Tough asymmetric thermochromic ionogels via dynamic in situ phase separation for dual-modal smart optical switching

Domain: biology
Published: 2026-03-18
Editorial outcome: major_revision

Abstract
Despite significant advances in thermochromic materials (TCMs) for smart optical switching, achieving simultaneous optimization of optical switching, mechanical robustness, and environmental tolerance remains a critical challenge for their real-world implementation. Herein, we present tough asymmetric thermochromic ionogels (ATIs) fabricated via dynamic in situ phase separation. The ATIs integrate a thermoresponsive light-scattering layer (LCST: 28°C to 41°C) and a mechanically reinforced supporting layer through sequential free-radical polymerization. The resulting material exhibits high transparency (>85% at 20°C), ultralow-temperature resistance (transparent at −70°C, even at −196°C), and exceptional toughness (tensile strength >5 MPa, toughness >17 MJ m-3). Leveraging hydrophobic ionic liquid as solvent, the ATIs achieve reversible optical switching (transmittance <10% at 40°C) without encapsulation, with autonomous adhesion (>400 N m-1 peel strength on glass). Applied to smart cooling windows, ATIs reduce solar radiation by 56.8% while enabling aesthetic customization. Combined with indirect/direct Joule heating technology, ATIs enable active optical switching and even dynamic projection display, offering a scalable platform for all-weather adaptive optical systems.

Introduction
The growing demand for adaptive intelligent systems—from advanced sensing, soft robotics to energy-efficient buildings—drives the development of smart materials towards emulating biological “sense-feedback-actuate” mechanisms for self-sensing and active regulation1. Among these, stimulus-responsive materials serve as foundational building blocks2, dynamically altering optical, mechanical, electric, or morphological properties in response to external triggers including light, pH, electric fields3, 4, humidity, and temperature5, 6, 7. Thermochromic materials (TCMs), which modulate transparency/color via temperature changes8, show promise for applications such as visual sensing 9, intelligent actuators10, and information encryption11, particularly for smart optical switching—a key technology in next-generation adaptive windows12, displays, and anti-counterfeiting systems13.

Existing TCMs—including inorganic compounds (VO2, WO3, halide perovskites)14, 15, 16, organic liquid crystals (cholesteric phase)17, and nanocomposites (metal nanofillers, quantum dots)18 — enable reversible light transmission modulation but suffer from high transition temperatures (>60°C), intrinsic rigidity, and complex fabrication processes, which limit their ability to meet emerging requirements for tunable transition temperature ranges, mechanical toughness, and on-demand responsiveness19. Thermochromic polymers (TCPs) offer a promising solution, bridging attributes of organic/inorganic materials20. TCPs are typically realized by incorporating thermosensitive polymers (e.g., poly(N-isopropylacrylamide) (PNIPAM), hydroxypropyl cellulose (HPC), poly(propylene oxide) (PPO), and polyurethane (PU) derivatives) into liquid matrices to form gels/blends21, 22. Like inorganic TCMs, TCPs exhibit rapid phase transitions between transparent and opaque states at lower (LCST) or upper critical solution temperatures (UCST), providing exceptional processability, tunable mechanics, and functional compatibility for advanced thermal-responsive devices. Yet, conventional TCPs like PNIPAM hydrogels—known for their favorable LCST (28-35°C)23—suffer from inherent drawbacks: low crosslinking and high water content yield weak tensile strength (<10 kPa), poor water retention, and sub-0°C failure24, necessitating rigid encapsulation that sacrifices flexibility and reprocessability in practical implementation. Although large-scale production is feasible25, post-polymerization purification involving chain transfer remains a critical barrier to widespread adoption. Efforts to modulate LCST and enhance performance (e.g., random copolymerization, interpenetrating networks, additive doping) have yielded only limited improvements26, 27. Ionic liquids (ILs) present a promising avenue for high-stability TCPs due to their polymer compatibility, thermal tolerance, and non-volatility. In recent years, Yan and colleagues have systematically optimized the supramolecular structures of IL-based functional materials, leading to the development of a series of high-strength and high-toughness ionogels. Remarkably, the mechanical performance of these ionogels surpasses that of most metals and alloys28, 29, providing a solid foundation for fabricating mechanically robust ILs-based TCPs. Comprehensive reviews by Men et al. summarize the progress in LCST- and UCST-type thermosensitive ionogels, highlighting their role in addressing the limitations of conventional hydrogels and organogels30, 31. Owing to the low glass transition temperatures and tunable supramolecular characteristics of ILs32, TCP-based ionogels are expected to maintain stable thermoresponsive behavior under complex and variable temperature conditions. For instance, IL-based thermochromic ionogels fabricated using modified PU/polyvinylidene fluoride (PVDF) matrices exhibit a tunable LCST between 20 to 40 °C, combined with robust mechanical properties and improved thermal stability33. However, challenges such as complex synthesis routes, stringent processing conditions, and high production costs currently hinder their large-scale commercialization. Therefore, facile fabrication strategies for high-performance TACPs remain a significant challenge, necessitating deeper understanding of the dynamic phase separation mechanisms governing IL-polymer network interactions—a fundamental prerequisite for optimizing ionogel-based TCPs and advancing next-generation smart thermal-responsive systems.

To achieve a balance between smart responsiveness and mechanical toughness, this study develops an asymmetric ionogel that merges thermochromism with high mechanical strength. Through sequential free-radical polymerization, we implement a synergistic strategy combining thermosensitive dynamic phase separation (reversible) and in situ phase separation (irreversible) to covalently conjugate a thermochromic ionogel layer with a high-strength ionogel layer. The resulting material achieves an optimal LCST of 34°C, exceptionally low temperature stability (maintaining transparency down to −70°C and even −196°C), and robust mechanical properties (tensile strength >5 MPa, elongation >800%, toughness >17 MJ·m-3). Hydrophobic monomers/ILs and abundant polar groups endow the ionogel with superior hydrophobicity (water contact angle >135°) and intrinsic self-adhesion (90° peel strength >400 N m-1), enabling direct adhesion to working panels without encapsulation and bonding while maintaining reliable functionality under harsh environmental conditions (hot, cold, dry, and rainy). Beyond enabling passive optical modulation for smart windows, this multifunctional ionogel serves as an active optical switching platform, facilitating local projection displays via indirect heating and acting as large-area projection screens under direct Joule heating.

