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

Tuning Pore Dimensions of Mesoporous Inorganic Films by Homopolymer Swelling

The functionality and applications of mesoporous inorganic films are closely linked to their mesopore dimensions. For material architectures derived from a block copolymer (BCP) micelle coassembly, the pore size is typically manipulated by changing the molecular weight corresponding to the pore-forming block. However, bespoke BCP synthesis is often a costly and time-consuming process. An alternative method for pore size tuning involves the use of swelling agents, such as homopolymers (HPs), which selectively interact with the core-forming block to increase the micelle size in solution. In this work, poly(isobutylene)-block-poly(ethylene oxide) micelles were swollen with poly(isobutylene) HP in solution and coassembled with aluminosilicate sol with the aim of increasing the resulting pore dimensions. An analytical approach implementing spectroscopic ellipsometry (SE) and ellipsometric porosimetry (EP) alongside atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS) in transmission and grazing-incidence (GISAXS) modes enabled us to study the material evolution from solution processing through the manifestation of the mesoporous inorganic film after BCP removal. The in-depth SE/EP analysis evidenced an increase of more than 45% in mesopore diameter with HP swelling and a consistent scaling of the overall void volume and number of pores. Importantly, our analytical toolbox enabled us to study the effect of swelling on the connecting necks between adjacent pores, with observed increases as high as ≈35%, offering novel pathways to sensing, electrochemical, and other mass-transfer-dependent applications

Structural Characterization of Mesoporous Thin Film Architectures: A Tutorial Overview

Mesoporous thin film architectures are an important class of materials that exhibit unique properties, which include high surface area, versatile surface functionalization, and bicontinuous percolation paths through a broad library of pore arrangements on the 10 nm length scale. Although porosimetry of bulk materials via sorption techniques is common practice, the characterization of thin mesoporous films with small sample volumes remains a challenge. A range of techniques are geared toward providing information over pore morphology, pore size distribution, surface area and overall porosity, but none of them offers a holistic evaluation and results are at times inconsistent. In this work, we present a tutorial overview for the reliable structural characterization of mesoporous films. Three model samples with variable pore size and porosity prepared by block copolymer (BCP) coassembly serve for a rational comparison. Various techniques are assessed side-by-side, including scanning electron microscopy (SEM), atomic force microscopy (AFM), grazing incidence small-angle X-ray scattering (GISAXS), and ellipsometric porosimetry (EP). We critically discuss advantages and limitations of each technique and provide guidelines for reliable implementation

Robust Operation of Mesoporous Antireflective Coatings under Variable Ambient Conditions

Generating mesoporous films with adequate film thickness and refractive index is a common method to achieve amplitude and phase matching in low-cost interference-based antireflective coatings (ARCs). For high-surface-energy materials, pores on the 2-50 nm (i.e., on the subwavelength scale) are subject to capillary condensation by surrounding gas phase water molecules, which hampers their functioning. In this work, we examine the effect of relative humidity on mesoporous ARCs and present a simple method for the preparation of ARCs with robust operation under variable conditions. The materials route is based on the generation of well-defined porous aluminosilicate networks by block copolymer co-assembly with poly(isobutylene)- block-poly(ethylene oxide) and postsynthesis grafting of trichloro(octyl)silane molecules to the pore walls. The functionalized films exhibited a maximum transmittance value of 99.8%, with an average transmittance of 99.1% in the visible wavelength range from 400 to 700 nm. Crucially, the antireflection performance was maintained at high humidity values, with an average transmittance decrease of only 0.2% and maximum values maintained at 99.7%. This compared to maximum and average losses of 3.6 and 2.7%, respectively, for nonfunctionalized reference samples. The ARCs were shown to retain their optical properties within 50 humidity cycles, indicating long-term stability against fluctuating environmental conditions

Synthetic guidelines for the precision engineering of gold nanoparticles

Gold nanoparticles (AuNPs) are one of the most studied nanomaterials with applications spanning from catalysis to biomedicine. While numerous chemical protocols exist that allow bespoke tailoring of chemical, physical and biological properties, their translation towards industrial-scale production remains a challenge. Batch synthesis often suffers from poor reproducibility and scalability, while emerging approaches, such as continuous flow synthesis, are not widely implemented in research labs. Herein, we provide a critical review of recent developments in the field of AuNP synthesis and identify synthetic guidelines for precision engineering of nanoparticle properties

Restoration of Southern Ecosystems

Restoration of the myriad communities of bottomland hardwood and wetland forests and of the diverse communities of fire-dominated pine forests is the subject of intense interest in the Southern United States. Restoration practice is relatively advanced for bottomland hardwoods and longleaf pine (Pinus palustris Mill.), and less so for swamps and shortleaf pine (P. echinata Mill.). Most bottomland hardwood restoration is taking place on private land, while restoration of swamps and shortleaf pine occurs mostly on public land. Both public and private landowners are involved in the restoration of longleaf pine. Proper matching of species to site is critical to successful restoration of bottomland hardwoods. Techniques for longleaf pine restoration include the reintroduction of growing-season fire and the planting of longleaf pine seedlings and understory species. Safely reintroducing growing-season fire, however, may require initial manipulation of other vegetation by mechanical or chemical means to reduce built-up fuels

