Polymer Inverse Opals Research Articles

Double Replication of Silica Colloidal Crystal Films.

Inverse opals made by polymerizing vinyl monomers inside a colloidal crystal have lattice dimensions that are contracted relative to the original hard template. This effect was studied in order to investigate the possibility of making double replicas of varying pore sizes from different materials, and to gain a better understanding of the polymer contraction behavior during replication. The degree of lattice contraction was measured using colloidal crystal films formed from silica spheres with diameters in the range 33-225 nm, and polymers pEDMA [poly(1,2-ethanediol dimethacrylate)], pDVB [poly(divinylbenzene)], pHDMA [poly(1,6-hexanediol dimethacrylate)], pBDMA [poly(1,4-butanediol dimethacrylate)], and a 5:4 copolymer mixture of pEDMA/pDVB. The degree of lattice contraction depended on the alkyl chain length of the monomer, as well as the degree of cross-linking, with up to 32% contraction observed for pEDMA when the silica template was removed. However, filling the polymer inverse opals with silica or titania returned the lattice spacing closer to its original size, an effect that can be rationalized in terms of the driving forces for contraction. Double replication of both single-component and binary silica colloidal crystals therefore generated silica and titania replicas of the original lattice. Thus, double replication provides a pathway for accessing periodic structures that are difficult to synthesize directly from materials such as titania.

Ordered Mesoporous Nickel Sphere Arrays for Highly Efficient Electrocatalytic Water Oxidation

We report the preparation and use of the three-dimensionally ordered mesoporous Ni sphere arrays (3D-OMNiSA) as a highly effective OER catalyst in alkaline electrolyte. The 3D-OMNiSA is fabricated through lyotropic liquid crystal templating within a polymer inverse opal. The prepared 3D-OMNiSA catalyst exhibits a low overpotential of 254 mV at 10 mA cm–2 and a small Tafel slope of 39 mV decade–1, better than the commercial precious RuO2 catalyst. The mass activity (166.5 A g–1) and turnover frequency (0.0281 s–1) of 3D-OMNiSA are about 4.3 and 2.2 times that of RuO2, respectively. Additionally, this 3D-OMNiSA catalyst shows a high durability under harsh water oxidation cycling test. The outstanding OER performance of the 3D-OMNiSA could be attributed to the large surface area, efficient mass and charge transport, and high structural stability arising from the unique 3D hierarchical porous structure of the 3D-OMNiSA consisting of ordered close-packed mesoporous spheres.

Preparation of conducting polymer inverse opals and its application as ammonia sensor

We developed an ammonia gas sensor by taking advantage of conductive inverse opal films. Conducting polymer inverse opals were fabricated by depositing conducting polymers (PEDOT and PPy) into the void space of silica colloidal crystal temples followed with silica-etching. When using the inverse opal structured conducting polymer films as ammonia gas sensor, both optical and electric signals were derived, and the accuracy of target information could be ensured.

Maleimide-containing polymer inverse opals: a new kind of reactive photonic structure with significant extendibility

In this work, maleimide-containing polymer inverse opals have been successfully prepared by utilization of an acrylate monomer bearing a masked (protected) maleimide unit. As an ideal clickable functional group, maleimide can promote the Michael addition of thiol-containing molecules and the thermoreversible Diels–Alder reaction of furan derivatives, providing tremendous opportunities to produce various functional materials from one maleimide-containing polymer. As a demonstration, four chemical systems were facilely evolved from the prepared maleimide-containing inverse opal. By exploiting the nucleophilic thiol–ene reaction of maleimide, the zwitterionic pH-responsive inverse opal and electroactive inverse opal were first fabricated by reacting with cysteine and thiol-containing ferrocene derivatives, respectively. Based on the same reaction, it was also found that the maleimide-containing inverse opal could serve as a self-reporting sensing platform to sensitively detect the reduction of oxidized glutathione by specific enzymes. On the other hand, the thermoreversible nature of the Diels–Alder reaction of the maleimide groups made it possible to construct a dynamic molecule gating system by reacting with alkyl-chain-substituted furan derivatives from the prepared interconnected macroporous film. In fact, due to the unlimited variety provided by the two kinds of reactions mentioned above, the described photonic material exhibits a significant extendibility and could be easily post-modified for special purposes with maintenance of the opaline structure. Thus, this novel clickable maleimide-containing polymer inverse opal could serve as a reactive platform for producing a variety of functional photonic materials.

Template synthesis of ordered arrays of mesoporous titania spheres

Three-dimensionally ordered arrays of submicron-sized mesoporous titania spheres with high surface area and high crystallinity have been prepared through triblock copolymer templating within the confinement of polymer inverse opals.

Optical Switching of a Birefringent Photonic Crystal

Photonic crystals with photocontrollable polarization-dependent stop-bands are fabricated by infiltrating photoresponsive nematic liquid crystals into a stretched polymer inverse opal. When the liquid crystal is in a nematic phase, molecules aligned along the stretching axis generate an optical birefringent effect, which disappears when the liquid crystal is in an isotropic phase. The two states can be reversibly switched by UV-vis light irradiation.

