Engineering the helical structure of chiral photonic materials in three dimensions remains a challenge. 3D helix engineered photonic materials are fabricated by local stratification in a ...photopolymerizable chiral nematic liquid crystal. The obtained chiral photonic materials reflect both handedness of circular polarized light and show super‐reflectivity. Simulations match the experimentally observed photonic properties and reveal a distorted helical structure. 3D engineered polymer films can be made that reflect both left‐ and right handed circular and linear polarized light dependent and exhibit a changing color contrast upon altering the polarization of incident light. Hence, these 3D engineered photonic materials are of interest for new and emerging applications ranging from anti‐counterfeit labels and data encryption to aesthetics and super‐reflective films.
3D engineered photonic materials are of interest for emerging applications, such as anticounterfeit labels, data encryption, and super‐reflective films. 3D engineered chiral nematic‐liquid‐crystal materials, which exhibit a changing color contrast between the image and the surroundings upon changes in the polarization of incident light, are reported.
Environmentally responsive photonic polymers van Heeswijk, Ellen P. A; Kragt, Augustinus J. J; Grossiord, Nadia ...
Chemical communications (Cambridge, England),
03/2019, Letnik:
55, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Stimulus-responsive photonic polymer materials that change their reflection colour as function of environmental stimuli such as temperature, humidity and light, are attractive for various ...applications (
e.g.
sensors, smart windows and communication). Polymers provide low density, tunable and patternable materials. This feature article focusses on various autonomously responding photonic polymer materials such as hydrogels, block copolymers and liquid crystals and discusses their potential industrial implementation.
This feature article focuses on photonic polymers that change colouration due to an environmental stimulus and highlights their industrial feasibility.
A new principle is developed to fabricate temperature-responsive, multicolor photonic coatings that are capable of switching color. The coating is composed of a non-cross-linked liquid crystal ...siloxane-based elastomer that is interpenetrated through an acrylate-based liquid crystal network. Discrete temperature changes induce phase separation and mixing between the siloxane and the acrylate polymers and change the reflective colors correspondingly. The temperature-responsive color change of the coatings can be programmed by the processing conditions and coating formulation, which allows for the fabrication of photopatterned multicolor images. The photonic ink can be coated on flexible poly(ethylene terephthalate) films using roll-to-roll flexographic printing, making these temperature-responsive, multicolor-changing polymers appealing for applications such as responsive color decors, optical sensors, and anticounterfeit labels.
The adaptive control of sunlight through photochromic smart windows could have a huge impact on the energy efficiency and daylight comfort in buildings. However, the fabrication of inorganic ...nanoparticle and polymer composite photochromic films with a high contrast ratio and high transparency/low haze remains a challenge. Here, a solution method is presented for the in situ growth of copper‐doped tungsten trioxide nanoparticles in polymethyl methacrylate, which allows a low‐cost preparation of photochromic films with a high luminous transparency (luminous transmittance Tlum = 91%) and scalability (30 × 350 cm2). High modulation of visible light (ΔTlum = 73%) and solar heat (modulation of solar transmittance ΔTsol = 73%, modulation of solar heat gain coefficient ΔSHGC = 0.5) of the film improves the indoor daylight comfort and energy efficiency. Simulation results show that low‐e windows with the photochromic film applied can greatly enhance the energy efficiency and daylight comfort. This photochromic film presents an attractive strategy for achieving more energy‐efficient buildings and carbon neutrality to combat global climate change.
A photochromic (PC) film that simultaneously regulates solar heat and visible light entrance is introduced. On a sunny day, the film tints and blocks sunlight, which reduces energy consumption for cooling and preventing excessive brightness and glare. With weak sunlight intensity, the photochromic film becomes transparent to let sunlight enter the room, which prevents additional heating and lighting energy use.
The fabrication of reversible and robust thermochromic coatings remains challenging. In this work, a temperature-responsive photonic coating with a protective topcoat is fabricated. A cholesteric ...oligosiloxane liquid crystal possessing a smectic-to-cholesteric phase-transition temperature response is synthesized. A planar alignment of its cholesteric phase is possible with blade coating. By stabilizing with 3 wt % of a crosslinked liquid crystal network, the photonic coating shows a color change ranging from red to blue upon heating. High transparency is retained, and the structural color changes are fully reversible. A transparent polysiloxane layer can be directly applied on top of the cholesteric layer to protect it against damage without affecting its optical properties. This approach satisfies the basic requirements of thermochromic polymer coatings, as it combines easy processability, coating robustness, and a reversible temperature response.
