Advanced Materials

Dong C. Hyun, Unyong Jeong, and coworkers report on p. 2642 the buckling-assisted patterning of multiple polymers. This work is based on the unique characteristics of buckling: reversibility and morphological variation. The buckling surfaces are employed as templates to confine multiple polymers in the trenches of the sinusoidal topology. Localized dewetting of the polymers enables the fabrication of unconventional patterns that can be transferred to other substrates.

The inside cover shows a structural model of DNA-wrapped single-walled carbon nanotubes with an AFM image of the DNA-SWNT network in the background. DNA-SWNTs provide an effective, scalable method of fabricating super-uniform networks of highly isolated, structure-sorted SWNTs for high-performance thin-film transistors. More details are reported by Yuki Asada, Hisanori Shinohara, and co-workers on p. 2698.

The novel properties of engineered nanomaterials may alter their interaction with the human body, especially for inhalation of unintentionally released biopersistent material. We discuss the characterization of nanoparticles in interaction with biological media and we review animal inhalation and cell culture studies in comparison to original results. We establish that an intrinsic size-specific toxicity does not exist and identify material-specific indicators of concern that help to select safe uses.

An optimized polymeric aqueous two-phase system allows direct and non-contact printing of cells onto a monolayer of living cells in arbitrary shapes as well as in a high-density microarray format to create heterocellular microenvironments and study the effect of direct cell–cell interactions on cell fate. The entire process is performed in aqueous media to support full cell viability and functionality.

Charge transfer between GaN and organic self-assembled monolayers is demonstrated. Alignment of charge-transfer levels allows for photocatalytic cleavage of aliphatic chains on the semiconductor surface. By variation of the Fermi level within GaN and by comparison to SiC, it is shown that charge transfer can be suppressed and the stability of molecular monolayers can be enhanced in the absence of the appropriate energetic alignment.

Color fine-tuning of carbon nanotubes@anodic aluminum oxide (CNTs@AAO )composite thin films is achieved via isotropically etching porous AAO in phosphoric acid before CNTs growth. With the increase of etching duration from 0 to 17.5 min, the interference band with the maximum reflectance (B_max) in visible region of the composite thin film shifts from ∼632 (salmon pink) to ∼498 nm (cyan).

Two-dimensional patterned microstructures of multicomponent polymers are fabricated by utilizing the reversible nature of buckling. The polymers were selectively deposited in the trenches of the buckled surfaces to form unconventional patterns that were transferred to other substrates.

A full-length accumulative photonic crystal fiber (PCF) that is surface-enhanced Raman scattering (SERS)-active is achieved by immobilizing Ag nanoparticles inside the air channels of solid-core and hollow-core PCFs using a polyelectrolyte-mediated process. Raman gain in PCFs prevails with coverage density below 0.5 nanoparticle µm⁻². Light attenuation dominates, however, at a higher density. Controlled coverage density and uniformity of nanoparticles is the key to the exploitation of the length benefit of the PCF platform.

The construction of a high-strength hydrogel with integrated functions by photo-initiated copolymerization of temperature-sensitive and hydrogen-bonding monomers is described. The hydrogen-bonding and thermoresponsive surface of hydrogels offers a multifunctional platform, where reverse gene transfection and gene-modified cell detachment can be achieved for the potential use in the regeneration and replacement of soft tissue.

Fluorescent polymer solutions can easily be electrospun into micrometer-sized fibers and subsequently encoded with long lasting digital codes by a photobleaching process. Such encoded fibers may find various applications; as illustrated in this report, placing encoded fibers in drug tablets may become a strategy to protect them from counterfeiting.

Highly elastic and electrically conductive composite sheets are prepared by infiltration of MWNT forests with polyurethane binder. After initial pretreatment, the composite provides highly reproducible changes in resistivity at elongations up to 40%. Almost no degradation in electrical properties and a linear dependence of resistivity on strain is observed for strains in 10%–20% range.

