New focus of the cloud point/Krafft point of nonionic/cationic surfactants as thermochromic materials for smart windows

A nonionic poly(oxyethylene) monoalkyl ether (C12(EO)6) and a cationic hexadecylpyridinium bromide (HPB) were used in featuring warm/cool transparency transition switchability, depending on the decrease in the hydration of the EO-headgroup...

Thermochromic and opacity behaviors in vanadium dioxide nanofilms: a theoretical study

Vanadium dioxide nanofilms are one of the most essential materials in electronic applications like smart windows. Therefore, studying and understanding the optical properties of such films is crucial to modifying the parameters that control these properties. To this end, this work focuses on investigating the opacity as a function of the energy directed at the nanofilms with different thicknesses (1 – 100) nm. Effective mediator theories (EMTs), which are considered as the application of Bruggeman's formalism and the Looyenga mixing rule, have been used to estimate the dielectric constant of VO2 nanofilms. The results show different opacity behaviors at different wavelength ranges (ultraviolet, visible, and infrared). The results depict that the highest opacity of the insulating phase is achieved at the ultraviolet region and it reduces for the metal phase. Besides, the results demonstrate that the opacity possesses a redshift during the changes at the three phases. Regarding the infrared region, the lowest opacity value is achieved at the insulator phase and it increases to the highest value at the metal phase. In the visible region, the opacity behavior remains similar in the three phases. It is worth noting that the lowest opacity is found for thinner nanofilm. Since both the refractive index and the extinction index are among the most essential optical constants, hence, both of them were compared with the experiment results, and an excellent agreement is achieved between them.

Efficiency definition of the deposition process of electrochromic Ni(OH)2-PVA films formed on a metal substrate from concentrated solutions

Electrochemical devices based on nickel hydroxide electrodes are used in different areas. The main ones are chemical current sources, variable transparency “smart” windows, devices for carrying out electrocatalytic reactions, sensors for determining various substances. In this regard, methods of nickel hydroxide synthesis are of great interest, especially those that allow forming nickel hydroxide directly on the surface of electrodes. One of these methods is electrochemical deposition with cathodic current polarization. The available information on nickel hydroxide synthesis from nickel solutions was considered. It was shown that the available data mainly covered information on dilute solutions from 0.01 to 0.25 mol/L Ni(NO3)2. In addition, no comparison was found in the literature for the efficiency of the cathodic formation of Ni(OH)2 at different concentrations of nickel nitrate. To eliminate the lack of information, the dependence of the current efficiency on the concentration of nickel nitrate in the electrodeposition solution was determined at a constant cathode current density of 0.625 mA/cm2. The resulting dependence decreased nonlinearly with increasing concentration. The nickel hydroxide deposit formed in this case had an X-ray amorphous structure, and it depended little on the Ni(NO3)2 concentration. In addition, the current efficiency reached zero at concentrations of 1.5 mol/L Ni(NO3)2 and higher. However, with polyvinyl alcohol in the solution and at Ni(NO3)2 concentrations of 1.5 and 2 mol/L, electrochemically and electrochromically active Ni(OH)2 films were deposited. The current efficiency calculated indirectly for 1.5 and 2 mol/L Ni(NO3)2 solutions was 3.2 and 2.3 %, respectively. Thus, it was concluded that polyvinyl alcohol affected the mechanism of nickel hydroxide electrodeposition from aqueous solutions of nickel nitrate.

Mechanoresponsive scatterers for high-contrast optical modulation

Smart chromatic materials with optical transmittances that can be modified by light scattering upon external stimuli are attracting extensive interest because of their appealing applications in smart windows, privacy protection, electronic displays, etc. However, the development of these scatterers, which are mostly activated by electric fields, is hindered by their intrinsic energy consumption, slow responses, and poor stability. Recently, mechanoresponsive scatterers based on a strain-driven reconfiguration of the surface or internal structure have emerged, featuring fast responses and a simple composition/fabrication. Because there is no energy consumption to maintain the transparency/opacity, this novel scheme for scatterers holds great promise to break the existing bottleneck. This article presents recent advances in the development of mechanoresponsive scatterers and compares different structural design strategies. The scatterers are categorized into 2D, 3D, and other types according to the dimensions of their functioning structures. The fabrication methods, mechanisms, and relationships between the structural parameters and optical modulating performances are discussed for each category. Next, the potential applications of these scatterers are outlined. Finally, the advantages and disadvantages of the mainstream 2D and 3D categories are summarized, followed by a perspective on future research directions.

Colorless-to-colorful switching of electrochromic MXene by reversible ion insertion

Electrochromic (EC) materials that change color with voltage have been widely studied for use in dynamic windows. However, colorless-to-colorful switching with high contrast ratio is generically unattainable, especially for colorless-to-black electrochromic materials with an ultrahigh contrast ratio over the entire visible region. In this work, we developed Nb1.33C MXene-based dynamic windows with colorless-to-black switching of up to 75% reversible change in transmittance from 300 to 1,500 nm. By exploring the electrochromic effects of different electrolytes through in situ optical changes and electrochemical quartz crystal microbalance (EQCM), it is found that electrochromic behavior is greatly influenced by the extent of reversible Li+ insertion/deinsertion between the two-dimensional Nb1.33C MXene nanosheets. In addition, a colorless-to-black EC device based on Nb1.33C with an overall integrated contrast ratio over 80% was successfully constructed by a solution-processable spin coating method. This work enables a simple route to fabricate MXene-based high-performance electrochromic smart windows, which is important for further expanding the application of MXenes to optoelectronic and photonic applications.