Multituning of Structural Color by Protonation and Conjugate Bases

Abstract

The pH (acidity/alkalinity) and type of acid are crucial parameters affecting the thermodynamics, kinetics, and reaction mechanism of acid–base systems. However, most reported pH-responsive materials can only determine the pH and cannot identify the acid type. Herein, we report the selective swelling of polystyrene-b-poly­(2-vinyl pyridine) (PS-b-P2VP) photonic crystals, which produces different morphologies with a change in pH or type of acid, based on Henderson–Hasselbalch principle and Coulomb coupling between pyridiniums and the conjugate bases. The swelling behavior in different acidic environments was modeled by the transfer matrix method (TMM), and the results were compared with the experimental reflectometry results. The thickness and refractive index of P2VP layers change with a change in H+ concentration or the hydration energy of the conjugate bases. Since the different morphologies produce distinct structural colors, the pH and type of acid can be directly identified visually. Furthermore, the structural color is affected by not only the molecular weight of PS-b-P2VP but also the cross-linking of the P2VP layers, which can shift the structural color wavelength, thereby changing the sensitivity to pH. Our findings can become a driving force to transcend the frontiers of conventional optical diagnostics or sensing technology.

High‐Efficiency Structural Coloration Enabled by Defect‐Free Block Copolymer Self‐Assembly for a Solar Cell Distributed Bragg Reflector

“…The most significant redshift of λ max = 638 nm was observed in the PS‐ b ‐(Q)P2VP film coupled with MSA because of the strong acidity that promotes the protonation of the P2VP block and coupling with the anions. [ 24 ] For the PS‐ b ‐(Q)P2VP films with EMIM + TFSI − , PEG, and Li + TFSI − , the λ max s of the PS‐ b ‐QP2VP films are slightly more red‐shifted than those of the PS‐ b ‐P2VP films because an increased charge density in the QP2VP block causes larger expansion in the microdomain size. However, the λ max for the films with SA and MSA are nearly identical between PS‐ b ‐P2VP and PS‐ b ‐QP2VP because of the same formation of a positive charge at the nitrogen atom in the P2VP block.…”

Recent Advances in 1D Photonic Crystals: Diverse Morphologies and Distinctive Structural Colors for Multifaceted Applications

“…Lee et al have presented an LBCP photonic lamella capable of not only determining solution pH values but also identifying the type of acid present. [103] Based on the Henderson-Hasselbalch principle and Coulomb coupling, the P2VP domain selectively swells in response to changes in H + concentration or the hydration energy of the conjugate base, leading to variations in the layer thickness and refractive index. As a result, distinct color alterations occur, enabling visual identification of pH levels and acid types.…”

4D Direct Laser Writing of Submerged Structural Colors at the Microscale

“…Among them, owing to the good biocompatibility, tunable toughness, high water content and reversible volume change, pH-responsive hydrogel (PRH) has been extensively studied that enables the sensing or display application through the transformation of shape in the solution. [16,17] For instance, Zhu et al developed a pH-responsive device by coating acrylic acid (AAC) and acrylamide (AAm) via in situ copolymerization onto Papilio Paris wings having lamellar structure, which provided the photonic crystals (PCs)-based pH sensor. [18] In addition, Park et al presented a 3D display based on multi-order reflection SCs with P2VP hydrogel.…”