Abstract
In this study, thermochromic photonic gels were fabricated using 2-hydroxyethyl methacrylate (HEMA) as a hydrogel building block, and 4-Acryloyl morpholine (ACMO) and N-isopropylacrylamide (NIPAAM) as thermoresponsive monomers with different critical solution temperature behaviors. Rapid photopolymerization of opal-templated monomer mixtures of varying ACMO contents formed five individual thermochromic inverse opal photonic gels integrated on a single substrate. With temperature variation from 10 °C to 80 °C, the changes in reflective colors and reflectance spectra of the respective thermochromic gels were noted, and λpeak changes were plotted. Because NIPAAM exhibits a lower critical solution temperature (LCST) at 33 °C, the NIPAAM-only gel showed a steep slope for dλpeak/dT below 40 °C, whereas the slope became flatter at high temperatures. As the ACMO content increased in the thermochromic gel, the curve of dλpeak/dT turned out to be gradual within the investigated temperature range, exhibiting the entire visible range of colors. The incorporation of ACMO in NIPAAM-based thermochromic gels therefore enabled a better control of color changes at a relatively high-temperature regime compared to a NIPAAM-only gel. In addition, ACMO-containing thermochromic gels exhibited a smaller hysteresis of λpeak for the heating and cooling cycle.
Highlights
Despite it being uncommon, there are some two-component liquid systems that exhibit a lower critical solution temperature (LCST) below which the mixed components are miscible
(N-isopropylacrylamide) (PNIPAAM) in water is one of the most studied examples of a polymer solution exhibiting LCST behavior; it is a swollen hydrogel below its LCST at 33 ◦ C, while a temperature increase above this results in a reversible collapse transition due to the exposed isopropyl moieties
LCST than NIPAAM, those two thermoresponsive vinyl monomers are simultaneously incorporated within an opal template in order to investigate temperature-sensing photonic gel operating at high temperatures
Summary
There are some two-component liquid systems that exhibit a lower critical solution temperature (LCST) below which the mixed components are miscible. The derivatives from PACMO have a wide variety of use in peptide synthesis, enzyme immobilization, membranes for blood plasma separation, and drug release applications [4] When it comes to “smart” drug delivery applications, the LCST of a material needs to be adjusted to be at near-body temperature [5,6,7]. There have been reports of thermochromic hydrogels utilizing temperature-driven volume changes in photonic crystal structures [8,9,10,11,12,13,14,15]; some studies have made use of this by applying an opal-templated PNIPAAM hydrogel in the fabrication of thermochromic sensors in order to induce reversible volume changes near the LCST of NIPAAM [8,9]. LCST than NIPAAM, those two thermoresponsive vinyl monomers are simultaneously incorporated within an opal template in order to investigate temperature-sensing photonic gel operating at high temperatures (i.e., above 50 ◦ C)
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