Triblock Comicelles Research Articles

Efficient and Controlled Seeded Growth of Poly(3-hexylthiophene) Block Copolymer Nanofibers through Suppression of Homogeneous Nucleation

Low-dispersity, length-tunable block copolymer nanofibers with spatially controlled functionalization and a crystalline core have recently become accessible using the ambient temperature, living crystallization-driven self-assembly (CDSA) seeded-growth method. The crystallizable π-conjugated polymer, poly(3-hexylthiophene) (P3HT), is of particular interest as a core-forming block as a result of its useful optoelectronic properties. However, attempts to apply the living CDSA method to P3HT diblock copolymers have had limited success as, in addition to seeded growth, homogeneous nucleation events result in the spontaneous formation of new fibers, which leads to a loss of length control. Herein, we demonstrate that by performing detailed variable temperature ultraviolet–visible (UV–vis) spectroscopic studies of the homogeneous nucleation of rrP3HT106-b-rsP3HT47 block copolymer (rr = regioregular and rs = regiosymmetric, respectively) we were able to identify conditions (40 °C) under which spontaneous (homogeneous) nucleation is suppressed. Addition of preformed seeds under these conditions allowed for highly efficient living CDSA to yield nanofibers with a rrP3HT106 core and controllable lengths up to ca. 4 μm with low length dispersity. Analogous use of this technique also allowed the efficient preparation of B-A-B triblock comicelles through the growth of P3HT70-b-PS197 from the termini of rrP3HT106-b-rsP3HT47 nanofibers that function as seed micelles, and also multiarm starlike arrays of fiberlike micelles with variable arm lengths, which were formed when seed micelles derived from rrP3HT150 homopolymer were used.

Linear and Branched Fiber-like Micelles from the Crystallization-Driven Self-Assembly of Heterobimetallic Block Copolymer Polyelectrolyte/Surfactant Complexes

The solution self-assembly of a heterobimetallic diblock copolymer with a crystallizable poly(ferrocenyldimethylsilane) (PFS) core-forming block and a corona-forming segment featuring a poly(cobaltoceniumethylene) (PCE)-based polyelectrolyte/surfactant complex, PFS50-b-[PCE][AOT]50 (AOT = bis(2-ethylhexyl) sulfosuccinate), has been explored. Fiber-like micelles were formed in selective solvents for the Co-containing block, yielding a corona in which every repeat unit bears a charge. We found that key features of the one-dimensional (1D) morphologies were dependent on both the polarity of the solvent medium and temperature. In the most polar of the explored solvent media (iPrOH), seeded growth from 1D seeds of PFS50-b-P2VP739 (P2VP = poly(2-vinylpyridine)) yielded tapered B-A-B triblock comicelles, where the width of the terminal B region derived from PFS-b-[PCE][AOT]n reduced on moving from the interface with the seed to the micelle termini. In addition, ca. 30% of the micelles featured branching to yield...

Preparing Semiconducting Nanoribbons with Tunable Length and Width via Crystallization-Driven Self-Assembly of a Simple Conjugated Homopolymer.

Precise control of width and length of one-dimensional (1D) semiconducting nanostructures has attracted much attention owing to its potential for optoelectronic applications. However, regulating both their length and width using conjugated polymers or even block copolymers is a huge challenge. To solve this problem, we synthesized a unique conjugated polyacetylene homopolymer by living cyclopolymerization, which spontaneously formed 1D nanoribbons via in situ nanoparticlization. Interestingly, their widths could be controlled from 8 to 41 nm, which were directly proportional to their degree of polymerization. Furthermore, a self-seeding technique via crystallization-driven self-assembly (CDSA) was used to control the length of the nanoribbons up to 5.2 μm with narrow distributions less than 1.1. Interestingly, adding a block copolymer unimer to these nanoribbons produced triblock comicelles by the living CDSA mechanism. Finally, these nanoribbons were visualized directly by super-resolution optical fluorescence microscopy. Now, one can modulate both length and width of 1D nanoribbons simultaneously.

Living Light-Induced Crystallization-Driven Self-Assembly for Rapid Preparation of Semiconducting Nanofibers.

