The appeal of MXenes lies in a rare combination of properties. These atomically thin sheets, first reported in 2011, are typically produced by etching layered ceramics such as the titanium carbide Ti3C2Tx, whose surface terminations can be chemically tuned. The review highlights electrical conductivities on the order of 10^3 to 10^4 S cm^-1, an exceptionally high aspect ratio and tunable surface chemistry, all of which make MXenes natural candidates for reinforcing the long-range molecular order that defines the liquid crystalline state while adding the fluidity and responsiveness that liquid crystals already possess.

When MXene nanosheets are dispersed into liquid crystal hosts, the electro-optical characteristics improve markedly. The review documents polymer-dispersed liquid crystal films reaching a transmittance of roughly 74 percent at a bias of 50 volts in 13 micrometer-thick cells, with switching speeds below one millisecond in the ON state. Perhaps most striking for practical display and smart-window applications, the doped films retained about 71 percent transmittance after 180 days, evidence that the nanosheet-liquid crystal interface can remain stable over months rather than degrading within days as many earlier nanodopants did.

The mechanisms behind these gains are traced in detail. MXene sheets carry surface charges and functional groups that interact with the dipolar liquid crystal molecules, anchoring them and raising the effective dielectric anisotropy of the mixture. This lowers the threshold voltage needed to reorient the director field and accelerates the relaxation dynamics once the field is removed. The high conductivity of the MXene network also screens internal fields more efficiently, reducing ion-driven image sticking that has long plagued conventional liquid crystal devices.

Beyond doped thermotropic systems, the review devotes substantial attention to MXenes that form liquid crystalline phases on their own. When sufficiently concentrated in solution, MXene nanosheets align into lyotropic nematic phases with a relatively low viscosity of about 0.14 Pa s and an excellent orienting ability, producing residual dipolar couplings of up to 37 Hz in nuclear magnetic resonance measurements. These intrinsic liquid crystalline phases open a route to ordered MXene films and fibers without needing a separate liquid crystal host, and they suggest that the two-dimensional sheets can self-organize into macroscopic aligned architectures suitable for electrodes, membranes and photonic structures.

Nonlinear optical behavior also benefits from the partnership. Certain MXene-based liquid crystal formulations exhibit Kerr coefficients as high as 4.9 × 10^-6 m V^-2 at a concentration of 4 mg per milliliter, values that compare favorably with conventional liquid crystals and point toward low-voltage optical modulators and beam-steering elements. The Kerr effect, in which a liquid crystal becomes birefringent under an applied electric field, scales with the square of the field, so a larger Kerr coefficient translates directly into stronger optical response at lower drive voltages, a key requirement for energy-efficient photonic devices.

Soft actuation represents another frontier. MXene-liquid crystal soft actuators bend to angles as high as roughly 67 degrees under near-infrared irradiation while remaining stable across 100 actuation cycles, exploiting the strong photothermal conversion of the MXene sheets to drive reversible shape changes. Liquid crystal elastomers incorporating MXenes generate actuation strains up to about 42 percent and stresses near 1.56 MPa under 400 mW of 808 nm near-infrared light, combining the large deformation of elastomer networks with the rapid, localized heating that MXenes provide. These numbers approach the performance regime needed for artificial muscles, soft robotics and adaptive optical components.

The review maps these laboratory results onto a broad application landscape. Smart windows that modulate transparency on demand, camouflage systems that adapt their appearance, wearable textiles that respond to body heat or light, biosensors that exploit the ordered MXene-liquid crystal interface for molecular recognition, and energy storage devices that benefit from the aligned conductive pathways all appear as realistic targets. The common thread is that the MXene-liquid crystal hybrid is not merely a better display material but a multifunctional platform whose optical, electrical, mechanical and thermal responses can be tuned independently.

Challenges remain before these systems reach commercial scale. The review notes that long-term colloidal stability of MXene nanosheets in liquid crystal hosts, oxidation of the sheets under ambient conditions, and the need for scalable, reproducible dispersion methods all require further work. Surface functionalization strategies and polymer-compatible MXene formulations are identified as promising directions, along with systematic studies of how nanosheet concentration, lateral size and surface chemistry govern the balance between enhanced order and increased viscosity that ultimately limits device speed.

What emerges from the survey is a coherent picture of a materials platform in rapid maturation. With electro-optical performance already meeting or exceeding key benchmarks for displays and smart windows, actuation strains approaching those of biological muscle, and nonlinear optical coefficients suitable for low-voltage photonics, MXene-doped liquid crystals are positioned as a candidate next-generation multifunctional material. The authors argue that continued progress in mechanism-level understanding, coupled with device-level engineering, could carry these hybrids from laboratory demonstrations into adaptable technologies spanning optics, wearables, sensing and energy within the coming decade.

