A block copolymer-templated construction approach for the creation of nano-patterned polyelectrolyte multilayers and nanoscale objects

Nanoparticle assembly by transient topography induced by applying soft lithography to block copolymer films

We present a simple approach for patterning metal nanoparticles into periodic superstructures on flat films spanning centimeter-square areas. Our approach is based on capillary force lithography, a soft lithography method that is used to impart topography to molten polymer films, and applies it to block copolymer films to obtain substrates featuring both topographic and chemical contrasts that can serve as templates for the selective deposition of nanoparticles. Here we show that flattening the films by exposure to solvent vapour prior to nanoparticle deposition not only retains chemical heterogeneity but also provides access to unique hierarchically-organized nanoparticle superstructures that are unattainable by other methods. Such structures could be useful for optical, sensor, and catalytic applications.

Coupling the chemistry and topography of block copolymer films patterned by soft lithography for nanoparticle organization

Soft lithography techniques have become leading mesoscale approaches for replicating topographic features in polymer films. So far, modified polymer films formed by soft lithography only featured topographic heterogeneity. Here we demonstrate the application of soft lithography techniques to block copolymer films, and show that the preferential affinity of one of the blocks to the stamping material leads to chemical heterogeneity that corresponds to the topographic features. Detailed surface and structural characterization of the patterned films provided information on its three-dimensional structure, revealing insights on the domain reorganization that takes place in the block copolymer film concomitantly with topography formation. The formed structures were utilized for the selective assembly of gold nanoparticles into hierarchical structures. The versatility of this combined nanofabrication/self-assembly approach was demonstrated by the assembly of two types of metallic nanoparticles into two different arrangements with full control over the location of each type of nanoparticles.

Periodic nanowire arrays with alternating compositions and structures fabricated using a simultaneous nanowire formation step

Arrays of alternating metallic nanostructures present hybrid properties, which are useful for applications in photonics and catalysis. Block copolymer films provide versatile templates for fabricating periodic arrays of nanowires. Yet, creating arrays with alternating compositions or structures requires different modifications of domains of the same kind. By controlling the penetration depth of metal precursors into the film we were able to impregnate different layers of copolymer cylinders with different metals. Capitalizing on the hexagonal packing of the cylinders led to simultaneous formation of nanowires with alternating compositions and periodic arrangement on the substrate after plasma etching. Selective deposition of nanoparticles on the film enabled creating alternating bare and decorated nanowires, as well as trimetallic nanowire arrays.

Layer-by-layer assembly in nanochannels: assembly mechanism and applications

Layer-by-layer (LbL) assembly is a versatile technology to construct multifunctional nanomaterials using various supporting substrates, enabled by the large selection freedom of building materials and diversity of possible driving forces. The fine regulation over the film thickness and structure provides an elegant way to tune the physical/chemical properties by mild assembly conditions (e.g. pH, ion strength). In this review, we focus on LbL in nanochannels, which exhibit a different growth mechanism compared to "open", convex substrates. The assembly mechanism in nanochannels is discussed in detail, followed by the summary of applications of LbL assemblies liberated from nanochannel templates which can be used as nanoreactors, drug carriers and transporting channels across cell membranes. For fluidic applications, robust membrane substrates are required to keep in place nanotube arrays for membrane-based separation, purification, biosensing and energy harvesting, which are also discussed. The good compatibility of LbL with crossover technologies from other fields allows researchers to further extend this technology to a broader range of research fields, which is expected to result in an increased number of applications of LbL technology in the future.

Ionic liquid-induced nanoporous structures of polymer films

Nanoporous polymer thin films can be fabricated using strong polyelectrolyte pairs in ionic liquid aqueous solutions.

Electrically Responsive, Nanopatterned Surfaces for Triggered Delivery of Biologically Active Molecules into Cells

Polyelectrolyte multilayers (PEMs) assembled layer-by-layer have emerged as functional polymer films that are both stable and capable of containing drug molecules for controlled release applications. Most of these applications concentrate on sustained release, where the concentration of the released molecules remains rather constant with time. However, high-efficiency delivery requires obtaining high local concentrations at the vicinity of the cells, which is achieved by triggered release. Here, we show that a nanopatterned PEM platform demonstrates superior properties with respect to drug retention and triggered delivery. A chemically modified block copolymer film was used as a template for the selective deposition of poly(ethylene imine) and a charged derivative of the electroactive poly(3,4-ethylenedioxythiophene) together with a drug molecule. This nanopatterned PEM shows the following advantages: (1) high drug loading; (2) enhanced retention of the bioactive molecule; (3) release triggered by an electrochemical stimulus; (4) high efficacy of drug delivery to cells adsorbed on the surface compared to the delivery efficacy of a similar concentration of drug to cells suspended in a solution.