Cholesteric liquid crystal oligomers are an interesting class of temperature responsive structurally colored materials. However, the role of endcap molecules in these oligomers is rather unexplored. ...In this work, we demonstrate the role of endcap molecules on structural color stability and hypsochromic shift in temperature-responsive cholesteric liquid crystal oligomers. First, new liquid crystal monoacrylate endcap molecules are synthesized, which are then used to synthesize various cholesteric liquid crystal oligomers. In addition, cholesteric oligomers using commercial monoacrylate endcap molecules are also prepared. It is found that the molecular weight and the polydispersity of the oligomers can be tuned by the endcapping molecules. The oligomers are used to produce reflective, structurally colored coatings. It was found that the coatings using the commercial monoacrylate lose their color and crystallize over time, most likely due to the presence of crystalline dimers. The coatings containing the newly synthesized monoacrylate endcap molecules did not exhibit this crystallization, resulting in structurally colored coatings that remained stable over time. These latter coatings possessed temperature responsive hypochromic behavior, which makes them interesting for advanced optical applications.
The fabrication of stimulus‐responsive coatings that change both reflectivity and topography is hampered by the lack of easy processable, patternable, and programmable elastomers. Here, an easily ...applied reflective coating based on a semi‐interpenetrating polymer network composed of a liquid crystal elastomer and a liquid crystal network (>15 wt%) is reported. The reflective wavelength of these polysiloxane elastomer photonic coatings can be readily programed by the concentration of chiral reactive mesogen dopant that forms the network. The coatings show a fast and reversible decrease in reflection band intensity with increasing temperature, which can be tuned by the polymer network density. In addition, hierarchical surface relief structures are prepared, which can be reversibly changed with temperature.
Responsive coatings based on liquid crystalline polysiloxane and reactive mesogens that change their reflectivity and topography are prepared. The semi‐interpenetrating network coating is fabricated by a very simple coating technique. The polymer coatings respond quickly to temperature changes by altering color and surface topographies and these properties can be easily programed by changing the ratio between the polysiloxane and the reactive mesogens.
A crosslinkable cholesteric main-chain liquid crystal oligomer was prepared, and coated on glass using blade-coating. The coating showed a reflection band that varied as a function of temperature ...over a range of several hundreds of nanometers. This allowed patterning of the coating in various colours using multiple crosslinking steps at different temperatures.
Introduction
Multiple sclerosis (MS) is a chronic inflammatory disease with an as yet not fully understood etiological background. The geographical distribution of MS is striking with a prevalence ...that increases with latitude. For this reason, vitamin D deficiency is considered a possible pathogenic co-factor in MS.
Materials and methods
To study the role of the vitamin D metabolism in MS, blood samples were taken twice (summer and winter) from 103 patients with MS and 110 healthy controls. Serum concentrations of 25-hydroxyvitamin D (25(OH) D) and 1,25-dihydroxyvitamin D (1,25(OH)2D) were measured, and detailed information on disease characteristics and environmental factors that might influence the vitamin D metabolite levels was collected.
Results
Mean serum 25(OH)D and 1,25(OH)2D concentrations were significantly higher in summer compared to winter in both patients and controls. Using logistic regression methods, we found that in women for every 10 nmol/L increase of serum 25(OH)D level the odds of MS was reduced by 19% (odds ratio 0.81; 95% confidence interval: 0.69–0.95), suggesting a “protective” effect of higher 25(OH)D serum levels. In addition, also restricted to women, a negative correlation was found between Expanded Disability Status Scale and 25(OH)D levels (r = −0.29, P = 0.020).
Conclusions
Our data suggest that higher circulating levels of 25(OH)D are associated with a lower incidence of MS and MS-related disability in women. This may imply clues to the pathogenesis of the sex difference in risk and to the nature of the environmental factors involved in MS.
Cholesteric liquid crystal oligomers are widely researched for their interesting thermochromic properties. However, structure–property relationships to program the thermochromic properties of these ...oligomers have been rarely reported. In this work, we use the versatile thiol-ene click reaction to synthesize a series of hetero-oligomers and study the impact of different compositions on the thermochromic behavior of the resulting material. Characterization of the oligomers shows significantly different rates of reaction for the monomers despite their very similar structures, which leads to oligomer compositions that do not match the original reaction feed. The oligomers are then used to produce thin near-infrared reflecting coatings. The best-performing thermochromic reflector has a room-temperature reflection band that shifts a total of 510 nanometers upon heating to 120 °C. The shift is repeatable for up to 10 times with no appreciable degradation. The room temperature reflection of the coatings is shown to be tunable not only by adjusting the chiral dopant concentration but also by the ratio of the monomers. Finally, we show that the oligomers can be chemically modified by making their reactive end groups undergo a reaction with monothiol compounds. These modifications allow for further fine-tuning of liquid crystal oligomers for heat-regulating window films, for example.
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