Subject of Research: Materials Science

Article Title: Review: recent advances in MXene-doped liquid crystals—mechanisms to multifunctional applications

Article References: Chinky, Malik, P., & Kumar, P. (2026). Review: recent advances in MXene-doped liquid crystals—mechanisms to multifunctional applications. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13943-x

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13943-x

Keywords: MXene, liquid crystals, Ti3C2Tx, electro-optical materials, soft actuators, liquid crystal elastomers, smart windows, 2D nanomaterials, Kerr effect, polymer-dispersed liquid crystals, Review, recent

The device at the heart of the study is a thermogalvanic cell, or TGC, a class of electrochemical system that generates voltage from a temperature difference. Unlike solid-state thermoelectric generators, which rely on the Seebeck effect in semiconductors, thermogalvanic cells exploit the temperature dependence of a redox couple dissolved in an electrolyte. When one electrode is warmer than the other, the redox reaction equilibria shift unevenly, producing a measurable potential difference across the cell. Because the electrolyte can be gelled into a quasi-solid film, TGCs can be made thin, bendable, and lightweight, which makes them attractive for low-grade heat harvesting and for wearable or building-integrated applications where rigid modules are impractical.

The catch has always been the temperature gradient. The voltage a thermogalvanic cell produces scales with the difference in temperature, ΔT, between its two electrodes, and under direct sunlight that difference tends to collapse. Sunlight warms the whole device fairly uniformly, so both sides heat up together and the gradient that should drive the electrochemical potential all but disappears. Earlier solar-driven designs relied purely on photothermal heating, depositing a light-absorbing layer on one electrode to make it hot. That helps, but the heat inevitably spreads through the thin, flexible structure to the cold side, eroding the very gradient the cell needs. The result has been modest voltages and limited power, holding back the idea of harvesting sunlight with TGCs.

The Donghua University-led team, working with a colleague at Ruijin Hospital of Shanghai Jiao Tong University School of Medicine, attacked the problem from both ends at once. Their cell is built on a bacterial cellulose substrate, a flexible, porous biopolymer film that hosts the quasi-solid electrolyte. On one side they coated a layer of carbon nanotubes, which act as an efficient photothermal converter, absorbing sunlight and turning it into localized heat at the hot electrode. On the opposite side they coated titanium dioxide, a material chosen for its radiative cooling properties: it emits thermal radiation strongly in the mid-infrared atmospheric transparency window, allowing that side to shed heat passively to the sky even while sitting in full sunlight.

This asymmetric coating is what makes the design clever. Radiative cooling is a passive phenomenon with no moving parts and no energy input; a surface engineered to emit in the 8-to-13-micrometer wavelength band can dump heat through the atmosphere into the roughly three-kelvin cosmic background, dropping below ambient temperature on a clear day. By pairing a photothermal hot side with a radiatively cooled cold side, the researchers created a device that manages its own thermal asymmetry under illumination. The sunlight simultaneously acts as a heat source on one electrode and, through the cooling layer’s transparency to the sky, is prevented from spoiling the cold electrode on the other. The team describes this as using sunlight not only as a heat source but also as a trigger for asymmetric thermal management.

The measured results are striking. Under one sun of illumination, the standard intensity of noonday sunlight, the optimized device sustained a temperature difference of 14.11 kelvin between its electrodes, and it generated an open-circuit voltage of 18.07 millivolts, substantially exceeding an otherwise identical cell that had only the photothermal heating layer. The parasitic heating that normally bleeds warmth across the device was effectively suppressed, and the cold side stayed cold. The maximum power density reached 13.98 milliwatts per square meter, a 214 percent enhancement over the photothermal-only counterpart, meaning the output more than tripled simply by adding the radiative cooling layer and optimizing the structure.

Those numbers may sound small in absolute terms, and they are, but the context matters. Thermogalvanic cells are low-power devices by nature, and millivolts of thermopower from a thin flexible film is respectable for the field. The real significance of the 214 percent gain is architectural: it shows that thermal management, not electrochemistry, was the bottleneck for solar-driven TGCs, and that the bottleneck can be broken with a passive, coating-level solution. No lenses, trackers, pumps, or active cooling were required. The gradient arises spontaneously the moment sunlight hits the device, which is exactly what a self-powered, maintenance-free harvester needs.

The team also moved beyond bench-top measurements. In a practical outdoor demonstration, the flexible cell operated under real sky and real sunlight, supporting the claim that the photothermal-plus-radiative-cooling scheme works outside the controlled conditions of a solar simulator. As a proof of concept for functionality beyond raw power generation, the researchers coupled the device to a voltage amplifier and used it as an intelligent light-control switch for smart windows: the illumination level determines the voltage the cell produces, and that signal can drive a responsive switching action. In that configuration the same film serves simultaneously as an energy harvester, a light sensor, and a control element, hinting at a platform that integrates energy harvesting, environmental sensing, and responsive control in a single flexible laminate.

