Competitive concurrence of surface wrinkling and dewetting of liquid crystalline polymer films on non-wettable substrates

Polymeric thin films coated on non-wettable substrates undergo film-instabilities, which are usually manifested as surface deformation in the form of dewetting or wrinkling. The former takes place in fluidic films, whereas the latter occurs in solid films. Therefore, there have rarely been reports of systems involving simultaneous deformations of dewetting and wrinkling. In this study, we propose polymeric thin films of liquid crystalline (LC) mesogens prepared on a non-wettable Si substrate and apply a treatment of plasma irradiation to form a thin polymerized layer at the surface. The resulting compressive stress generated in the surface region drives the formation of wrinkles, while at the same time, dipolar attraction between LC molecules induces competitive cohesive dewetting. Intriguing surface structures were obtained whereby dewetting-like hole arrays are nested inside the randomly propagated wrinkles. The structural features are readily controlled by the degree of surface cross-linking, hydrophilicity of the substrates, and the LC film thickness. In particular, dewetting of LC mesogens is observed to be restricted to occur at the trough regions of wrinkles, exhibiting the typical behavior of geometrically confined dewetting. Finally, wrinkling-dewetting mixed structures are separated from the substrate in the form of free standing films to demonstrate the potential applicability as membranes.

Colloidal Mesoporous Silica Nanoparticles as Strong Adhesives for Hydrogels and Biological Tissues

Sub-100 nm colloidal mesoporous silica (CMS) nanoparticles are evaluated as an adhesive for hydrogels or biological tissues. Because the adhesion energy is proportional to the surface area of the nanoparticles, the CMS nanoparticles could provide a stronger adhesion between two hydrogels than the nonporous silica nanoparticles. In the case of 50 nm CMS nanoparticles with a pore diameter of 6.45 nm, the maximum adhesion energy was approximately 35.0 J/m² at 3.0 wt %, whereas the 10 wt % nonporous silica nanoparticle solution showed only 7.0 J/m². Moreover, the CMS nanoparticle solution had an adhesion energy of 22.0 J/m² at 0.3 wt %, which was 11 times higher than that of the nonporous nanoparticles at the same concentration. Moreover, these CMS nanoparticles are demonstrated for adhering incised skin tissues of mouse, resulting in rapid healing even at a lower nanoparticle concentration. Finally, the CMS nanoparticles had added benefit of quick degradation in biological media because of their porous structure, which may prevent unwanted accumulation in tissues.

Halide Welding for Silver Nanowire Network Electrode

We developed a method of chemically welding silver nanowires (AgNWs) using an aqueous solution containing sodium halide salts (NaF, NaCl, NaBr, or NaI). The halide welding was performed simply by immersing the as-coated AgNW film into the sodium halide solution, and the resulting material was compared with those obtained using two typical thermal and plasmonic welding techniques. The halide welding dramatically reduced the sheet resistance of the AgNW electrode because of the strong fusion among nanowires at each junction while preserving the optical transmittance. The dramatic decrease in the sheet resistance was attributed to the autocatalytic addition of dissolved silver ions to the nanowire junction. Unlike thermal and plasmonic welding methods, the halide welding could be applied to AgNW films with a variety of deposition densities because the halide ions uniformly contacted the surface or junction regions. The optimized AgNW electrodes exhibited a sheet resistance of 9.3 Ω/sq at an optical transmittance of 92%. The halide welding significantly enhanced the mechanical flexibility of the electrode compared with the as-coated AgNWs. The halide-welded AgNWs were successfully used as source-drain electrodes in a transparent and flexible organic field-effect transistor (OFET). This simple, low-cost, and low-power consumption halide welding technique provides an innovative approach to preparing transparent electrodes for use in next-generation flexible optoelectronic devices.

