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We describe reversible force-induced metal–ligand coordination in spiropyran (SP) mechanophore linked PDMS elastomers. In the presence of lithium, calcium, or magnesium ions, SP is in equilibrium w...

A low temperature, vapor phase approach to improve the thermal stability of nonrefractory deterministically structured inverse opals is demonstrated. Specifically, pack aluminization at 550 °C was conducted on Ni inverse opals, introducing controlled amounts of Al into the structure. This enabled the formation of a strengthening Ni3Al phase, resulting in enhanced high temperature strength and stability. Following aluminization, the deterministic structures remained stable up to 1000 °C, a 500 °C increase relative to the starting Ni inverse opals. The thermal stability of the aluminized structures is comparable to that of much more difficult to fabricate deterministically structured refractory structures. Additionally, the pack aluminized structures exhibited a 17.6% increase in elastic modulus and an 81.6% increase in hardness relative to the initial Ni inverse opal. This is a promising combination of thermo-mechanical properties for very fine, deterministic structures used in high temperature, chemically...

Single crystal semiconductors almost always exhibit better optoelectrical properties than their polycrystalline or amorphous counterparts. While three-dimensionally (3D) nanostructured semiconductor devices have been proposed for numerous applications, in the vast majority of reports, the semiconductor is polycrystalline or amorphous, greatly reducing the potential for advanced properties. While technologies for 3D structuring of semiconductors via use of a 3D template have advanced significantly, approaches for epitaxially growing nanostructured single crystal semiconductors within a template remain limited. Here, we demonstrate the epitaxial growth of 3D-structured ZnO through colloidal templates formed from 225 and 600 nm diameter colloidal particles via a low-temperature (∼80 °C) hydrothermal process using a flow reactor. The effects of the pH of the reaction solution as well as the additive used on the 3D epitaxy process are investigated. The optical and electrical properties of the epitaxially grown...

Ni scaffolded mesostructured 3D Fe2O3 electrodes were fabricated by colloidal templating and pulsed electrodeposition. The scaffold provided short pathways for both lithium ions and electrons in the active phase, enabling fast kinetics and thus a high power density. The scaffold also resulted in a reduced voltage hysteresis. The electrode showed a reversible capacity of ∼1000 mAh g–1 at 0.2 A g–1 (∼0.2 C) for about 20 cycles, and at a current density of 20 A g–1 (∼20 C), the deliverable capacity was about 450 mAh g–1. The room-temperature voltage hysteresis at 0.1 A g–1 (∼0.1 C) was 0.62 V, which is significantly smaller than that normally reported in the literature. The hysteresis further reduced to 0.42 V at 45 °C. Potentiostatic electrochemical impedance spectroscopy (PEIS) studies indicated that the small voltage hysteresis may be due to a reduction in the Li2O/Fe interfacial area in the electrode during cycling relative to conventional conversion systems.

Significant efforts have been made over the past few decades to realize functional three-dimensional photonic crystal devices including zero-threshold lasers, waveguides, light-emitting diodes (LEDs), and solar cells; however, progress has been limited because of difficulties in creating three-dimensional photonic crystals from single-crystal materials. Most have been formed from polycrystalline materials and thus have generally exhibited poor electronic properties. Realization of materials containing complex three-dimensional mesostructures, in single-crystal form, remains a significant challenge. Here, we demonstrate the epitaxial growth of three-dimensionally mesostructured Cu2O by bottom-up electrodeposition through a 3D silica colloidal template. Not only is the templated Cu2O single crystal, but when the electrodeposition continues past the colloidal template, the crystallinity of the overlying solid Cu2O appears to be improved because the template blocks threading dislocations, resulting in substan...

We report a general diffusion based method to form micrometer-scale lateral chemical gradients in polymer brushes via selective alkylation. A quaternized brush gradient is derived from a concentration gradient of alkylating agent formed by diffusion in permeable media around a microchannel carrying the alkylating agent. Polymer brushes containing both charge and aromatic gradients are formed using the alkylating agents, methyl iodide and benzyl bromide, respectively. The gradients are quantitatively characterized by confocal Raman spectroscopy and qualitatively by fluorescence microscopy. The length and gradient strength can be controlled by varying the diffusion time, concentrations, and solvents of the alkylating agent solutions. This microfluidic brush gradient generation method enables formation of 2-D chemical potential gradients with a diversity of shapes.

This Perspective overviews many of the developments in templated porous three-dimensional photonics, with a particular focus on functional architectures, and provides suggestions for future opportunities for research. A significant diversity of 3D structures is available today with characteristic dimensions appropriate for providing strong light–matter interactions, in no small part due to recent advances in 3D patterning techniques. However, the optical functionality of these structures has generally remained limited. Advances in materials chemistry have the opportunity to dramatically increase the function of templated 3D photonics, and a few examples of highly functional templated 3D photonics for sensing, solar energy harvesting, optical metamaterials, and light emission are presented as first examples of success.

Polymers that respond in a productive fashion to their environment are under active development as they offer significant advantages over traditional materials. For example, polymers with the ability to self-heal and recover a significant fraction of their initial properties after being subjected to a damage event are of significant interest. Here we study the effect of healing agent viscosity and catalyst activity on self-healing at and near room temperature. The viscosity of the PDMS healing agent was varied from 14 to 40 000 cP, and the tin-based catalysts di-n-butyltin dilaurate, dimethyl-dineodacanoate tin, di-n-butyl bis(2-ethylenehexanoate), tin II oleate, and tetrakis(acetoxydibutyl tinoxy)silane were studied. Both vinyl ester and epoxy matrices were investigated. By optimizing the viscosity of the PDMS healing agent and the catalytic activity, as well as selection of the appropriate adhesion promoter, a PDMS-based self-healing system which healed at room temperature was obtained.