Results
Design strategy of tough asymmetric thermochromic ionogels
This asymmetric thermochromic ionogel (ATIs) with exceptional mechanical robustness integrates: i) a thermoresponsive light-scattering ionogel layer engineered via thermosensitive dynamic phase separation (a temperature-mediated reversible process), and ii) a high-strength ionogel supporting layer fabricated by in situ phase separation (irreversible process)—the two covalently bonded at the interface through sequential photopolymerization (Fig. 1a, Supplementary Fig. 1). The resulting ATIs exhibit not only sensitive thermochromism and high mechanical strength but also remarkable freeze-resistance and tunable hydrophobicity, enabling reliable operation under all-weather conditions. Specifically, the dynamic phase-separated homopolymer (light-scattering ionogel layer, denoted ATI-B) was formed via free radical polymerization of n-butyl acrylate (BA) in the hydrophobic IL 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][TFSI]) (Fig. 1b). Concurrently, the high-strength layer consists of in situ phase-separated P(BA-co-NIPAM) copolymers (denoted ATI-BN) synthesized from BA and NIPAM monomers. Both layers share the same IL solvent, photoinitiator, and crosslinker (Supplementary Fig. 2). The resulting ATIs exhibit high optical transparency and mechanical integrity at room temperature (below LCST) (Supplementary Fig. 3), combining flexibility and impact resistance — properties unattainable in conventional high-strength transparent materials like glass—while demonstrating observable thermochromic performance (Fig. 1c).

Environmental tolerance, especially to high and low temperatures, is an important evaluation index for TCPs34. The ATI maintains high transmittance exceeding 80% at room temperature (below LCST) (Supplementary Fig. 4), which is essential for real-world implementations. Upon exposure to temperatures above the LCST—whether through ambient heating or intrinsic Joule heating—it exhibits rapid thermochromic behavior, with transmittance dropping to below 10% at 40°C (Fig. 1d-i, Supplementary Fig. 5, Movie 1). Owing to the IL solvent matrix, the ATI retains high optical transparency even under low temperature conditions at −70°C (Fig. 1d-ii), and demonstrates negligible visible-light scattering at liquid nitrogen temperatures (−196°C) (Supplementary Movie 2), confirming exceptional anti-frost capability. A comprehensive performance comparison between ATIs and reported TCMs was conducted, evaluating transparency, low temperature resistance, self-supporting (without additional encapsulation), stretchability, solar modulation capability, and self-adhesion (Fig. 1e) 21, 35, 36, 37, 38. Notably, ATIs demonstrate superior low-temperature stability and mechanical strength while maintaining their solar modulation capability. For practical applications, the study critically validates ATIs' optical modulation efficacy for smart cooling windows. Beyond this, ATIs are further demonstrated as an active optical switching platform—enabling localized projection displays via indirect heating and global projection screens through direct Joule heating (Fig. 1f, Supplementary Fig. 6). This work not only expands the application scope of ATIs in energy-efficient smart windows but also establishes a preliminary reference paradigm for next-generation display systems based on thermally responsive optical switches.

Asymmetric structure achieved via dynamic in situ phase separation
Sequential free radical polymerization was employed in the preparation of ATIs. Specifically, ATI-B was prepared by one-step photopolymerization, while ATI-BN was in situ photocured based on the former, resulting in the asymmetric Janus structure of ATIs (Supplementary Fig. 7). The hydrophobic monomer BA demonstrates good compatibility with the solvent [Emim][TFSI], forming a homogeneous TCP system through ion-dipole interactions. In contrast, NIPAM is less compatible in imidazolium-based ILs and requires the formation of ATI-BN precursors with assisted solvation of BA (Supplementary Fig. 8 and 9). The ion-dipole interaction sites between the monomer and the solvent in ionogels are given by electrostatic potential (ESP) simulations (Fig. 2a). Fourier transform infrared spectroscopy (FTIR) shows that both homopolymer PBA and copolymer P(BA-co-NIPAM) form ion-dipole interactions with the solvent [Emim][TFSI] to stabilize the intrinsic gel state (Fig. 2b, Supplementary Fig. 10, Note 1). The ATI-BN at 3380 cm-1 attributed to the -N-H stretching vibration confirms the formation of intramolecular hydrogen bonds during polymerization of NIPAM due to its high incompatibility with the solvent (Supplementary Fig. 11). The cross-section scanning electron microscopy (SEM) image of the homopolymer ATI-B exhibits a smooth homogeneous morphology; whereas ATI-BN shows a rough morphology with peak-like protrusions (Fig. 2c). The reason for this is that the low compatibility of PNIPAM within [Emim][TFSI] causes the formation of a bicontinuous network of alternating polymer-rich and solvent-rich phases within the ionogel (Supplementary Fig. 12)39. Meanwhile, the energy dispersive spectroscopy (EDS) results confirm the asymmetric distribution of the elements in ATI (Supplementary Fig. 13).

The in situ and dynamic phase separation in ATIs were analyzed at the microscopic level using small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) techniques. The SAXS results show that ATI-B is highly homogeneous on the 1-50 nm scale, and the absence of scattering rings in the 2D SAXS spectrum proves that there is almost no internal phase separation at room temperature (RT) (Fig. 2d-i). In contrast, ATI-BN exhibits more pronounced scattering rings, and its SAXS spectrum displays distinct step-like peaks. Through computational fitting, its phase separation size was determined to be approximately 7.3 nm (Supplementary Fig. 14)40. This size is far below the visible light wavelength range, so ATI-BN remains highly transparent. The thermally induced transparent-to-opaque transition of ionogels is solely related to ATI-B. The variable-temperature WAXS results of ATI-B reveal that the characteristic dimensions of its scattering peaks shift from 4.5 Å and 7.7 Å to 4.6 Å and 7.2 Å (Fig. 2d-ii, Supplementary Fig. 15 and Table 1). This change can be attributed to the increase in polymer chain spacing due to thermal expansion effects, coupled with the entropy-driven contraction of [Emim]+–[TFSI]– ion clusters41. To further characterize the asymmetric structure of ATI, spatial Raman spectroscopy was employed. The intensity of the absorption bands of ATI-BN at 1160 cm-1, 1267 cm-1, and 1550 cm-1 is significantly stronger than that of ATI-B, which shows the differences in their components (Fig. 2e i-ii). The close and seamless connection between the two phases in the asymmetric structure of ATI can be visualized by 2D Raman mapping of the cross section (Fig. 2e-iii)42. Physical bilayer gels prepared by direct electrostatic adhesion are characterized by weak electrostatic interactions between the interfaces of two layers, and interfacial fragmentation or peeling occurs under slight external peeling forces43. ATI, on the other hand, exhibits distinct interfacial toughness, which may be attributed to in situ layer-by-layer photopolymerization that allows physical entanglement and chemical cross-linking between polymer networks at the interface between ATI-BN and ATI-BN to achieve strong interfacial bonding (Fig. 2f, Supplementary Fig. 16)44, 45. To validate the impact of the asymmetric structure on the viscoelastic behavior of the ionogels, a comprehensive rheological analysis of ATI was performed. The results show that the storage modulus (G') of ATI is larger than the loss modulus (G'') in a wide range of amplitude and frequency sweepings as well as temperature ramping (Fig. 2g). The above results indicate that the polymer network inside the ATI exhibits notable dynamic reversibility under complex external forces, and exhibits an intrinsic gel state over a wide range of operating temperatures, and the asymmetric two-phase interface does not fail due to the occurrence of fracture, which is a precursor to microscale phase separation.

