Windows are vital elements in the built environment that have a large impact on the energy consumption in indoor spaces, affecting heating and cooling and artificial lighting requirements. Moreover, ...they play an important role in sustaining human health and well‐being. In this review, we discuss the next generation of smart windows based on organic materials which can change their properties by reflecting or transmitting excess solar energy (infrared radiation) in such a way that comfortable indoor temperatures can be maintained throughout the year. Moreover, we place emphasis on windows that maintain transparency in the visible region so that additional energy is not required to retain natural illumination. We discuss a number of ways to fabricate windows which remain as permanent infrared control elements throughout the year as well as windows which can alter transmission properties in presence of external stimuli like electric fields, temperature and incident light intensity. We also show the potential impact of these windows on energy saving in different climate conditions.
In this review, smart windows are discussed which reflect excess of solar energy (infrared radiations) in summer and allow entrance into the building during winter, without interfering with visible light, to save significant amounts of energy in heating, cooling and lighting.
A blue reflective photonic polymer coating which can be patterned in full color, from blue to red, by printing with an aqueous calcium nitrate solution has been fabricated. Color change in the ...cholesteric liquid-crystalline polymer network over the entire visible spectrum is obtained by the use of nonreactive mesogen. The pattern in the coating is hidden in the blue color dry state and appears upon exposure to water or by exhaling breath onto it due to different degrees of swelling of the polymer network. The degree of swelling depends on the printed amount of calcium which acts as a cross-linker. The printed full color pattern can also be hidden simply by using a circular polarizer. The responsive full color camouflage polymers are interesting for various applications ranging from responsive house and automobile decors to anticounterfeit labels and data encryption.
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.
Hierarchical self-assembly offers a powerful strategy for producing molecular nanostructures. Although widely used, the mechanistic details of self-assembly processes are poorly understood. We ...spectroscopically monitored a nucleation process in the self-assembly of p-conjugated molecules into helical supramolecular fibrillar structures. The data support a nucleation-growth pathway that gives rise to a remarkably high degree of cooperativity. Furthermore, we characterize a helical transition in the nucleating species before growth. The self-assembly process depends strongly on solvent structure, suggesting that an organized shell of solvent molecules plays an explicit role in rigidifying the aggregates and guiding them toward further assembly into bundles and/or gels.
While the microfluidic device itself may be small, often the equipment required to control fluidics in the chip unit is large
e.g.
pumps, valves and mixing units, which can severely limit practical ...use and functional scalability. In addition, components associated with fluidic control of the device, more specifically the valves and pumps, contribute significantly to the overall unit cost. Here we sketch the problem of a gap between high end accurate, but expensive sensor platforms,
versus
less accurate, but widely employable hand-held low-cost devices. Recent research has shown that the integration of light-responsive materials within microfluidic devices can provide the function of expensive fluidic components, and potentially enable sophisticated measurements to be made using much less expensive equipment. An overview of the most recent developments will be presented for valves, mixers, transport and sample handling inside microfluidic devices.
Light responsive polymers will drive revolutionary changes in microfluidics by reducing costs, platform dimensions and complexity.
The iridescence of structural color and its polarization characteristics originate from the nanoscale organization of materials. A major challenge in materials science is generating the bright, ...lustrous hues seen in nature through nanoscale engineering, while simultaneously controlling interaction of the material with different light polarizations. In this work, a suitable chiral nematic liquid crystal elastomer ink is synthesized for direct ink writing, which self‐assembles into a chiral photonic structure. Tuning the writing direction and speed leads to the programmed formation of a slanted photonic axis, which exhibits atypical iridescence and polarization selectivity. After crosslinking, a freely programmable, chiroptical photonic polymer material is obtained. The strongly perspective‐dependent appearance of the material can function as specialized anticounterfeit markers, as optical elements in decorative iridescent coatings, or, as demonstrated here, in optically based signaling features.
