Enhanced control over crystallization-driven self-assembly (CDSA) of coil-crystalline block copolymers has led to the formation of intricate structures with well-defined morphology and dimensions. ...While approaches to build those sophisticated structures may strongly differ from each other, they all share a key cornerstone: a polymer crystallite. Here we report a trapping technique that enables tracking of the change in length of one-dimensional (1D) polymer crystallites as they are annealed in solution at different temperatures. Using the similarities between 1D polymeric micelles and bottle-brush polymers, we developed a model explaining how the dissolving crystallites reach a critical size independent of the annealing temperature, and then explode in a cooperative process involving the remaining polymer chains of the crystallites. This model also allows us to demonstrate the role of the distribution in seed core crystallinity on the dissolution of the crystallites.
Block copolymers consist of two or more chemically distinct polymer segments, or blocks, connected by a covalent link. In a selective solvent for one of the blocks, core-corona micelle structures are ...formed. We demonstrate that living polymerizations driven by the epitaxial crystallization of a core-forming metalloblock represent a synthetic tool that can be used to generate complex and hierarchical micelle architectures from diblock copolymers. The use of platelet micelles as initiators enables the formation of scarf-like architectures in which cylindrical micelle tassels of controlled length are grown from specific crystal faces. A similar process enables the fabrication of brushes of cylindrical micelles on a crystalline homopolymer substrate. Living polymerizations driven by heteroepitaxial growth can also be accomplished and are illustrated by the formation of tri- and pentablock and scarf architectures with cylinder-cylinder and platelet-cylinder connections, respectively, that involve different core-forming metalloblocks.
Nucleated self-assembly in selective solvents of core-crystalline block copolymers (BCPs) is a special case of living supramolecular polymerization, leading to rodlike micelles of controlled and ...uniform length. For the crystallization-driven self-assembly of PFS-containing BCPs (PFS = polyferrocenyldimethylsilane), the formation of block comicelles by sequential addition of different BCPs is well-established. But there are only a few examples of living copolymerization, the simultaneous addition of pairs of BCPs with different corona-forming chains. At present, relatively little is known about the competitive kinetics of different BCPs crystallizing on a common seed. Here we report a systematic study of the competitive seeded growth kinetics of pairs of linear PFS-containing BCPs and show that one can manipulate the kinetics to control the morphology of the comicelles. We found that the seeded-growth kinetics of the individual BCP unimer dominates the coassembly behavior and thus the morphology of the corona. Patchy comicelles with microphase-segregated corona chains are formed when the epitaxial growth rates of the two different BCPs on the common seed are similar. In contrast, factors that lead to dissimilar growth rates (long corona-forming blocks or introduction of charges on corona-forming chains) promote large-scale separation of the corona blocks, leading to block comicelles. Because the termini of the comicelles remain living, they can further direct the growth of unimers, resulting in hierarchical block comicelles with patchy blocks and single-component (homo) blocks. Furthermore, the patchy comicelles can be loaded with either gold or platinum nanoparticles, generating organic–inorganic hybrid materials with potential application in catalysis.
We have found that the width and shape (from rectangular to elliptical, to almost circular in cross-section) of the crystalline core of fiberlike micelles of polyferrocenyldimethylsilane (PFDMS) ...diblock copolymers can be varied by altering the degree of polymerization of PFDMS, and also the chemistry of the complementary corona-forming block. This enabled detailed studies of living crystallization-driven self-assembly (CDSA) processes that involved the addition of unimers with a short, crystallizable core-forming PFDMS block to a seed solution of short micelles with a large diameter crystalline core, derived from block copolymers with a longer PFDMS block. The morphology of resultant micelles was found to be highly dependent on the polarity of the solvent and temperature. For example, linear micelles were formed in less polar solvents (which are moderately poor solvents for PFDMS) and/or at higher temperatures. In contrast, the formation of branched structures could be “switched on” when the opposite conditions were used. Thus, the use of more polar solvents (which are very poor solvents for PFDMS) and ambient or subambient temperatures allowed the formation of branched micelles and block comicelles with variable and spatially distinct corona chemistries, including amphiphilic nanostructures. Rapid crystallization of added unimers at the seed micelle termini under nonequilibrium self-assembly conditions appears to facilitate the formation of the branched micellar structures as a kinetically trapped morphology. This is evidenced by the transformation of the branched micelles into linear micelles on heating at elevated temperatures.