Reversible thermochromic response triggered by dynamic phase separation
The thermochromic behavior of ionogels originates from dynamic phase separation within ATI-B. At low temperatures, the IL remains uniformly dispersed in the PBA matrix via ion-dipole interactions (primarily cations and the -C=O group in ester moieties), maintaining a homogeneous single phase (Fig. 3a)46. With increasing temperature above the LCST, uniformly distributed anions and cations aggregate around the polymer network47, forming distinct liquid domains that result in a two-phase system (Fig. 3b, Supplementary Fig. 17 and Movie 3). When dynamic phase separation occurs, a large number of “island-like” IL domains inside ATI-B scatter light, resulting in an opaque state (Fig. 3c). The transmittance of ATI-B in the visible light range decreases from more than 85% to less than 10% when the temperature increases from 20°C to 45°C, and haze within the visible light spectrum increases dramatically from below 10% to around 94% (Supplementary Fig. 18 and 19). In contrast, ATI-BN exhibits thermal stability within the same temperature range (Supplementary Fig. 20 and 21). The LCST of ATI-B was analyzed by the differential scanning calorimetry (DSC) technique, and a small enthalpy change was found around 34°C, indicating that the material undergoes a phase transition (Supplementary Fig. 22 and Note 2). The lower ΔH implies that the ionogel has considerable dimensional stability, since a large enthalpy change always implies a large-scale phase separation that occurs in parallel with the liquid efflux48. By varying the ratio of the polymer to the IL, the LCST of ATI-B can be tailored between 28°C and 41°C to meet specific requirements (Supplementary Fig. 23 and Table 2). Except for LCST, the formulation adjustments to the ATI-B will not significantly affect the mechanical properties or low-temperature transparency of ATIs (Supplementary Fig. 24 and Table 3).

For LCST-type TCPs, the sensitivity and long-term resistance to temperature changes directly affect their performance in practical application49. ATI exhibits rapid response and significant optical changes above and below LCST (Fig. 3d). It is noteworthy that, owing to the intrinsic nonvolatile nature and amorphous structure of the ILs, along with the suppression of IL crystallization through ion–dipole interactions50, ATI remains transparent without undergoing transparency transition caused by ice crystal formation, even after prolonged exposure to a low temperature of −70 °C (Supplementary Fig. 25, Note 3, and Movie 4). Even after prolonged exposure to low temperatures, ATI undergoes opacity switching in a short period when returning to temperatures above LCST (Supplementary Fig. 26). In contrast, the growth of ice crystals in PNIPAM hydrogels leads to the destruction of the integrity of the polymer network after multiple freeze-thaw cycles (Supplementary Fig. 27). In 100 cycles of testing from −45°C to 40°C, the transmittance of ATI to 550 nm wavelength light does not undergo significant degradation (Supplementary Fig. 28). Moreover, ATI does not experience significant dimensional shrinkage or functional failure even when subjected to long-term operating conditions above LCST (Supplementary Fig. 29). The above advantages enable ATI to effectively circumvent the limitations of low-temperature freezing and high-temperature water loss faced by hydrogel-based TCPs. The stability of ATI was further evaluated under a series of complex accelerated aging protocols, including cyclic high-temperature/humidity conditions, salt spray tests, and UVA/UVB radiation. The experimental results confirm its robustness (Supplementary Fig. 30 and 31). It is noteworthy that while intense UV exposure leads to some photo-induced yellowing, this phenomenon is temporary. The discoloration significantly recedes after storage in ambient air, and the thermochromic functionality and low-temperature tolerance remain almost unaffected (Supplementary Fig. 32).

The microscopic interactions in thermosensitive dynamic phase separation were analyzed by in situ characterization and computational chemistry techniques. The temperature-dependent FTIR results (Fig. 3e) indicate a redshift of the characteristic peaks of ATI-B (from 1052 to 1050 cm-1 and 1348 to 1346 cm-1), suggesting a weakening of the ion–dipole interaction between the IL and polymer51. This observation is strongly corroborated by density functional theory (DFT) calculation, which shows a significant decrease in the PBA-ion interaction energy per unit area (Supplementary Fig. 33). Likewise, the temperature-dependent Raman spectroscopy (TDRS) reveals a shift of the v(-N-S) peak (Fig. 3f, Supplementary Fig. 34) to lower wavenumbers, implying enhanced Coulomb interaction between [Emim]+ and [TFSI]−52. This phenomenon is perfectly reflected in the molecular dynamics (MD) simulation, where the [Emim]+-[TFSI]− interaction energy increases with rising temperature and becomes dominant (Fig. 3g). Furthermore, two-dimensional correlation infrared spectroscopy (2DCOS FTIR) analysis suggests that the phase separation is triggered by the preferential dissociation of anions from the polymer, followed by cation re-association (Supplementary Fig. 35, Table 4 and Note 4). Taken together, these tightly coupled experimental and theoretical results provide compelling evidence for an entropy-driven dynamic phase separation mechanism above the LCST, wherein enhanced Coulomb forces promote the aggregation of solvent molecules detached from the polymer (Supplementary Note 5)53.

