Depth profiling of polymer films with grazing-incidence small-angle X-ray scattering

Lyotropic Liquid Crystal (LLC)-Templated Nanofiltration Membranes by Precisely Administering LLC/Substrate Interfacial Structure

Mesoporous materials based on lyotropic liquid crystal templates with precisely defined and flexible nanostructures offer an alluring solution to the age-old challenge of water scarcity. In contrast, polyamide (PA)-based thin-film composite (TFC) membranes have long been hailed as the state of the art in desalination. They grapple with a common trade-off between permeability and selectivity. However, the tides are turning as these novel materials, with pore sizes ranging from 0.2 to 5 nm, take center stage as highly coveted active layers in TFC membranes. With the ability to regulate water transport and influence the formation of the active layer, the middle porous substrate of TFC membranes becomes an essential player in unlocking their true potential. This review delves deep into the recent advancements in fabricating active layers using lyotropic liquid crystal templates on porous substrates. It meticulously analyzes the retention of the liquid crystal phase structure, explores the membrane fabrication processes, and evaluates the water filtration performance. Additionally, it presents an exhaustive comparison between the effects of substrates on both polyamide and lyotropic liquid crystal template top layer-based TFC membranes, covering crucial aspects such as surface pore structures, hydrophilicity, and heterogeneity. To push the boundaries even further, the review explores a diverse array of promising strategies for surface modification and interlayer introduction, all aimed at achieving an ideal substrate surface design. Moreover, it delves into the realm of cutting-edge techniques for detecting and unraveling the intricate interfacial structures between the lyotropic liquid crystal and the substrate. This review is a passport to unravel the enigmatic world of lyotropic liquid crystal-templated TFC membranes and their transformative role in global water challenges.

Synthetic control over orientational degeneracy of spacer cations enhances solar cell efficiency in two-dimensional perovskites

Two-dimensional perovskites have emerged as more intrinsically stable materials for solar cells. Chemical tuning of spacer organic cations has attracted great interest due to their additional functionalities. However, how the chemical nature of the organic cations affects the properties of two-dimensional perovskites and devices is rarely reported. Here we demonstrate that the selection of spacer cations (i.e., selective fluorination of phenethylammonium) affects the film properties of two-dimensional perovskites, leading to different device performance of two-dimensional perovskite solar cells (average n = 4). Structural analysis reveals that different packing arrangements and orientational disorder of the spacer cations result in orientational degeneracy and different formation energies, largely explaining the difference in film properties. This work provides key missing information on how spacer cations exert influence on desirable electronic properties and device performance of two-dimensional perovskites via the weak and cooperative interactions of these cations in the crystal lattice.

Understanding how excess lead iodide precursor improves halide perovskite solar cell performance

The presence of excess lead iodide in halide perovskites has been key for surpassing 20% photon-to-power conversion efficiency. To achieve even higher power conversion efficiencies, it is important to understand the role of remnant lead iodide in these perovskites. To that end, we explored the mechanism facilitating this effect by identifying the impact of excess lead iodide within the perovskite film on charge diffusion length, using electron-beam-induced current measurements, and on film formation properties, from grazing-incidence wide-angle X-ray scattering and high-resolution transmission electron microscopy. Based on our results, we propose that excess lead iodide in the perovskite precursors can reduce the halide vacancy concentration and lead to formation of azimuthal angle-oriented cubic α-perovskite crystals in-between 0° and 90°. We further identify a higher perovskite carrier concentration inside the nanostructured titanium dioxide layer than in the capping layer. These effects are consistent with enhanced lead iodide-rich perovskite solar cell performance and illustrate the role of lead iodide.

Excess lead iodide in the mixed halide perovskites solar cells leads to high device performance but its origin remains elusive. Here Park et al. unveil the underlying microscopic mechanism to be promoting the oriented growth of the perovskites crystals and reducing the defect concentration.

Visualization of Individual Images in Patterned Organic-Inorganic Multilayers Using GISAXS-CT

Using grazing-incidence small-angle scattering (GISAXS) with computed tomography (CT), we have individually reconstructed the spatial distribution of a thin gold (Au) layer buried under a thin poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) layer. Owing to the difference between total reflection angles of Au and PS-b-P2VP, the scattering profiles for Au nanoparticles and self-assembled nanostructures of PS-b-P2VP could be independently obtained by changing the X-ray angle of incidence. Reconstruction of scattering profiles allows one to separately characterize spatial distributions in Au and PS-b-P2VP nanostructures.

Rapid ordering of block copolymer thin films

Block-copolymers self-assemble into diverse morphologies, where nanoscale order can be finely tuned via block architecture and processing conditions. However, the ultimate usage of these materials in real-world applications may be hampered by the extremely long thermal annealing times-hours or days-required to achieve good order. Here, we provide an overview of the fundamentals of block-copolymer self-assembly kinetics, and review the techniques that have been demonstrated to influence, and enhance, these ordering kinetics. We discuss the inherent tradeoffs between oven annealing, solvent annealing, microwave annealing, zone annealing, and other directed self-assembly methods; including an assessment of spatial and temporal characteristics. We also review both real-space and reciprocal-space analysis techniques for quantifying order in these systems.

Fat crystallisation at oil-water interfaces

This review focuses on recent advances in the understanding of lipid crystallisation at or in the vicinity of an interface in emulsified systems and the consequences regarding stability, structure and thermal behaviour. Amphiphilic molecules such as emulsifiers are preferably adsorbed at the interface. Such molecules are known for their ability to interact with triglycerides under certain conditions. In the same manner that inorganic crystals grown on an organic matrix see their nucleation, morphology and structure controlled by the underlying matrix, recent studies report a templating effect linked to the presence of emulsifiers at the oil/water interface. Emulsifiers affect fat crystallisation and fat crystal behaviour in numerous ways, acting as impurities seeding nucleation and, in some cases, retarding or enhancing polymorphic transitions towards more stable forms. This understanding is of crucial importance for the design of stable structures within emulsions, regardless of whether the system is oil or water continuous. In this paper, crystallisation mechanisms are briefly described, as well as recent technical advances that allow the study of crystallisation and crystal forms. Indeed, the study of the interface and of its effect on lipid crystallisation in emulsions has been limited for a long time by the lack of in-situ investigative techniques. This review also highlights reported interfacial effects in food and pharmaceutical emulsion systems. These effects are strongly linked to the presence of emulsifiers at the interface and their effects on crystallisation kinetics, and crystal morphology and stability.

Near-surface relaxation structure of annealed block copolymer film on Si substrates examined by grazing-incidence small-angle scattering utilizing soft X-rays

Two-dimensional grazing-incidence small-angle X-ray scattering (GISAXS) measurements of SEBS8 block copolymer films deposited on Si(001) substrates have been performed to demonstrate depth-sensitive GISAXS utilizing soft X-rays of 1.77 keV. Remarkable elongation of the Bragg spots in theqzdirection, corresponding to microphase separation, was observed for an angle of incidence close to the critical angle. The elongation was explained in terms of the penetration depth, which limits the effective size in the direction perpendicular to the sample surface. Lattice distortion near the surface was confirmed.

Diastereoselective alkylations of a protected cysteinesulfenate

To further understand stereoselection in the alkylation of sulfenate anions, a protected cysteinesulfenate was generated in THF solution at low temperature. Introduction of a reactive alkylating agent brings about a cysteinyl sulfoxide in 51-75% yield, with diastereomeric ratios at the sulfinyl group ranging from 83:17 to 95:5. An internally complexed lithium counterion is proposed to account for the stereoselectivity.