Centrifugation-Induced Water-Tunable Photonic Colloidal Crystals with Narrow Diffraction Bandwidth and Highly Sensitive Detection of SCN^–

Abstract

Novel opal hydrogels with water-tunable photonic bandgap (PBG) exhibiting responses to external stimuli were self-assembled from polystyrene-co-poly(N,N-dimethylacrylamide) (PS-co-PDMAA) microspheres. The polymeric microspheres with narrow size distribution were successfully prepared in water, consisting of two regions. The inner region is rich in PS which is hard and hydrophobic; the outer region is rich in PDMAA which is soft and hydrophilic. The self-assembly of the PS-co-PDMAA hydrogel microspheres is ready induced by centrifugation and resulted in highly ordered three-dimensional (3D) photonic colloidal crystals (PCCs). With an increase of the amount of water, the PBG of the opal hydrogels shifted from the visible to near-infrared region of the electromagnetic spectrum. The maximum shift of diffraction peak positions could be larger than 500 nm with narrow full width at half maximum (FWHM) in the range of 20 to 40 nm only. The change in color was visible to the naked eye. The remarkable sensitivity to water of the lattice spacing of the opal hydrogels was repeatable after centrifugation. These observations are attributed to a reproducible degree of hydration of the hydrophilic outer region of the polymeric microspheres. Furthermore, the diffraction of the opal hydrogels was particularly sensitive to the presence of thiocyanate (SCN(-)) ions. The interaction between SCN(-) ions and DMAA repeat units is argued to block hydrogen bonds between DMAA and water molecules. Our PS-co-PDMAA opal hydrogels could be a practical system for diffraction-based detections.

25th Anniversary Article: Ordered Polymer Structures for the Engineering of Photons and Phonons

“…The structure showed a wavelength shift of 150 nm for a change in Hg 2+ concentration from 0 to 1 μM. Opal hydrogels of PS‐ co ‐PDMAA spheres could detect SCN − ions in the concentration range from 10–10 4 nmol/g Modified methods using the opal hydrogel PhCs were developed for the detection of Hg 2+ and ionic strength . Quaternized PS‐ b ‐P2VP (denoted PS‐ b ‐QP2VP) gels (Figure b) have pyridnium rings, which makes the film water swellable and ion exchangeable.…”

Gold Nanoparticles in Photonic Crystals Applications: A Review

“…The key factor in these results are the size and shape control of the polymeric particles, that permitted to use them for following self assembly procedures [85,86,87]. In fact, the fabrication of polymeric PCs can also be made using different technique, such as top-down lithography [88,89], or solvent-driven self-assembly [90,91]. …”

Highly Crystallized Brilliant Polymeric Photonic Crystals via Repulsion‐Induced Precipitation Assembly toward Multiresponsive Colorimetric Films

“…To address this problem, soft stimuli‐responsive microgel colloids, especially poly( N ‐isopropylacrylamide) (PNIPAM) are considered to substitute conventionally used hard microspheres such as polystyrene, poly(methyl methacrylate), or silica, generating brilliant close‐packed microgel PCs with good responsiveness . Unfortunately, their lattice structure is fragile and the issue of inferior color purity remains unsolved …”