Langmuir-blodgett thin film characterization and vapor sensing properties of boron containing materials

Abstract

Three materials, Mesitylene-2-boronic acid (MBA), phenylboronic acid (PBA) and 1-naphthylboronic acid (NBA), were selected for fabrication of Langmuir-Blodgett (LB) thin films in order to investigate the sensing properties of these materials against volatile organic vapors. UV-visible and quartz crystal microbalance (QCM) techniques were employed for monitoring of the fabrication process of thin film layers. QCM system was also used for investigating volatile organic vapor sensing abilities of LB films. In order to produce homogeneous LB thin film from the monolayer on water surface, optimum surface pressure was determined by taking the (A-t) graph, which gives the area per molecule versus time. The thin film qualities of selected molecules were found to be over 90% for the first bilayers. QCM transfer determination gave the amount of transferred mass on quartz crystal as 74 ng for MBA, 114 ng for PBA and 55 ng for NBA. All of the prepared films were found to be more sensitive to chloroform vapor than benzene, toluene and ethyl alcohol vapors. They showed fast and large responses. Reversibility was also fast following chloroform, benzene and toluene exposure. However; ethyl alcohol vapor results in irreversible changes on the films.