Photofluidic Near-Field Mapping of Electric-Field Resonance in Plasmonic Metasurface Assembled with Gold Nanoparticles

We present a near-field mapping of electric fields from the individual superspherical and ultrasmooth gold nanoparticles (AuNPs) and artificially assembled AuNP nanostructures by measuring the reconfiguration of an azobenzene-containing polymer(azo-polymer) film. Various configurations of AuNPs and the azo-polymer were studied with atomic force microscopy measurements and calculations. The interference was systematically studied with AuNP dimers of various gap distances and different embedding depth in the polymer film. Finally, we successfully demonstrated the interference of standing waves in artificially assembled plasmonic metasurface.

Stimuli-Responsive, Shape-Transforming Nanostructured Particles

Development of particles that change shape in response to external stimuli has been a long-thought goal for producing bioinspired, smart materials. Herein, the temperature-driven transformation of the shape and morphology of polymer particles composed of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) block copolymers (BCPs) and temperature-responsive poly(N-isopropylacrylamide) (PNIPAM) surfactants is reported. PNIPAM acts as a temperature-responsive surfactant with two important roles. First, PNIPAM stabilizes oil-in-water droplets as a P4VP-selective surfactant, creating a nearly neutral interface between the PS and P4VP domains together with cetyltrimethylammonium bromide, a PS-selective surfactant, to form anisotropic PS-b-P4VP particles (i.e., convex lenses and ellipsoids). More importantly, the temperature-directed positioning of PNIPAM depending on its solubility determines the overall particle shape. Ellipsoidal particles are produced above the critical temperature, whereas convex lens-shaped particles are obtained below the critical temperature. Interestingly, given that the temperature at which particle shape change occurs depends solely on the lower critical solution temperature (LCST) of the polymer surfactants, facile tuning of the transition temperature is realized by employing other PNIPAM derivatives with different LCSTs. Furthermore, reversible transformations between different shapes of PS-b-P4VP particles are successfully demonstrated using a solvent-adsorption annealing with chloroform, suggesting great promise of these particles for sensing, smart coating, and drug delivery applications.

Assembly of "3D" plasmonic clusters by "2D" AFM nanomanipulation of highly uniform and smooth gold nanospheres

Atomic force microscopy (AFM) nanomanipulation has been viewed as a deterministic method for the assembly of plasmonic metamolecules because it enables unprecedented engineering of clusters with exquisite control over particle number and geometry. Nevertheless, the dimensionality of plasmonic metamolecules via AFM nanomanipulation is limited to 2D, so as to restrict the design space of available artificial electromagnetisms. Here, we show that “2D” nanomanipulation of the AFM tip can be used to assemble “3D” plasmonic metamolecules in a versatile and deterministic way by dribbling highly spherical and smooth gold nanospheres (NSs) on a nanohole template rather than on a flat surface. Various 3D plasmonic clusters with controlled symmetry were successfully assembled with nanometer precision; the relevant 3D plasmonic modes (i.e., artificial magnetism and magnetic-based Fano resonance) were fully rationalized by both numerical calculation and dark-field spectroscopy. This templating strategy for advancing AFM nanomanipulation can be generalized to exploit the fundamental understanding of various electromagnetic 3D couplings and can serve as the basis for the design of metamolecules, metafluids, and metamaterials.

Microtopography-Guided Conductive Patterns of Liquid-Driven Graphene Nanoplatelet Networks for Stretchable and Skin-Conformal Sensor Array