Templated Mesoporous Silica Colloids with Controlled Internal Structures

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-dimensionally confining environment for the cooperative assembly of silica precursors and the associated triblock copolymer mesophase, which appears to be maintained in the final MSCs. The internal mesostructure of the MSCs is regulated by the diameter, surface chemistry, and connectivity of the cavities in the polymer inverse opal. The diameter of the MSCs is controlled by the diameter of the cavities in the polymer inverse opal. When formed in hydrophilic polymer inverse opals, simple MSCs exhibiting a circularly wound concentric mesostructure are formed. At intermediate surface energies, the mesostructure exhibits a pseudo-rhombohedral dodecahedral organization, and when the MSCs are formed in a hydrophobic polymer inverse opal, their mesostructure becomes disordered. The average number of interconnects between cavities of the polymer inverse opal could be modulated by intentionally ordering or disordering the silica colloidal crystal used to template the polymer inverse opal; increasing disorder decreased the average number of interconnects between cavities. With use of such templates, the effect of interconnects on the MSCs was determined.

Fabrication of Polymer Inverse Opals on Substrate by Transfer Technique

Polymer inverse opals have been fabricated with good replication fidelity on a polymer substrate by the transfer technique, in which self-assembled silica opals on a quartz substrate were used as templates. Transferred polymer inverse opals showed a smaller contraction of the original periodicity than the conventional self-standing inverse opals. In addition, the standard deviation value of the wavelengths at the photonic band gap for the trasnsferred polymer inverse opals is almost the same as that of silica opals which are used as templates, whereas that of self-standing inverse opals is larger. The film thickness dependance of the maximum attenuations of photonic band gap, 10 log (transmission minimum/transmission maximum), showed that polymer inverse opals are modulated more strongly than silica opals.

Fabrication of Polymer−Nanoparticle Composite Inverse Opals by a One-Step Electrochemical Co-deposition Process

We describe a one-step electrochemical co-deposition method to prepare nanoparticle (NP)-containing semiconducting polymer inverse opals with well-defined pore structure. Gold and cadmium telluride NPs were electrodeposited along with pyrrole in the interstitial voids of colloidal crystals of polymer spheres, and following template removal, composite inverse opals were obtained. The optical characteristics (position of the optical stopband) of the resulting composite films can be tuned through variation of the type and concentration of the NPs embedded in the film.

Fabrication and Optical Properties of π-Conjugated Polymer Inverse Opal

Polymer inverse opals were fabricated by directly infiltrating a molten polymer into silica opal templates at an elevated temperature. The main-chain π-conjugated polymer, poly[2-(9',9'-dihexylfluorenyl)-1,4-phenylenevinylene] (DHF-PPV) was adopted for fabricating an inverse opal. The DHF-PPV inverse opal maintained well-defined periodic structures of the silica opal template, showing ordered and well-packed spherical air-pores by scanning electron microscopy. The DHF-PPV inverse opal showed an optical stop band based on the periodic pattern of the refractive index in the visible wavelength region. A dip in the photoluminescence spectrum resulting from the influence of the stop band was observed.

Optical properties and gel characteristics in inverse opals made from poly(3-alkylthiophene) and photopolymer

Inverse opals of conducting polymer and photopolymer have been fabricated by infiltrating polymers into SiO 2 opal and subsequently removing SiO 2 particles with a chemical treatment. The reflection spectrum change upon heating and electrochemically doping has been demonstrated in the conducting polymer inverse opals, which originates from the refractive index change due to the change in electronic states in conducting polymer. The gel characteristics have also been observed in a photopolymer inverse opal. The inverse opal swells depending on a kind of solvents infiltrated into the inverse opal.

Tuning the Optical Properties of Inverse Opal Photonic Crystals by Deformation

Simple uniaxial elongation of the air spheres in polymer inverse opal is used to tune the material’s stop band. Stretching causes the distance between the (111) planes parallel to the film surface to decrease, resulting in a shift of the stop band to shorter wavelength. This is coupled with a shift to longer wavelength of the stop band associated with periodicity in the stretching direction. The Figure shows the resulting elongated air voids.

Replicating the Structure of a Crosslinked Polyferrocenylsilane Inverse Opal in the Form of a Magnetic Ceramic

Crosslinked polyferrocenylsilane inverse opals have been prepared by the thermal ring-opening polymerization of spirocyclic [1]silaferrocenophanes confined within the interstitial void spaces of silica crystal colloidal templates. These organometallic polymer inverse opals were converted to magnetic ceramic replicas through pyrolysis at 900 °C in high yields.

Electric Field Tuning of the Stop Band in a Liquid-Crystal-Infiltrated Polymer Inverse Opal

A polymer inverse opal with a tunable bandgap is presented. It is shown that, when the opal is infiltrated with a nematic liquid crystal, tuning of the stop band upon the application of an electric field is possible (see Figure for an SEM image of the structure). A discontinuous transition of the λLC shift upon a change in the voltage is observed.

Semiconducting Polymer Inverse Opals Prepared by Electropolymerization

Electropolymerization of pyrrole or thiophene in the voids of a polystyrene colloidal crystal, followed by template removal with THF, provides a simple synthetic route to high-quality sensor-suitable, semiconducting inverse opals. Control of the film thickness is achieved by choice of the electrode potential and reaction time. The Figure shows a polythiophene inverse opal.

Synthesis and Photonic Bandgap Characterization of Polymer Inverse Opals

Polymer inverse opals with long-range order (see Figure) have been fabricated and their photonic crystal behavior examined. Good agreement between band structure calculations and experiment is found. It is envisaged that these inverse opals could be used for the modification of the electronic properties of incorporated luminescent materials and as matrices for the synthesis of spherical colloidal particles.