Ordered mesoporous titania from highly amphiphilic block copolymers: tuned solution conditions enable highly ordered morphologies and ultra-large mesopores

Crystalline transition metal oxides with controlled mesopore architectures are in increasing demand to enhance the performance of energy conversion and storage devices. Solution based block copolymer self-assembly routes to achieve ordered mesoporous and crystalline titania have been studied for more than a decade, but have so far mostly been limited to water and alcohol dispersible polymers. This constraint has limited the accessible morphology space as well as structural dimensions. Moreover, synthetic approaches are mostly performed in a trial-and-error fashion using chemical intuition rather than being based on well-defined design parameters. We present solubility design guidelines that facilitate coassembly with highly amphiphilic block copolymers, enabling the formation of ordered structures with diverse length scales (d10 = 13.8–63.0 nm) and bulk-type morphologies. Thus, highly ordered and crystalline titania with the largest reported pores (d = 32.3 nm) was demonstrated for such a coassembly approach without the use of pore-expanders. Furthermore, the use of an ABC triblock terpolymer system led to a 3D ordered network morphology. In all cases, subsequent calcination treatments, such as the CASH procedure, enabled the formation of highly crystalline mesoporous materials while preserving the mesostructure

Improved conductivity in dye-sensitised solar cells through block-copolymer confined TiO2 crystallisation

Anatase TiO2 is typically a central component in high performance dye-sensitised solar cells (DSCs). This study demonstrates the benefits of high temperature synthesised mesoporous titania for the performance of solid-state DSCs. In contrast to earlier methods, the high temperature stability of mesoporous titania is enabled by the self-assembly of the amphiphilic block copolymer polyisoprene-block-polyethylene oxide (PI-b -PEO) which compartmentalises TiO2 crystallisation, preventing the collapse of porosity at temperatures up to 700 degrees C. The systematic study of the temperature dependence on DSC performance reveals a parameter trade-off: high temperature annealed anatase consisted of larger crystallites and had a higher conductivity, but this came at the expense of a reduced specific surface area. While the reduction in specific surface areas was found to be detrimental for liquid-electrolyte DSC performance, solid-state DSCs benefitted from the increased anatase conductivity and exhibited a performance increase by a factor of three

Synthesis and characterization of poly(amino acid methacrylate)-stabilized diblock copolymer nano-objects

Amino acids constitute one of Nature's most important building blocks. Their remarkably diverse properties (hydrophobic/hydrophilic character, charge density, chirality, reversible cross-linking etc.) dictate the structure and function of proteins. The synthesis of artificial peptides and proteins comprising main chain amino acids is of particular importance for nanomedicine. However, synthetic polymers bearing amino acid side-chains are more readily prepared and may offer desirable properties for various biomedical applications. Herein we describe an efficient route for the synthesis of poly(amino acid methacrylate)stabilized diblock copolymer nano-objects. First, either cysteine or glutathione is reacted with a commercially available methacrylate-acrylate adduct to produce the corresponding amino acid-based methacrylic monomer (CysMA or GSHMA). Well-defined water-soluble macromolecular chain transfer agents (PCysMA or PGSHMA macro-CTAs) are then prepared via RAFT polymerization, which are then chain-extended via aqueous RAFT dispersion polymerization of 2-hydroxypropyl methacrylate. In situ polymerization-induced self-assembly (PISA) occurs to produce sterically-stabilized diblock copolymer nano-objects. Although only spherical nanoparticles could be obtained when PGSHMA was used as the sole macro-CTA, either spheres, worms or vesicles can be prepared using either PCysMA macro-CTA alone or binary mixtures of poly(glycerol monomethacrylate) (PGMA) with either PCysMA or PGSHMA macro-CTAs. The worms formed soft free-standing thermo-responsive gels that undergo degelation on cooling as a result of a worm-to-sphere transition. Aqueous electrophoresis studies indicate that all three copolymer morphologies exhibit cationic character below pH 3.5 and anionic character above pH 3.5. This pH sensitivity corresponds to the known behavior of the poly(amino acid methacrylate) steric stabilizer chains

Optical Properties of Gyroid Structured Materials: From Photonic Crystals to Metamaterials

The gyroid is a continuous and triply periodic cubic morphology which possesses a constant mean curvature surface across a range of volumetric ll fractions. Found in a variety of natural and synthetic systems which form through self-assembly, from buttery wing scales to block copolymers, the gyroid also exhibits an inherent chirality not observed in any other similar morphologies. These unique geometrical properties impart to gyroid structured materials a host of interesting optical properties. Depending on the length scale on which the constituent materials are organised, these properties arise from starkly di erent physical mechanisms (such as a complete photonic band gap for photonic crystals and a greatly depressed plasma frequency for optical metamaterials). This article reviews the theoretical predictions and experimental observations of the optical properties of two fundamental classes of gyroid structured materials: photonic crystals (wavelength scale) and metamaterials (subwavelength scale).This work was supported by the EPSRC through the Cambridge NanoDTC EP/G037221/1, EP/G060649/1, EP/L027151/1, and ERC LINASS 320503.This is the accepted manuscript version of the article. The final version is available from Wiley via http://dx.doi.org/10.1002/adom.20140033