Flexible thin-film sensors have been developed for practical uses in invasive or noninvasive cost-effective healthcare devices, which requires high sensitivity, stretchability, biocompatibility, skin/organ-conformity, and often transparency. Graphene nanoplatelets can be spontaneously assembled into transparent and conductive ultrathin coatings on micropatterned surfaces or planar substrates via a convective Marangoni force in a highly controlled manner. Based on this versatile graphene assembled film preparation, a thin, stretchable and skin-conformal sensor array (144 pixels) is fabricated having microtopography-guided, graphene-based, conductive patterns embedded without any complicated processes. The electrically controlled sensor array for mapping spatial distributions (144 pixels) shows high sensitivity (maximum gauge factor ≈1697), skin-like stretchability (<48%), high cyclic stability or durability (over 10⁵ cycles), and the signal amplification (≈5.25 times) via structure-assisted intimate-contacts between the device and rough skin. Furthermore, given the thin-film programmable architecture and mechanical deformability of the sensor, a human skin-conformal sensor is demonstrated with a wireless transmitter for expeditious diagnosis of cardiovascular and cardiac illnesses, which is capable of monitoring various amplified pulse-waveforms and evolved into a mechanical/thermal-sensitive electric rubber-balloon and an electronic blood-vessel. The microtopography-guided and self-assembled conductive patterns offer highly promising methodology and tool for next-generation biomedical devices and various flexible/stretchable (wearable) devices.

Colloidal alloys with preassembled clusters and spheres

Self-assembly is a powerful approach for constructing colloidal crystals, where spheres, rods or faceted particles can build up a myriad of structures. Nevertheless, many complex or low-coordination architectures, such as diamond, pyrochlore and other sought-after lattices, have eluded self-assembly. Here we introduce a new design principle based on preassembled components of the desired superstructure and programmed nearest-neighbour DNA-mediated interactions, which allows the formation of otherwise unattainable structures. We demonstrate the approach using preassembled colloidal tetrahedra and spheres, obtaining a class of colloidal superstructures, including cubic and tetragonal colloidal crystals, with no known atomic analogues, as well as percolating low-coordination diamond and pyrochlore sublattices never assembled before.

Morphological Evolution of Block Copolymer Particles: Effect of Solvent Evaporation Rate on Particle Shape and Morphology

Shape and morphology of polymeric particles are of great importance in controlling their optical properties or self-assembly into unusual superstructures. Confinement of block copolymers (BCPs) in evaporative emulsions affords particles with diverse structures, including prolate ellipsoids, onion-like spheres, oblate ellipsoids, and others. Herein, we report that the evaporation rate of solvent from emulsions encapsulating symmetric polystyrene-b-polybutadiene (PS-b-PB) determines the shape and internal nanostructure of micron-sized BCP particles. A distinct morphological transition from the ellipsoids with striped lamellae to the onion-like spheres was observed with decreasing evaporation rate. Experiments and dissipative particle dynamics (DPD) simulations showed that the evaporation rate affected the organization of BCPs at the particle surface, which determined the final shape and internal nanostructure of the particles. Differences in the solvent diffusion rates in PS and PB at rapid evaporation rates induced alignment of both domains perpendicular to the particle surface, resulting in ellipsoids with axial lamellar stripes. Slower evaporation rates provided sufficient time for BCP organization into onion-like structures with PB as the outermost layer, owing to the preferential interaction of PB with the surroundings. BCP molecular weight was found to influence the critical evaporation rate corresponding to the morphological transition from ellipsoid to onion-like particles, as well as the ellipsoid aspect ratio. DPD simulations produced morphologies similar to those obtained from experiments and thus elucidated the mechanism and driving forces responsible for the evaporation-induced assembly of BCPs into particles with well-defined shapes and morphologies.

Long-Circulating Au-TiO2 Nanocomposite as a Sonosensitizer for ROS-Mediated Eradication of Cancer

Although sonodynamic therapy (SDT) has emerged as a potential alternative to conventional photodynamic therapy, the low quantum yield of the sonosensitizer such as TiO₂ nanoparticles (NPs) is still a major concern. Here, we have developed hydrophilized Au-TiO₂ nanocomposites (HAu-TiO₂ NCs) as sonosensitizers for improved SDT. The physicochemical properties of HAu-TiO₂ NCs were thoroughly studied and compared with their counterparts without gold deposition. Upon exposure of HAu-TiO₂ NCs to ultrasound, a large quantity of reactive oxygen species (ROS) were generated, leading to complete suppression of tumor growth after their systemic administration in vivo. Overall, it was evident that the composites of gold with TiO₂ NPs significantly augmented the levels of ROS generation, implying their potential as SDT agents for cancer therapy.

