Annual Energy-Saving Smart Windows with Actively Controllable Passive Radiative Cooling and Multimode Heating Regulation.

Smart windows with radiative heat management capability using the sun and outer space as zero-energy thermodynamic resources have gained prominence, demonstrating a minimum carbon footprint. However, realizing on-demand thermal management throughout all seasons while reducing fossil energy consumption remains a formidable challenge. Herein, an energy-efficient smart window that enables actively tunable passive radiative cooling (PRC) and multimode heating regulation is demonstrated by integrating the emission-enhanced polymer-dispersed liquid crystal (SiO2@PRC PDLC) film and a low-emission layer deposited with carbon nanotubes. Specifically, this device can achieve a temperature close to the chamber interior ambient under solar irradiance of 700 W m-2, as well as a temperature drop of 2.3 °C at sunlight of 500 W m-2, whose multistage PRC efficiency can be rapidly adjusted by a moderate voltage. Meanwhile, synchronous cooperation of passive radiative heating (PRH), solar heating (SH), and electric heating (EH) endows this smart window with the capability to handle complicated heating situations during cold weather. Energy simulation reveals the substantial superiority of this device in energy savings compared with single-layer SiO2@PRC PDLC, normal glass, and commercial low-E glass when applied in different climate zones. This work provides a feasible pathway for year-round thermal management, presenting a huge potential in energy-saving applications.

Highly Efficient Wavelength-Tunable Circularly Polarized Luminescence Film Constructed by Responsive Chiral Aggregation-induced Emission Luminophore.

Key Lab of Environment-friendly Chemistry and Circularly polarized luminescent (CPL) materials with multitudinous inherent advantages shows extensive application. In this work, we prepare a kind of highly efficient wavelength-tunable CPL free-standing films by responsive chiral aggregation-induced emission mesogen. Firstly, the pyridine-functionalized tetraphenylethene monomer (MPy) is designed and synthesized. Then, the different ration of the monomer MPy mixed with the liquid crystal (LC) reactive monomer (LC242) to fabricate a free-standing film by photopolymerization. The obtained film presents efficient CPL with a constant luminescence asymmetry factor (glum ) of +0.75, as well as sensitive wavelength tunability. Finally, this wavelength-tunable CPL film with both fluorescence and CPL modes is successfully applied in anti-counterfeiting and information encryption. This work provides a simple way to construct CPL apparatus with adjustable luminescence wavelength and high glum .

Organic Persistent Luminescent Materials: Ultralong Room-Temperature Phosphorescence and Multicolor-Tunable Afterglow.

Organic persistent luminescent materials have attracted special attention due to their significant applications in optoelectronics, sensors, and security technology areas. In this work, a series of organic compounds (1-4) with twisted electron donor-acceptor structures are successfully designed and synthesized, and then the resultant compounds are dissolved in methyl methacrylate (MMA), and afterward, in situ polymerization realizes single-molecular organic room-temperature phosphorescent (RTP) materials (P1-P4). All RTP materials show long lifetime, especially P2 exhibits ultralong lifetime of 1.51 s. When the compounds are grown into single crystals, multicolor-tunable afterglow is obtained at different delay times due to the dual emission of phosphorescence and delayed fluorescence, which is promising to be applied in high-level anticounterfeiting.

Luminescent Liquid Crystals Based on Carbonized Polymer Dots and Their Polarized Luminescence Application.

Traditional luminescent liquid crystals (LLCs) suffer from fluorescence quenching caused by aggregation, which greatly limits their further application. In this work, a kind of novel LLCs (named carbonized polymer dot liquid crystals (CPD-LCs)) are designed and successfully synthesized through grafting the rod-shaped liquid crystal (LC) molecules of 4'-cyano-4-(4″-bromohexyloxy) biphenyl on the surface of CPDs. The peripheral LC molecules not only increase the distance between different CPDs to prevent them from aggregating and reduce intermolecular energy resonance transfer but also make this LLC have an ordered arrangement. Thus, the obtained CPD-LCs show good LC property and excellent high luminous efficiency with an absolute photoluminescence quantum yield of 14.52% in the aggregated state. Furthermore, this kind of CPD-LC is used to fabricate linearly polarized devices. The resultant linearly polarized dichroic ratio (N) and polarization ratio (ρ) are 2.59 and 0.44, respectively. Clearly, this type of CPD-LC shows promising applications for optical devices.

