Living crystallization-driven self-assembly (CDSA) is a seeded growth method for crystallizable block copolymers (BCPs) and related amphiphiles in solution and has recently emerged as a highly ...promising and versatile route to uniform core–shell nanoparticles (micelles) with control of dimensions and architecture. However, the factors that influence the rate of nanoparticle growth have not been systematically studied. Using transmission electron microscopy, small- and wide-angle X-ray scattering, and super-resolution fluorescence microscopy techniques, we have investigated the kinetics of the seeded growth of poly(ferrocenyldimethylsilane)-b-(polydimethylsiloxane) (PFS-b-PDMS), as a model living CDSA system for those employing, for example, crystallizable emissive and biocompatible polymers. By altering various self-assembly parameters including concentration, temperature, solvent, and BCP composition our results have established that the time taken to prepare fiber-like micelles via the living CDSA method can be reduced by decreasing temperature, by employing solvents that are poorer for the crystallizable PFS core-forming block, and by increasing the length of the PFS core-forming block. These results are of general importance for the future optimization of a wide variety of living CDSA systems. Our studies also demonstrate that the growth kinetics for living CDSA do not exhibit the first-order dependence of growth rate on unimer concentration anticipated by analogy with living covalent polymerizations of molecular monomers. This difference may be caused by the combined influence of chain conformational effects of the BCP on addition to the seed termini and chain length dispersity.
Branched and barbed structures are common in nature but rare in nanoscale or mesoscale objects formed by bottom‐up self‐assembly. Key characteristics of the morphology of natural objects, such as ...various types of insects and conifer branches, is that despite their similarities no two individual objects are exactly the same. Here we report the self‐assembly conditions for a series of poly(ferrocenyldimethylsilane)‐block‐polyisoprene (PFS‐b‐PI) diblock copolymers that generate structures with biomorphic shapes. All of these polymers yield long uniform fiber‐like micelles with a crystalline PFS core in decane. Injection of a concentrated THF solution of these polymers into THF/decane mixtures, however, leads to barbed and branched mesostructures, with shapes that depend upon the final THF content of the mixed solvent. Interestingly, evaporation of the THF from suspensions of the colloidal biomorphic structures led to elongated fiber‐like structures.
PFS‐b‐PI (poly(ferrocenyldimethylsilane)‐block‐polyisoprene) diblock copolymers self‐assemble into biomorphic structures with shapes that depend on the assembly conditions. Long fiber‐like micelles of uniform width are formed with a crystalline PFS core in decane. Injection of a THF polymer solution into THF/decane leads to micrometer‐scale barbed and branched structures with shapes that depend upon the final THF content.
Mixed micelles formed by co‐assembly of pairs of block copolymers (BCPs) can develop novel morphologies and generate useful properties not accessible from homomicelles. For micelles consisting of two ...different polymers in the corona, identifying the location of the corona chains is a critical part of morphology characterization. Coronal segregation in mixed micelle is often characterized by transmission electron microscopy in combination with selective staining of individual polymers. In this study, Karstedt’s catalyst is used for selective Pt(0)‐olefin coordination staining of polyisoprene (PI) and poly(methylvinylsiloxane) (PMVS) corona chains in the presence of poly(dimethylsiloxane) (PDMS) corona chains in cylindrical mixed micelles with a crystalline poly(ferrocenyldimethylsilane) (PFS) core. Previous experiments using OsO4 as a stain did not enable visualization of nanoscale coronal segregation in mixed micelles obtained from co‐assembly of PFS‐b‐PI and PFS‐b‐PDMS, as well as PFS‐b‐PMVS and PFS‐b‐PDMS.
Karstedt’s catalyst can be used as a staining agent for visualizing nanoscale coronal segregation in core‐crystalline comicelles through Pt(0)‐olefin coordination.
Liposomes immobilized onto polymeric hydrogel microbeads have potential advantages both in tissue engineering applications and as drug delivery vehicles. Here we demonstrate, quantify, and optimize ...lipid vesicle binding to polymeric hydrogel microbeads via the avidin−biotin conjugation system and characterize the stability of the resulting microgel-bound liposomes. Microgels consisting of a copolymer of N-isopropylacrylamide (NIPAM) and acrylic acid (AA), cross-linked with bis-acrylamide, that is, p(NIPAM-co-AA), were biotinylated using aqueous carbodiimide chemistry. Extruded liposomes consisting of 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) plus a small fraction of a biotin-derivatized phosphatidylethanolamine (B-PE) were saturated with avidin and allowed to bind to biotinylated hydrogel beads. Using a combination of fluorescence spectroscopy, quenching, and microscopy and 31P NMR static and magic angle spinning (MAS) spectroscopies, we demonstrate conditions for near-quantitative liposome binding to p(NIPAM-co-AA) microbeads and show that liposome fusion does not occur under such conditions, that the liposomes remain intact and impermeable when so bound, and that they can function as slow release vehicles for entrapped aqueous species.