Tough mechanical properties enabled by in situ phase separation
The in-situ phase-separated structure of ATI-BN features a bicontinuous network comprising a polymer-rich phase (dominated by rigid NIPANM segments with strong intermolecular hydrogen bonding) and a solvent-rich phase (dominated by elastic, gel-like BA segments). This structure enables a interphase load-transfer mechanism and energy-dissipation pathway54, ultimately toughening the ionogel (Supplementary Fig. 36). Under stress, the rigid polymer-rich phase preferentially dissipates energy, while the solvent-rich phase acts as a “hidden length” that accommodates stress through large deformation. The toughness, Young's modulus, and elongation at break of ATI increase by 2500%, 3390%, and 110%, respectively, compared to the homogeneous pure PBA ionogel (Fig. 4a and 4b, Supplementary Fig. 37). However, the overall mechanical properties of ATI are relatively weak compared with those of pure P(BA-co-NIPAM) ionogel (Supplementary Fig. 38), which is consistent with the toughening law of in situ phase separation strategy55. When compared with pure PBA ionogel and PNIPAM hydrogel, ATI demonstrates significant advantages in terms of practical mechanical performance (Fig. 4c and 4d, Supplementary Fig. 39 and Movie 5). The interfacial strength between ATI-B and ATI-BN was tested by lap-shear experiments, and the interfacial shear strength of ATI reaches 600 kPa, which is 110 times higher than that of the physical bilayer ionogel; and the strong interfacial strength of ATI shows a significant advantage even when compared with commercial adhesive tapes (Fig. 4e, Supplementary Fig. 40). We simulate the interfacial peeling process in physical bilayer ionogel and ATI using finite element analysis (FEA). The results show that under pulling of vertically upward force, ATI exhibits higher stress concentration than the bilayer ionogel, and the near-perpendicular angle between upper and lower layer indicates that the interfacial bonding of ATI is significantly stronger (Fig. 4f). After puncture resistance testing, ATI maintains structural integrity without observable morphological damage or interfacial failure, demonstrating high reliability in complex environments (Fig. 4g). During cyclic compression tests with increasing strain, ATI consistently displays complete hysteresis loops in stress-strain curves and retains structural integrity throughout (Fig. 4h, i). Performing more uninterrupted compression cycles (70% compression) on ATI, it is found that, except for the first cycle, the hysteresis loops of all cycles almost overlap, indicating that the elastic polymer network in ATI has a highly reversible deformation capacity and fatigue resistance (Fig. 4h-ii)56. Robust mechanical properties and a suitable LCST range are important indicators for evaluating the performance of TCPs in practical applications, especially in smart windows and flexible optical displays. Comparing with the reported TCPs, ATI has significant advantages in mechanical performance (in terms of tensile strength) (Fig. 4i)57, 58, 59, 60, 61. The transition temperature (τc) is also in the range of the average high temperatures (30-40°C) of the human living environment, ensuring the thermal activation under ambient conditions. Notably, the property of not requiring additional encapsulation allows ATI to be directly applied to non-planar objects and stably maintain the thermochromic function (Fig. 4j). The realization of the above advantages is expected to bridge the gap between rigid TCP devices and flexible smart systems.

Smart cooling window enabled by passive thermochromic optical switching
Passive thermochromic smart windows dynamically adjust UV-Vis-NIR light transmittance in response to temperature changes (Fig. 5a), thereby enabling building energy savings62. Unlike conventional TCP-based smart windows requiring glass encapsulation, ATI smart windows are fabricated by direct application of ionogel on to window surfaces. Rich hydrophobic groups on ATI (e.g., butyl chains from BA and perfluoroalkyl chains from IL) impart intrinsic hydrophobicity63, achieving water contact angles up to 135 ± 1°—significantly higher than tempered glass and PNIPAM hydrogel (Fig. 5b-i, Supplementary Fig. 41). The surface adhesion work of ATI-BN is calculated to be 20.8 mN m-1, which is about 510% lower compared to tempered glass, indicating that water droplets have lower sliding resistance on the ATI surface (Fig. 5b-ii). Further field tests demonstrate that water droplets easily slipped off the ATI surface, and the surface could be easily cleaned with water directly (Fig. 5b-iii, Supplementary Movie 6). On the other hand, the abundance of polar groups on the surface provides ATI with high adhesion ability, enabling it to autonomously adhere to the surfaces of various transparent building materials (Fig. 5c), including tempered glass, polymethylmethacrylate (PMMA), polyvinyl chloride (PVC), and polycarbonate (PC). In particular, 90° peel strength of ATI on glass is greater than 400 N m-1 (Supplementary Fig. 42). The above advantages ensure the convenience and practicality of ATI when used as a smart window.

For smart optical modulation and cooling performance, the transmittance of ATI to UV-Vis-NIR light waves is negatively correlated with temperature (Fig. 5d). At 20°C, ATI is highly transparent with a solar transmittance (Tsol) of 75.7%. When warmed up to 45°C, ATI undergoes a transparency transition and Tsol decreases to 18.9%, showing a notable ΔTsol of 56.8%. Similarly, the luminous transmittance (Tlum) of ATI shows a ΔTlum of up to 78.3% (Supplementary Table 5 and Note 6). Compared to the recently reported adjustable phase-change materials for energy-saving smart windows, ATI still demonstrates competitive solar modulation capabilities (Supplementary Fig. 43). Under simulated sunlight (xenon lamp), the model house equipped with ATI smart window exhibits a slower heating rate compared to the tempered glass reference house. After heating termination, the house with the ATI window shows a slower cooling rate, demonstrating superior thermal insulation performance compared to conventional windows. (Fig. 5e). The performance of the ATI-based smart windows in regulating natural sunlight real daytime conditions was further evaluated (Fig. 5f). When the ambient temperature reaches about 40°C at midday in summer, the room temperature of the model house with air windows (semi-open system) reaches 52°C; with glass windows (fully closed system) reaches an intimidating 66°C; and with ATI smart windows (fully closed system) is only 56°C (Fig. 5g). To assess the energy-saving potential of ATI smart windows, annual energy simulations were performed using EnergyPlus on a building model equipped with ATI windows (Supplementary Fig. 44). Compared to clear windows with pure glasses, ATI smart windows deliver more significant energy savings in China's warmer urban areas, highlighting their potential for application in solar-regulated devices (Fig. 5h). For the aesthetic and personalized design of windows, ATI can be easily customized into complex window patterns or colors through simple reprocessing such as templating, cutting, dyeing, and modular splicing, without affecting its intrinsic thermally-induced transparency transition (Supplementary Fig. 45).