Inspired by natural examples of patterned iridescence, an ink based on a chiral nematic liquid crystal that can be processed with a direct ink writer 3D printer is shown. Tuning the writing direction and speed leads to the programmed formation of a slanted photonic axis that exhibits atypical iridescence and polarization selectivity.
We report on the fabrication of a rewritable and reprogrammable dual‐photoresponsive liquid crystalline‐based actuator containing an azomerocyanine dye that can be locally converted into the ...hydroxyazopyridinium form by acid treatment. Each dye absorbs at a different wavelength giving access to programmable actuators, the folding of which can be controlled by using different colors of light. The acidic patterning is reversible and allows the erasing and rewriting of patterns in the polymer film, giving access to reusable, adjustable soft actuators.
Bending patterns: Rewritable and reprogrammable actuators can be obtained by using the local activation of an initially chemically homogenous film. The locally activated material is exposed to UV light, which results in the precise folding of the actuator. By switching the wavelength, a different shape can be obtained. Furthermore, the pattern can be erased and a new one can be written, giving access to a multitude of actuated shapes.
3D Helix Engineering in Chiral Photonic Materials Kragt, Augustinus J. J.; Hoekstra, Davey C.; Stallinga, Sjoerd ...
Advanced materials (Weinheim),
08/2019, Letnik:
31, Številka:
33
Journal Article
Recenzirano
Odprti dostop
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.
Transparent, ultradrawn, ultrahigh molecular weight polyethylene (UHMWPE)/graphene nanocomposite films with a high thermal conductivity are successfully fabricated by solution‐casting and solid‐state ...drawing. It is found that the low optical transmittance (<75%) of the ultradrawn UHMWPE/graphene composite films is drastically improved (>90%) by adding 2‐(2H‐benzontriazol‐2‐yl)‐4,6‐ditertpentylphenol (BZT) as a second additive. This high transmission is interpreted in terms of a reduced void content in the composite films and the improved dispersion of graphene both of which decrease light scattering. The high thermal conductivity is attributed to the π–π interaction between BZT and graphene. In addition, a high specific thermal conductivity of ≈75 W m−1 K−1 ρ−1 of the ultradrawn UHMWPE/graphene/BZT composite films is obtained, which is higher than most metals and polymer nanocomposite. These transparent films are potentially excellent candidates for thermal management in various applications due to a combination of low density, ease of processing, and high thermal conductivity.
Highly transparent, ultradrawn, ultrahigh molecular weight polyethylene (UHMWPE)/graphene nanocomposite films without light scattering are fabricated by adding small amounts of graphene/2‐(2H‐benzontriazol‐2‐yl)‐4,6‐ditertpentylphenol (BZT) mixtures. Such transparent films exhibit a high specific thermal conductivity in comparison to most metals, which suggests that these films are potentially useful in applications such as windows.
An optical calcium sensor is fabricated based on a cholesteric liquid crystalline (CLC) polymer containing benzoic acid metal binding sites. A chiral imprinted CLC polymer is made which is ...subsequently treated with KOH to yield a responsive green reflecting film. On investigation of various metal ions, the polymer film shows a high optical response, and selectivity for calcium ions, which is related to the preorganized binding sites in the ordered liquid crystalline phase, leading to a blue reflecting film. The photonic polymer film is sensitive to Ca2+ within the physiologically relevant concentration range of 10−4 to 10−2 m. Measurement of total calcium concentration in serum is also investigated using the film. The optical responses of normal serum and samples mimicking hypocalcemia and hypercalcemia can be clearly distinguished, providing a cheap, battery‐free, and easy‐to‐use alternative for calcium determination in clinical diagnostics.
Detection of calcium ions in aqueous solutions is realized by an optical sensor based on a cholesteric liquid crystalline polymer. It shows a color change from green to blue discernable by the naked eye. A proof of principle for the viability of this calcium sensor in the field of clinical diagnostics is also presented.
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