Programmable 3D Shape-Change Liquid Crystalline Elastomer Based on a Vertically Aligned Monodomain with Cross-link Gradient.

A liquid crystalline elastomer (LCE) as a kind of stimuli-responsive materials, which can be fabricated to present the three-dimensional (3D) change in shape, shows a wide range of applications. Herein, we propose a simple and robust way to prepare a 3D shape-change actuator based on gradient cross-linking of the vertically aligned monodomain of liquid crystals (LCs). First, gold nanoparticles grafted by liquid crystalline polymers (LCPs) are used to induce the homeotropic orientation of the LC monomer and cross-linkers. Then, photopolymerization under UV irradiation is carried out, which can result in the LCE film with a cross-link gradient. Different from the typical LCEs with homogenous alignment that usually show the shape change of extension/contraction, the obtained vertically aligned LCE film exhibits excellent bendability under a thermal stimulus. The nanoindentation experiment demonstrates that the deformation of LCE films comes from the difference in Young's modulus on two sides of the thin film. Simply scissoring the thin film can prepare the samples with different bending angles under the fixed length. Moreover, using a photomask to pattern the film during photopolymerization can realize the complex 3D deformation, such as bend, fold, and buckling. Further, the patterned LCE film doped with multiwalled carbon nanotubes modified by LCPs (CNT-PDB) can act as a light-fueled microwalker with fast crawl behavior.

Responsive Smart Windows Enabled by the Azobenzene Copolymer Brush with Photothermal Effect.

An azobenzene side chain liquid crystalline copolymer (MAzo-co-GMA) is successfully synthesized through copolymerizing the monomer 6-(4-((4-butylphenyl)diazenyl)phenoxy)hexyl methacrylate (MAzo) with glycidyl methacrylate (GMA). The obtained MAzo-co-GMA copolymer can form stabilized polymer brush on the surface after thermal annealing. The obtained polymer brush not only induces the alignment of liquid crystals but also shows a photothermal effect under UV light irradiation due to the azobenzene side group. On basis of these results, the LC cell with this polymer brush as the substrate is further used to fabricate the polymer-stabilized liquid crystal (PSLC) smart window. The resultant PSLC smart window shows the transparent state because the homeotropic alignment in the SmA* phase of PSLC is induced by the polymer brush on the surface of the LC cell. The opaque state can be achieved in the scattering N* phase by UV light irradiation or heating. The response time of the PSLC smart window can be regulated by adjusting the concentration of MAzo-co-GMA copolymer brush and the intensity of UV light. This kind of PSLC smart window with both thermal and UV response shows good reversibility and stability, which endows enormous promising applications in energy-saving devices.

Color-Tunable and Stimulus-Responsive Luminescent Liquid Crystalline Polymers Fabricated by Hydrogen Bonding.

Luminescent liquid crystalline polymers (LLCPs) show extensive application potentials, such as liquid crystal displays and circularly polarized luminescence. In this work, we employ a hydrogen-bonding strategy different from the traditional covalent-bonding method to fabricate LLCPs. First, the acceptor and donor of hydrogen bonding, (4,4'-dibutanoxy tetraphenylethylene)-1-pyridine (PTPEC4) and poly(2-vinyl terephthalic acid) (PPA), respectively, are successfully synthesized. Then, mixtures with different molar ratios ( x's) of PTPEC4 to PPA are used to prepare a series of LLCPs [denoted as PPA(PTPEC4) x]. The resultant LLCPs show a smectic A phase ( x ≥ 0.8), a columnar nematic phase (0.6 ≤ x ≤ 0.05), and an amorphous state ( x = 0.025), depending on the x value. Meanwhile, all polymers exhibit typical aggregation-induced emission behavior. More interestingly, with the variation of the PTPEC4 content, the series of LLCPs show different colors, that is, the emission peak red shifts from 510 nm ( x = 1.0) to 551 nm ( x = 0.025). Furthermore, because of the reversible protonation effect of the N atom of pyridine in PTPEC4 by the strong proton acid, PPA(PTPEC4) x shows reversible color transformation. This work provides a new method to construct LLCPs with different emission colors and reversible color transformation.

Alignment Control of Nematic Liquid Crystal using Gold Nanoparticles Grafted by the Liquid Crystalline Polymer with Azobenzene Mesogens as the Side Chains.

