Preparation of Humidity-Sensitive Poly(Ethylene Glycol) Inverse Opal Micropatterns Using Colloidal Lithography

Humidity-sensitive poly(ethylene glycol) (PEG) inverse opals with micropatterns of 2 μm wide anti-swell-broken grooves were prepared using polystyrene (PS) colloidal crystals as templates and colloidal lithography. Monodisperse PS colloids were deposited in an ordered manner onto glass slides using a double-substrate vertical deposition method to form colloidal crystal templates. Poly(ethylene glycol) diacrylate (PEGDA) with photoinitiator was infiltrated into the interspaces of the colloidal crystals and photo-crosslinked by UV irradiation through a photomask. After removal the PS templates and unexposed PEGDA by tetrahydrofuran (THF), PEG hydrogel micropatterns with three-dimensional ordered porous structures were obtained. The band gaps of the PS colloidal crystals and corresponding PEG hydrogel inverse opals were measured by UV-VIS reflection spectrometer, calculated by Bragg law and simulated by Band SOLVE. The obtained PEG hydrogel inverse opal micropatterns can be used as sensors for humidity sensing due to absorption and desorption of moisture in the band gap structures. The sensor had a very reliable performance after repeated humidity sensing, and could be mass produced facilely with very low cost. The photopatterned anti-swell-broken grooves play an important role in the reliability of the sensors.