End Coupling of Block Copolymer Nanotubes to Nanospheres

Hairy Core-Shell Polymer Nano-objects from Self-Assembled Block Copolymer Structures

Fabrication of core-shell polymer nano-objects with well-defined shape and hairy shell has been a subject of immense interest in polymer chemistry for more than two decades now. Different approaches such as those involving synthesis (grafting approaches) and block copolymer self-assembly (solution as well as bulk) have been used for the preparation of such nano-objects. Of these approaches that involving bulk self-assembled structures of block copolymers have been of special interest because of the simplicity and range of shape and structures possible. The present review focuses on the advances which have been made in this direction using diblock and triblock self-assembled structures. It will be shown that this approach allows to fabricate hairy nano-objects of not only simple shapes such as spheres, rods, and sheets but also those with more complex shape and morphology such as multicompartment micelles, which are not possible to obtain with synthetic or solution self-assembly approaches. Furthermore, interesting structures such as Janus nano-objects could also be fabricated using this approach. The review further highlights the use of such nano-objects for templating applications.

Preparation of superhydrophobic films based on the diblock copolymer P(TFEMA-r-Sty)-b-PCEMA

The diblock copolymer P(TFEMA-r-Sty)-b-PCEMA was synthesized and self-assembled to form spherical micelles. Photo-cross-linking the PCEMA domains of these micelles yielded cross-linked nanoparticles. The cross-linked nanoparticles were used to prepare superhydrophobic films.

Temperature-driven switching of the catalytic activity of artificial glutathione peroxidase by the shape transition between the nanotubes and vesicle-like structures

Smart supramolecular nanoenzymes with temperature-driven switching property have been successfully constructed by the self-assembly of supra-amphiphiles formed by the cyclodextrin-based host-guest chemistry. The self-assembled nanostructures were catalyst-functionalized and thermosensitively-functionalized through conveniently linking the catalytic center of glutathione peroxidase and thermosensitive polymer to the host cyclodextrin molecules.The ON-OFF switches for the peroxidase activity by reversible transformation of nanostructures from tube to sphere have been achieved through changing the temperature. We anticipate that such intelligent enzyme mimics could be developed to use in an antioxidant medicine with controlled catalytic efficiency according to the needs of the human body in the future.

Self-assembly and chemical processing of block copolymers: a roadmap towards a diverse array of block copolymer nanostructures

Block copolymers can yield a diverse array of nanostructures. Their assembly structures are influenced by their inherent structures, and the wide variety of structures that can be prepared especially becomes apparent when one considers the number of routes available to prepare block copolymer assemblies. Some examples include self-assembly, directed assembly, coupling, as well as hierarchical assembly, which can yield assemblies having even higher structural order. These assembly routes can also be complemented by processing techniques such as selective crosslinking and etching, the former technique leading to permanent structures, the latter towards sculpted and the combination of the two towards permanent sculpted structures. The combination of these pathways provides extremely versatile routes towards an exciting variety of architectures. This review will attempt to highlight destinations reached by LIU Guojun and coworkers following these pathways.

Chiral imprinting of diblock copolymer single-chain particles

This Article reports the molecular imprinting of polymer single-chain particles that have a radius ∼3.7 nm. For this, the template L-phenylalanine anilide or L-ΦAA and a diblock copolymer PtBA-b-P(CEMA-r-CA) were used. Here, PtBA denotes poly(tert-butyl acrylate), and P(CEMA-r-CA) denotes a random block consisting of cinnamoyloxyethyl methacrylate (CEMA) and carboxyl-bearing (CA) units. In CHCl(3)/cyclohexane (CHX) with 64 vol % of CHX or at f(CHX) = 64%, a block-selective solvent for PtBA, PtBA-b-P(CEMA-r-CA) formed spherical micelles. The core consisted of the insoluble P(CEMA-r-CA) block and L-ΦAA, which complexed with the CA groups. Pumping slowly this micellar solution into stirred CHCl(3)/(CHX) at f(CHX) = 64% triggered micelle dissociation into single-chain micelles, which comprised presumably a solubilized PtBA tail and a collapsed P(CEMA-r-CA)/L-ΦAA head. Because the solvent reservoir was under constant UV irradiation, the photo-cross-linkable units in the P(CEMA-r-CA) head cross-linked, and the single-chain micelles were converted into cross-linked single-chain micelles or tadpoles. Synchronizing the micelle addition and photoreaction rates allowed the preparation, from this protocol, of essentially pure tadpoles at high final polymer concentrations. Imprinted tadpoles were procured after L-ΦAA was extracted from the tadpole heads. Under optimized conditions, the produced imprinted tadpoles had exceptionally high binding capacity and high selectivity for L-ΦAA. In addition, the rates of L-ΦAA release from and rebinding by the particles were high.