Optimising Light Source Positioning for Even and Flux-Efficient Illumination

Designing imaging systems is a challenge faced by researchers in many fields including fluorescent imaging in life sciences and optical set-ups for automated capture of experimental data. The position of light sources within an imaging system has significant consequences for the downstream usability of the data it generates. Non-uniform illumination can contribute to low quality (or in some cases unusable) images, particularly so when illumination variation approaches or exceeds the sensitivity range of the capture device/camera. Similarly, low flux efficiency (i.e. ratio of flux through the imaging plane divided by the total flux from the source) will negatively affect the image acquisition and subsequent analysis. Often flux efficiency is sacrificed for illumination uniformity i.e. choosing to deliver less light to the target in order to keep the variation of light intensity low. Furthermore, the large number of possible positional configurations of a light source within an imaging system precludes manual optimisation. To tackle this issue, we offer a software for modelling the illumination profile for a given light source. The code can be easily adjusted to model a variety of positional configurations and rapidly calculates results for many thousands of variable combinations. We envisage the exploitation of this software for research as well as in the early stages of prototyping. For example, in the university environment where resources and time are limited. Furthermore, we demonstrate an approach by which a user can reduce the amount of possible multi-variable combinations down to the most viable options. This is performed using a modified convex hull approach in two-dimensions (optimising for two figures of merit, i.e. the total flux and the illumination variation). In principle, this method can be extended to n-dimensional space to include additional figures of merit for optimisation. Our model describes positions of a light source in Cartesian coordinates (x, y and z) relative to the centre of the illuminated area. The spatial region available for light source placement must be chosen by the user. In addition, the user defines a range of allowed angles of illumination in Polar coordinates (theta and phi) relative to the surface normal (see Figure 1a). Based on these user inputs, the software creates a set of illumination configurations. These are then tested for feasibility with regard to the requirements and limitations of the imaging device. This pre-filtering process can also be augmented by the user to suit the needs of their particular system

Using Nanocavity Plasmons to Improve Solar Cell Efficiency

Although in principle very promising, photovoltaic technology has so far failed to deliver robust high efficiency modules at affordable prices. Despite considerable research, high efficiency silicon based cells remain expensive, while the more recent organic photovoltaics are still struggling with low efficiencies and short lifetimes. Meanwhile, over the last few years, the study of localized plasmons [1,2] has also received great attention due to the high field enhancements associated with confined fields , with a wide range of applications possible, from optical switches to substrates for surface enhanced Raman spectroscopy (SERS). Here we discuss how combining the structures normally used in photovoltaic devices with metallic cavities supporting localized plasmons can lead to considerable improvements in the performance of solar cells. In particular we show how by changing the shape and size of spherical voids on a metallic surface, one can tune the plasmon modes to obtain significant absorptions across the solar spectrum [3]. By coating one such nanocavity surface with a sub 100 nm-layer of semiconductor, we can create a nanostructured solar cell, where the localised Mie modes efficiently couple light into the semiconductor layer. As the plasmons electric field enhancement is largest very close to the surface, significant absorption can be maintained even when the semiconductor thickness is reduced to below the typical exciton diffusion length. In addition minority carrier transport is improved. That means we can beat the usual balance between light absorption and exciton recombination loses, and so significantly increase the overall efficiency of the photovoltaic devices. Keywords: plasmons, solar cells, nanostructured surfaces

Block Copolymer Directed Metamaterials and Metasurfaces for Novel Optical Devices

Optical metamaterials are artificially engineered architectures that exhibit desired optical properties not found in nature. Bespoke design requires the ability to define shape, size, orientation, and composition of material structures on the nanometer length scale. Bottom-up self-assembly methods, such as block copolymer (BCP) templating, offer unique pathways to tailored features, at spatial resolution not routinely achieved by conventional top-down techniques. In this review, the authors provide the general readership with basic concepts of the underlying fabrication processes and examine optical phenomena arising from BCP-derived metamaterials and nanoresonators, with both dielectric and plasmonic characteristics. A number of diverse structural conformations designed by BCP templating and their implementation in optical devices is evaluated. The discussion includes 3D metamaterials, such as gyroidal and hyperbolic arrangements, as well as 2D metasurfaces. Based on recent developments in exploring these emerging structural and material configurations, the review further highlights unexplored opportunities offered by BCP self-assembly for novel metamaterials and metasurface devices

Novel approaches to acoustic immunosensing of extracellular vesicles

Extracellular vesicles (EVs) constitute a promising source of biomarkers for disease diagnostics and can be obtained via liquid biopsies from various bodily fluids. While much progress has been made in recent years, challenges remain on the sensitivity, specificity and clinical implementation of current analytical workflows