Active dynamic optical display enabled by indirect/direct Joule heating
The optical properties of ATI vary with ambient temperature. Leveraging the intrinsic advantages of temperature as a stimulus— ubiquitous availability, non-contact operation64, and precise controllability—establishes ATI as a promising active optical switch for temperature-controlled applications (Fig. 6a). Integrating a flexible conductive heating layer as a thermal switch, this indirect Joule heating approach enables reversible optical modulation between transparent and opaque states (Fig. 6b). By customizing the conductive heating layer with patterning, the same opaque patterns can be displayed on ATI, thus achieving the effect of dynamic localized optical display (Fig. 6c-i). Since the conductive heating layer employs a flexible graphene heating sheet driven by a direct current (DC) power supply, the ATI-based optical display device is no longer limited by a rigid plane substrate and can be applied to curved surface carriers (Fig. 6c-ii). When this localized optical display device is applied to a window, dynamic information display can be achieved. Indoor users can display information externally on the window utilizing temperature stimulation, such as an emergency distress signal (Supplementary Fig. 46). Such innovative attempts allow future smart windows to serve not only the energy efficiency of a passive cooling building, but also have the potential to be applied as a dynamic optical display.

To further demonstrate the potential application of ATI in the next generation of optical display systems, we combine the Joule heating function of ATI with its optical characteristics to realize an integrated global dynamic optical switching. This behavior leverages the inherent ionic conductivity of ionogels, enabling Joule self-heating through ionic conduction65. ATI exhibits temperature-dependent ionic conductivity, while maintaining high robustness under thermal cycling conditions (Supplementary Fig. 47). As a proof-of-concept demonstration, a high-frequency alternating current was applied to the ATI here using two Cu electrodes and an alternating current (AC) power supply (Fig. 6d). Within 15 s after applying voltage (180 V, 10 kHz), the local temperature of the ATI reaches up to 55°C and undergoes a complete transparent-to-opaque transition (Fig. 6e-i, Supplementary Movie 7). Further testing indicates that the temperatures resulting from Joule heating on the surface of ATI is positively correlated with the applied AC voltage (Supplementary Fig. 48). This global photoswitch display maintains effective heating effect and stable light scattering ability even when subjected to stretching and bending (Fig. 6e-ii). On this basis, a global dynamic light switch based on in situ Joule heating is designed and demonstrated as a kind of intelligent projection screen (Fig. 6f). ATI with reduced light transmittance acts as a natural projection screen at room temperatures above the LCST. When the ambient temperature is below the LCST of ATI, transparent-to-opaque transition can also be achieved through in situ Joule heating. Projections of classical artworks onto the opaque ATI surface maintained high color saturation and display resolution (Fig. 6g). Finally, a smart screen for localized projection by indirect Joule heating is also demonstrated, and localized weather information can be displayed on a smart window without affecting the perspective effect (Fig. 6h, Supplementary Movie 8). The above attempts not only provide innovative ideas for next-generation optical display devices, but also address the shortcomings of existing smart windows that only have a single function.

Methods
Preparation of asymmetric thermochromic ionogels
Asymmetric ionogels were prepared via a sequential UV-curing process. Firstly, 23.4 mmol of BA was ultrasonically dissolved in 5.1 mmol of [Emim][TFSI]. Irgacure 1173 (0.05 mol% relative to monomer) and the cross-linker ethylene glycol dimethacrylate (EGDMA, 0.05 mol% relative to monomer) were added to form the ATI-B precursor solution. After nitrogen purging to remove dissolved oxygen, this solution was injected into a sealed glass mold (1 mm silicone spacer) and cured under UV light (365 nm, 24 W) for 60 s. Subsequently, the mold was disassembled, and the spacer was replaced with a 2 mm one. The ATI-BN precursor solution was prepared by ultrasonically dissolving 15.6 mmol of BA and 17.6 mmol of NIPAM in 2.5 mmol of [Emim][TFSI], with Irgacure 1173 and EGDMA added at the same 0.05 mol% (relative to monomer). Following dissolved oxygen removal, this solution was injected into the mold and subjected to in situ UV-curing (365 nm, 48 W). Due to significant exothermic heat release during NIPAM radical polymerization in [Emim][TFSI], this curing step was performed in an ice-water bath.

Material characterization
FTIR (Nicolet iS 50, Thermo Fisher Scientific, USA) was used for characteristic peak measurements with a resolution of 0.4 cm-1 and a wavelength range of 4000-800 cm-1. Temperature-dependent diffuse reflectance FTIR tests were performed in the range of 25-50°C utilizing a temperature-controlled accessory. The temperature-dependent FTIR data were processed by the 2D Correlation Spectroscopy analysis v1.20 plug-in in Origin. The surface morphology of the cross sections of ATIs was observed using an optical microscope (Axio Scope A1, Zeiss, Germany) and a Field emission scanning electron microscope (FE-SEM, GeminiSEM 500, Zeiss, Germany), which was brittlely fractured using liquid nitrogen before the FE-SEM observation. Energy dispersive X-ray spectroscopy (EDS) analysis was performed simultaneously with FE-SEM. Raman spectroscopy and spatial Raman mapping of ATIs were performed using a Raman imaging microscope (InVia Qontor, Renishaw, UK). The excitation laser wavelength was 532 nm, and a spatial resolution of 2 m was used. Dynamic viscoelasticity tests were performed on ATIs using a rheometer (MCR302, Anton Paar, Austria), including amplitude sweeping tests, frequency sweeping tests, and temperature ramping tests. Small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) experiments were conducted with an Xeuss 3.0 system (Xenocs, France). X-Ray wavelength: 1.54189 Å ; detector: Eiger2R 1M; sample to detector distance: 1000 mm; WAXS experimental environment: vacuum, 20℃, 30℃, and 40℃. The lengths of the scattering vector q were 0.02 Å -1 to 0.25Å -1 for SAXS, and were 0.64 Å -1 to 3.20 Å -1 for WAXS. Perform fitting calculations on SAXS results using SASfit software (version 0.94.12) and Origin software (version 9.9.0.225). The phase separation size in ATI-BN was characterized using the Debye-Anderson-Brumberger (DAB) model. The appropriateness of this model for the determination of correlation lengths in random, non-granular two-phase systems is confirmed by its assumption of smooth interfaces, a feature consistent with the bicontinuous structure of ATI-BN. The pair correlation function γ(r) is given by Equation 1：
γ(r) = exp(-r/ξ) (1)
where r is radial distance.
The macroscopic scattering cross-section in the DBA model is given by Equation 2:
I(q) = (πΔηξ3)2 / (1+q2ξ2)2 (2)
where q is scattering vector; I(q) is scattering intensity; ξ is correlation length; Δη is scattering length density contrast.
Bragg spacing in WAXS is given by Equation 3:
d = 2π / q (3)
where d is the real-space feature distance; q is the scattering vector, defined by the Equation 4:
q = 4πsinθ / λ (4)
where θ is half-scattering angle; λ is wavelength of the incident X-rays.

