An Optical Vapor Sensor Based on Amphiphilic Block Copolymer Langmuir–Blodgett Films

Abstract

Amphiphilic block copolymers containing poly [N,N-(dimethylamino)ethyl methacrylate] block was used as a chemical sensor material in this paper. The amphiphilic block copolymer Langmuir-Blodgett (LB) thin films were prepared onto a gold-coated glass, quartz crystal and quartz glass substrates to fabricate a thin film chemical sensor element. Atomic force microscopy, quartz crystal microbalance, UV-visible spectroscopy, and surface plasmon resonance (SPR) techniques were used to characterize all the copolymer LB thin films. The mass deposited onto a quartz crystal and the frequency shifts per layer were found to be 4258.01 ng per layer (16.06 ng mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ) and 188.07 Hz per layer, respectively. Using Winspall software, all experimental SPR data were fitted and the film thickness of this the copolymer LB thin film can be evaluated. The refractive index and thickness per monolayer of LB films were determined as 1.63 ± 0.02 nm and 1.46 ± 0.07 nm, respectively. Amphiphilic block copolymer LB thin film chemical sensor element was exposed to dichloromethane, chloroform, benzene, and toluene vapors. The SPR kinetic measurements showed that the photodetector response change, ΔI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rf</sub> for saturated dichloromethane vapor is much larger than the other vapors with the ΔI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rf</sub> value of 0.081 au and with 3.5-s recovery time/4.5-s response time. It can be proposed that amphiphilic block copolymer LB thin film chemical sensor element has a good sensitivity and selectivity for saturated dichloromethane vapor.