Tungsten inverse opal photonic crystals were fabricated using a template directed electrodeposition method. The electrodeposition was accomplished using a molten salt solution at elevated temperatures. Following template removal, the tungsten inverse opals were conformally coated with hafnia or alumina via atomic layer deposition. This surface passivation layer increased the thermal stability of the tungsten microarchitectures by limiting surface diffusion. Alumina protected tungsten inverse opals were thermally stable up to 1000 °C for at least 12 h in forming gas (5% H2 in Ar). Hafnia protected inverse opals were thermally stable up to 1400 °C for at least 12 h in forming gas. We expect that this surface passivation technique can also be implemented to increase the thermal stability of other refractory metal microarchitectures. The demonstrated thermal stability is an important property for the realization of metallic photonic crystals as narrow band emitters for thermophotovoltaics.

The effect of surface chemistry of SiO2 colloids dispersed in a nonionic surfactant based lyotropic liquid crystal (LLC) on the double direct templating of hollow mesostructured ZnS capsules was investigated. In double direct templating, a LLC templates the mineralization of ZnS on the surface of a colloidal particle. Removal of the colloid results in a periodically mesostructured hollow capsule. After ZnS mineralization and a subsequent etching of the sacrificial SiO2 core, the ZnS mesostructure was imaged using transmission electron microscopy (TEM). The highest quality mesostructure was observed for poly(acrylic acid) (PAA) functionalized colloids, while other surface chemistries, including bare silica, poly(ethylene glycol), amine, and thiol surface chemistries yielded much less favorable results. In the PAA system, the order of the hexagonally arranged 3 nm mesopores in the ZnS shell closely matched that of the lyotropic liquid crystal template. Detailed TEM revealed the presence of regions where the...

Mesoporous silica colloids (MSCs) are synthesized in the cavities of a polymer-based inverse opal. The spherical cavities of the polymer inverse opal provide a highly defined complex three-dimensio...

Using an evaporation-driven, room-temperature infiltration technique, we filled the interstitial space within an opal formed from 1 μm polystyrene spheres with preformed germanium nanoparticles. Subsequently, the Ge nanoparticles were bound together by backfilling with a photocuring adhesive, and the original polystyrene template was etched away to yield an inverse opal of air spheres in a matrix of Ge nanoparticles and photoadhesive. The reflectance spectra of these photonic materials were compared to computed band structures to deduce the refractive index of the air-germanium and air-photoadhesive composites; in conjunction with the Maxwell-Garnett model of dielectric mixing, this comparison also allowed the estimation of the Ge volume fraction within each composite material. On the basis of these methods, the interstitial space of the initial polystyrene opal template was filled to 49 vol % with Ge nanoparticles, acquiring an effective refractive index of 1.74. Backfilling with photoadhesive, followed by removal of the polystyrene opal, produced a Ge-in-polymer composite with a refractive index contrast of 2.05.

A new methodology for the synthesis of nanoparticles using lyotropic liquid crystals as nanoreactors has been developed. The hydrophilic and hydrophobic domains of lyotropic phases have characteristic dimensions of 2-10 nm and thus can be used to confine reactants that are selectively soluble in only one domain to nanoscopic dimensions. Here, synthesis of Bi (a metal) and PbS (a compound semiconductor) nanoparticles is driven by bringing together reactants via the shear mixing of two liquid crystals, each containing dissolved reactants that are selectively soluble in one of the two phases, as proof-of-principle for this method. Modulating the phase of the lyotropic liquid crystals allows control over the geometry and interconnectivity of the nanoreactors, giving control over the diameter of nanoparticles produced. Decreasing concentration of precursors is shown to decrease particle size. It is also demonstrated that the nanoparticles produced are not agglomerated in the lyotropic liquid crystal during synthesis. The synthesized nanoparticles are characterized with TEM, electron diffraction, EDAX, and UV-Vis-NIR spectroscopy.

Here we report the synthesis and characterization of a stable suspension of fluorescent erbium-doped titania nanoparticles and their assembly into thin films and photonic crystals. The nanoparticles were synthesized through a sol−gel process followed by peptization with tetramethylammonium hydroxide and hydrothermal treatment. As expected, following the hydrothermal treatment, X-ray diffraction shows the particles to be exclusively anatase. The nanoparticles form a stable suspension in water and were cast into 2- and 20-μm-thick films and formed into an inverse opal structure through templating with a colloidal crystal. As synthesized, only a faint fluorescence at 1532 nm was observed from the particles when pumped with 795-nm laser radiation; however, heat treatment at temperatures as low as 100 °C resulted in a significant increase in the fluorescence. The fluorescence was observed to increase further with annealing up to 500 °C, perhaps due to removal of hydroxyl groups and other surface species. Throu...

We report the synthesis of cadmium sulfide containing a periodic array of nanometer-sized cylindrical pores. The nanostructured cadmium sulfide was synthesized in a hexagonal lyotropic liquid crystal by the reaction between H2S and various cadmium salts. Interestingly, the counterion of the cadmium salt had a pronounced effect on the regularity and periodicity of the pores. The dimension of the pores is commensurate with the hydrophobic cores of the liquid crystal, and one counterion even leads to hexagonally faceted nanostructured particles.