Novel Reversible Humidity‐Responsive Light Transmission Hybrid Thin‐Film Material Based on a Dispersive Porous Structure with Embedded Hygroscopic and Deliquescent Substances

Abstract

The article describes a new concept of an optical hybrid thin-film material that exhibits reversible humidity-driven light transmittance (scattering) properties. The film consists of a dispersive porous structure, with embedded hygroscopic and deliquescent compounds, that is able to scavenge water molecules from humid air to fill up the pores and become transparent to the incident light. Upon exposure to dry air, water is released from the structure and the material recovers its original light scattering properties. The developed thin films can change their transparency when exposed to air with different relative humidity (RH), adjusting the light throughput. This material can, therefore, be used to design new optical switching systems, having the advantage that they do not require liquid crystal, transparent conductive glass substrates, or complex layer-by-layer architectures for operation. In this work, a thin film was prepared by the sol-gel technique using calcium chloride as deliquescent substance embedded in a hybrid silica-titania matrix. At dry air, the thin films show a highly dispersive state, with a light transmittance T = 0.06, while at 51% RH the film exhibits a transparent state with a transmittance T =0.67 (measured at 633 nm).

Fast Dual-Stimuli-Responsive Dynamic Surface Wrinkles with High Bistability for Smart Windows and Rewritable Optical Displays

“…Upon moisturizing, the transmittance of the film in the whole visible region increases quickly from initially 10 to 90% in a short moisturizing time of ∼0.7 s (Figure b,c). The moisture-responsive time of the current wrinkling film is faster than that of the previously reported surface wrinkles (generally over 5 s), , promoting the applications in fast-responsive areas. For the reversible formation process of surface wrinkles, the dewrinkling film was first remained at 70% RH for 10 min.…”

“…Stimuli-responsive optical materials (SROMs) that can reversibly change color or transparency have aroused great interest because of their promising applications in optoelectronics, optical displays, sensors, security features, and smart windows. − Despite many efforts made in the development of SROMs triggered by light, − temperature, electric stimulus, , mechanical force, − solvent, , etc., most of the developed SROMs only respond to a single stimulus. Recently, SROMs that can respond to multiple external stimuli have been highly desired to dramatically enhance their versatility and capacity in applications. − However, the design of new SROMs that can respond to dual external stimuli remains a great challenge.…”

Application of New Energy Thermochromic Composite Thermosensitive Materials of Smart Windows in Recent Years

“…The thickness effect of “thin” hydrogels with thickness less than 100 μm was further studied. When the thickness increases from 26 μm to 78 μm and the temperature decreases from 40 °C to 20 °C [ 32 ], the water absorption strength at 1930 nm and 1430 nm increases significantly ( Figure 3 a). It can be seen from Table 1 that the T lum(20 °C) of the three samples remained unchanged [ 7 ], while the T lum(40 °C) decreased monotonically from 80% (26 μm) to 20% (78 μm) [ 33 ].…”

Multi‐stimuli‐responsive and Multi‐functional Smart Windows

“…Optical changes have been also achieved as a result of humidity‐induced conformational changes of cellulose crystals in the hydroscopic matrix [159–161] and wrinkling‐stretching switching of a multilayer polymer composite films [162,163] . A hybrid film material with porous structure containing hygroscopic and deliquescent materials was also suggested as a humidity‐sensitive smart window material [164] . One study proposed that hydrogels composed of non‐stoichiometric zinc can switch between the hydrated (i. e., by absorbing water from the atmosphere) and dehydrated states, thereby altering their optical characteristics [165] …”

“…[162,163] A hybrid film material with porous structure containing hygroscopic and deliquescent materials was also suggested as a humiditysensitive smart window material. [164] One study proposed that hydrogels composed of non-stoichiometric zinc can switch [156] Copyright 2018, American Chemical Society. (c) A schematic illustrating the working principle of a hydrochromic smart window based on Au nanoparticle arrays with a DNA spacer.…”