Thermochromic performance and low-temperature resistance test
Thermosensitive dynamic phase separation of ATIs was observed using an optical microscope (BX51, Olympus, Japan) with a temperature-controlled accessory. Measurement of glass transition temperature and critical transition temperature of ionogels using a differential scanning calorimeter (DSC2500, TA Instruments, USA). The transmittance and haze value of ATI in the visible range (380-780 nm) were measured using a spectrometer (QEPro, Ocean Optics, USA) with a temperature-controlled accessory over a temperature range of 20-45°C. The haze value (H) can be calculated using the following Equation 5 and 6:
H = (Tdiffusive / Ttotal) × 100% (6)
where Ttotal is the total transmitted luminous flux; Tdiffusive is the diffusive transmitted luminous flux. Tspecular is the specular transmitted luminous flux66. Ttotal is measured using an integrating sphere; Tspecular is obtained through direct vertical measurement.
Different temperature environments were created using blast ovens or hot water (40°C), room temperature water (RT 25°C), dry ice alcohol baths (−70°C), and liquid nitrogen (−196°C) to test the thermochromic properties of ATIs and the ability to maintain transparency at low temperatures. For thermochromic stability testing, the transmittance at 550 nm was read after 2 min of holding at each temperature point.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This manuscript reports on the fabrication of an asymmetric thermochormic ionogel with a bilayer structure comprised of a thermoresponsive light-scattering layer and a tough supporting layer. The thermochromic layer serves as the active layer to modulate light transmittance upon temperature changes. The main thermochromic mechanism lies in the thermoresponsive phase separation of IL and PBA at temperatures higher than its LCST. Meanwhile, the microphase-separated structures of P(BA-co-NIPAM) serve as energy dissipation mechanism to yield a tough ionogel. The bilayer can shift from transparent to opaque states as the temperature shuttles between temperatures below and above the LCST. The thermochromic property is utilized to modulate solar radiation through windows, which is demonstrated to lower the room temperature. The ion conductive ionogel shows Joule heating characteristic, which is used to motivate phase transition through electro-stimulation. This research is recognized as an interesting contribution to the field of smart materials with switchable and tunable optical properties. Although the demonstration to potential applications is fascinating, the fundamental sections on the materials design, synthesis, and characterizations are not clear or adequate to establish the new concept. Besides, the biomimetic design principle is not correct or necessary. The manuscript needs extensive revisions before it could be considered for publication in Nature Communications.\n\n1, The biomimetic concept is not correct or necessary. The asymmetric bilayer structure has nothing to do with the beetle carapace. No resemblance could be found between the current bilayer ionogel and the composite bilayer structure of the carapace. Such an analouge in fact harms the main idea of this study.\n2, Some important terms, including phase separation and dynamic phase separation, are used without a clearly and precise definition. It is difficult to understand them in the ionogels and the thermochromic behavior.\n3, LCST is a most important characteristic of the ATIs (particularly for ATI-B). But this LCST is not clearly defined or explained. What is the mechanism? How to determine LCST? The DSC curve shows two transitions and the author assign the one at 34C as the LCST. What is the criterion? Supplementary Figure 17 shows different transition temperatures of ATI-Bs with different formulations. But why should the author identify them as LCST? How to tune the LCST (if it is true)? This section is very important for the whole study.\n4, Concerning the SAXS and WAXS results, the authors attribute the scattering peaks to the contraction of the ionic clusters and the increase of pi-pi stacking distance caused by enhanced ion-ion interactions. This is quite arbitrary. It is not clear why should the ion-ion interaction be enhanced. What are the so-called ionic clusters? The authors claim the formation of bicontinuous structures in the ATI-BNs. But the SAXS pattern does not provide any useful information on the phase separated structures of ATI-BNs.\n5, The interface robustness if key to the bilayer structure. The interface strength should be tested.\n6, Most schematic illustrations look fancy. But some of them are over rendering. In figure 3a, for example, what is the ion-dipole interaction? What is the dipole? in Figure 3b, it is difficult to image that the light can be \"scattered\" throughout the opaque ionogel. It is violating the basic optical physics.\n7, It is very important to separately characterize the optical properties and transitions of ATI-Bs and ATI-BNs. So far, no picture or systematic data are presented for these single layers. In most cases, photos of ATIs are presented, so it is difficult to identify the contribution to the optical transition.\n8, The solar modulation capability is low even at the visible range. This reminds of Figure 1g, where the authors compare the performances of the current TCMs with those reported in the literature. Unfortunately, the thermochromic and solar modulation performance is not included in this radar chart for some reason. It is tricky and unfair to mislead the readers.\n9, Figures 5h and 5i do not add much to the manuscript.\n10, For the Joule heating, what is the voltage used to heat the ionogel above its transition temperature? \"Equivalent opacity can be achieved below the LCST via in situ Joule heating.\" What does this mean? Is the temperature of the ionogel below its LCST when it remains opaque? This statement is quite confusing and misleading. What is the merit or signifiance to use such an opaque \"screen\" for projection?", "reviewer_2": "This manuscript reports an asymmetric thermochromic ionogel (ATI) inspired by Janus structures: a thermally induced light‐scattering layer (tunable LCST) is integrally coupled to a mechanically tough support layer via sequential radical polymerizations and in-situ phase separation. The device claims high optical contrast, low-temperature tolerance, high toughness, self-adhesion without edge sealing, and both passive and active optical switching, with demonstrations spanning model-building windows and patterned heating for simple displays. The thermal scattering and high toughness are considered through the covalent/entanglement interface of \"dynamic thermally induced phase separation (scattering layer) in-situ phase separation (toughening layer)\", which is rarely seen in PNIPAm hydrogel or single-phase ionic gel systems. The concept is compelling. To meet Nature Communications standards, the manuscript would benefit from stronger evidence connecting thermal, optical, and mechanical responses; from durability and lifetime statistics; and from explicit safety and energy metrics for device operation.\n\n1. Given the ionogel’s advertised customizability, I encourage the authors to expand the property space they present so that readers can see how formulation choices map onto performance.\n2. Because the switching mechanism is fundamentally scattering-based, haze is the pivotal figure of merit for privacy glazing and projection/screen-like use. Please report haze as a function of wavelength and temperature across the visible range and, ideally, include angle-resolved measurements.\n3. How does the polymer ionogel system maintain a transparent phase below the LCST at deep sub-zero temperatures. To what extent is the observed stability a general property of ionic liquids, and can the authors compare hydrophobic, low-water-activity ILs with more hygroscopic ones to establish whether hydrophobicity and low volatility are necessary conditions for low-temperature durability and frost-free transparency?