Stable colloidal dispersions of polyaniline (PAni) nanofibers with controlled lengths from about 200 nm–1.1 μm and narrow length distributions (Lw/Ln<1.04; Lw=weight average micelle length, Ln=number average micelle length) were prepared through the template‐directed synthesis of PAni using monodisperse, solution‐self‐assembled, cylindrical, block copolymer micelles as nanoscale templates. These micelles were prepared through a crystallization‐driven living self‐assembly method from a poly(ferrocenyldimethylsilane)‐b‐poly(2‐vinylpyridine) block copolymer (PFS25‐b‐P2VP425). This material was initially self‐assembled in iPrOH to form cylindrical micelles with a crystalline PFS core and a P2VP corona and lengths of up to several micrometers. Sonication of this sample then yielded short cylinders with average lengths of 90 nm and a broad length distribution (Lw/Ln=1.32). Cylindrical micelles of PFS25‐b‐P2VP425 with controlled lengths and narrow length distributions (Lw/Ln<1.04) were subsequently prepared using thermal treatment at specific temperatures between 83.5 and 92.0 °C using a 1D self‐seeding process. These samples were then employed in the template‐directed synthesis of PAni nanofibers through a two‐step procedure, where the micellar template was initially stabilised by deposition of an oligoaniline coating followed by addition of a polymeric acid dopant, resulting in PAni nanofibers in the emeraldine salt (ES) state. The ES–PAni nanofibers were shown to be conductive by scanning conductance microscopy, whereas the precursor PFS25‐b‐P2VP425 micelle templates were found to be dielectric in character. 相似文献
With the aim of accessing colloidally stable, fiberlike, π‐conjugated nanostructures of controlled length, we have studied the solution self‐assembly of two asymmetric crystalline–coil, regioregular poly(3‐hexylthiophene)‐b‐poly(2‐vinylpyridine) (P3HT‐b‐P2VP) diblock copolymers, P3HT23‐b‐P2VP115 (block ratio=1:5) and P3HT44‐b‐P2VP115 (block ratio=ca. 1:3). The self‐assembly studies were performed under a variety of solvent conditions that were selective for the P2VP block. The block copolymers were prepared by using Cu‐catalyzed azide–alkyne cycloaddition reactions of azide‐terminated P2VP and alkyne end‐functionalized P3HT homopolymers. When the block copolymers were self‐assembled in a solution of a 50 % (v/v) mixture of THF (a good solvent for both blocks) and an alcohol (a selective solvent for the P2VP block) by means of the slow evaporation of the common solvent; fiberlike micelles with a P3HT core and a P2VP corona were observed by transmission electron microscopy (TEM). The average lengths of the micelles were found to increase as the length of the hydrocarbon chain increased in the P2VP‐selective alcoholic solvent (MeOH<iPrOH<nBuOH). Very long (>3 μm) fiberlike micelles were prepared by the dialysis of solutions of the block copolymers in THF against iPrOH. Furthermore the widths of the fibers were dependent on the degree of polymerization of the chain‐extended P3HT blocks. The crystallinity and π‐conjugated nature of the P3HT core in the fiberlike micelles was confirmed by a combination of UV/Vis spectroscopy, photoluminescence (PL) measurements, and wide‐angle X‐ray scattering (WAXS). Intense sonication (iPrOH, 1 h, 0 °C) of the fiberlike micelles formed by P3HT23‐b‐P2VP115 resulted in small (ca. 25 nm long) stublike fragments that were subsequently used as initiators in seeded growth experiments. Addition of P3HT23‐b‐P2VP115 unimers to the seeds allowed the preparation of fiberlike micelles with narrow length distributions (Lw/Ln <1.11) and lengths from about 100‐300 nm, that were dependent on the unimer‐to‐seed micelle ratio. 相似文献
Nanoporous thin films with pore size of sub‐10 nm are fabricated using an acid‐cleavable block copolymer (BCP), a benzoic imine junction between poly(ethylene oxide) (PEO) and poly(methacrylate) (PMAAz) bearing an azobenzene side chain (denoted as PEO‐bei‐PMAAz) as the precursor. After a thermal annealing, the block copolymers are self‐assembled to form highly ordered PEO cylinders within a PMAAz matrix normal to the film, even in the case of low BCP molecular weight due to the existing of the liquid crystalline (LC) azobenzene rigid segment. Thus, PMAAz thin films with pore size of ≈7 nm and density of ≈1012 cm−2 are obtained after removal of the PEO minor phase by breaking the benzoic imine junction under mild acidic conditions. This work enriches the nanoporous polymer films from BCP precursors and introduces the LC property as a functionality which can further enhance the mechanical properties of the films and broaden their applications.