Block copolymer mimetic self-assembly of inorganic nanoparticles

Emerging strategies for assembling inorganic nanoparticles into ensembles with multiscale organization are establishing a new paradigm for the synthesis of devices and functional materials with applications ranging from drug delivery to photonics. In this work, the solution self-assembly of amphiphilic ionic block copolymers into morphologically tunable aggregates provides the inspiration and design strategy for nanoparticle building blocks with the essential chemical and conformational features of ionic block copolymer chains in aqueous media. We produce inorganic nanoparticles with surface-tethered mixed brushes of hydrophobic and chargeable hydrophilic chains which self-assemble in polar solvent mixtures into unprecedented hierarchical superstructures analogous to known ionic block copolymer aggregates but with complex organizations of nanoparticles in three dimensions. Electrostatic repulsion between hydrophilic chains forces nonequilibrium pathways to variable kinetic structures with internal lamellar organization of nanoparticles; however, decreasing electrostatic interactions through salt or acid addition allows tunable equilibrium assemblies, including supermicelles and bilayer vesicles of nanoparticles, to be formed. The application of ionic block copolymer assembly principles and mechanisms opens a new chemical toolbox for the organization of nanoparticles into functional assemblies.

Layer-by-layer deposition of block copolymer nanofibers and porous nanofiber multilayer films

We report in this paper the preparation of multilayer films from the layer-by-layer deposition of block copolymer nanofibers bearing carboxyl and amine groups in their coronas. The film formation process was followed by atomic force microscopy and UV absorbance measurements. For the large size of the nanofibers and probably also for the difficulty associated with reshuffling the positions of nanofibers once they were adsorbed by an underlying layer, nanofibers could not be packed densely. We took advantage of this "defective" feature and showed that these porous nanofiber multilayer films could be used to separate nanospheres of different sizes and probably also of different surface functionalities.

Coating and structural locking of dipolar chains of cobalt nanoparticles

Above a critical size, Co nanoparticles aggregate because of magnetic dipole-dipole interaction into chains. Reported in this paper is the coating of such chains by an AB diblock copolymer in a block-selective solvent for the A block. Also reported is the cross-linking of the deposited or anchored B block of the diblock copolymer to lock in the coating and thus the dipolar chain structure. The Co nanoparticles used were prepared from the high-temperature decomposition of Co(2)(CO)(8) using poly(2-cinnamoyloxyethyl methacrylate)-block-poly(acrylic acid) or PCEMA-b-PAA as surfactant. To coat the dipolar chains, the particles and diblock copolymer poly(tert-butyl acrylate)-block-poly(2-cinnamoyloxyethyl methacrylate), PtBA-b-PCEMA, were dispersed in a good solvent for PCEMA and PtBA. Methanol, a precipitant for PCEMA and a good solvent for PtBA, was then added. This induced the collapsing of the PCEMA blocks and the deposition of the PCEMA block of PtBA-b-PCEMA onto the surface of PCEMA-b-PAA-coated Co nanoparticle chains. The dipolar chains remained colloidally stable in solution for steric stabilization provided by PtBA. The coating was cured by photocrosslinking the PCEMA layer. Such "permanent" and solvent-dispersible Co dipolar chains are novel and may have interesting applications.

Structure-defined c60/polymer colloids supramolecular nanocomposites in water

We report a new supramolecular method for the synthesis of well-defined pristine C 60/polymer colloid nanocomposites in water. The colloids include polymer micelles and emulsion particles. To a polymer colloid solution in water or alcohol, we introduced C 60 solution in a solvent that is miscible with water or alcohol. After the two solutions mixed, polymer colloids and C 60 spontaneously assembled into stable colloidal nanocomposites. After a dialysis process, a nanocomposite dispersion in pure water was obtained. As characterized by DLS and (Cryo-)TEM, the nanocomposites have a core-shell structure with C 60 aggregated on the surface of emulsion particles or micellar cores. The resulting nanocomposites have many potential applications such as biomedicals and photovoltaics.

Grafting and Patterned Grafting of Block Copolymer Nanotubes onto Inorganic Substrates

Chemical patterning of inorganic substrates by soft lithography has enabled various high-tech applications and cutting-edge fundamental research. In this paper, we report on methods for the grafting and patterned grafting of block copolymer nanotubes onto glass and mica surfaces. Under optimized conditions the density of such grafted nanotubes can be high, and most of the grafted tubes are in a standing position even after solvent evaporation. Surfaces modified with exotic reagents such as block copolymer nanofibers or nanotubes may find applications in biosensing, etc.

Polymer Nano- and Microspheres with Bumpy and Chain-Segregated Surfaces

Reported is a novel and simple method for the preparation of polymer spheres bearing hemispherical surface bumps where one type of polymer chains concentrates. The method is used to produce spheres with a diameter between approximately 30 and approximately 500 nm. Spheres with chain-segregated bumpy surfaces may find applications in drug delivery and other areas.