Self-seeding is a useful protocol for generating elongated fiberlike block copolymer micelles of uniform length starting with micelle fragments obtained by sonication of long polydisperse micelles. ...In this process, the suspension of micelle fragments is heated in the selective solvent to temperatures where nearly all the fragments dissolve. The surviving fragments serve as seed nuclei for micelle growth when the solution is cooled. While there is evidence that the nature and length of the corona polymer plays a role in determining the characteristic dissolution temperature (T c) of the micelle fragments and other aspects of the self-seeding process, our understanding of these effects are limited. Here, we examine self-seeding of fiberlike micelle fragments in ethanol of an oligo(p-phenylenevinylene)-b-poly(2-vinylpyridine) (OPV5-b-P2VP42, the subscripts denote degrees of polymerization) block copolymer in which we introduced different amounts of divalent metal ions (Cu2+, Zn2+ Mn2+, and Cd2+) to promote complexation without affecting the packing of the micellar core. We found that the resistance of seed micelles of OPV5-b-P2VP42 toward dissolution increased significantly as the percentage of metal ions to pyridyls was increased from 0 to about 5% and then showed a more gradual increase as the metal ion content was increased to 20%. These phenomena can be interpreted in terms of the formation of noncovalent cross-linking within the P2VP layer. Metal complexation should lead to contraction of the dimension of the corona chains, decreasing corona chain repulsion and the tension exerted on the core by the stretched P2VP chains in the metal-free micelles. Cross-linking would also require additional energy to break interchain coordinating bonds between pyridyls and metal ions for both the detachment of unimers from micelles and fragmentation of micelles. Metal ion complexation also reduces the mobility of P2VP chains. This effect appears to slow the addition rate of the free unimer to the surviving seed micelles in the cooling/aging step in the self-seeding process.
This review paper describes a new technology, mass cytometry, that addresses applications typically run by flow cytometer analyzers, but extends the capability to highly multiparametric analysis. The ...detection technology is based on atomic mass spectrometry. It offers quantitation, specificity and dynamic range of mass spectrometry in a format that is familiar to flow cytometry practitioners. The mass cytometer does not require compensation, allowing the application of statistical techniques; this has been impossible given the constraints of fluorescence noise with traditional cytometry instruments. Instead of “colors” the mass cytometer “reads” the stable isotope tags attached to antibodies using metal-chelating labeling reagents. Because there are many available stable isotopes, and the mass spectrometer provides exquisite resolution between detection channels, many parameters can be measured as easily as one. For example, in a single tube the technique allows for the ready detection and characterization of the major cell subsets in blood or bone marrow. Here we describe mass cytometric immunophenotyping of human leukemia cell lines and leukemia patient samples, differential cell analysis of normal peripheral and umbilical cord blood; intracellular protein identification and metal-encoded bead arrays.
