Dynamic Refractive Index‐Matching for Adaptive Thermoresponsive Smart Windows

Abstract

stimuli, such as electricity (electroresponsive), heat (thermoresponsive), and strain (mechanoresponsive), are being intensively investigated for energy applications and intelligent optical modulation. [1][2][3][4][5][6][7] In this context, thermoresponsive SWs (TRSWs) with self-adaptiveness, external energy consumption-free nature, as well as maximum use of daylight have attracted considerable interest. [8][9][10] Common strategies to construct thermoresponsive SWs are using the thermally induced phase transition accompanied by a sharp change in the optical properties at a welldefined critical temperature (T c ). [8,11] For example, vanadium dioxide (VO 2 ) undergoes a reversible metal-semiconductor phase transition at 68 °C, achieving the desired optical transmittance reduction, especially in the IR spectral range. [9,[12][13][14][15] Similarly, hydrogels, [10,[16][17][18][19][20] halide perovskites, [21][22][23] liquid crystals, [24][25][26] and ionic liquids, [27,28] achieve light modulation in response to temperature change by means of different reversible transitions, e.g., hydrophilic-hydrophobic, crystal structure and configuration transition, etc.However, common challenges with phase transition-based TRSWs, such as a fixed T c , matrix environment dependence, and the materials' unfavorable physicochemical characteristics, continue to impede the rapid development and popularity of TRSWs. For example, the high T c of 68 °C in VO 2 and even higher of 100 °C in certain perovskites render these materials less useful for energy-efficient building applications that require response near room temperature. [29][30][31] Moreover, the occurrence of some phase transitions relies on moisture or even a liquid matrix environment (e.g., the orientation change in liquid crystals, the recrystallization in some perovskites, and the hydrophilic-hydrophobic transition of the hydrogel), so that vigorous encapsulation is necessary to maintain the stability of TRSWs, increasing the complexity and cost of manufacturing. [10,32,33] Meanwhile, inherent physicochemical properties of these phase-transition materials might bring adverse effects to the SWs: the low transmittance in VO 2 -based TRSW weakens its ability to transmit sunlight and brings poor aesthetic effect; [9] the inherent water-swollen structure and fragile mechanical strength of hydrogels raise concerns over the durability of the TRSWs. [10] Critically, all reported phase-transition materials like VO 2 , Poly(N-isopropyl acrylamide), and lead Thermoresponsive smart windows (TRSWs) take great advantages in energyefficient buildings and on-demand devices owing to their self-adaptiveness and external energy consumption-free nature. Currently used TRSWs largely rely on thermal-induced phase transitions in single-material systems, however, the intrinsic characteristics of which may not be suited for practical window utilization, such as poor luminous transparency and fixed critical temperature (T c ). Herein, an adaptive TRSW based on dynamic refractive index (RI) matchin...

A thermoresponsive hydrogel with a wide‐range tunable phase transition temperature triggered by small molecules

“…36 And more Ac contents made it harder to form hydrogen bond between PMAAm, thus reducing the UCST. Compared to the reported works, 8,14,18,20,[37][38][39][40][41][42][43][44] our hydrogels exhibit an outstanding performance in the phase transition temperature range and temperature hysteresis (Figure 2b). It is noteworthy that above UCST, the transmittance of all samples exceeded 90%, while below UCST, the transmittance was below 0.5% and the transmittance curves showed narrow hysteresis which was beneficial for light management applications.…”

Determining the Local Refractive Index of Single Particles by Optical Imaging Technique

“…The image obtained from scanning electron microscopy in Figure A reveals the symmetrical morphology and diameter of single SiO 2 MP, and the corresponding refractive index determination of the same particle is shown in Figures B and C. The light scattering property of individual particles can be probed in a set of immersion media with refractive indices approaching that of the particles. , The liquid mixtures of 1-bromonaphthalene (1BrN), N , N -dimethylformamide (DMF) and deionized water (DIW) with different proportions are found to be the suitable immersion media, which are defined as RI standard solutions. The accurate RIs of standard solutions were varied from 1.3327 to 1.6563, as measured by a commercial Abbe refractometer.…”

“…Refractive index (RI) is an indispensable optical property revealing the inner links between light scattering and individual characteristics of single entities, such as morphology and chemical composition. − Determination of the refractive index can be applied to predict and identify different components of a single entity, and also has strategic significance in material and environmental sciences. − To date, RI measurement has been achieved by a variety of methods including standard refractometry, − laser diffractometry, , Mie resonance spectroscopy, − and index matching techniques. − These traditional ensemble strategies provide high sensitivity in studying averaged RI properties in bulk liquid systems and suspended droplets.…”

Recent advances in solar infrared light regulating smart windows based on organic materials

“…Luminous transmittance was around 90% at 30°C, but 25% at the extremes (Figure 10). [54] In this PDMS device, the window showed a wavelength dependent response with red light shielded at higher temperatures, but there is no information provided for wavelengths >800 nm. While the PDMS devices could be made flexible, the presence of scattering phases at both lower and higher temperatures may preclude their practical use.…”