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    Molecular weight sensing properties of ionic liquid-polymer composite films: theory and experiment

    Year: 2014

    Journal: J. Mater. Chem. C, 2014,2, 4867-4878, 20141010

    Authors: Bishnu P. Regmi Nicholas C. Speller Michael J. AndersonJean Olivier Brutus Yonathan Merid Susmita DasBilal El-Zahab Daniel J. Hayes Kermit K. MurrayIsiah M. Warner

    Last authors: Isiah M. Warner

    Organizations: a Department of Chemistry, Louisiana State University, Baton Rouge, USA b Department of Chemistry, Columbus State University, Columbus, USA c Biomedical Engineering Department, State University of New York at Stony Brook, Stony Brook, USA d Mechanical and Materials Engineering Department, College of Engineering and Computing, Florida International University, Miami, USA e Department of Biological and Agricultural Engineering, Louisiana State University, Baton Rouge, USA

    Country: USA, United States of America

    Ionic liquids (ILs) are rapidly emerging as important coating materials for highly sensitive chemical sensing devices. In this regard, we have previously demonstrated that a quartz crystal microbalance (QCM) coated with a binary mixture of an IL and cellulose acetate can be employed for detection and molecular weight estimation of organic vapors (J. Mater. Chem. 2012, 22, 13732). Herein, we report follow-up studies aimed at formulating the theoretical basis for our previously observed relationship between molecular weight and changes in the QCM parameters. In the current work, we have investigated the vapor sensing characteristics of a series of binary blends of ILs and polymers over a wider concentration range of analytes, and a quadratic equation for estimating the approximate molecular weight of an organic vapor is proposed. Additionally, the frequency (f) and dissipation factor (D) at multiple harmonics were measured by use of a quartz crystal microbalance with dissipation monitoring (QCM-D). These QCM-D data were then analyzed by fitting to various models. It is observed that the behavior of these films can be best described by use of the Maxwell viscoelastic model. In light of these observations, a plausible explanation for the correlation between the molecular weight of absorbed vapors and the QCM parameters is presented. Our previous findings appear to be a special case of this more general observation. Overall, these results underscore the true potential of IL-based composite materials for discrimination and molecular weight estimation of a broad range of chemical vapors.