Browsing by Subject "Nanofluidics"

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    Core/shell-structured, covalently bonded TiO2/poly(3,4-ethylenedioxythiophene) dispersions and their electrorheological response: The effect of anisotropy
    (Royal Society of Chemistry, 2015) Erol, O.; Unal, H. I.
    As a new electrorheological (ER) material, core/shell nanorods composed of a titania core and conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) shell were prepared via covalent bonding to achieve a thin polymer shell and make the interfacial interactions between the two components more impressive. The successful coating of PEDOT on the nanorod-TiO2 particles was confirmed by TEM analysis. The antisedimentation stability of the core/shell nanorod-TiO2/PEDOT particles was determined to be 100%. The ER properties of the materials were studied under controlled shear, oscillatory shear and creep tests. The dielectric spectra of the dispersions were obtained to further understand their ER responses and fitted with the Cole-Cole equation. The ER behavior of the dispersions was also observed using an optical microscope. The flow curves of these ER fluids were determined under various electric field strengths and their flow characteristics examined via a rheological equation using the Cho-Choi-Jhon (CCJ) model. In addition, the results were also compared with nanoparticle-TiO2/PEDOT. It was concluded that the conducting thin polymer shell and elongated structure of the hybrid material introduced a synergistic effect on the electric field induced polarizability and colloidal stability against sedimentation, which resulted in stronger ER activity, storage modulus and higher recovery after stress loadings when compared to nanoparticle-TiO2/PEDOT. © The Royal Society of Chemistry.
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    Nanomechanical measurement of the Brownian force noise in a viscous liquid
    (American Chemical Society, 2020) Arı, A. B.; Hanay, Mehmet Selim; Paul, M. R.; Ekinci, K. L.
    We study the frequency spectrum of the thermal force giving rise to Brownian motion of a nanomechanical beam resonator in a viscous liquid. In the first set of experiments, we measure the power spectral density (PSD) of the position fluctuations of the resonator around its fundamental mode at its center. Then, we measure the frequency-dependent linear response of the resonator, again at its center, by driving it with a harmonic force that couples well to the fundamental mode. These two measurements allow us to determine the PSD of the Brownian force noise acting on the structure in its fundamental mode. The PSD of the force noise from multiple resonators spanning a broad frequency range displays a “colored spectrum” and follows the dissipation of a blade oscillating in a viscous liquid—by virtue of the fluctuation–dissipation theorem of statistical mechanics.