\n4. The device reads as mechanically robust and therefore promising; nevertheless, optical components must withstand harsh environments and strong UV exposure in real service. I recommend adding accelerated aging test like high temperature–humidity, UV-A/B exposure, or salt-fog/corrosive atmospheres.\n5. To illustrate practical impact, the measured optical states should be coupled to building-scale energy simulations under representative climates.\n6. The current SAXS analysis is qualitative; please perform quantitative structure-factor fitting to extract real-space correlation lengths or domain sizes and present their temperature-dependent evolution alongside scattering intensity.\n7. please undertake a careful language and figure audit. Avoid typos like, in Fig. 5d the axis label should be labeled “wavelength.”", "reviewer_3": "The manuscript by Du et al. presents a technically impressive and well-executed study on a bio-inspired, asymmetric thermochromic ionogel (ATI). The authors have successfully engineered a material with an outstanding combination of mechanical toughness, environmental resilience (especially low-temperature performance), and dual-mode optical switching capabilities. The experimental work is thorough, spanning multi-scale characterization and theoretical simulations. Overall, this work is highly innovative and significant, and its findings will be of broad interest to the fields of smart materials, flexible electronics, and energy-saving buildings. I recommend that this manuscript be accepted for publication in Nature Communications after the authors address the following minor points.\n\nSpecific Comments for Revision:\n1. In the main text (Fig. 3), the authors use MD simulations to show that an increase in temperature weakens the interaction energy between PBA and the ions while significantly strengthening the ion-ion interactions. This is a central argument. It is suggested that this point be more explicitly linked in the main text to the peak shifts observed in the FTIR and Raman spectra. This would create a stronger connection between theory and experiment and more directly lead to the conclusion of \"entropy-driven phase separation.\" For example:” The temperature-dependent FTIR results (Fig. 3e) indicate a weakening of the ion-dipole interaction, an observation strongly corroborated by our MD simulations (Fig. 3h), which calculate a significant decrease in the PBA-ion interaction energy. Likewise, the TDRS spectra (Fig. 3f) suggest an enhancement of the ion-ion Coulomb forces, a phenomenon perfectly mirrored in our simulations where the [Emim]⁺-[TFSI]⁻ interaction becomes dominant. Taken together, these tightly coupled experimental and theoretical results provide compelling evidence for an entropy-driven phase separation mechanism.”\n2. The manuscript demonstrates excellent stability over 100 heating-cooling cycles (Supplementary Fig. 20) and stability after 24 hours of continuous heating (Supplementary Fig. 21). While this is sufficient for a laboratory evaluation, real-world applications like smart windows require the material to endure much longer periods (several years) of UV irradiation and temperature fluctuations. The authors are advised to add a brief perspective or preliminary assessment in the discussion section regarding the material's long-term chemical stability under UV irradiation.\n3. In the active optical display section (Fig. 6), the authors demonstrate both direct and indirect Joule heating. The main text or figure captions should explicitly state the voltage, current, or power density required to achieve the corresponding temperatures. For example, the SI mentions that a voltage of 180V and a frequency of 10 kHz are used to achieve global opacity.\n4. To broaden the context and impact of the manuscript, the authors might consider expanding the Introduction to include more foundational literature on ionogel science. While the review of smart windows is relevant, acknowledging the pioneering work on thermo-sensitive gels by Yongjun Men (Donghua University), high-strength ionogels by Feng Yan (Soochow University), and related supramolecular systems by Minghua Liu (Beihang University) would provide a more complete scientific background for the achievements presented here."}, "author_response": "Point-by-Point Response to Reviewers' Comments\nManuscript ID: NCOMMS-25-68161A\n(Comments in black, responses in light blue, revised texts in blue italics)\nWe express our sincere appreciation to the editor and reviewers for their thorough review of our manuscript and for providing valuable and insightful feedback. In response to each comment, we have provided detailed point-to-point responses below, and we hope that the editors and reviewers will find them satisfactory. Thank you again for your time and expertise in reviewing our work.\nReviewer #1 (Remarks to the Author)\nThis manuscript reports on the fabrication of an asymmetric thermochormic ionogel with a bilayer structure comprised of a thermoresponsive light-scattering layer and a tough supporting layer. The thermochromic layer serves as the active layer to modulate light transmittance upon temperature changes. The main thermochromic mechanism lies in the thermoresponsive phase separation of IL and PBA at temperatures higher than its LCST. Meanwhile, the microphase-separated structures of P(BA-co-NIPAM) serve as energy dissipation mechanism to yield a tough ionogel. The bilayer can shift from transparent to opaque states as the temperature shuttles between temperatures below and above the LCST. The thermochromic property is utilized to modulate solar radiation through windows, which is demonstrated to lower the room temperature. The ion conductive ionogel shows Joule heating characteristic, which is used to motivate phase transition through electro-stimulation. This research is recognized as an interesting contribution to the field of smart materials with switchable and tunable optical properties. Although the demonstration to potential applications is fascinating, the fundamental sections on the materials design, synthesis, and characterizations are not clear or adequate to establish the new concept. Besides, the biomimetic design principle is not correct or necessary. The manuscript needs extensive revisions before it could be considered for publication in Nature Communications.\nResponse: We would like to express our deep gratitude to the reviewers for their expertise and the valuable time they dedicated to our manuscript. We sincerely appreciate the constructive feedback, which has helped us significantly improve the manuscript.\nIn particular, we have paid close attention to the comment regarding the biomimetic design principle. Upon careful reconsideration, we agree with the reviewer that the original framing was not sufficiently reasonable or necessary for the core narrative of the work. Consequently, we have thoroughly removed all claims and discussions related to the biomimetic design principle throughout the manuscript. This revision helps sharpen the focus on the material’s intrinsic properties and performance, and we believe the manuscript now presents a more accurate and convincing story. Meanwhile, we have also extensively revised the sections on materials design, synthesis, and characterization to provide clearer explanations and additional data where needed, ensuring the logic and novelty of this work are firmly established. All modifications have been highlighted in the revised manuscript for your convenience. Below, we provide a point-by-point response to each comment. We are grateful for the opportunity to revise the manuscript and hope that the changes we have made adequately address the reviewers’ concerns.\n1. The biomimetic concept is not correct or necessary. The asymmetric bilayer structure has nothing to do with the beetle carapace. No resemblance could be found between the current bilayer ionogel and the composite bilayer structure of the carapace. Such an analouge in fact harms the main idea of this study.