The materials choices also carry practical weight. Bacterial cellulose is inexpensive, biodegradable, and mechanically robust, and its use as the TGC substrate aligns with growing interest in sustainable flexible electronics. Carbon nanotubes are among the most broadband solar absorbers known, converting incident photons to heat with high efficiency, while titanium dioxide is cheap, stable, non-toxic, and widely used in coatings and pigments, which eases scaling. Because both functional layers are coatings on opposite faces of the same film, the fabrication route is compatible with roll-to-roll and textile-style processing, a natural fit for the dyeing and finishing expertise of the Donghua group and for applications such as smart fabrics, building skins, and conformable sensors.

There are, of course, caveats before such devices reach everyday use. Milliwatts per square meter will not power a phone, so near-term applications lie in ultra-low-power electronics: intermittent sensors, electronic skin, status indicators, and switching functions of the kind demonstrated. Performance will depend on sky conditions, since radiative cooling weakens under clouds and humidity, and on the long-term stability of the quasi-solid electrolyte and coatings under weathering. Still, the study establishes a clear design principle with broad reach: in any solar-thermal conversion device, the cold side deserves as much engineering attention as the hot side. By letting one face drink in the sun and the other face whisper its heat into space, the researchers turned a persistent weakness of thermogalvanic cells into their strongest asset, and showed that the sky itself can be recruited as a heat sink for flexible power generation.

Subject of Research: Solar-driven thermogalvanic cells enhanced by combined photothermal heating and passive radiative cooling

Article Title: Thermopower amplification in thermogalvanic cells via radiative cooling-mediated photothermal conversion

Article References: Geng, Y., Li, T., Fan, G., Zhong, R., Rong, L., Wang, B., Zhong, Y., Mao, Z., Xie, S., & Feng, X. (2026). Thermopower amplification in thermogalvanic cells via radiative cooling-mediated photothermal conversion. npj Flexible Electronics. https://doi.org/10.1038/s41528-026-00646-1

Image Credits: AI Generated

DOI: 10.1038/s41528-026-00646-1

Keywords: thermogalvanic cell, radiative cooling, photothermal conversion, flexible electronics, low-grade heat harvesting, carbon nanotubes, titanium dioxide, bacterial cellulose, thermoelectric conversion, smart windows, self-powered devices, temperature gradient

The research team, composed of Vilya K and Shaik Kaleemulla from the Department of Physics at Vellore Institute of Technology, set out to answer a deceptively simple question: when vanadium pentoxide and molybdenum trioxide are combined, is it better to mix them into a single composite film or to stack them into a layered heterostructure? Both approaches use the same two transition metal oxides, both films are deposited by the same thermal evaporation technique, and both are subjected to the same annealing treatment. The only difference is geometry, and that difference turns out to be decisive. The heterostructure, arranged as a V2O5/MoO3/V2O5 sandwich, outperformed the mixed composite in optical modulation by roughly eleven percent, achieving a coloration efficiency of 40.42 square centimeters per coulomb along with improved cycling stability.

To understand why this comparison matters, it helps to consider what happens inside an electrochromic film at the atomic scale. When a negative voltage is applied, positively charged ions from an electrolyte insert themselves into the oxide lattice, a process called intercalation. Electrons follow to maintain charge neutrality, and the resulting change in the electronic structure of the material alters which wavelengths of light it absorbs. In cathodic coloring materials such as the oxides studied here, this insertion process shifts the film from a relatively transparent state to a colored one. The efficiency of this transformation depends on how easily ions can travel through the film, how many insertion sites are available, and how well the material withstands repeated swelling and contraction as ions shuttle in and out over thousands of cycles.

Thermal evaporation, the deposition method chosen by the researchers, is one of the oldest and most scalable techniques in thin film fabrication. Material is heated in a vacuum chamber until it vaporizes, and the vapor condenses onto a substrate to form a film. The technique is attractive for electrochromic applications because it produces dense, adherent coatings without the solvents or binders that can contaminate electrochemical performance. In this study, the same evaporation process was used to create two distinct architectures. For the composite, vanadium and molybdenum oxides were co-deposited into a single mixed layer. For the heterostructure, the deposition was staged sequentially, first vanadium pentoxide, then molybdenum trioxide, then vanadium pentoxide again, creating three distinct layers with sharp interfaces. An annealing step followed in both cases, and this thermal treatment modified the morphology of the films in ways that proved central to their electrochemical behavior.