Well-defined nanostructures composed of conjugated polymers have attracted significant attention due to their intriguing electronic and optical properties. However, precise control of the size and uniformity of these semiconducting nanostructures is still rare and challenging, despite recent advances in strategies to obtain self-assembled nanostructures with narrow dispersions. Herein, we demonstrate the preparation of fluorescent conjugated block copolymers by one-shot polymerization and rapid formation of nanofibers in a few minutes via light-induced crystallization-driven self-assembly, driven by facile cis-to- trans photoisomerization of its poly( p-phenylenevinylene) blocks. Furthermore, living self-assembly was possible, allowing not only nanofibers with excellent length control and narrow size distribution but also ABA triblock comicelles and gradient comicelles, to be produced by seeded growth. Lastly, the seeded growth could be activated and deactivated repeatedly by switching the light on and off, analogous to light-induced living radical polymerization.

Monodisperse Fiber-like Micelles of Controlled Length and Composition with an Oligo(p-phenylenevinylene) Core via "Living" Crystallization-Driven Self-Assembly.

We report the preparation of a series of fiber-like micelles of narrow length distribution with an oligo(p-phenylenevinylene) (OPV)-core and a poly(N-isopropylacrylamide) (PNIPAM) corona via two different crystallization-driven self-assembly (CDSA) strategies. The average length Ln of these micelles can be varied up to 870 nm by varying the temperature in self-seeding experiments. In addition, seeded growth was employed not only to prepare uniform micelles of controlled length, but also to form fiber-like A-B-A triblock comicelles with an OPV-core.

Hierarchical Assembly of Cylindrical Block Comicelles Mediated by Spatially Confined Hydrogen-Bonding Interactions.

Hydrogen bonds are among the most common interactions used by nature for the creation of hierarchical structures from smaller building blocks. Herein, we describe an in-depth study of the hierarchical assembly of cylindrical block comicelles with a crystallizable poly(ferrocenyldimethylsilane) (PFS) core via H-bonding interactions to form complex supermicellar structures. Well-defined block comicelles bearing H-bond donor (HD) segments (M(PFS-b-PMVSOH)), or H-bond acceptor (HA) segments (M(PFS-b-P2VP)), and non-interacting (N) segments (M(PFS-b-PtBA)) were created by the living crystallization-driven self-assembly (CDSA) method [PMVSOH = hydroxyl-functionalized poly(methylvinylsiloxane), P2VP = poly(2-vinylpyridine), PtBA = poly(tert-butyl acrylate), M = micelle segment]. Due to the control provided by the living CDSA approach, both the block comicelles and the individual segments were virtually monodisperse in length, which facilitated their predictable hierarchical assembly into higher-level structures. Two cases were investigated in detail: first, the interaction of N-HA-N triblock comicelles with the HD homopolymer PMVSOH, and second, the interaction of N-HD-N triblock comicelles with very short HA cylinders (seeds). By manipulation of several factors, namely coronal steric effects (via the PtBA corona chain) and attractive interaction strength (via the H-bonding interaction between P2VP and PMVSOH), the aggregation of the triblock comicelles could be controlled, and well-defined multi-micrometer-size structures such as "shish-kebab"-shaped supermicelles were prepared. The ability of the seeds adsorbed on the block comicelles to function as initiators for living CDSA to generate fence-like "shish-kebab" superstructures was also explored.

"Cross" Supermicelles via the Hierarchical Assembly of Amphiphilic Cylindrical Triblock Comicelles.

