Adaptable Ultraviolet Reflecting Polymeric Multilayer Coatings of High Refractive Index Contrast

Abstract

a series of undesirable photoreactions promoted by the absorption of UV photons, which lead to the deterioration of their mechanical and optical properties. Polymers are usually transparent to part of the UV spectrum, so a commonly employed synthetic strategy to attain UV blocking fi lms is based on embedding inorganic [3][4][5][6][7] or organic [8][9][10] UV absorbers within a polymeric matrix. The main drawback of this approximation is the short term durability of the shielding effect as a result of the photodegradation of either host, guest, or both, caused by the absorption of the same radiation from which protection is sought after. [11][12][13] Approaches based on fl exible inorganic nano structured multilayers that effi ciently refl ect radiation in an arbitrary spectral range as a result of interference effects, rather than by absorption, present a promising alternative route worth to be explored. [14][15][16][17] Unfortunately, a similar approach based on the alternation of polymeric fi lms exclusively is not feasible since the refractive index contrast typically achieved is so small that a large number of layers is required to reach a signifi cant refl ectance, and only in a narrow spectral range. [ 18,19 ] The use of all-polymeric materials of high refractive index contrast to build multilayer back refl ectors or UV shields will also be an advantage in the fi eld of fl exible and polymeric solar cells, in which some approaches based on inorganic materials have already been developed. [ 20,21 ] Very recently, some of us proved that a porous stratifi ed structure displaying strong refl ection peaks in the UV range can be attained from a block copolymer (BCP) fi lm. [ 22 ] In particular, it was demonstrated that a fi lm made of a diblock copolymer containing polystyrene (PS) and polymethyl methacrylate (PMMA), in brief [poly(styreneblock -methyl methacrylate) PS-b -PMMA)], can be used as starting material to attain ordered porous multilayers through a process that involves collective osmotic shock (COS). The fi nal structure shows alternate dense and porous layers, with signifi cant refractive index contrast, which endow it with photonic crystal properties in the UV range. At that moment, the appearance of the layered structure was hypothetically attributed to dynamic effects during the COS process occurring over ordered arrangements of isolated PMMA spheres embedded in a cross-linked PS matrix in the starting slab, which had previously been subjected to thermal and UV annealing processes. Further studies, herein reported, have demonstrated that the mechanism of formation of the porous layered structure is different to that originally A synthetic route is demonstrated to build purely polymeric nanostructured multilayer coatings, adaptable to arbitrary surfaces, and capable of effi ciently blocking by refl ection a targeted and tunable ultraviolet (UV) range. Refl ection properties are determined by optical interference between UV light beams refl ected at the interfaces between polystyrene layers of diff...

Transparent and UV‐Reflective Photonic Films and Supraballs Composed of Hollow Silica Nanospheres

“…In addition, nanoparticles are not preferred especially for cosmetic applications because growing evidence suggests that the nanoparticles could be hazardous to human health. Furthermore, a multilayer film, Bragg reflector, can be fabricated by repeated vapor deposition of ZrO 2 and SiO 2 , which can also efficiently reflect UV,4,7 but it has angle‐dependency. By contrast, colloidal glasses or correlated amorphous colloidal structures8–19 may show strong angle‐independent UV reflection when “intraparticle” or “interparticle” backscattering resonance conditions4,7 are matched for UV.…”

Lithium Tin Sulfide—a High‐Refractive‐Index 2D Material for Humidity‐Responsive Photonic Crystals

“…Although a high RI contrast and good optical device quality were achieved, the sensitivity toward vapors is severely reduced due to the limited textural porosity of the titania layer. Another approach to increase the RI contrast is to identify new porous materials with a similar or even higher RI compared to TiO 2 , although current alternatives such as WO 3 sol ( n = 2.03), ZrO 2 nanoparticles ( n = 1.70), Ta 2 O 5 nanoparticles ( n = 1.80), undoped or antimony‐doped SnO 2 films ( n (undoped) = 1.83, n (3% Sb‐doped) = 2.34) all feature lower RIs compared to dense titania or suffer from low transparency in the visible range. Thus, the highest RI contrast BSs reported so far combine highly porous silica layers stacked with dense titania layers, exhibiting an RI contrast of Δ n = 0.83, Δ n = 0.84, and Δ n = 0.89 .…”

Laser induced periodic surface structures formation by nanosecond laser irradiation of poly (ethylene terephthalate) reinforced with Expanded Graphite

“…and nanoscale. Micro-and nanostructures have been reported to modify the optical properties of the polymer surface by providing antireflective properties [20,21] or reflective ones, which allows the use as photonic crystals [22], to modify the hydrophobic or hydrophilic character [21,23], or to improve light harvesting for more efficient organic solar cells [24]. In particular, surface structuring of carbon-based polymer composites by nanoimprint lithography (NIL) has been reported to modify the wettability and mechanical properties of the materials [25] and demonstrated that the fabrication of materials with different functionalities is possible by combining the use of fillers and the control of the surface structure.…”