Colorimetric Humidity Sensor Using Inverse Opal Photonic Gel in Hydrophilic Ionic Liquid

We demonstrate a fast response colorimetric humidity sensor using a crosslinked poly(2-hydroxyethyl methacrylate) (PHEMA) in the form of inverse opal photonic gel (IOPG) soaked in 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM+][BF4−]), a non-volatile hydrophilic room temperature ionic liquid (IL). An evaporative colloidal assembly enabled the fabrication of highly crystalline opal template, and a subsequent photopolymerization of PHEMA followed by solvent-etching and final soaking in IL produced a humidity-responsive IOPG showing highly reflective structural color by Bragg diffraction. Three IOPG sensors with different crosslinking density were fabricated on a single chip, where a lightly crosslinked IOPG exhibited the color change response over entire visible spectrum with respect to the humidity changes from 0 to 80% RH. As the water content increased in IL, thermodynamic interactions between PHEMA and [BMIM+][BF4−] became more favorable, to show a red-shifted structural color owing to a longitudinal swelling of IOPG. Highly porous IO structure enabled fast humidity-sensing kinetics with the response times of ~1 min for both swelling and deswelling. Temperature-dependent swelling of PHEMA in [BMIM+][BF4−] revealed that the current system follows an upper critical solution temperature (UCST) behavior with the diffraction wavelength change as small as 1% at the temperature changes from 10 °C to 30 °C.

[1]  Lei Jiang,et al.  Colorful humidity sensitive photonic crystal hydrogel , 2008 .

[2]  S. Asher,et al.  Responsive ionic liquid-polymer 2D photonic crystal gas sensors. , 2014, The Analyst.

[3]  Wonmok Lee,et al.  Optimization of Emulsion Polymerization for Submicron-Sized Polymer Colloids towards Tunable Synthetic Opals , 2010 .

[4]  Daihyun Kim,et al.  Quasi‐Amorphous Colloidal Structures for Electrically Tunable Full‐Color Photonic Pixels with Angle‐Independency , 2010, Advanced materials.

[5]  C. Friedrich,et al.  Study of the PVA hydrogel behaviour in 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid , 2011 .

[6]  Di Zhang,et al.  Full-color CO2 gas sensing by an inverse opal photonic hydrogel. , 2013, Chemical communications.

[7]  Younan Xia,et al.  Assembly of Nanoparticles into Opaline Structures over Large Areas , 1999 .

[8]  Edward J Maginn,et al.  Influence of water on diffusion in imidazolium-based ionic liquids: a pulsed field gradient NMR study. , 2009, The journal of physical chemistry. B.

[9]  Sanford A. Asher,et al.  Photonic Crystal Chemical Sensors: pH and Ionic Strength , 2000 .

[10]  T. Kanai,et al.  Swelling of Gel-Immobilized Colloidal Photonic Crystals in Ionic Liquids , 2011 .

[11]  Wonmok Lee,et al.  Rapid on-chip integration of opal films and photonic gel sensor array via directed enhanced water evaporation for colloidal assembly , 2016 .

[12]  G. Ozin,et al.  Electroactive inverse opal: a single material for all colors. , 2009, Angewandte Chemie.

[13]  O. Wichterle,et al.  Hydrophilic Gels for Biological Use , 1960, Nature.

[14]  Yadong Yin,et al.  Highly tunable superparamagnetic colloidal photonic crystals. , 2007, Angewandte Chemie.

[15]  Sangyoon Lee,et al.  Full Color Tunable Photonic Crystal from Crystalline Colloidal Arrays with an Engineered Photonic Stop‐Band , 2012, Advanced materials.

[16]  Tsutomu Sawada,et al.  Photonic rubber sheets with tunable color by elastic deformation. , 2006, Langmuir : the ACS journal of surfaces and colloids.

[17]  Mingfang Yu,et al.  The Physical Properties of Aqueous Solutions of the Ionic Liquid [BMIM][BF4] , 2006 .

[18]  J. Holtz,et al.  Polymerized colloidal crystal hydrogel films as intelligent chemical sensing materials , 1998 .

[19]  D. Armstrong,et al.  Solvent properties of the 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid , 2003, Analytical and bioanalytical chemistry.

[20]  Anjal C. Sharma,et al.  Photonic crystal aqueous metal cation sensing materials. , 2003, Analytical chemistry.

[21]  Jane F. Bertone,et al.  A lost-wax approach to monodisperse colloids and their crystals. , 2001, Science.

[22]  Seung-Man Yang,et al.  Dynamic Modulation of Photonic Bandgaps in Crystalline Colloidal Arrays Under Electric Field , 2010, Advanced materials.

[23]  Paul V Braun,et al.  Glucose-sensitive inverse opal hydrogels: analysis of optical diffraction response. , 2004, Langmuir : the ACS journal of surfaces and colloids.

[24]  André C. Arsenault,et al.  Photonic-crystal full-colour displays , 2007 .

[25]  Masayoshi Watanabe,et al.  Tuning Structural Color Changes of Porous Thermosensitive Gels through Quantitative Adjustment of the Cross-Linker in Pre-gel Solutions , 2003 .

[26]  Pierre Wiltzius,et al.  Humidity-sensing inverse opal hydrogels. , 2006, Langmuir : the ACS journal of surfaces and colloids.

[27]  S. Asher,et al.  Enabling Thermoreversible Physically Cross-Linked Polymerized Colloidal Array Photonic Crystals. , 2008, Chemistry of materials : a publication of the American Chemical Society.

[28]  Wonmok Lee,et al.  Dually tunable inverse opal hydrogel colorimetric sensor with fast and reversible color changes , 2012 .