We report a study of the dissolution of core-crystalline polyferrocenyldimethylsilane-block-polyisoprene (PFS53-b-PI637, where the subscripts are the degrees of polymerization of the two blocks) ...micelle fragments in decane for different concentrations (ranging from 0.01 to 6 mg mL–1) by a combination of transmission electron microscopy (TEM) and high-temperature 1H NMR. We used self-seeding experiments at different temperatures as an efficient, although indirect, way to evaluate the dissolution of these micelles fragments. We annealed micelle fragment solutions at five different temperatures (50, 60, 65, 70, and 75 °C) for 30 min and cooled them to room temperature to regrow the micelles. The amount of micelle fragments that dissolved at the annealing temperature was then evaluated by comparing the length of the regrown micelles with that of the starting micelle fragments. We show that seed crystallites are less prone to dissolution as their concentration increases. In addition, by combining results of self-seeding experiments and 1H NMR measurements at 75 °C, we evaluated the percentage of unimer released upon the partial dissolution of seed fragments at 75 °C and established that the mechanism of seed fragment dissolution is also concentration dependent: at low concentrations, they dissolve in a cooperative process, whereas at high concentrations, they dissolve partially from both ends.
Immobilizing uniform nanostructures on a mesoscale substrate is a promising approach to prepare nanometer to micrometer sized materials with new functionalities. The hierarchical structures formed ...depend on both the nature of the substrate and the components deposited. In this paper, we describe the use of colloidal polystyrene microbeads as a sacrificial template to create a nanofibrous network coating consisting of elongated block copolymer micelles. This network has a secondary structure very different from that of conformal coatings obtained by other methods. In addition, the fibers of the network could be elongated by crystallization-driven self-assembly. The network was locked in place by cross-linking the micelles through in situ generation of small Pt nanoparticles. Subsequent removal of the sacrificial template gave an open vesicular structure. To demonstrate further transformation of the membrane, we showed that the cross-linked micelles could also be used to embed silver nanoparticles. The sacrificial template contained known amounts of Tb and Tm ions, allowing us to estimate via atomic mass spectrometry that 85% of the template surface was covered with micelle seeds. This approach to fabricating hierarchical coating structures expands the generality and scope of template-assisted synthesis to build advanced hierarchical materials with precise morphological control.
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 PI1000-PFS50 (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 PI637-PFS53 in decane, PFS60-PDMS660 in decane (PDMS = polydimethylsiloxane), and PFS30-P2VP300 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.
A polyferrocenyldimethylsilane-block-poly(2-vinylpyridine) sample with a photocleavable o-nitrobenzyl ester (ONB) group at the junction (PFS35-hv-P2VP400) was synthesized by copper-catalyzed ...coupling of a P2VP-ONB-alkyne with a PFS-azide. Rodlike core-crystalline micelles of uniform length and uniform width were prepared in 2-propanol, a selective solvent for P2VP. Samples of these micelles were photoirradiated with UV-A light (peak emission 360 nm), which induced cleavage at the core–corona junction. Prolonged irradiation (24 h) led to aggregation and precipitation of the corona-cleaved micelles. One could see by TEM that the width of the micelles in the aggregates was significantly reduced (from 49 to 21 nm) because of the loss of the P2VP block, while the PFS core length (L) remained unchanged. For one micelle sample with L w = 320 nm (650 polymer molecules per micelle), the time course of the irradiation was monitored by GPC, TEM, and multiangle light scattering. After 1 h irradiation, 60% of the corona chains were cleaved, but only small amounts of aggregates had formed. Most of the rodlike micelles maintained their colloidal stability even after 70% of the corona chains had been cleaved. By GPC, we detected formation of an unexpected PFS dimer that became more prominent as the irradiation continued. Dimer formation could be explained by a photoredox coupling of o-nitrosobenzaldehyde groups at the ends of adjacent PFS chains embedded in the micelle core.
Self-seeding is a process unique to polymer crystals, which consist of regions of different chain packing order and different crystallinity. Here we report the synergistic self-seeding behaviour of ...pairs of core-crystalline block copolymer (BCP) micelle fragments and show how this strategy can be employed to control the morphology of these BCP comicelles. Each micelle fragment has a critical dissolution temperature (
T
c
), and unimers of each BCP have a characteristic epitaxial growth rate. The
T
c
value affects the dissolution sequence of the fragments upon heating, while the unimer growth rate affects the growth sequence upon cooling. By carefully choosing micelle fragments having different
T
c
values as well as growth rates, we could prepare patchy comicelles and block comicelles with uniform and controllable length. This synergistic self-seeding strategy is a simple yet effective route to control both length and morphology of core-crystalline comicelles
By manipulating both the dissolution sequence of polymer crystallites and the growth rate of polymer unimers, patchy comicelles and block comicelles with uniform and controllable length can be obtained.
By manipulating both the dissolution sequence of polymer crystallites and the growth rate of polymer unimers, patchy comicelles and block comicelles with uniform and controllable length can be ...obtained.
Self-seeding is a process unique to polymer crystals, which consist of regions of different chain packing order and different crystallinity. Here we report the synergistic self-seeding behaviour of pairs of core-crystalline block copolymer (BCP) micelle fragments and show how this strategy can be employed to control the morphology of these BCP comicelles. Each micelle fragment has a critical dissolution temperature (
T
c
), and unimers of each BCP have a characteristic epitaxial growth rate. The
T
c
value affects the dissolution sequence of the fragments upon heating, while the unimer growth rate affects the growth sequence upon cooling. By carefully choosing micelle fragments having different
T
c
values as well as growth rates, we could prepare patchy comicelles and block comicelles with uniform and controllable length. This synergistic self-seeding strategy is a simple yet effective route to control both length and morphology of core-crystalline comicelles
PDF
