Optical characterization of acetone-sensitive thin films of poly(vinyl alcohol)-g-poly(methyl acrylate)

Organic solvents are widely used as reaction media and/or for separation and purification of synthetic products in chemical and pharmaceutical industries. Many of those solvents, among them acetone, are considered to be harmful to human health. Detecting vapors of such volatile solvents present in the air can be achieved by multiple devices, but optical detection have few important advantages- easy room temperature detection without need of electrical power supply and detection based only on color/reflectance change. Among the great variety of materials, that can be implemented as sensitive media in optical chemical sensors excel polymers which change their refractive index, extinction coefficient or thickness in presence of solvent’s vapors.

In this work, acetone-sensitive thin films were deposited on a silica substrates by spin-coating of aqueous dispersions of poly(vinyl alcohol)-graft-poly(methyl acrylate) of different copolymer characteristics. In order to study the optical and sensing properties of the films thickness d, refractive index n and extinction coefficient k were calculated from measured reflectance spectra by using two-stage nonlinear curve fitting method. Sensing properties of the films were studied by measuring reflectance spectra before and after exposure to acetone vapors at room temperature and maximum reflectance change ∆R_max was calculated. The influence of copolymer characteristics on the acetone vapor-responsive properties of studied films is demonstrated and discussed.

Acknowledgments: S. Bozhilova acknowledge the National Scientific Program for young scientists and postdoctoral fellows, funded by the Bulgarian Ministry of Education and Science (MES) with DCM 577/17.08.2018.