Lamellar and liquid crystal ordering in solvent-annealed all-conjugated block copolymers

Prospects of glove-box versus air-processed organic solar cells

In the search for alternate green energy sources to offset dependence on fossil fuels, solar energy can certainly meet two needs with one deed: fulfil growing global energy demands due to its non-depletable nature and lower greenhouse gas emissions. As such, third generation thin film photovoltaic technology based organic solar cells (OSCs) can certainly play their role in providing electricity at a competing or lower cost than 1st and 2nd generation solar technologies. As OSCs are still at an early stage of research and development, much focus has been placed on improving power conversion efficiencies (PCEs) inside a controlled environment i.e. a glove-box (GB) filled with an inert gas such as N₂. This was necessary until now, to control and study the local nanomorphology of the spin-coated blend films. For OSCs to compete with other solar energy technologies, OSCs should produce similar or even better morphologies in an open environment i.e. air, such that air-processed OSCs can result in similar PCEs in comparison to their GB-processed counterparts. In this review, we have compared GB- vs. air-processed OSCs from morphological and device physics aspects and underline the key features of efficient OSCs, processed in either GB or air.

In situ preparation of hydroxyapatite in lamellar liquid crystals for joint lubrication and drug delivery

Arthritis is a disease that seriously affects the quality of human life, which is partly caused by the reduction of joint lubrication performance. Thus, for the treatment of arthritis, how to improve the lubrication performance of joints is important. The lamellar liquid crystals (LLCs) systems have the potential to be used as joint lubrication due to their double-layer structure and good biocompatibility, however, the LLCs system alone could not provide a satisfactory lubrication effect. Herein, this work synthesized hydroxyapatite (HAP) in situ inside Tween 85/Tween 80/H₂O LLCs to construct a biocompatible HAP/Tween 85/Tween 80/H₂O LLCs (HAP/LLCs) lubrication system with both sustained drug release properties and anti-wear properties. HAP is the main component of bone with good stability and bioactivity. The LLCs have good lubricating and drug-carrying properties. The impact of HAP on the structure and lubrication properties of LLCs, the mechanism of friction, and the anti-wear reduction of HAP/LLCs were investigated. Moreover, the drug release behavior of the ibuprofen-loaded HAP/LLCs during the friction process was also studied. The results indicated that the addition of HAP could improve the lubricity performance of LLCs. The cumulative drug releasing increased with the friction frequency and was less affected by the load. The related studies provided the theoretical basis for HAP/LLCs for joint lubrication and synergistic therapy.

Cesium Lead Halide Perovskite Nanocrystals Assembled in Metal-Organic Frameworks for Stable Blue Light Emitting Diodes

All inorganic cesium lead trihalide nanocrystals are promising light emitters for bright light emitting diodes (LEDs). Here, CsPb(BrCl)1.5 nanocrystals in metal-organic frameworks (MOF) thin films are demonstrated to achieve bright and stable blue LEDs. The lead metal nodes in the MOF thin film react with Cs-halide salts, resulting in 10-20 nm nanocrystals. This is revealed by X-ray scattering and transmission electron microscopy. Employing the CsPbX3 -MOF thin films as emission layers, bright deep blue and sky-blue LEDs are demonstrated that emit at 452 and 476 nm respectively. The maximum external quantum efficiencies of these devices are 0.72% for deep blue LEDs and 5.6% for sky blue LEDs. More importantly, the device can maintain 50% of its original electroluminescence (T50 ) for 2.23 h when driving at 4.2 V. Detailed optical spectroscopy and time-of-flight secondary ion mass spectroscopy suggest that the ion migration can be suppressed that maintains the emission brightness and spectra. The study provides a new route for fabricating stable blue light emitting diodes with all-inorganic perovskite nanocrystals.

Lubrication and Dynamically Controlled Drug Release Properties of Tween 85/Tween 80/H2O Lamellar Liquid Crystals

Lamellar liquid crystals have amazing lubricating and drug-solubilizing properties. Hence, the combination of drug molecules with lamellar liquid crystals is expected to be used in joint lubrication and treatment. In this study, the partial phase diagram of the Tween 85/Tween 80/H₂O three-component system was determined. The phase structure of the system changed from a hexagonal liquid crystal to a lamellar liquid crystal with the increase of Tween 85 content. The lamellar liquid crystals showed superior lubricating properties due to their unique lamellar structure. Furthermore, the model of drug release during friction was established for the first time. It was found that the order of the lamellar liquid crystals increased with the increase of the mass ratio of Tween 85/Tween 80, leading to the decrease of the ibuprofen release rate. In addition, the release rate of ibuprofen increased progressively with the increase of the friction frequency, but the load had little effect on it. Therefore, the lamellar liquid crystals consisting of nonionic surfactants with good biocompatibility have potential application prospects for joint lubrication and treatment of arthritis.

