Block copolymer self-assembly for nanophotonics

The ability to control and modulate the interaction of light with matter is crucial to achieve desired optical properties including reflection, transmission, and selective polarization. Photonic materials rely upon precise control over the composition and morphology to establish periodic interactions with light on the wavelength and sub-wavelength length scales. Supramolecular assembly provides a natural solution allowing the encoding of a desired 3D architecture into the chemical building blocks and assembly conditions. The compatibility with solution processing and low-overhead manufacturing is a significant advantage over more complex approaches such as lithography or colloidal assembly. Here we review recent advances on photonic architectures derived from block copolymers and highlight the influence and complexity of processing pathways. Notable examples that have emerged from this unique synthesis platform include Bragg reflectors, antireflective coatings, and chiral metamaterials. We further predict expanded photonic capabilities and limits of these approaches in light of future developments of the field

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Ordered Mesoporous to Macroporous Oxides with Tunable Isomorphic Architectures: Solution Criteria for Persistent Micelle Templates

Porous and nanoscale architectures of inorganic materials have become crucial for a range of energy and catalysis applications, where the ability to control the morphology largely determines the transport characteristics and device performance. Despite the availability of a range of block copolymer self-assembly methods, the conditions for tuning the key architectural features such as the inorganic wall-thickness have remained elusive. Toward this end, we have developed solution processing guidelines that enable isomorphic nanostructures with tunable wall-thickness. A new poly(ethylene oxide-b-hexyl acrylate) (PEO-b-PHA) structure-directing agent (SDA) was used to demonstrate the key solution design criteria. Specifically, the use of a polymer with a high Flory-Huggins effective interaction parameter, χ, and appropriate solution conditions leads to the kinetic entrapment of persistent micelle templates (PMT) for tunable isomorphic architectures. Solubility parameters are used to predict conditions for maintaining persistent micelle sizes despite changing equilibrium conditions. Here, the use of different inorganic loadings controls the inorganic wall-thickness with constant pore size. This versatile method enabled a record 55 nm oxide wall-thickness from micelle coassembly as well as the seamless transition from mesoporous materials to macroporous materials by varying the polymer molar mass and solution conditions. The processing guidelines are generalizable and were elaborated with three inorganic systems, including Nb2O5, WO3, and SiO2, that were thermally stable to 600 °C for access to crystalline materials

Between Horizontality and Centralisation: Organisational Form and Practice in the Finns Party

This article provides the first comprehensive analysis of the Finns Party’s (Perussuomalaiset [PS]) formal organisation and how it operates in practice. Following the framework of this thematic issue, to what extent does the PS’s organisation follow the mass-party model and how centralised is the party in its internal decision-making? Analysis of party documents, association registries, and in-depth interviews with 24 party elite representatives reveal that the PS has developed a complex organisational structure and internal democracy since 2008. However, the power of members in regard to the party’s internal decision-making remains limited, despite the party’s leadership having facilitated a more horizontal and inclusionary organisational culture after 2017. The study reveals how the party combines radically democratic elements of its leadership selection and programme development with a very high level of centralisation of formal power in the party executive, and how the party organisationally relies on a vast and autonomous but heterogeneous network of municipal associations. The article also discusses how PS elites perceive the advantages of having a wide and active organisation characterised by low entry and participation requirements, and how party-adjacent online activism both complements and complicates the functioning of the formal party organisation

Nanostructure Dependence of T‐Nb₂O₅ Intercalation Pseudocapacitance Probed Using Tunable Isomorphic Architectures

Intercalation pseudocapacitance has emerged as a promising energy storage mechanism that combines the energy density of intercalation materials with the power density of capacitors. Niobium pentoxide was the first material described as exhibiting intercalation pseudocapacitance. The electrochemical kinetics for charging/discharging this material are surface‐limited for a wide range of conditions despite intercalation via diffusion. Investigations of niobium pentoxide nanostructures are diverse and numerous; however, none have yet compared performance while adjusting a single architectural parameter at a time. Such a comparative approach reduces the reliance on models and the associated assumptions when seeking nanostructure–property relationships. Here, a tailored isomorphic series of niobium pentoxide nanostructures with constant pore size and precision tailored wall thickness is examined. The sweep rate at which niobium pentoxide transitions from being surface‐limited to being diffusion‐limited is shown to depend sensitively upon the nanoscale dimensions of the niobium pentoxide architecture. Subsequent experiments probing the independent effects of electrolyte concentration and film thickness unambiguously identify solid‐state lithium diffusion as the dominant diffusion constraint even in samples with just 48.5–67.0 nm thick walls. The resulting architectural dependencies from this type of investigation are critical to enable energy‐dense nanostructures that are tailored to deliver a specific power density

