Photopatternable Nanolayered Polymeric Films with Fast Tunable Color Responses Triggered by Humidity

Abstract

Smart surfaces that can dynamically respond to environmental stimuli have demonstrated great promise in wearable electronics and optical detectors. Herein, a photopatternable nanolayered polymeric film that can reversibly display and hide structural colors in the visible range in response to relative humidity (RH) changes is reported. This film is fabricated on a silicon substrate using layer-by-layer assembly of chitosan and photoreactive carboxymethyl cellulose-azido derivative, and selectively crosslinked through UV irradiation from a photomask. Compared to crosslinked regions, un-crosslinked ones swell more and result in a larger thickness at high RH; as a result, those two regions show distinguishable color differences. The correlation of displayed color with film thickness at various RHs is plotted in an International Commission on Illumination (CIE) chromaticity diagram, which is in good agreement with the results obtained from modeling based on the interference theory. It is demonstrated that the structural color patterns on the film can be hidden and displayed spontaneously by contact with humid air, including human breath.This humidity-triggered color change is fast, of fine resolution, highly reversible, and compatible with most silicon-based devices. This film is low-cost, stable, and ready to be applied to large surface areas for potential applications in anticounterfeiting, humidity sensors, and optical color filters.

Tunable Surface Nanotopography with Disordered Hyperuniformity in Poly(ethylenimine)/Alginate-Based Multilayered Films

“…This observation aligns well with previously reported film systems in the literature. , , The mechanism underlying the two growth regimes observed in PEM films is attributed to the diffusion behavior of the polyelectrolyte chains “in and out” of the film matrix. During each deposition step, the incoming polyelectrolyte chains diffuse into the preassembled layers, while in the subsequent step, partial outward diffusion occurs upon exposure to the oppositely charged polyelectrolyte solution.…”

Tunable Surface Nanotopography with Disordered Hyperuniformity in Poly(ethylenimine)/Alginate-Based Multilayered Films

“…This observation aligns well with previously reported film systems in the literature. , , The mechanism underlying the two growth regimes observed in PEM films is attributed to the diffusion behavior of the polyelectrolyte chains “in and out” of the film matrix. During each deposition step, the incoming polyelectrolyte chains diffuse into the preassembled layers, while in the subsequent step, partial outward diffusion occurs upon exposure to the oppositely charged polyelectrolyte solution.…”

Nanophotonic Structural Colors

“…Due to the fade-resistant nature of structural colors, they can be used in unique and covert product tagging of luxury items, ,, for example, with colorful miniature models, as shown in Figure a, where colors are realized by shrinking three-dimensional (3D) photonic crystals . Another interesting application is colorimetric sensing. − Structural color elements can be designed such that they visually respond to different external stimuli such as temperature, chemicals, and humidity through the use of suitable materials in an optically resonant system. − The benefit of colorimetric sensing is in realizing passive devices that are untethered to an energy source. Figure b depicts a colorimetric sensor in that weakly cross-linked polydimethylsiloxane (PDMS) is used in an FP cavity with a porous Ni film on top.…”

Structural Color Materials for Optical Anticounterfeiting

“…Gan and co‐workers reported a photopatternable crosslinking strategy for invisible encryption based on a hydrogel interferometer of photoreactive carboxymethyl cellulose‐azido derivative. [ 98 ] The Bragg reflector was formed via layer‐by‐layer assembly of chitosan and a photoreactive cellulose. A masked UV irradiation led to crosslinked regions.…”

Tunable Surface Nanotopography with Disordered Hyperuniformity in Poly(ethylenimine)/Alginate-Based Multilayered Films

“…This observation aligns well with previously reported film systems in the literature. , , The mechanism underlying the two growth regimes observed in PEM films is attributed to the diffusion behavior of the polyelectrolyte chains “in and out” of the film matrix. During each deposition step, the incoming polyelectrolyte chains diffuse into the preassembled layers, while in the subsequent step, partial outward diffusion occurs upon exposure to the oppositely charged polyelectrolyte solution.…”

Nanophotonic Structural Colors

“…Due to the fade-resistant nature of structural colors, they can be used in unique and covert product tagging of luxury items, ,, for example, with colorful miniature models, as shown in Figure a, where colors are realized by shrinking three-dimensional (3D) photonic crystals . Another interesting application is colorimetric sensing. − Structural color elements can be designed such that they visually respond to different external stimuli such as temperature, chemicals, and humidity through the use of suitable materials in an optically resonant system. − The benefit of colorimetric sensing is in realizing passive devices that are untethered to an energy source. Figure b depicts a colorimetric sensor in that weakly cross-linked polydimethylsiloxane (PDMS) is used in an FP cavity with a porous Ni film on top.…”

Structural Color Materials for Optical Anticounterfeiting

“…Gan and co‐workers reported a photopatternable crosslinking strategy for invisible encryption based on a hydrogel interferometer of photoreactive carboxymethyl cellulose‐azido derivative. [ 98 ] The Bragg reflector was formed via layer‐by‐layer assembly of chitosan and a photoreactive cellulose. A masked UV irradiation led to crosslinked regions.…”

Tunable Surface Nanotopography with Disordered Hyperuniformity in Poly(ethylenimine)/Alginate-Based Multilayered Films

“…This observation aligns well with previously reported film systems in the literature. , , The mechanism underlying the two growth regimes observed in PEM films is attributed to the diffusion behavior of the polyelectrolyte chains “in and out” of the film matrix. During each deposition step, the incoming polyelectrolyte chains diffuse into the preassembled layers, while in the subsequent step, partial outward diffusion occurs upon exposure to the oppositely charged polyelectrolyte solution.…”

Nanophotonic Structural Colors

“…Due to the fade-resistant nature of structural colors, they can be used in unique and covert product tagging of luxury items, ,, for example, with colorful miniature models, as shown in Figure a, where colors are realized by shrinking three-dimensional (3D) photonic crystals . Another interesting application is colorimetric sensing. − Structural color elements can be designed such that they visually respond to different external stimuli such as temperature, chemicals, and humidity through the use of suitable materials in an optically resonant system. − The benefit of colorimetric sensing is in realizing passive devices that are untethered to an energy source. Figure b depicts a colorimetric sensor in that weakly cross-linked polydimethylsiloxane (PDMS) is used in an FP cavity with a porous Ni film on top.…”

Structural Color Materials for Optical Anticounterfeiting

“…Gan and co‐workers reported a photopatternable crosslinking strategy for invisible encryption based on a hydrogel interferometer of photoreactive carboxymethyl cellulose‐azido derivative. [ 98 ] The Bragg reflector was formed via layer‐by‐layer assembly of chitosan and a photoreactive cellulose. A masked UV irradiation led to crosslinked regions.…”