GIWAXS-SIIRkit: scattering intensity, indexing and refraction calculation toolkit for grazing-incidence wide-angle X-ray scattering of organic materials

Grazing-incidence wide-angle X-ray scattering (GIWAXS) has become an increasingly popular technique for quantitative structural characterization and comparison of thin films. For this purpose, accurate intensity normalization and peak position determination are crucial. At present, few tools exist to estimate the uncertainties of these measurements. Here, a simulation package is introduced called GIWAXS-SIIRkit, where SIIR stands for scattering intensity, indexing and refraction. The package contains several tools that are freely available for download and can be executed in MATLAB. The package includes three functionalities: estimation of the relative scattering intensity and the corresponding uncertainty based on experimental setup and sample dimensions; extraction and indexing of peak positions to approximate the crystal structure of organic materials starting from calibrated GIWAXS patterns; and analysis of the effects of refraction on peak positions. Each tool is based on a graphical user interface and designed to have a short learning curve. A user guide is provided with detailed usage instruction, tips for adding functionality and customization, and exemplary files.

Improved efficiency of single-component active layer photovoltaics by optimizing conjugated diblock copolymers

Using an A–B type monomer instead of an AA + BB type monomer to synthesise diblock copolymers, the PCE of a single-component photovoltaic device reached 1.22%.

Microstructure and Tribological Properties of Lamellar Liquid Crystals Formed by Ionic Liquids as Cosurfactants

Lamellar liquid crystals (LLCs) have been shown to have lubrication properties in many documents due to their bilayer structure. Ionic liquids are often used as additive or surfactant in LLCs. However, ionic liquids used as cosurfactants, which lead to a transition from the hexagonal liquid crystals to LLCs, are relatively rare. Herein, the microstructure of Triton X-100/C _nmimNTf₂/H₂O LLCs formed by using 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid (C _nmimNTf₂, n = 8, 12, 16) as cosurfactant has been determined by polarized light microscopy, small angle X-ray scattering, and ²H NMR technique, and their rheological and tribological properties were investigated. These LLCs show good friction-reducing and antiwear performances. The correlation between the microstructure of the LLCs and their lubricating mechanism is established. The increase of the concentration of C _nmimNTf₂ and the length of alkyl chain in the LLCs can lead to an obvious reduction in friction coefficients and wear volumes, which are attributed to the higher order of amphiphilic molecules, the thickness of the amphiphilic bilayer, and the smaller cross-sectional area of the polar head group at the hydrophilic and hydrophobic interfaces. The protective film formed by the physical adsorption of ionic liquid LLCs on the surface of friction disk pair and the tribochemical reaction has effectively promoted the lubrication effect. The good lubricating property and antiwear capability indicate their promising and potential applications in water lubrication and biological lubrication.

Advances toward the effective use of block copolymers as organic photovoltaic active layers

Donor/acceptor block copolymers for organic photovoltaic active layers are discussed from first principles through the modern state-of-the-art and future perspectives.

Semiconducting alternating multi-block copolymers via a di-functionalized macromonomer approach

A route to fully-conjugated semiconducting block copolymers is presented and the prototype exhibits nanoscopic phase domain separation and good mobility.

Complex liquid-crystal nanostructures in semiflexible ABC linear triblock copolymers: A self-consistent field theory

We show that two series of ABC linear triblock copolymers possess sequences of order-to-order phase transitions between microphase-separated states, as the degree of flexibility of the semiflexible middle B-blocks varies. The spatial and orientational symmetries of these phases, some of them containing liquid-crystal ordering, are analysed in comparison with related structures previously determined experimentally and theoretically. A theoretical framework based on the self-consistent field treatment of the wormlike-chain model, which incorporates the Flory-Huggins and Maier-Saupe interactions in the free energy, is used here as a basic foundation for numerical calculations. We suggest that tuning the flexibility parameter, which reduces to the concept of degree of polymerization in the coil-like limit and characterizes the chain-persistency in the rod-like limit, provides a promising approach that can be used to design the resulting microphase-separated structures in semiflexible copolymer melts.

Selective porous gates made from colloidal silica nanoparticles

Highly selective porous films were prepared by spin-coating deposition of colloidal silica nanoparticles on an appropriate macroporous substrate. Silica nanoparticles very homogenous in size were obtained by sol-gel reaction of a metal oxide silica precursor, tetraethyl orthosilicate (TEOS), and using polystyrene-block-poly(ethylene oxide) (PS-b-PEO) copolymers as soft-templating agents. Nanoparticles synthesis was carried out in a mixed solvent system. After spin-coating onto a macroporous silicon nitride support, silica nanoparticles were calcined under controlled conditions. An organized nanoporous layer was obtained characterized by a depth filter-like structure with internal porosity due to interparticle voids. Permeability and size-selectivity were studied by monitoring the diffusion of probe molecules under standard conditions and under the application of an external stimulus (i.e., electric field). Promising results were obtained, suggesting possible applications of these nanoporous films as selective gates for controlled transport of chemical species in solution.

Phase transitions in semiflexible-rod diblock copolymers: a self-consistent field theory

We investigate the phase behavior of semiflexible-rod diblock copolymers in a parameter range where the system displays columnar and lamella structures, using a self-consistent field theory based on the wormlike-chain model. Both Flory-Huggins and Maier-Saupe orientational interactions are incorporated in the formalism, which allows us to explore microphase separation and liquid-crystal ordering simultaneously. Order-to-order phase transitions induced by chain rigidity and orientational interaction are both reported and analyzed. Coupled orientational ordering and spatial inhomogeneity of the four microphase-separated states are discussed in this work: hexagonal column, ellipse column, smectic-A, and smectic-C.