Three well-defined crystalline–coil diblock copolymers of oligo(p-phenylenevinylene)-b-poly(N-isopropylacrylamide) (OPV5-b-PNIPAM18, OPV5-b-PNIPAM49, and OPV5-b-PNIPAM75; the subscripts represent ...the number of repeat units of each block) with the same crystallizable core-forming OPV segment but different corona-forming PNIPAM blocks of various chain lengths were synthesized. Their solution self-assembly behavior was examined in methanol, ethanol, and isopropanol. Both the solvent and the length of the PNIPAM block were found to affect the self-assembly of the block copolymers. In methanol, OPV5-b-PNIPAM18 formed a mixture of fiber-like micelles of uniform width and two-dimensional platelet-like structures with fiber-like micelles protruding from the ends. In ethanol and in isopropanol, this polymer only formed long fiber-like micelles of uniform width. OPV5-b-PNIPAM49 formed long fiber-like micelles (several micrometers) of uniform width in all three solvents, but under the same self-assembly conditions, OPV5-b-PNIPAM75 only formed short fiber-like micelles with lengths of several hundred nanometers. We systematically examined the temperature-induced self-seeding behavior of all three block copolymers, exploring the influence of PNIPAM chain length, solvent, annealing time, and concentration of copolymer. The most remarkable result of these experiments is our finding that fiber-like micelles of uniform length with controlled lengths up to 1 μm can be easily prepared from all three block copolymers, even from OPV5-b-PNIPAM75 that formed only much shorter micelles under self-nucleated self-assembly. We also showed that the self-seeding strategy can be extended to other OPV-containing diblock copolymer such as OPV5-b-poly(2-(diethylamino)ethyl methacrylate) for preparing monodisperse fiber-like micelles of controllable length. These results show that the self-seeding approach to crystallization-driven self-assembly can be a versatile route to prepare uniform fiber-like micelles with controllable lengths for OPV-containing block copolymers.
Micelles formed by the self-assembly of block copolymers in selective solvents have attracted widespread attention and have uses in a wide variety of fields, whereas applications based on their ...electronic properties are virtually unexplored. Herein we describe studies of solution-processable, low-dispersity, electroactive fibre-like micelles of controlled length from π-conjugated diblock copolymers containing a crystalline regioregular poly(3-hexylthiophene) core and a solubilizing, amorphous regiosymmetric poly(3-hexylthiophene) or polystyrene corona. Tunnelling atomic force microscopy measurements demonstrate that the individual fibres exhibit appreciable conductivity. The fibres were subsequently incorporated as the active layer in field-effect transistors. The resulting charge carrier mobility strongly depends on both the degree of polymerization of the core-forming block and the fibre length, and is independent of corona composition. The use of uniform, colloidally stable electroactive fibre-like micelles based on common π-conjugated block copolymers highlights their significant potential to provide fundamental insight into charge carrier processes in devices, and to enable future electronic applications.
Living crystallization-driven self-assembly (CDSA) is of growing interest as a seeded growth route to colloidally stable one-dimensional (1D) and two-dimensional (2D) nanoparticles and more complex ...hierarchical assemblies with low size dispersity and predetermined dimensions from crystallizable polymeric and molecular amphiphiles. The origin of the low size dispersities has previously been explained in terms of an analogy between living CDSA with living covalent polymerizations of molecular monomers, in particular, for the case where initiation is faster than propagation and chain terminating or chain breaking processes are absent. Recently, based on Brownian dynamics simulations, an alternative explanation for this behavior involving length-dependent growth has been suggested for 1D fiber-like micelle formation where the growth rate decreases as the length increases. Herein, we have investigated this possibility experimentally by comparing the simultaneous growth from relatively short (L n = ca. 100 nm) and long (L n = ca. 1000 nm) seed fibers derived from crystallizable poly(ferrocenyldimethylsilane) (PFS) block copolymers with polar or nonpolar corona-forming blocks. Using a statistical analysis of fiber lengths based on transmission electron microscopy (TEM) data, we found that the growth rate from the termini of the short and long fibers was identical within experimental error in either polar or nonpolar media at both ambient (22 °C) and elevated (35 °C) temperatures. Analogous length-independent growth was found for the case of the formation of fiber-like triblock comicelles and for 1D micelles with a different, crystallizable poly(fluorenetrimethylenecarbonate) (PFTMC) core-forming block. The results therefore strongly indicate that the low dispersities characteristic of living CDSA processes do not arise from a gradual reduction in growth rate with fiber length. The length-independent growth observed experimentally is therefore consistent with the previously proposed explanation for length control and low dispersities based on an analogy with living covalent polymerizations of molecular monomers.
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