Azobenzene-containing polymer for solar thermal energy storage and release: Advances, challenges, and opportunities

Systematic investigation of the structure-property relationship of substituted p-alkoxy-azothiophenes

Differently substituted p-alkoxy azothiophenes with increasing alkoxy chains were systematically investigated in terms of their structure-property relationships. In particular, it was observed that increasing the length of the alkoxy chain had an unusual effect on the melting point, which did not follow the expected odd-even effect. It was also shown that changing the length of the alkoxy chain did not significantly affect the thermal half-life, a finding that disagrees with results reported in other studies. These observations provide valuable insights into structure-property relationships with important implications for the design and development of azobenzenes as molecular materials for various applications. Furthermore, each p-alkoxy azothiophene was investigated in terms of neat solid-state photoisomerisation or photoinduced liquefaction, which is a critical parameter for application as a molecular solar thermal phase-change (MOST-PCM) energy storage system.

Ultrathin Polymersomes with Controllable Light-Responsivity via Adjusting the Electronic Effect from Para-Substituents of Azobenzene

Achieving ultrathin polymersomes (UTPSs) with controllable light-responsive kinetics poses a prospective strategy to address the growing demands of intelligent and miniature systems, but it remains challenging. Herein, we reported the self-assembly of numerous side-chain-type amphiphilic alternating azocopolymers (AAACs) into a series of UTPSs with diameters spanning 210-270 nm and ultrathin vesicular thickness spanning 1.91-2.14 nm. The light-triggered reversible size transitions for these UTPSs are rendered by the photo-isomerization of azobenzene moiety upon alternating irradiation with UV and visible light. The systematical isomerization kinetic study proved that the light-responsive rate of distinct UTPSs was highly dependent on the electronic effect of para-substituents of azobenzenes within AAACs. Notably, the rate constant of electron-withdrawing nitro-modified UTPSs was 6.7 times greater than that of electron-donating hydroxyl-modified UTPSs. The proof-of-concept cargo release activity for different UTPSs was evaluated using a hydrophilic model drug of methylene blue (MB), with a light-controllable releasing performance that highly depended on the para-substituent-induced light-responsive kinetics. Our work offers an innovative strategy to fabricate stimuli-responsive UTPSs with a controllable responsive performance for the targeted applications in bionanotechnology.

Research progress in the preparation of sodium-ion battery anode materials using ball milling

Sodium-ion batteries are regarded as one of the most promising alternatives to lithium-ion batteries due to the greater abundance and lower cost of sodium compared to lithium. However, sodium-ion batteries have not yet been widely adopted. The main reason is that, compared to lithium-ion batteries, sodium-ion batteries have lower energy density and shorter cycle life, with the performance of anode materials directly affecting the energy density and cycle stability of sodium-ion batteries. Notably, ball milling, as an efficient material processing technique, has been widely applied in the preparation and modification of sodium-ion battery anode materials in recent years. This paper reviews the recent progress in the preparation of sodium-ion battery anode materials using ball milling. The process is categorized into ball milling mixing, ball milling exfoliation, ball milling synthesis, and ball milling doping. First, the basic principles and mechanisms of ball milling technology are introduced. Then, the preparation of different types of sodium-ion battery anode materials is discussed based on four specific categories. For various material systems, the effects of ball milling on the structure, morphology, and electrochemical performance are discussed. Additionally, the advantages and challenges of using ball milling in the preparation of sodium-ion battery anode materials are summarized. Finally, the future directions and development trends in the preparation of sodium-ion battery anode materials using ball milling are forecasted, aiming to provide insights and references for further research in this field.

An Innovative Azobenzene-Based Photothermal Fabric with Excellent Heat Release Performance for Wearable Thermal Management Device

Azobenzene (azo)-based photothermal energy storage systems have garnered great interest for their potential in solar energy conversion and storage but suffer from limitations including rely on solvents and specific wavelengths for charging process, short storage lifetime, low heat release temperature during discharging, strong rigidity and poor wearability. To address these issues, an azo-based fabric composed of tetra-ortho-fluorinated photo-liquefiable azobenzene monomer and polyacrylonitrile fabric template is fabricated using electrospinning. This fabric excels in efficient photo-charging (green light) and discharging (blue light) under visible light range, solvent-free operation, long-term energy storage (706 days), and good capacity of releasing high-temperature heat (80-95 °C) at room temperature and cold environments. In addition, the fabric maintains high flexibility without evident loss of energy-storage performance upon 1500 bending cycles, 18-h washing or 6-h soaking. The generated heat from charged fabric is facilitated by the Z-to-E isomerization energy, phase transition latent heat, and the photothermal effect of 420 nm light irradiation. Meanwhile, the temperature of heat release can be personalized for thermal management by adjusting the light intensity. It is applicable for room-temperature thermal therapy and can provide heat to the body in cold environments, that presenting a promising candidate for wearable personal thermal management.

