While numerous near-infrared (NIR) materials have emerged, most of them are strongly colored or black due to the absorption band or tails in the visible region. Here, a highly transparent and soluble NIR-absorbing ionic salt, isobutyl-substituted diimmonium borate (IDI), is synthesized and fabricated, through a solution process, as a thin film that shows a transmittance of over 93% in the whole visible region. A transparent photothermal (PT) film heater is fabricated with the IDI-doped polymer solution, which shows a photothermal conversion efficiency (ηPT) of 75.2%. Additionally, the prepared PT heater shows a high water evaporation conversion efficiency (ηw) of 68.8% upon exposure to a 1064 nm laser. Furthermore, the transparent IDI film affords the development of a wireless transparent actuator for the first time, generating a bending angle over 75°, with over 2700 bending cycles. The transparent IDI film creates a hot transparent Venus flytrap and a colorful or fluorescent actuator upon the addition of colorants without losing the actuation properties.
Bibliographical noteFunding Information:
This research was supported by a National Research Foundation (NRF) grant funded by Korean government (Ministry of Science, ICT & Future Planning, MSIP) through the Global Research Lab (GRL: 2016K1A1A2912753) and Creative Materials Discovery Program (2018M3D1A1058536). E.K. conceived and designed the experiments. M.H. performed all the experiments related to IDI synthesis, preparation of PT films, and most of the characterizations. B.K. and H.L. helped mechanisms and the reproducibility test. H.J. performed SEM analysis. E.K. wrote the manuscript and commented on the results. E.K. supervised the project and is the principal investigator of the supporting grants.
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All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Mechanics of Materials
- Mechanical Engineering