Photochemically Controlled Cross-Linking in Polymerized Crystalline Colloidal Array Photonic Crystals

Abstract

We developed photochemically controlled photonic crystals which may be useful in novel recordable and erasable memories and/or display devices. Information is recorded and erased by exciting the photonic crystal with ∼360 nm UV light or ∼480 nm visible light. The information recorded is read out by measuring the photonic crystal diffraction wavelength. The active element of the device is an azobenzene cross-linked hydrogel which contains an embedded crystalline colloidal array. UV excitation forms cis-azobenzene cross-links while visible excitation forms trans-azobenzene cross-links. The less favorable free energy of mixing of cis-azobenzene cross-linked species causes the hydrogel to shrink and blue-shift the photonic crystal diffraction. This is completely the opposite behavior as observed from pendant azobenzene groups we reported previously. We also observe fast nano-, micro-, and millisecond transient dynamics associated with fast heating lattice constant changes, refractive index changes, and thermal relaxations.

Advances in smart materials: Stimuli‐responsive hydrogel thin films

“…The cis‐trans isomerization photoresponse of azobenzene is commonly used in photoresponsive materials . Liu et al examined the release kinetics, poration, and swelling kinetics of a gel containing azobenzene .…”

“…Pioneering work by the Anseth group, 147 using The cis-trans isomerization photoresponse of azobenzene is commonly used in photoresponsive materials. [154][155][156] Liu et al examined the release kinetics, poration, and swelling kinetics of a gel containing azobenzene. 157 It was shown that the cis conformation allows widening of the pores, facilitating water release from the hydrogel.…”

Poly(vinyl alcohol) Rehydratable Photonic Crystal Sensor Materials

“…Alterations to the hydrogel polymer that result in an increase in the polymer solubility make the free energy of mixing more favorable, thereby swelling the hydrogel and red-shifting the diffraction wavelength. This motif was previously demonstrated for photochemically controlled photonic crystal materials [82][83][84][85] and utilized with the sensing of creatinine. [68] This new PVA photonic crystal hydrogel material efficiently Bragg diffracts light and can be reversibly dried and rehydrated, without the use of fillers, while retaining the original diffraction and swelling properties.…”

Photoresponsive interpenetrating network photonic crystal

“…This type of opticallyinduced isomerization is also of particular interest because the changes in molecular orientation of azobenzene species can affect the surrounding molecules. In addition, the induced dipole change that results from molecular reorientation can be used to induce a volume phase transition of the polymer in the vicinity of the polar azobenzene molecules [4].…”