Magnetorheological fluids (MRFs) are a type of magnetic smart material that consist of magnetic particles dispersed in a non-magnetic carrier liquid. MRFs transit reversibly from a liquid state in the absence of a magnetic field to a solid-like state on application of a magnetic field in a fraction of milliseconds due to the formation of chain-like structures by the magnetic particles. The transition from a liquid to a solid-like state is frequently studied as a function of MRF viscosity. One of the common challenges of MRFs is that with time and storage magnetic particles exhibit oxidation, corrosion, and settling. To improve the colloidal, chemical, and thermal stability of MRFs, this study focuses on introducing self-assembled monolayers, composed of alkanethiols, on the commonly used magnetic particle, iron. Despite significant work on self-assembled monolayers of alkanethiols on gold, nickel, and copper substrates, limited work has been performed on iron. To fill this knowledge gap, adsorption isotherms for alkanethiols on iron were developed and the magnetic characteristics as well as the rheological properties of the iron and alkanethiol-adsorbed iron MRFs were analyzed. While alkanethiol adsorption was strongly a function of alkyl chain length and the solvent polarity, with the maximum adsorption increasing with increasing alkyl chain length and decreasing solvent polarity in presence of polar solvents, alkanethiol adsorption had negligible effect on magnetic characteristics of the iron and rheological properties of MRFs. The effect of alkanethiol SAMs on MRF colloidal stability was also studied as a function of SAM composition and processing. The overall goal of the magnetorheological work is to develop a stable MRF with improved performance (both chemically and colloidally) using organic molecule coating to extend MRF applications.

Magnetic smart liquids: Magnetorheological fluids

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