The mechanically soft behavior of the magnetic shape-memory material Fe₇₀Pd₃₀ allows huge tetragonal distortions to be stabilized in sputtered thin films by coherent epitaxial growth on various metallic buffers. Furthermore, it is demonstrated that epitaxial films more than 1 µm thick can be grown, which makes possible freestanding films in an artificial single variant state suitable for microactuators and sensors.

A solution-phase DNA chip is produced using DNA origami-based asymmetric self-assembled tiles incorporating single-stranded DNA linear probes. This DNA origami chip is fully spatially addressable, without having to use position index oligonucleotides. The DNA hybridization is readily detected via atomic force microscopy.

A periodic array of dye-doped disks that form a 2D photonic lattice is fabricated and characterized. The array was generated by interference lithography, and the voids of the template were filled by SU8 without doping. This creates a photonic lattice with a uniform real part of the refractive index, but a periodically modulated imaginary part. The structure is characterized by diffraction measurements; the structure only diffracts light in the spectral range where the dye absorbs, hence acts like a truly imaginary index photonic crystal.

Multiple polymer cholesteric liquid crystal (PCLC) layers with different pitches and a sandwich structure of nematic liquid crystal by these PCLC films are presented. The former serves as broadband-distributed Bragg reflectors and the latter as multiple-band electrotunable filters. Using the latter dye-doped hybrid film red–green–blue simultaneous lasing due to Fabry–Perot cavity modes is achieved (see figure).

Processing metal–organic frameworks with spatial and temporal control over crystal formation will increase the applicability of these highly porous materials. By exploiting solvent effects, stable synthesis solutions can be obtained, which can be used in combination with soft lithographic techniques to deposit oriented crystals in patterns by in situ crystallization (see figure).

Cation-selective microcontact printing (μCP) is achieved by the combination of a surface-molecular-imprinted layer-by-layer (SMILbL) films with μCP. The SMILbL film greatly enhances the charge selectivity of the imprinted-film-modified stamp and the PDMS stamp modified by the SMILbL film shows a high selectivity to multiply charged cations. The SMILbL-film-modified stamp can also be used for selective transfer of single-charged chemical species.

It is demonstrated from stress-induced Raman bands shiftsthat stress can be transferred from a polymer matrix to a graphene monolayer (see image) in a model nanocomposite. It is shown further that the behavior can be modeled using continuum mechanics and that the interface between the graphene and the polymer breaks down at a shear stress of the order of 2 MPa.

Controlling the morphology of single-walled carbon nanotubes (SWNTs) is essential to realize their excellent device characteristics in electronics. DNA-wrapped SWNTs provides an effective, scalable way to fabricate the super-uniform networks of highly isolated, structure-sorted SWNTs for thin-film transistors (TFTs). The DNA-SWNTs are easily formed into uniform, desired-density networks of individual nanotubes.

The first white-emissive cross-linked films and devices obtained by electrochemical copolymerization that have significantly improved color stability are reported (see figure). The device exhibited the CIE coordinates of (0.33, 0.35), a CRI of 88, and extremely stable white-light emission over a wide range of driving voltages of 8–22 V. This kind of new ECP film afforded more opportunities to develop color-stable white-light-emission.

Geometrically constrained magnetic domain walls (DWs) in magnetic nanowires can be manipulated at the nanometer scale. The inhomogeneous magnetic stray field generated by a DW can capture a magnetic nanoparticle in solution. On-chip nanomanipulation of individual magnetic beads coated with proteins is demonstrated through the motion of geometrically constrained DWs in specially designed magnetic nanoconduits fully integrated in a lab-on-a-chip platform.

Periodic magnetic domains on cobalt filaments can be stabilized by nanoscale corrugations on the surface, which are spontaneously generated by a unique electrodeposition method. The type of magnetic domains varies from anti-parallel single domains to vortex domains depending on the ratio of the spatial periodicity of the corrugations and the filament width (see figure), and can be experimentally tuned.