Fiber‐like π‐conjugated nanostructures are important components of flexible organic electronic and optoelectronic devices. To broaden the range of potential applications, one needs to control not only the length of these nanostructures, but the introduction of diverse functionality with spatially selective control. Here we report the synthesis of a crystalline‐coil block copolymer of oligo(p‐phenylenevinylene)‐b‐poly(2‐vinylpyridine) (OPV5‐b‐P2VP44), in which the basicity and coordinating/chelating ability of the P2VP segment provide a landscape for the incorporation of a variety of functional inorganic NPs. Through a self‐seeding strategy, we were able to prepare monodisperse fiber‐like micelles of OPV5‐b‐P2VP44 with lengths ranging from 50 to 800 nm. Significantly, the exposed two ends of OPV core of these fiber‐like micelles remained active toward further epitaxial deposition of OPV5‐b‐PNIPAM49 and OPV5‐b‐P2VP44 to generate uniform A‐B‐A and B‐A‐B‐A‐B segmented block comicelles with tunable lengths for each block. The P2VP domains in these (co‐)micelles can be selectively decorated with inorganic and polymeric nanoparticles as well as metal oxide coatings, to afford hybrid fiber‐like nanostructures. This work provides a versatile strategy toward the fabrication of narrow length dispersity continuous and segmented π‐conjugated OPV‐containing fiber‐like micelles with the capacity to be decorated in a spatially selective way with varying functionalities. 相似文献
A novel approach to rationalize micellar systems is expounded in which the structural behavior of tablet‐shaped micelles is theoretically investigated as a function of the three bending elasticity constants: spontaneous curvature (H0), bending rigidity (kc), and saddle‐splay constant (k?c). As a result, experimentally accessible micellar properties, such as aggregation number, length‐to‐width ratio, and polydispersity, may be related to the different bending elasticity constants. It is demonstrated that discrete micelles or connected cylinders form when H0>1/4ξ, where ξ is the thickness of a surfactant monolayer, whereas various bilayer structures are expected to predominate when H0<1/4ξ. Our theory predicts, in agreement with experiments, a transition from discrete globular (tablet‐shaped) micelles to a phase of ordered, or disordered, connected cylinders above a critical surfactant concentration. Moreover, a novel explanation for the mechanism of growth, from small globular to long rodlike or wormlike micelles, follows as a consequence from the theory. In accordance, polydisperse elongated micelles (large length‐to‐width ratio) form as the bending rigidity is lowered, approaching the critical point at kc=0, whereas monodisperse globular micelles (small length‐to‐width ratio) are expected to be present at large kc values. The spontaneous curvature mainly determines the width of tablet‐shaped or ribbonlike micelles, or the radius of disklike micelles, whereas the saddle‐splay constant primarily influences the size but not the shape of the micelles. 相似文献
A diblock copolymer system constituting both achiral and chiral blocks, polystyrene‐block‐poly(L ‐lactide) (PS‐PLLA), was designed for the examination of chiral effects on the self‐assembly of block copolymers (BCPs). A unique phase with three‐dimensional hexagonally packed PLLA helices in PS matrix, a helical phase (H*), can be obtained from the self‐assembly of PS‐rich PS‐PLLA with volume fraction of PLLA f = 0.34, whereas no such phase was found in racemic polystyrene‐block‐poly(D .L ‐lactide) (PS‐PLA) BCPs. Moreover, various interesting crystalline PS‐PLLA nanostructures can be obtained by controlling the crystallization temperature of PLLA (Tc,PLLA), leading to the formation of crystalline helices (PLLA crystallization directed by helical confined microdomain) and crystalline cylinders (phase transformation of helical nanostructure dictated by crystallization) when Tc,PLLA < Tg,PS (the glass transition temperature of PS) and Tc,PLLA ≧ Tg,PS, respectively. As a result, a spring‐like behavior of the helical nanostructure can be driven by crystallization so as to dictate the transformation (i.e., stretching) of helices and to result in crystalline cylinders. For PS‐PLLA with PLLA‐rich fraction (f = 0.65), another unique phase, a hexagonally packed core‐shell cylinder phase with helical sense (CS*), in which the PS microdomains appear as shells and PLLA microdomains appear as matrix and cores, can be found in the self‐assembly of PLLA‐rich PS‐PLLA BCPs. The formation of those novel phases: helix and core‐shell cylinder is attributed to the chiral effect on the self‐assembly of BCPs, so we named this PS‐PLLA BCP as chiral BCP (BCP*). For potential applications of those materials, the spring‐like behavior with thermal reversibility might provide a method for the design of switchable nanodevices, such as nanoscale actuators. In addition, the PLLA blocks can be hydrolyzed. After hydrolysis, helical nanoporous PS bulk and PS tubular texture can be obtained and used as templates for the formation of nanocomposites.
The fabrication of block copolymer (BCP) vesicles (polymersomes) exhibiting synchronized covalent crosslinking and bilayer permeabilization remains a considerable challenge as crosslinking typically leads to compromised membrane permeability. Herein it is demonstrated how to solve this dilemma by employing a stimuli‐triggered crosslinking strategy with amphiphilic BCPs containing photolabile carbamate‐caged primary amines. Upon self‐assembling into polymersomes, light‐triggered self‐immolative decaging reactions release primary amine moieties and extensive amidation reactions then occur due to suppressed amine pKa within hydrophobic milieu. This leads to serendipitous vesicle crosslinking and the process is associated with bilayer hydrophobicity‐to‐hydrophilicity transition and membrane permeabilization. 相似文献