Fast Switching of Bright Whiteness in Channeled Hydrogel Networks

Amanda Eklund, Hang Zhang*, Hao Zeng, Arri Priimagi, Olli Ikkala

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

6 Citations (Scopus)
34 Downloads (Pure)

Abstract

Beside pigment absorption and reflection by periodic photonic structures, natural species often use light scattering to achieve whiteness. Synthetic hydrogels offer opportunities in stimuli-responsive materials and devices; however, they are not conventionally considered as ideal materials to achieve high whiteness by scattering due to the ill-defined porosities and the low refractive index contrast between the polymer and water. Herein, a poly(N-isopropylacrylamide) hydrogel network with percolated empty channels (ch-PNIPAm) is demonstrated to possess switchable bright whiteness upon temperature changes, obtained by removing the physical agarose gel in a semi-interpenetrating network of agarose and PNIPAm. The hydrogel is highly transparent at room temperature and becomes brightly white above 35 °C. Compared to conventional PNIPAm, the ch-PNIPAm hydrogel exhibits 80% higher reflectance at 800 nm and 18 times faster phase transition kinetics. The nanoscopic channels in the ch-PNIPAm facilitate water diffusion upon phase transition, thus enabling the formation of smaller pores and enhanced whiteness in the gel. Furthermore, fast photothermally triggered response down to tens of milliseconds can be achieved. This unique property of the ch-PNIPAm hydrogel to efficiently scatter visible light can be potentially used for, e.g., smart windows, optical switches, and, as demonstrated in this report, thermoresponsive color displays.

Original languageEnglish
Article number2000754
Pages (from-to)1-11
Number of pages11
JournalAdvanced Functional Materials
Volume30
Issue number28
DOIs
Publication statusPublished - 1 Jul 2020
MoE publication typeA1 Journal article-refereed

Keywords

  • double networks
  • hydrogels
  • interpenetrating networks
  • lower critical solution temperature
  • whiteness

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