Zwitterionic mesoporous nanoparticles with a bioresponsive gatekeeper for cancer therapy

To enhance cellular uptake and site-specific drug release in the tumor microenvironment, zwitterionic mesoporous silica nanoparticles (Z-MSN) were prepared by introducing a bioresponsive gatekeeper composed of negatively charged carboxylic groups and positively charged quaternary amine groups. When these Z-MSN encountered a mildly acidic environment, their surface charge readily switched from negative to positive by cleavage of an acid-labile maleic amide linkage, thus allowing for effective cellular uptake into tumor tissue. Doxorubicin (DOX) encapsulated in Z-MSN was not significantly released in physiological conditions (pH 7.4), whereas the release rate of DOX remarkably increased in mildly acidic conditions through disintegration of the gatekeeper. The antitumor efficacy of DOX-loaded Z-MSN (DOX-Z-MSN) was evaluated after their systemic administration to tumor-bearing mice. Compared to free DOX and DOX-loaded MSN without the gatekeeper, DOX-Z-MSN exhibited much higher antitumor efficacy in vivo. Overall, these results demonstrated that the hydrophilic negative surface of Z-MSN, with their closed gate, allowed for their effective accumulation in tumor tissue after systemic administration, and that their charge-swapping and gate-opening in the tumor environment enhanced their cellular uptake and drug release rate simultaneously, implying a highly promising potential for development of Z-MSN as a drug carrier for cancer therapy.

STATEMENT OF SIGNIFICANCE

In an attempt to address the issues of enhanced cellular uptake and site-specific drug release of nanoparticles, we herein report on zwitterionic MSN (Z-MSN) with a pH-responsive gatekeeper which can be internalized into cancer cells via switching their surface charge from negative, in physiological conditions, to positive, in the tumor microenvironment. We hypothesized that the hydrophilic negative surface of Z-MSN with a closed gate allows for their accumulation into tumor tissue after systemic administration, whereas their charge-swapping and gate-opening in the tumor environment enhance cellular uptake and drug release rate simultaneously. Overall, Z-MSN constitute a promising drug delivery carrier for cancer therapy.

Interplay Between Optical Bianisotropy and Magnetism in Plasmonic Metamolecules

The smallness of natural molecules and atoms with respect to the wavelength of light imposes severe limits on the nature of their optical response. For example, the well-known argument of Landau and Lifshitz and its recent extensions that include chiral molecules show that the electric dipole response dominates over the magneto-electric (bianisotropic) and an even smaller magnetic dipole optical response for all natural materials. Here, we experimentally demonstrate that both these responses can be greatly enhanced in plasmonic nanoclusters. Using atomic force microscopy nanomanipulation technique, we assemble a plasmonic metamolecule that is designed for strong and simultaneous optical magnetic and magneto-electric excitation. Angle-dependent scattering spectroscopy is used to disentangle the two responses and to demonstrate that their constructive/destructive interplay causes strong directional scattering asymmetry. This asymmetry is used to extract both magneto-electric and magnetic dipole responses and to demonstrate their enhancement in comparison to ordinary atomistic materials.

Anion-Mediated End-Shape Control in Seed-Mediated Growth of Gold Nanorods

End-shape-controlled gold nanorods (GNRs) were synthesized at room-temperature by a seeded-growth method, in which hexadecyltrimethylammonium bromide (CTAB) was used as a stabilizer and capping agent. The average dimension of the GNRs was 46 nm in length and 15 nm in diameter, which corresponds to aspect ratio of c.a. 3.0. Then, their both ends were further grown at the presence of silver precursor (AgNO3), resulting in formation of arrow-head GNRs. By tuning the amount of the silver precursor, the end-shape of the GNRs was changed to dumbbell like shape. Moreover, the growth rate of gold could be controlled by tuning the amount of hydrochloric acid (HCl). While arrow-headed GNRs having sharp edges were produced without HCl, the GNRs having dog-bone like or round-head shape at both ends were obtained with HCl.

