer corresponding to the core-forming block of the BCP enables uniform 1D micelles (mean lengths L n = 0.6 to 9.7 μm) to be obtained in a single step, simply by heating the mixture in a selective solvent followed by slow cooling. A series of poly­(ferrocenyldimethylsilane) (PFS) BCPs with different corona-forming blocks and different compositions as well as PFS homopolymers of different lengths were examined. Dye labeling and confocal fluorescence microscopy showed that the homopolymer ends up in the center of the micelle, signaling that it served as the initial seed for epitaxial micelle growth. The rate of unimer addition was strongly enhanced by the length of the PFS block, and this enabled more complex structures to be formed in one-pot self-assembly experiments from mixtures of two or three BCPs with different PFS block lengths. Furthermore, BCP mixtures that included PFS-b-PI (PI = polyisoprene) and PFS-b-PDMS with similar PFS block lengths resulted in simultaneous addition to growing micelles, resulting in a patchy block that could be visualized by staining the vinyl groups of the PI with Pt nanoparticles. This approach also enabled scale up, so that uniform 1D micelles of controlled architecture can be obtained at concentrations of 10 w/w % solids or more.

A clear understanding of the surface of nanocrystals informs our views of nucleation and growth, and allows for tailored ligand exchanges to meet target applications. PbS colloidal quantum dots are attractive for infrared optoelectronic devices, but PbS nanocrystals made using excess PbCl2 (PbS-eCl NCs) have found limited use, despite showing advantageous ensemble properties. Here, we use 1D and 2D 1H NMR to determine that the native passivation of PbS-eCl NCs involves bound oleylammonium. Then, by mapping the set of permissible ligand exchanges, we uncover that the surface of these nanocrystals matches the behavior of lead halide perovskites. Building on this insight, we infer the ligand binding motif and perovskite-like atomic structure that forms a thin, intrinsic shell on the PbS core. Indeed, we show that two-dimensional L2PbCl4 (L = oleylammonium) sheets are readily formed in the reaction mixture prior to the nucleation of PbS-eCl NCs. Our structural model for the surface then allowed us to develop techniques to improve nanocrystal purification, colloidal stability, and the postsynthetic installation of X-type ligands. In all, we show that the synthesis and surface of PbS-eCl NCs should be treated differently compared to traditional PbS NCs prepared from lead oleate, and highlight instead that ligand exchanges developed for lead halide perovskites can translate to this infrared material. The framework that we present for the manipulation of PbS-eCl NCs in solution can advance their wider use in optoelectronic devices.

Self-assembly of block copolymers (BCP) into uniform 3D structures in solution is an extremely rare phenomenon. Furthermore, the investigation of general prerequisites for fabricating a specific uniform 3D structure remains unknown and challenging. Here, through a simple one-pot direct self-assembly (heating and cooling) protocol, we show that uniform spherulite-like structures and their precursors can be prepared with various poly­(ferrocenyldimethylsilane) (PFS) BCPs in a variety of polar and non-polar solvents. These structures all evolve from elongated lamellae into hedrites, sheaf-like micelles, and finally spherulites as the annealing temperature and supersaturation degree are increased. The key feature leading to this growth trajectory is the formation of secondary crystals by self-nucleation on the surface of early-elongated lamellae. We identified general prerequisites for fabricating PFS BCP spherulites in solution. These include corona/PFS core block ratios in the range of 1–5.5 that favor the formation of 2D structures as well as the development of secondary crystals on the basal faces of platelets at early stages of the self-assembly. The one-pot direct self-assembly provides a general protocol to form uniform spherulites and their precursors consisting of PFS BCPs that match these prerequisites. In addition, we show that manipulation of various steps in the direct self-assembly protocol can regulate the size and shape of the structures formed. These general concepts show promise for the fabrication and optimization of spherulites and their precursors from semicrystalline BCPs with interesting optical, electronic, or biomedical properties using the one-pot direct self-assembly protocol.

Self-assembly of crystalline-coil block copolymers (BCPs) in selective solvents is often carried out by heating the mixture until the sample appears to dissolve and then allowing the solution to cool...

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