Self-assembled "cross" architectures are well-known in biological systems (as illustrated by chromosomes, for example); however, comparable synthetic structures are extremely rare. Herein we report an in depth study of the hierarchical assembly of the amphiphilic cylindrical P-H-P triblock comicelles with polar (P) coronal ends and a hydrophobic (H) central periphery in a selective solvent for the terminal segments which allows access to "cross" supermicelles under certain conditions. Well-defined P-H-P triblock comicelles M(PFS-b-PtBA)-b-M(PFS-b-PDMS)-b-M(PFS-b-PtBA) (M = micelle segment, PFS = polyferrocenyldimethylsilane, PtBA = poly(tert-butyl acrylate), and PDMS = polydimethylsiloxane) were created by the living crystallization-driven self-assembly (CDSA) method. By manipulating two factors in the supermicelles, namely the H segment-solvent interfacial energy (through the central H segment length, L1) and coronal steric effects (via the PtBA corona chain length in the P segment, L2 related to the degree of polymerization DP2) the aggregation of the triblock comicelles could be finely tuned. This allowed a phase-diagram to be constructed that can be extended to other triblock comicelles with different coronas on the central or end segment where "cross" supermicelles were exclusively formed under predicted conditions. Laser scanning confocal microscopy (LSCM) analysis of dye-labeled "cross" supermicelles, and block "cross" supermicelles formed by addition of a different unimer to the arm termini, provided complementary characterization to transmission electron microscopy (TEM) and dynamic light scattering (DLS) and confirmed the existence of these "cross" supermicelles as kinetically stable, micron-size colloidally stable structures in solution.

Monodisperse Cylindrical Micelles and Block Comicelles of Controlled Length in Aqueous Media.

Cylindrical block copolymer micelles have shown considerable promise in various fields of biomedical research. However, unlike spherical micelles and vesicles, control over their dimensions in biologically relevant solvents has posed a key challenge that potentially limits in depth studies and their optimization for applications. Here, we report the preparation of cylindrical micelles of length in the wide range of 70 nm to 1.10 μm in aqueous media with narrow length distributions (length polydispersities <1.10). In our approach, an amphiphilic linear-brush block copolymer, with high potential for functionalization, was synthesized based on poly(ferrocenyldimethylsilane)-b-poly(allyl glycidyl ether) (PFS-b-PAGE) decorated with triethylene glycol (TEG), abbreviated as PFS-b-(PEO-g-TEG). PFS-b-(PEO-g-TEG) cylindrical micelles of controlled length with low polydispersities were prepared in N,N-dimethylformamide using small seed initiators via living crystallization-driven self-assembly. Successful dispersion of these micelles into aqueous media was achieved by dialysis against deionized water. Furthermore, B-A-B amphiphilic triblock comicelles with PFS-b-poly(2-vinylpyridine) (P2VP) as hydrophobic "B" blocks and hydrophilic PFS-b-(PEO-g-TEG) "A" segments were prepared and their hierarchical self-assembly in aqueous media studied. It was found that superstructures formed are dependent on the length of the hydrophobic blocks. Quaternization of P2VP was shown to cause the disassembly of the superstructures, resulting in the first examples of water-soluble cylindrical multiblock comicelles. We also demonstrate the ability of the triblock comicelles with quaternized terminal segments to complex DNA and, thus, to potentially function as gene vectors.

Cylindrical polymer micelles pack in 3D

Micelle Assembly When you control chemistry, solvents, temperature, and concentration, surfactants and block copolymers will readily assemble into micelles, rods, and other structures. Qiu et al. take this to new lengths through precise selection of longer polymer blocks that self-assemble through a crystallization process (see the Perspective by Lee et al. ). They chose polymer blocks that were either hydrophobic or polar and used miscible solvents that were each ideal for only one of the blocks. Their triblock comicelles generated a wide variety of stable three-dimensional superstructures through side-by-side stacking and end-to-end intermicellar association. Science , this issue p. [1329][1]; see also p. [1310][2] [1]: /lookup/doi/10.1126/science.1261816 [2]: /lookup/doi/10.1126/science.aaa8681

Micelle assembly. Multidimensional hierarchical self-assembly of amphiphilic cylindrical block comicelles.

Self-assembly of molecular and block copolymer amphiphiles represents a well-established route to micelles with a wide variety of shapes and gel-like phases. We demonstrate an analogous process, but on a longer length scale, in which amphiphilic P-H-P and H-P-H cylindrical triblock comicelles with hydrophobic (H) or polar (P) segments that are monodisperse in length are able to self-assemble side by side or end to end in nonsolvents for the central or terminal segments, respectively. This allows the formation of cylindrical supermicelles and one-dimensional (1D) or 3D superstructures that persist in both solution and the solid state. These assemblies possess multiple levels of structural hierarchy in combination with existence on a multimicrometer-length scale, features that are generally only found in natural materials.

