Andriy Horechyy

Highly ordered arrays of magnetic nanoparticles prepared via block copolymer assembly

In the present study we report a simple and reproducible method to prepare highly ordered arrays of Fe3O4 superparamagnetic nanoparticles (MNPs) via block copolymer (BCP) self assembly. Pre-synthesized MNPs with a mean diameter of 6.1 nm are selectively segregated within the lamellae or hexagonally packed cylinders composed of PVP blocks in poly(styrene-b-vinylpyridine) (PS-b-PVP) block copolymers without any additional surface modification. The density of the stabilizing shell in the MNPs as well as the position of pyridine nitrogen in the PVP block of the BCPs are found to be crucial for selective incorporation of MNPs into the PVP domains. The obtained results suggest a key importance of a mutual affinity between active blocks and the nanoparticles which should be maximized in order to attain high nanoparticles loadings and long-range structural orders.

Helical Packing of Nanoparticles Confined in Cylindrical Domains of a Self‐Assembled Block Copolymer Structure

Theoretical models predict that a variety of self-assembled structures of closely packed spherical particles may result when they are confined in a cylindrical domain. In the present work we demonstrate for the first time that the polymer-coated nanoparticles confined in the self-assembled cylindrical domains of a block copolymer pack in helical morphology, where we can isolate individual fibers filled with helically arranged nanoparticles. This finding provides unique possibilities for fundamental as well as application-oriented research in similar directions.

Polymer microcapsules loaded with Ag nanocatalyst as active microreactors

We report on the fabrication of a new complex catalytic system composed of silica-supported silver nanoparticles (AgNP) encapsulated inside polymer microcapsules (MC)s. The silver nanocatalyst itself was obtained by reduction of silver salt in the presence of SiO2 particles acting as AgNP carriers, to provide a complex Ag/SiO2 catalyst with the Ag surface completely free of capping agents. Ag/SiO2 particles were enclosed inside the interior of polymer microcapsules. Due to the presence of the hydrophobic shell on the MC surface, catalytic reactions become feasible in an organic solvent environment. On the other hand, the hydrophilic nature of the MC interior forces the water-soluble reactants to concentrate inside the capsules which act as microreactors. Based on the example of catalytically driven reduction of 4-nitrophenol we demonstrate that encapsulated Ag/SiO2 particles possess enhanced catalytic activity as compared to the catalyst being freely dispersed in reaction medium.

High-Resolution Metal Nanopatterning by Means of Switchable Block Copolymer Templates

In this review, recent developments in the fabrication of hexagonal and parallel ordered arrays of metallic nanodomains on a substrate are described. We focus on the nanopatterning approach by means of switchable block copolymer thin films. This approach is highly advantageous, because it can lead to extremely regular patterns with metal subunits of only a few nanometers in diameter and center-to-center distances of tens of nanometers. Hence, the resulting 1D or 2D periodic arrays of metal nanodots and nanowires on silicon substrates can be fabricated with extremely high unit densities and on very large areas. The templated deposition of presynthesized metal nanoparticles on functional block copolymers is described in detail. Current challenges are discussed and an outlook for further developments is given.

Hairy polymer nanofibers via self-assembly of block copolymers

We demonstrate a simple approach to prepare hairy polymer nanorods/nanofibres by exploiting the self-assembly behavior of block copolymers. The hairy nanofibres were prepared from an asymmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer whose self-assembled morphology consisted of PS cylinders dispersed in P4VP matrix. The dissolution of the block copolymer in a P4VP selective solvent resulted in the isolation of individual PS cylinders wrapped with a shell consisting of covalently bound P4VP chains. The diameter of these hairy nanofibres was ∼80 nm, whereas the length was in the range of several hundred nanometers. We further show that such hairy nanofibres provide interesting possibilities for doing further chemistry on their surface. This, in principle, allows one to prepare a range of functional hybrid organic/inorganic nanofibres of diameter less than 100 nm using the hairy polymer nanofibres as template. The organic fraction of the nanofibres can then be further removed by thermal treatment to produce pure inorganic nano-objects.