Near-infrared light-triggered thermochemotherapy of cancer using a polymer-gold nanorod conjugate

A biocompatible polymer-gold nanorod (P-AuNR) conjugate was developed as a thermo-chemotherapeutic nano-sized drug carrier for cancer therapy using near-infrared (NIR) light as an external trigger. The amphiphilic polymer, poly(ethylene glycol)-block-poly(caprolactone) (PEG-b-PCL) bearing a disulfide bond, was prepared using a facile synthetic route via copper(I)-free click chemistry and covalently linked to AuNR. The chemical structures and successful conjugation of PEG-b-PCL were analyzed using (1)H NMR and FT-IR. Doxorubicin (DOX), a hydrophobic anticancer drug, was effectively loaded into the hydrophobic PCL domain of P-AuNR through a simple dialysis method. P-AuNR showed longitudinal plasmon resonance absorption at the NIR region, thus generating heat under irradiation at 808 nm. Interestingly, exposure of P-AuNRs to NIR induced a structural change in the PCL block from a crystalline to an amorphous state, leading to the temporally controlled release of DOX. No significant release of DOX was observed from P-AuNRs under physiological conditions (pH 7.4), whereas the release rate of DOX was remarkably enhanced in response to NIR irradiation. In vitro cellular experiments to assess cytotoxicity and intracellular drug release behavior of DOX-P-AuNRs demonstrated that the release of DOX could be selectively regulated by NIR irradiation. Overall, DOX-P-AuNRs might have the potential to overcome the indiscriminate toxicity of free DOX.

A 3D triple-deck photoanode with a strengthened structure integrality: enhanced photoelectrochemical water oxidation

WO3/BiVO4 is one of the attractive Type II heterojunctions for photoelectrochemical (PEC) water splitting due to its well-matched band edge positions and visible light harvesting abilities. However, two light absorption components generally suffer from poor charge collection and cannot be efficiently utilized because of non-ideal interfaces. Herein, a triple-deck three-dimensional (3D) architecture was designed through a one-step shaping process with an additional stress relaxation WO3 underlayer. The final photoanodes showed a promising photocurrent density of 5.1 mA cm(-2) at 1.23 V vs. RHE under AM 1.5G illumination. Using the uniformly distributed oxygen evolution co-catalyst (OEC) layer as the outer most shell of the WO3/BiVO4/OEC triple-deck 3D structure with a dense WO3 underlayer, the water splitting efficiency was improved dramatically by facilitating the charge transfer process at the electrode/electrolyte interface.

Highly stable electrical manipulation of reflective colors in colloidal crystals of sulfate iron oxide particles in organic media

We report the method for decorating charged functional groups on the Fe₃O₄@C nanoparticle and demonstrate reversible structural transition of suspension under external electric field with long term cyclic stability.

Effect of the ordered meso–macroporous structure of Co/SiO2 on the enhanced activity of hydrogenation of CO to hydrocarbons

Ordered meso–macroporous silica (MMS) was applied for the cobalt-based FTS reaction, and the enhanced activity on the Co/MMS was mainly due to the larger macropore cavity by enhancing the mass transfer rate which can be easily regenerated by in situ feeding of liquid hydrocarbons.

Nanoparticles based on quantum dots and a luminol derivative: implications for in vivo imaging of hydrogen peroxide by chemiluminescence resonance energy transfer

Hybrid nanoparticles allow for imaging hydrogen peroxide via chemiluminescence resonance energy transfer in the near-infrared wavelength range.