\nResponse: We sincerely thank the reviewer for this critical comment regarding the biomimetic analogy in our manuscript. We have carefully reconsidered this perspective and agree that forcing a direct comparison with the beetle carapace was not essential to highlight the core innovation of our work, and may indeed have distracted from the primary focus on the material's intrinsic properties. In direct response to this suggestion, we have thoroughly revised the manuscript to remove all claims and discussions that directly linked the asymmetric bilayer structure of our ionogel to the specific composite Janus structure of the beetle carapace. The biomimetic narrative has been completely eliminated.\nThe focus of the manuscript has been reframed to concentrate squarely on the material's structural innovation, its outstanding performance (including mechanical toughness, environmental resilience, and dual-mode optical switching), and the underlying mechanism of the \"thermosensitive dynamic phase separation\" itself. We believe this shift in narrative strengthens the manuscript by placing undivided emphasis on the novel material design and its experimentally demonstrated capabilities, which stand on their own merits. The revised Figure 1 is shown below:\n[...]"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have made extensive revisions by addressing all the comments and provide additional experimental results.\nNow the statements and conclusions are well supported by experimental data and proper analysis. It is recommended for publication in Nature Communications in its current form.\n[Editor's Note: This Reviewer was asked to evaluate the response to Reviewer #2's comments, and provided the following:]\nThe authors have tried to respond to all the previous comments from Reviewer #2. However, some critical issues remain.\n1, The SAXS and WAXS results indicate a phase separation domain size of about 7.2 nm, and some unspecified characteristic dimension of 4.5 A and 7.2 A. These dimensions could not result in any severe scattering of visible-NIR light that causes a transparency-to-opaque transition.\n2, On the other hand, the authors' explanation to the dynamic phase separation is based on the ion-dipole interaction at low temperatures and its transition to ion-ion transition at high temperatures, which may violate some basic physics. Once again, the origin of LCST of the ionogels is not well established.\n3, The correlation between formulation and performance is not well investigated. The authors only provide on the LCST values of different formulations. Some other important properties, including mechanical properties, low temperature transparency, high temperature transmittance, etc, should also be investigated, compared, and discussed. This will help readers better understand the materials design and proposed mechanisms.\nThe authors are requested to resolve these fundamental problems and provide more solid experimental data before it can be recommended for publication in Nature Communications.", "reviewer_3": "The authors have fully addressed all my concerns and have improved the quality and robustness of the manuscript through these revisions. I believe the work is highly innovative and meets the standards for publication. I recommend the acceptance of this manuscript in its current form."}, "author_response": "Point-by-Point Response to Reviewers' Comments\nManuscript ID: NCOMMS-25-68161B\n(Comments in black, responses in light blue, revised texts in blue italics)\nWe are deeply grateful to the editor and reviewers for their thorough review and valuable comments, which have greatly improved our work. Our point-by-point responses are provided below. We sincerely appreciate the time and expertise you have dedicated to our manuscript.\nReviewer #1 (Remarks to the Author)\nThe authors have made extensive revisions by addressing all the comments and provide additional experimental results. Now the statements and conclusions are well supported by experimental data and proper analysis. It is recommended for publication in Nature Communications in its current form.\nResponse: Thank you for your kind words and positive assessment of our revisions. We are very pleased that you find the manuscript now suitable for publication. We sincerely appreciate your time and insightful guidance throughout the review process, which have been valuable in strengthening our work.\n[Editor's Note: This Reviewer was asked to evaluate the response to Reviewer #2's comments, and provided the following:]\nThe authors have tried to respond to all the previous comments from Reviewer #2. However, some critical issues remain.\nResponse: Thank you for your continued evaluation and for highlighting that some critical issues require further attention. We have carefully considered all points raised and are fully committed to addressing all remaining concerns. Below is the detailed point-by-point response:\n1. The SAXS and WAXS results indicate a phase separation domain size of about 7.2 nm, and some unspecified characteristic dimension of 4.5 A and 7.2 A. These dimensions could not result in any severe scattering of visible-NIR light that causes a transparency-to-opaque transition.\nResponse: Thank you for your professional review and attention to this manuscript. We apologize for any confusion caused by inaccurate expressions. The following provides further clarification regarding X-ray scattering characterization:\n[...]"}, {"round": 3, "reviewer_comments": {"reviewer_1": "The X-ray scattering/diffraction results show some ordered/crystalline structures, and the dimension of about 7 nm cannot cause opaque or transluncent appearance of the hydrogels. The authors hypothesize that the 7 nm objects may aggregate to cause opaqueness. But no scattering data support this key hypothesis. I would like to recommend it to Nature Communications only when this important fundamental issue is supported by solid experimental data that verify the formation of phase separated structures."}, "author_response": "Point-by-Point Response to Reviewers' Comments\nManuscript ID: NCOMMS-25-68161C\n(Comments in black, responses in light blue, revised texts in blue italics,\nimportant revision in highlighted blue italics)\nWe sincerely thank the editor and reviewers for dedicating additional time and effort to re-evaluate our work. Your comments have been invaluable in helping us improve the clarity and rigor of the manuscript. We have carefully considered all points and have revised the manuscript and supplementary information accordingly. Below, we provide a detailed, point-by-point response.\nReviewer #1 (Remarks to the Author)\nThe X-ray scattering/diffraction results show some ordered/crystalline structures, and the dimension of about 7 nm cannot cause opaque or transluncent appearance of the hydrogels. The authors hypothesize that the 7 nm objects may aggregate to cause opaqueness. But no scattering data support this key hypothesis. I would like to recommend it to Nature Communications only when this important fundamental issue is supported by solid experimental data that verify the formation of phase separated structures.\nResponse: Thank you very much for your thorough evaluation and insightful comments on our manuscript. We sincerely apologize for any misunderstandings caused by unclear expressions in our original submission. Your feedback has been invaluable in helping us refine our work. We agree that solid experimental evidence for phase separation is paramount. We believe the concern stems from a conflation of the structures and functions of two independent layers in our asymmetric thermochromic ionogel (ATI). Below, we provide a point-by-point response to address your concerns.\nWe first clarify this fundamental design to resolve the misunderstanding, and then present the direct experimental evidence for phase separation in the relevant layer.\n1. Clarification of the distinct roles of two layers: the origin of the misunderstanding.\nOur ATI is intentionally designed as a bilayer asymmetric system, where each layer has a distinct and independent function:\n[...]"}, {"round": 4, "reviewer_comments": {"reviewer_1": "The manuscript can be accepted for publication in Nature Communications in its current form."}, "author_response": ""}]

Decision letter