Swelling and Shrinkage of Lamellar Domain of Conformationally Restricted Block Copolymers by Metal Chloride

Fluorescence Switchable Block Copolymer Particles with Doubly Alternate-Layered Nanoparticle Arrays

The precise self-assembly of block copolymers (BCPs) and inorganic nanoparticles (NPs) under 3D confinement offers microparticles with programmable nanostructures and functionalities. Here, fluorescence-switchable hybrid microspheres are developed by forming doubly alternating arrays of Au NPs and CdSe/ZnS quantum dots (QDs) within polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) BCP domains. These doubly alternating arrays afford controlled nonradiative energy transfer (NRET) between the QDs and Au NPs that is dependent on the layer-to-layer distance. Solvent-selective swelling of the hybrid particles tunes the distance between layers, modulating their NRET behavior and affording switchable fluorescence. The particle fluorescence is "OFF" in water through strong NRET from the QDs to Au NPs, but is "ON" in alcohols due to the increased distance between the Au NP and QD arrays in the swollen P4VP domains. The experimentally observed NRET intensity as a function of interparticle distance shows larger quenching efficiencies than those theoretically predicted due to the enhanced quenching within a 3D-confined system. Finally, the robust and reversible fluorescence switching of the hybrid particles in different solvents is demonstrated, highlighting their potentials for bioimaging, sensing, and diagnostic applications.

Three-Dimensional Nanoporous Metal Structures from Poly(2-vinylpyridine)-block-Poly(4-vinylpyridine) Copolymer Thin Film

We fabricated 3D nanoporous metal structures from poly(2-vinylpyridine)-block-poly(4-vinylpyridine) copolymer (P24VP) thin film with vertically oriented lamellar nanodomains by coordinating corresponding metal precursors followed by reduction to metals. Although metal precursors are coordinated with both P2VP and P4VP blocks, the metal coordination power toward P4VP block is much greater than that toward P2VP block. Thus, most of the metal precursors are located in the P4VP block, while a few exist in the P2VP block. After the metal precursors were reduced to corresponding metals by reactive ion etching, metals located in P4VP regions became continuous main frames. However, metals in P2VP regions could not be continuous because of smaller amounts, resulting in nanoporous structures. Using these 3D nanoporous structures, we measured the electrocatalytic activity for hydrogen evolution reaction. 3D nanoporous platinum (Pt) showed enhanced catalytic activity compared with Pt flat film due to the large surface area. Moreover, 3D nanoporous Pt/cobalt bimetallic structures showed better catalytic activity than 3D nanoporous Pt structures.

Precise control of grafting density in periodically grafted amphiphilic copolymers: an alternate strategy to fine-tune the lamellar spacing in the sub-10 nm regime

By exactly locating pendant PEG550 segments at varying intervals along a hydrocarbon-rich polyester backbone, the lamellar dimension has been precisely tuned.

Fabrication of Ordered Nanopattern by using ABC Triblock Copolymer with Salt in Toluene

Ordered nanopatterns of triblock copolymer polystyrene-block-poly(2-vinylpyridine)-block- poly (ethylene oxide)(PS-b-P2VP-b-PEO) have been achieved by the addition of lithium chloride (LiCl). The morphological and structural evolution of PS-b-P2VP-b-PEO/LiCl thin films were systematically investigated by varying different experimental parameters, including the treatment for polymer solution after the addition of LiCl, the time scale of ultrasonic treatment and the molar ratio of Li⁺ ions to the total number of oxygen atoms (O) in PEO block and the nitrogen atoms (N) in P2VP block. When toluene was used as the solvent for LiCl, ordered nanopattern with cylinders or nanostripes could be obtained after spin-coating. The mechanism of nanopattern transformation was related to the loading of LiCl in different microdomains.

Intra- and intermolecular-interaction-controlled reversible core–shell structures and photoluminescent properties of lanthanide ion-doped diblock copolymers

Lanthanide-based nanotechniques continue to attract considerable attention due to their current range of applications and broad potential in optical devices and biomedicine.

Rapid ordering of block copolymer thin films

Block-copolymers self-assemble into diverse morphologies, where nanoscale order can be finely tuned via block architecture and processing conditions. However, the ultimate usage of these materials in real-world applications may be hampered by the extremely long thermal annealing times-hours or days-required to achieve good order. Here, we provide an overview of the fundamentals of block-copolymer self-assembly kinetics, and review the techniques that have been demonstrated to influence, and enhance, these ordering kinetics. We discuss the inherent tradeoffs between oven annealing, solvent annealing, microwave annealing, zone annealing, and other directed self-assembly methods; including an assessment of spatial and temporal characteristics. We also review both real-space and reciprocal-space analysis techniques for quantifying order in these systems.

Direct synthesis of a mesoporous TiO2–RuO2 composite through evaporation-induced polymeric micelle assembly

Evaporation-induced assembly of spherical micelles made of an asymmetric triblock copolymer enables the fabrication of a mesoporous TiO₂–RuO₂ composite with a uniform pore size.

Fabrication and modification of ordered nanoporous structures from nanophase-separated block copolymer/metal salt hybrids

We report facile preparation of nanoporous thin films by rinsing out a metal salt from nanophase-separated hybrid films composed of a block copolymer and a water-soluble metal salt. Nanophase-separated hybrids were prepared by mixing polystyrene-b-poly(4-vinylpyridine) (PS-P4VP) and iron(III) chloride in a solvent of pyridine, followed by solvent-casting and thermal-annealing. Film samples with a thickness of ca. 100 nm were fabricated from the nanophase-separated hybrids by using a microtoming technique. Metal salts in the films were removed by immersion into water to fabricate nanopores. Morphological observations were conducted by using transmission electron microscopy (TEM). Ordered cylindrical nanopores were clearly observed in the thin films prepared from the water-immersed hybrids which originally present cylindrical nanodomains. These nanoporous films were modified by loading another metal salt, samarium(III) nitrate, into the nanopores on the basis of the coordination ability of P4VP tethered to the pore walls. The samples after loading treatment were evaluated by TEM observation and elemental analysis with energy dispersive X-ray spectroscopy.

In situ synthesis and alignment of Au nanoparticles within hexagonally packed cylindrical domains of diblock copolymers in bulk

We present a simple method to prepare hexagonally packed metallic nanocylinders based on gold nanoparticles embedded in a copolymeric matrix. The gold nanoparticles are generated selectively within the P4VP-rich cylindrical domains of a polystyrene-b-poly-4-vinylpyridine (PS-b-P4VP) diblock copolymer. In order to achieve this selectivity, a gold precursor (HAuCl4) is coupled to the pyridine blocks of a spherical PS327-b-P4VP27 block copolymer. In consequence, the hybrid block copolymer is able to self-assemble in a hexagonally packed cylinders morphology. The application of mechanical oscillatory shear improved markedly the alignment of these nanocylinders, while simultaneously the gold precursor was reduced in situ into gold nanoparticles. Following rheological characterization in the linear viscoelastic regime, a set of alignment parameters were comprehensively selected and checked with a series of transmission electron microscopy (TEM) micrographs. An optimal temperature of alignment was found after systematic evaluation of samples sheared at different temperatures. The block copolymer exhibited an increase in the domain period as a consequence of chain rearrangements around the newly formed gold nanoparticles. The hexagonally packed morphology was preserved, and under the optimal conditions single grain sizes showed significant improvement to macroscale order in comparison to nonaligned samples. In contrast to current multistep lithographic techniques, the present method constitutes a simple path to produce three-dimensional organic-inorganic conductive nanowires with periodicities at the macroscopic level.