Form factor of asymmetric elongated micelles: playing with Russian dolls has never been so informative.

Scattering techniques (i.e., static light scattering, small angle neutron scattering,11 or small angle X-ray scattering) are excellent tools to study nanoscopic objects in solution. However, to interpret the experimental data, one needs to use the appropriate form factor. While recent progress has been made in the writing of form factors for complex structures, there is still a need to develop a method to evaluate the form factor of inhomogeneous elongated scatterers. Here, we propose an approach based on the principle of "Russian dolls". Multiblock rods are represented as multi generations of rods (mother, daughter, granddaughter, etc.), where each rod is nested within the rod of the previous generation, like Russian dolls. A shift parameter is used to introduce asymmetry in the rod along its long axis. This approach not only allowed us to write the form factor of multiblock rods, but it also gave us the possibility to account for the polydispersity in length of each block and of the shift parameter. Finally, we applied these equations to the case of a series of solutions of triblock comicelles slightly polydisperse in length.

Uniform, High Aspect Ratio Fiber-like Micelles and Block Co-micelles with a Crystalline π-Conjugated Polythiophene Core by Self-Seeding

Monodisperse fiber-like micelles with a crystalline π-conjugated polythiophene core with lengths up to ca. 700 nm were successfully prepared from the diblock copolymer poly(3-hexylthiophene)-block-polystyrene using a one-dimensional self-seeding technique. Addition of a polythiophene block copolymer with a different corona-forming block to the resulting nanofibers led to the formation of segmented B-A-B triblock co-micelles by crystallization-driven seeded growth. The key to these advances appears to be the formation of a relatively defect-free crystalline micelle core under the self-seeding conditions.

Tunable Supermicelle Architectures from the Hierarchical Self‐Assembly of Amphiphilic Cylindrical B–A–B Triblock Co‐Micelles

Tunable Supermicelle Architectures from the Hierarchical Self‐Assembly of Amphiphilic Cylindrical B–A–B Triblock Co‐Micelles

Tunable Supermicelle Architectures from the Hierarchical Self‐Assembly of Amphiphilic Cylindrical B–A–B Triblock Co‐Micelles

Tunable Supermicelle Architectures from the Hierarchical Self‐Assembly of Amphiphilic Cylindrical B–A–B Triblock Co‐Micelles

Length Control and Block-Type Architectures in Worm-like Micelles with Polyethylene Cores

We present evidence for "living"-like behavior in the crystallization-driven self-assembly of triblock copolymers with crystallizable polyethylene middle blocks into worm-like crystalline-core micelles (CCMs). A new method of seed production is introduced utilizing the selective self-assembly of the triblock copolymers into spherical CCMs in appropriate solvents. Seeded growth of triblock copolymer unimers from these spherical CCMs results in worm-like CCMs with narrow length distributions and mean lengths that depend linearly on the applied unimer-to-seed ratio. Depending on the applied triblock copolymer, polystyrene-block-polyethylene-block-polystyrene (SES) or polystyrene-block-polyethylene-block-poly(methyl methacrylate) (SEM), well-defined worm-like CCMs with a homogeneous or patch-like corona, respectively, can be produced. In a subsequent step, these worm-like CCMs can be used as seeds for the epitaxial growth of a different polyethylene containing triblock copolymer. In this manner, ABA-type triblock co-micelles containing blocks with a homogeneous polystyrene corona and those with a patch-like polystyrene/poly(methyl methacrylate) corona were prepared. While the epitaxial growth of SEM unimers from worm-like SES CCMs with a homogeneous corona yields triblock co-micelles almost quantitatively, the addition of SES unimers to patchy SEM wCCMs results in a mixture of ABA- and AB-type block co-micelles together with residual patchy wCCMs. Following reports on self-assembled block-type architectures from polymers containing core-forming polyferrocenylsilane blocks, these structures represent the first extension of the concept to block co-micelles from purely organic block copolymers.