The gold nanoparticles highly grafted by a liquid crystalline polymer (LCP) with azobenzene mesogens as the side chain (denoted as Au@TE-PAzo NPs) are successfully designed and synthesized by the two-phase Brust-Schiffrin method. The chemical structures of the monomer and polymer ligands have been confirmed by nuclear magnetic resonance, and the molecular weight of the polymer is determined by gel permeation chromatography. The combined analysis of transmission electron microscopy and thermogravimetric analysis shows that the size of the nanoparticles is 2.5(±0.4) nm and the content of the gold in the Au@TE-PAzo NPs is ca. 17.58%. The resultant Au@TE-PAzo NPs can well disperse in the nematic LC of 5CB. The well-dispersed mixture with appropriate doping concentrations can automatically form a perfect homeotropic alignment in the LC cell. The homeotropic alignment is attributed to the brush formed by Au@TE-PAzo NPs on the substrate, wherein the Au@TE-PAzo NPs gradually diffuse onto the substrate from the mixture. On the contrary, the pure side chain LCPs cannot yield vertical alignment of 5CB, which indicates that the alignment of 5CB is ascribed to the synergistic interaction of the nanoparticles and the grafted LCPs. Moreover, Au@TE-PAzo NPs show excellent film-forming property on account of their periphery of high densely grafted LCPs, which can form uniform thin film by spin-coating. The resultant thin film also can prompt the automatical vertical alignment of the nematic 5CB. Further, upon alternative irradiation of UV and visible light, the alignment of 5CB reversibly switches between vertical and random orientation because of the trans-cis photoisomerization of the azobenzene group on the periphery of Au@TE-PAzo NPs. These experimental results suggest that this kind of nanoparticles can be potentially applied in constructing the remote-controllable optical devices.

A self-healing photoinduced-deformable material fabricated by liquid crystalline elastomers using multivalent hydrogen bonds as cross-linkers.

Liquid crystalline elastomers (LCEs) using multivalent hydrogen bonds as cross-linkers were successfully fabricated, which showed both self-healing and photoinduced-deformable properties. More interestingly, this LCE could be readily molded into different shapes through a versatile and efficient procedure, and the fibrous and filmy samples showed different photoinduced-deformable behavior originating from the difference in molecular orientations.

Hierarchical supramolecular ordering with biaxial orientation of a combined main-chain/side-chain liquid-crystalline polymer obtained from radical polymerization of 2-vinylterephthalate.

The liquid-crystalline (LC) phase structures and transitions of a combined main-chain/side-chain LC polymer (MCSCLCP) 1 obtained from radical polymerization of a 2-vinylterephthalate, poly(2,5-bis{[6-(4-butoxy-4'-oxybiphenyl) hexyl]oxycarbonyl}styrene), were studied using differential scanning calorimetry, one- and two-dimensional wide-angle X-ray diffraction (1D and 2D WAXD), and polarized light microscopy. We have found that 1 with sufficiently high molecular weight can self-assemble into a hierarchical structure with double orderings on the nanometer and subnanometer scales at low temperatures. The main chains of 1, which are rodlike as a result of the "jacketing" effect generated by the central rigid portion of the side chains laterally attached to every second carbon atom along the polyethylene backbone, form a 2D centered rectangular scaffold. The biphenyl-containing side chains fill the space between the main chains, forming a smectic E (SmE)-like structure with the side-chain axis perpendicular to that of the main chain. This biaxial orientation of 1 was confirmed by our 2D WAXD experiments through three orthogonal directions. The main-chain scaffold remains when the SmE-like packing is melted at elevated temperatures. Further heating leads to a normal smectic A (SmA) structure followed by the isotropic state. We found that when an external electric field was applied, the main-chain scaffold greatly inhibited the motion of the biphenyls. While the main chains gain a sufficiently high mobility in the SmA phase, macroscopic orientation of 1 can be achieved using a rather weak electric field, implying that the main and side chains with orthogonal directions can move cooperatively. Our work demonstrates that when two separate components, one offering the "jacketing" effect to the normally flexible backbone and the other with mesogens that form surrounding LC phases, are introduced simultaneously into the side chains, the polymer obtained can be described as an MCSCLCP with a fascinating hierarchically ordered structure.