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.

Nanoparticle directed domain orientation in thin films of asymmetric block copolymers

We investigated the thin film morphology of two different asymmetric block copolymers (BCP), polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and poly(n-pentyl methacrylate)-block-poly(methyl methacrylate) (PPMA-b-PMMA), loaded with pre-synthesized iron oxide nanoparticles (NP). The chemical composition of the BCP constituents determines the strength of the interaction between polymer chains and nanoparticles. In the case of NP/PS-b-P4VP system, the nanoparticles interact preferentially with the P4VP block and hence localize selectively in the P4VP cylindrical microdomains. However, for the NP/PPMA-b-PMMA system, the nanoparticles have no significant preference for the copolymer blocks and segregate at the polymer/substrate interface. Interestingly, this changes the effective substrate surface energy and hence leads to a remarkable change in domain orientation from parallel to perpendicular with respect to the substrate. These results clearly demonstrate the importance of both enthalpic and entropic factors which determine spatial distribution of NP in BCP films and influence domain orientation.

Silica-supported Au@hollow-SiO2 particles with outstanding catalytic activity prepared via block copolymer template approach

Catalytically active Au@hollow-SiO2 particles embedded in porous silica support (Au@hollow-SiO2@PSS) were prepared by using spherical micelles from poly(styrene)-block-poly(4-vinyl pyridine) block copolymer as a sacrificial template. Drastic increase of the shell porosity was observed after pyrolytic removal of polymeric template because the stretched poly(4-vinyl pyridine) chains interpenetrating with silica shell acted as an effective porogen. The embedding of Au@hollow-SiO2 particles in porous silica support prevented their fusion during pyrolysis. The catalytic activity of Au@hollow-SiO2@PSS was investigated using a model reaction of catalytic reduction of 4-nitrophenol and reductive degradation of Congo red azo-dye. Significantly, to the best of our knowledge, Au@hollow-SiO2@PSS catalyst shows the highest activity among analogous systems reported till now in literature. Such high activity was attributed to the presence of multiple pores within silica shell of Au@hollow-SiO2 particles and easy accessibility of reagents to the catalytically active sites of the ligand-free gold surface through the porous silica support.

Synthesis of hollow silica nanostructures using functional hairy polymer nanofibers as templates

Hollow silica nanofibers and nanospheres were synthesized from functional hairy polymer nanofibers as sacrificial templates. The polymer nanofibers were isolated from a cylinder-forming polystyrene-block-poly(4-vinylpyridine) block copolymer using a selective-swelling approach.

Multifunctional core–shell polymer–inorganic hybrid nanofibers prepared via block copolymer self-assembly

We demonstrate a simple and robust approach for preparing multifunctional core–shell hybrid nanofibers via block copolymer self-assembly. The approach utilizes the different chemistry and solubilities of the two blocks of a diblock copolymer and different affinity of functional inorganic nanoparticles towards block copolymer constituents. In the first step, the silver nanoparticles (Ag) modified with short-chain polystyrene (PS) ligand are incorporated in the cylindrical domains of a polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer, constituted of PS blocks. The Ag-loaded cylindrical domains are then isolated as nanofibers by swelling the matrix forming P4VP phase using a selective solvent. The isolated nanofibers exhibit core–shell morphology with the core constituted of Ag-loaded PS phase and shell consisting of P4VP chains. The reactive P4VP shell of the nanofibers is subsequently used as a host for depositing a second type of nanoparticles. The second type of nanoparticles could be either directly synthesized on the P4VP shell or deposited from an aqueous dispersion of pre-synthesized nanoparticles. In this work, gold (Au) and cadmium sulfide (CdS) nanoparticles were deposited on the nanofiber shell. The approach is versatile and, in principle, could be extended to the fabrication of various combinations of targeted functionalities in a single nanofiber with core–shell morphology.