Porous Hollow TiO2 Microparticles for Photocatalysis: Exploiting Novel ABC Triblock Terpolymer Templates Synthesised in Supercritical CO2

Reversible addition–fragmentation chain transfer (RAFT) mediated dispersion polymerisation in supercritical carbon dioxide (scCO2) is an efficient and green method for synthesising block copolymer microparticles with internal nanostructures. Here we report for the first time the synthesis of phase separated poly(methyl methacrylate-block-styrene-block-4-vinylpyridine) (PMMA-b-PS-b-P4VP) triblock terpolymer microparticles using a simple two-pot sequential synthesis procedure in scCO2, with high monomer conversions and no purification steps. The microparticles, produced directly and without further processing, show a complex internal nanostructure, appearing as a “lamellar with spheres” [L + S(II)] type morphology. The P4VP block is then exploited as a structure-directing agent for the fabrication of TiO2 microparticles. Through a simple and scalable sol–gel and calcination process we produce hollow TiO2 microparticles with a mesoporous outer shell. When directly compared to porous TiO2 particles fabricated using an equivalent PMMA-b-P4VP diblock copolymer, increased surface area and enhanced photocatalytic efficiencies are observed

HIGHLY CRYSTALLINE INVERSE OPAL TRANSITION METAL OXIDES VIA A COMBINED ASSEMBLY OF SOFT AND HARD CHEMISTRIES

A combined assembly of soft ansd hard chemistries is employed to generate highly crystalline three-dimensionality ordered macroporous (3DOM) niobia (Nb2O5) and titania (TiO2) structures by colloidal crystal templating. Polysterene spheres with sp(2) hybridized carbon are used in a reverse-template infiltration technique based on the aqueous liquid phase deposition of the metal oxide in the interstitial spaces of a colloidal assembly. Heating under inert atmospheres as high as 900 degrees C converts the polymer into study carbon that acts as a scaffold and keeps the macropores open while the oxides crystalize. Using X-ray diffraction it is demonstrate that for both oxides this approach leads to highly crystalline materials while heat treatments to lower temperatures commonly used for polymer colloidal templating, in particular for niobia, results in only weakly crystallized materials. Furthermore it is demonstrated that heat treatment directly to higher temperatures without generating the carbon scaffold leads to collapse of the macrostructure. The approach should in principle be applicable to othe 3DOM materials that require heat treatments to higher termperatures.X116268sciescopu

MICROWAVE SPECTROSCOPIC INVESTIGATION OF HNO3⋯(H2O)2HNO_{3}\cdots(H_{2}O)_{2}

$^{a}$P. R. McCurdy, W. P. Hess, S. S. Xantheas J. Phys. Chem. A 106(33), 7628, (2002).Author Institution: Department of Chemistry, University of Minnesota; Department of Chemistry, Concordia UniversityNitric acid is an important reactive species in the atmosphere and the study of its hydrates is of considerable interest. We report the observation of the 1:2 complex $HNO_{3}\cdots(H_{2}O)_{2}$ via Fourier transform microwave spectroscopy. A-type spectra for a total of 18 isotpomers were recorded, including $^{15}N$, and several $H^{18}_{2}O$ and deuterium containing species. No b-type transitions were found despite calculations predicting a significant dipole moment along the b-principal axis. Spectral splittings observed indicate internal motion of one or both water units within this complex. The $HNO_{3}\cdots(H_{2}O)_{2}$ system adopts a cyclic structure in which the second water unit inserts into the weak, secondary hydrogen bond of $HNO_{3}\cdots(H_{2}O)$, previously studied in our laboratory. The near-linear hydrogen bond between the acidic proton and the closest water unit is $1.632 (16) {\AA}$, a contraction of $0.15 {\AA}$ relative to $HNO_{3}\cdots H_{2}O$. The $O\cdots O$ distance between the hydroxyl unit of the acid and the closest water unit is $2.625(16){\AA}$. Detailed structural analysis, discussion of internal dynamics, and comparison to ab initio $calculations^{a}$ will be presented. Structural characterization of $HNO_{3}\cdots(H_{2}O)_{2}$ will be discussed in the context of proton transfer, as complexes of this nature help answer the fundamental question of how many water molecules are required to ionize a simple mineral acid