Soft Patchy Particles of Block Copolymers from Interface-Engineered Emulsions

We report a simple and practical method for creating colloidal patchy particles with a variety of three-dimensional shapes via the evaporation-induced assembly of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer (BCP) in an oil-in-water emulsion. Depending on the particle volume, a series of patchy particles in the shapes of snowmen, dumbbells, triangles, tetrahedra, and raspberry can be prepared, which are then precisely tuned by modulating the interfacial interaction at the particle/water interface using a mixture of two different surfactants. Moreover, for a given interfacial interaction, the stretching penalty of the BCPs in the patchy particles can be systematically controlled by adding P4VP homopolymers, which decreases the number of patches of soft particles from multiple patches to a single patch but increases the size of the patch. Calculations based on the strong segregation theory supported the experimental observation of various soft patchy particles and identified the underlying principles of their formation with tunable 3D structures.

Conformal Coating Strategy Comprising N-doped Carbon and Conventional Graphene for Achieving Ultrahigh Power and Cyclability of LiFePO4

Surface carbon coating to improve the inherent poor electrical conductivity of lithium iron phosphate (LiFePO4, LFP) has been considered as most efficient strategy. Here, we also report one of the conventional methods for LFP but exhibiting a specific capacity beyond the theoretical value, ultrahigh rate performance, and excellent long-term cyclability: the specific capacity is 171.9 mAh/g (70 μm-thick electrode with ∼10 mg/cm(2) loading mass) at 0.1 C (17 mA/g) and retains 143.7 mAh/g at 10 C (1.7 A/g) and 95.8% of initial capacity at 10 C after 1000 cycles. It was found that the interior conformal N-C coating enhances the intrinsic conductivity of LFP nanorods (LFP NR) and the exterior reduced graphene oxide coating acts as an electrically conducting secondary network to electrically connect the entire electrode. The great electron transport mutually promoted with shorten Li diffusion length on (010) facet exposed LFP NR represents the highest specific capacity value recorded to date at 10 C and ultralong-term cyclability. This conformal carbon coating approach can be a promising strategy for the commercialization of LFP cathode in lithium ion batteries.

Synthetic Strategies Toward DNA-Coated Colloids that Crystallize

We report on synthetic strategies to fabricate DNA-coated micrometer-sized colloids that, upon thermal annealing, self-assemble into various crystal structures. Colloids of a wide range of chemical compositions, including poly(styrene), poly(methyl methacrylate), titania, silica, and a silica-methacrylate hybrid material, are fabricated with smooth particle surfaces and a dense layer of surface functional anchors. Single-stranded oligonucleotides with a short sticky end are covalently grafted onto particle surfaces employing a strain-promoted alkyne-azide cycloaddition reaction resulting in DNA coatings with areal densities an order of magnitude higher than previously reported. Our approach allows the DNA-coated colloids not only to aggregate upon cooling but also to anneal and rearrange while still bound together, leading to the formation of colloidal crystal compounds when particles of different sizes or different materials are combined.

Deterministic assembly of metamolecules by atomic force microscope-enabled manipulation of ultra-smooth, super-spherical gold nanoparticles

Atomic force microscope (AFM)-enabled manipulation of individual metallic nanoparticles (NPs) has proven useful for assembling diverse structural motifs of metamolecules. However, for the reliable verifications of their electric/magnetic behaviors and translations into practical applications (e.g., metasurfaces), currently available assembly of polygonal shaped metallic NPs with size and shape distributions should be further advanced. Here, we discover conditions for AFM-enabled, deterministic assembly of highly uniform, super-spherical gold NPs (AuNPs) into the metamolecules, which can show the designed electric/magnetic resonance behaviors in a highly reliable fashion. The use of super-spherical AuNPs together with the controlled adhesive properties of an AFM tip allows us to linearly and continuously push AuNPs toward the pre-programed directions and positions with minimized slipping away effect. Thus, a versatile and fast (as little as few minutes per each metamolecule) assembly of metamolecules with unprecedented structural fidelity becomes possible via AFM-enabled manipulation; enabling a high precision engineering of electromagnetic properties with metamolecules.