Before any electrochromic testing began, the team subjected both film types to a rigorous structural interrogation. X-ray diffraction revealed the crystalline phases present in the deposited layers, confirming that the films had formed the expected oxide structures. Raman spectroscopy provided complementary vibrational fingerprints that further verified the lattice structure, while X-ray photoelectron spectroscopy probed the oxidation states of the metal atoms at the film surface. This last measurement is particularly important for electrochromic materials because the ratio of different oxidation states, such as the presence of reduced molybdenum species alongside fully oxidized ones, directly influences how the material responds to ion insertion. Field emission scanning electron microscopy paired with energy dispersive spectroscopy then mapped the physical landscape of the films, revealing a rod-shaped morphology with uniform elemental distribution across both architectures.

With the structural groundwork established, the electrochemical characterization delivered the study’s most consequential findings. Cyclic voltammetry, a technique that sweeps the voltage back and forth while measuring current, confirmed that both films exhibit cathodic coloring behavior, darkening when ions insert and bleaching when they are extracted. The shape and magnitude of the voltammetric curves provided insight into how reversibly each film could accommodate the intercalation process. Electrochemical impedance spectroscopy added a second layer of understanding by probing how readily ions diffuse through the films and how the films behave as capacitive elements. Together, these measurements painted a picture of two materials that are chemically similar but kinetically distinct, with the layered heterostructure offering more favorable pathways for ion transport.

The headline result came from chronoamperometry combined with optical transmission measurements. When the researchers quantified the optical modulation, the change in transmittance between the bleached and colored states, the heterostructure films delivered approximately eleven percent more modulation than the composite films. In practical terms, this means the layered architecture can swing more dramatically between transparent and colored states for the same electrical input, which translates directly into deeper, more saturated blue hues in a display application. The coloration efficiency, defined as the optical density change achieved per unit of charge inserted, reached 40.42 square centimeters per coulomb for the heterostructure, a figure that indicates the film converts electrical energy into optical change with notable economy. Equally important, the heterostructure demonstrated enhanced cycling stability compared to the composite, meaning it can endure many more coloration and bleaching cycles before its performance degrades.

The physical explanation for the heterostructure’s advantage likely lies in the interfaces between its layers. In a sandwich structure, each vanadium pentoxide layer is bounded by molybdenum trioxide, and these heterointerfaces can act as highways for ion transport while also buffering the mechanical stress that accompanies repeated ion insertion. The composite, by contrast, distributes both oxides randomly throughout the film volume, which can create regions of poor connectivity and uneven ion distribution. The rod-shaped morphology observed in both films, with its high surface area and open channels, benefits both architectures, but the layered design appears to organize those channels more effectively. This interpretation is consistent with a growing body of literature on molybdenum oxide and vanadium oxide hybrid systems, where bilayer and multilayer configurations have repeatedly shown superior electrochromic kinetics compared to homogeneous mixtures.

The broader significance of this work extends well beyond the laboratory bench. Displays that can reproduce the full RGB color space using electrochromic materials would enable a new generation of low-power, reflective screens that remain legible in bright sunlight without backlights. Smart windows based on the same chemistry could dynamically regulate solar heat gain in buildings, reducing air conditioning loads in an era of rising energy demand. Electrochromic materials are also finding unexpected applications in biosensing, where color changes signal the presence of target molecules, and in adaptive camouflage and automotive glazing. For all of these applications, the blue channel has been the bottleneck, because few materials combine the deep blue coloration, fast switching, and long-term stability that commercial products require. By demonstrating that a simple change in film architecture can meaningfully improve blue hue modulation using two abundant and well-characterized oxides, the Vellore team has added a practical design rule to the electrochromic engineer’s toolkit.

What makes the study especially compelling is its methodological discipline. Rather than introducing new dopants or exotic synthesis routes, the researchers held every variable constant except the arrangement of the two oxides, isolating architecture as the sole determinant of performance. The annealing step, applied identically to both film types, modified the morphology in parallel, ensuring that the comparison remained fair. The comprehensive characterization suite, spanning diffraction, spectroscopy, microscopy, and multiple electrochemical techniques, provides the kind of complete evidence base that allows other researchers to reproduce and extend the findings. As electrochromic technology moves from laboratory curiosity toward commercial reality in displays, windows, and sensors, studies of this kind, which carefully disentangle the factors that govern performance, will be essential guides. The message from Vellore is clear: in the quest for better blue, how you stack the layers matters as much as what you put in them.

Subject of Research: Electrochromic performance of V2O5-MoO3 composite and heterostructure thin films for blue hue modulation

Article Title: Comparative study of V2O5-MoO3 based composite and heterostructure films prepared by thermal evaporation for enhanced electrochromic blue hue modulation

Article References: K, V., & Kaleemulla, S. (2026). Comparative study of V2O5-MoO3 based composite and heterostructure films prepared by thermal evaporation for enhanced electrochromic blue hue modulation. Ionics. https://doi.org/10.1007/s11581-026-07494-z

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07494-z

Keywords: electrochromic, V2O5, MoO3, heterostructure, composite films, thermal evaporation, thin films, coloration efficiency, metal oxides, ion intercalation, smart windows, display technology