Study on Thermophysical Properties and Phase Change Regulation Mechanism of Optically-Controlled Phase Change Materials: Synthesis, Crystal Structure and Molecular Dynamics

Optically-controlled phase change materials, which are prepared by introducing molecular photoswitches into traditional phase change materials (PCMs), can convert and store solar energy into photochemical enthalpy and phase change enthalpy. However, the thermophysical properties of optically controlled PCMs, which are crucial in the practical, are rarely paid attention to. 4-(phenyldiazenyl)phenyl decanoate (Azo-A-10) is experimentally prepared as an optically-controlled PCMs, whose energy storage density is 210.0 kJ·kg-1, and the trans single crystal structure is obtained. The density, phase transition temperature, thermal conductivity, and other parameters in trans state are measured experimentally. Furthermore, a microscopic model of Azo-A-10 is established, and the thermophysical properties are analyzed based on molecular dynamics. The results show that the microstructure parameter (order parameters) and thermophysical properties (density, radial distribution function, self-diffusion coefficient, phase change temperature, and thermal conductivity) of partially or completely isomerized Azo-A-10, which are challenging to observe in experiments, can be predicted by molecular dynamics simulation. The optically-controlled phase change mechanism can be clarified according to the differences in microstructure. The optically-controlled switchability of thermophysical properties of an optically-controlled PCM is analyzed. This study provides ideas for the improvement, development, and application of optically-controlled PCMs in the future.

Emerging solid-state cycloaddition chemistry for molecular solar thermal energy storage

Recently discovered designs of solid-state molecular solar thermal energy storage systems are illustrated, including alkenes, imines, and anthracenes that undergo reversible [2 + 2] and [4 + 4] photocycloadditions for photon energy storage and release. The energy storage densities of various molecular designs, from 6 kJ mol-1 to 146 kJ mol-1 (or up to 318 J g-1), are compared and summarized, along with effective strategies for engineering their crystal packing structures that facilitate solid-state reactions. Many promising molecular scaffolds introduced here highlight the potential for achieving successful solid-state solar energy storage, guiding further discoveries and the development of new molecular systems for applications in solid-state solar thermal batteries.

Photoisomerization of two 2-hydroxy-5-arylazobenzaldehydes in solvents of different polarities

Two azo dyes 2-hydroxy-5-(4-nitrophenylazo)benzaldehyde and 2-hydroxy-5-(4-chlorophenylazo)benzaldehyde dissolved in carbon tetrachloride, hexane, acetone and acetonitrile were irradiated with 365 nm UV light, and processes, occurring in them, were studied by NMR and UV-vis spectroscopy. It was established that reversible trans/cis photoisomerization of the molecules occurs in the non-polar solvents and is not observed in the polar solvents. 2D NOESY NMR spectroscopy was used to identify isomers of the azo compounds. Based on the chemical shifts of the signals, it was established that these compounds are in the trans-form before UV irradiation. Spectra of the azo dyes before and after UV irradiation allowed assignment of the chemical shifts of the cis-isomers. In polar solvents these compounds undergo a hypochromic effect under heating or irradiation with UV light. Both compounds exhibit solvatochromism. The shifts in NMR signals caused by photoisomerization of the molecules were compared with the shifts in the NMR signals of other azo compounds such as Disperse Orange 3, Disperse Red 1 and azobenzene.

Spatiotemporal Utilization of Latent Heat in Erythritol-based Phase Change Materials as Solar Thermal Fuels

Solar thermal fuels (STFs) have been particularly concerned as sustainable future energy due to their impressive ability to store solar energy in chemical bonds and controllably release thermal energy. However, currently studied STFs mainly focus on molecule-based materials with high photochemical activity, toxicity, and compromised features, which greatly restricts their applications in practical scenarios of solar energy utilization. Herein, we present a novel erythritol-based composite phase change material (PCM) as a new type of STFs with an outstanding capability to store solar energy as latent heat in its stable supercooling state and release thermal energy as needed. This composite PCM with stored thermal energy can be maintained stably at room temperature and subsequently release latent heat as high as 224.9 J/g during the crystallization process triggered by thermal stimuli. Remarkably, solar energy can be converted into latent heat stored in the composite PCM over months. Through mechanical stimulations, the released latent heat can increase the temperature of the composite up to 91 °C. This work presents a new concept of using spatiotemporal storage and release of latent heat in PCMs for solar energy utilization, making it a potential candidate as STFs for developing future clean energy techniques.

Manipulation of photoresponsive liquid-crystalline polymers and their applications: from nanoscale to macroscale

We summarize the molecular design of photoresponsive liquid-crystalline polymers, manipulation at multiple scales and various applications based on their intrinsic properties, providing an opportunity for future development in this field.

Visible light activated dendrimers for solar thermal energy storage and release below 0 °C

Molecular solar thermal (MOST) fuels offer a closed-cycle and renewable energy storage strategy that can harvest photons within the chemical conformations and release heat on demand through reversible isomerization of molecular photoswitches.