A Study On The Assembly And Response Of Hydrogel Photonic Crystals

In this paper, poly (N-isopropylacrylmaide-co-acrylic acid) (PNIPAM-co-AAc) and poly N-isopropylacrylamide (PNIPAM) opal hydrogel photonic crystals were prepared by an easy and convenient method---hydrophobic induced method. The structures of the opal hydrogel photonic crystals were characterized by SEM and TEM. The structural color and Bragg diffraction peak of the opal hydrogel photonic crystals responsed to external stimuli. Meanwhile, the response of inverse opal hydrogel polyacrylmaide (IOH_PAM) photonic crystal to alcohol was investigated.Firstly, the monodisperse PNIPAM and PNIPAM-co-AAc microgels were prepared by precipitation polymerization. The dry diameters of microgels were about 200-300 nanometer.Secondly, the opal hydrogel photonic crystals were assembled from the monodisperse microgels by hydrophobic induced method. The sedimentary time and temperature had an effect on the preparation of hydrogel photonic crystals. The high temperature made the microgels array easily due to PNIPAM became hydrophobic above the lower critical solution temperature (LCST). The color-tunable opal hydrogel photonic crystals could be fabricated with proper sedimentary time or water content. While, the structural color and reflection spectra of the opal hydrogel photonic crystals changed with adjusting the dosage of AAc or the degree of cross- linking.Thirdly, the PNIPAM-co-AAc opal hydrogel photonic crystal could swell or shrink in response to external stimuli, such as water content, temperature or solvent (ethanol and acetone) and the structural color and reflection spectra reversibly red shifted or blue shifted. Furthermore, the structural color of the photonic crystals changed depending on incident and observation angles. The structural color blue shifted with increasing observation angle.Finally, IOH_PAM photonic crystals were prepared by template---induced capillary force method. They responded to different alcohol with variation of structural color and reflection spectra. The structural color and reflection spectra of IOH_PAM blue shifted in response to monohydric alcohol (methanol, ethanol, propanol, tertiary butyl alcohol), dihydric alcohol (1, 2-propanediol) and polyethylene glycol and red shifted in response to dihydric alcohol (ethylene glycol) and polyhydric alcohol (glycerol, sorbitol). Moreover, the response of IOH_PAM changed under the existence of different interferent in system. The interference between monohydric alcohols can be omitted, as well as the interference of monohydric alcohol to dihydric alcohol. However, the interference of dihydric alcohol to monohydric alcohol was obvious. The structural color and reflection spectra of IOH_PAM red shifted clearly with the existence of a few dihydric alcohols.