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. 2021 Jan 20;13(2):3153-3160.
doi: 10.1021/acsami.0c19236. Epub 2021 Jan 6.

Reversible Thermochromic Photonic Coatings with a Protective Topcoat

Weixin Zhang  1   2   3 , Albert P H J Schenning  1   3 , Augustinus J J Kragt  1   3   4 , Guofu Zhou  1   2   5   4 , Laurens T de Haan  1   2
Affiliations

Reversible Thermochromic Photonic Coatings with a Protective Topcoat

Weixin Zhang et al. ACS Appl Mater Interfaces. .

Abstract

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.

Keywords: cholesteric liquid crystals; reflective coatings; stimuli-responsive photonic materials; structural color; thermochromic polymers.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Scheme 1
Scheme 1. Synthetic Route of Sm–Ch LC Siloxane 2
Scheme 2
Scheme 2. Chemical Structure of the Sm–Ch Polymer Siloxane 2 and the Fabrication of the Network-Stabilized Coatings with a Protective Topcoat
Figure 1
Figure 1
Thermochromic response of siloxane 2 coatings containing 1–4 wt % diacrylate 1 network. (a,b) Reflection band center wavelength during the first (a) heating and (b) cooling cycles between 22 °C (Sm) and 61 °C (isotropic). In (b), the data of the 1 wt % network coating are not shown due to strong scattering. (c,d) Transmission spectra of the fabricated coating with 3 wt % of network during the first (c) heating and (d) cooling cycles.
Figure 2
Figure 2
(a,b) Transmission spectra of siloxane 2-3 wt % diacrylate 1 network coating with a Sylgard topcoat, during heating (a) and cooling (b) rounds between the room temperature and isotropic temperature. (c) Comparison of the reflection band shift of the 3 wt % network coating with and without a topcoat. Data collected during the cooling round of the cycle. (d,e) Photographic images of the 3 wt % network coating with a topcoat (d) in front of a pictured background at a distance, and (e) on a black background during a temperature cycle to the isotropic phase.
Figure 3
Figure 3
Transparency (T % at 500 nm) and reflection center wavelength of the siloxane 2-3 wt % network coating with a Sylgard topcoat, during 10 cycles of heating to isotropic and cooling to room temperature (the range was 20–65 °C for each cycle). Measurements started within 1 min after the target temperature was reached.
Figure 4
Figure 4
Images of the network-stabilized coating with the topcoat partially removed before and after finger touching. The experiment was performed at 50 °C.
See this image and copyright information in PMC

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