Ultrafast nonlinear response of gold gyroid three-dimensional metamaterials

We explore the nonlinear optical response of 3D gyroidal metamaterials, which show >10-fold enhancements compared to all other metallic nanomaterials as well as bulk gold. A simple analytical model for this metamaterial response shows how the reflectivity spectrum scales with the metal fill fraction and the refractive index of the material that the metallic nanostructure is embedded in. The ultrafast response arising from the interconnected 3D nanostructure can be separated into electronic and lattice contributions with strong spectral dependences on the dielectric filling of the gyroids, which invert the sign of the nonlinear transient reflectivity changes. These metamaterials thus provide a wide variety of tuneable nonlinear optical properties, which can be utilised for frequency mixing, optical switching, phase modulators, novel emitters, and enhanced sensing.This is the author's accepted manuscript. The final version is available from APS in Physical Review Applied at http://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.2.044002#fulltext#fulltext

Controlling the coassembly of highly amphiphilic block copolymers with a hydrolytic sol by solvent exchange

The coassembly of an inorganic sol by organic structure-directing agents is a widely established technique for solution processed mesoporous metal oxides. Block copolymers with highly amphiphilic blocks are promising candidates for fast and robust material assembly into a range of periodic nano-morphologies. The high polarity difference is however an inherent challenge for the simultaneous processing of hydrophilic and hydrophobic components. Here, we show that a solvent exchange through the evaporation of the initial volatiles and redissolution in an azeotrope mixture of polar and apolar solvents with a common high boiling point allows the evolution of a micellar solution towards block copolymer-dictated structures near thermodynamic equilibrium, with controlled access to inorganic cylinders, lamellae and organic cylinders within a continuous inorganic matrix

Integrating Collaboration and Activity-Oriented Planning for Coalition Operations Support

The University of Edinburgh and research sponsors are authorised to reproduce and distribute reprints and on-line copies for their purposes notwithstanding any copyright annotation hereon. The views and conclusions contained herein are the author’s and shouldn’t be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of other parties.The use of planning assistant agents is an appropriate option to provide support for members of a coalition. Planning agents can extend the human abilities and be customised to attend different kinds of activities. However, the implementation of a planning framework must also consider other important requirements for coalitions, such as the performance of collaborative activities and human-agent interaction (HAI). This paper discusses the integration of an activity-oriented planning with collaborative concepts using a constraint-based ontology for that. While the use of collaborative concepts provides a better performance to systems as a whole, a unified representation of planning and collaboration enables an easy customisation of activity handlers and the basis for a future incorporation of HAI mechanisms

The future of enterprise groupware applications

This paper provides a review of groupware technology and products. The purpose of this review is to investigate the appropriateness of current groupware technology as the basis for future enterprise systems and evaluate its role in realising, the currently emerging, Virtual Enterprise model for business organisation. It also identifies in which way current technological phenomena will transform groupware technology and will drive the development of the enterprise systems of the future

Low temperature crystallisation of mesoporous TiO2

Conducting mesoporous TiO2 is rapidly gaining importance for green energy applications. To optimise performance, its porosity and crystallinity must be carefully fine-tuned. To this end, we have performed a detailed study on the temperature dependence of TiO2 crystallisation in mesoporous films. Crystal nucleation and growth of initially amorphous TiO2 derived by hydrolytic sol-gel chemistry is compared to the evolution of crystallinity from nanocrystalline building blocks obtained from non-hydrolytic solgel chemistry, and mixtures thereof. Our study addresses the question whether the critical temperature for crystal growth can be lowered by the addition of crystalline nucleation seeds