Browsing by Subject "Microscopes"

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    ItemOpen Access
    The formation and characterization of cyclodextrin functionalized polystyrene nanofibers produced by electrospinning
    (2009) Uyar, Tamer; Havelund, R.; Hacaloglu J.; Zhou X.; Besenbacher F.; Kingshott P.
    Polystyrene (PS) nanofibers containing the inclusion complex forming beta-cyclodextrin (β-CD) were successfully produced by electrospinning aimed at developing functional fibrous nanowebs. By optimization of the electrospinning parameters, which included varying the relative concentration of PS and β-CD in the solutions, bead-free fibers were produced. Homogeneous solutions of β-CD and PS in dimethylformamide (DMF) were used with concentrations of PS varying from 10% to 25% (w/v, with respect to DMF), and β-CD concentrations of 1% to 50% (w/w, with respect to PS). The presence of β-CD facilitated the production of bead-free PS fibers even from lower polymer concentrations as a result of the higher conductivity of the PS/CD solutions. The morphology and the production of bead-free PS/CD fibers were highly dependent on the β-CD contents. Transmission electron microscope (TEM) and atomic force microscope (AFM) images showed that incorporation of β-CD yielded PS fibers with rougher surfaces. Thermogravimetric analysis (TGA) and direct insertion probe pyrolysis mass spectroscopy (DP-MS) results confirmed the presence of β-CD in the PS fibers. X-ray diffraction (XRD) spectra of the fibers indicated that the β-CD molecules are distributed within the PS matrix without any phase separated crystalline aggregates up to 40% (w/w) β-CD loading. Furthermore, chemical analyses by Fourier transform infrared (FTIR) spectroscopy studies confirm that β-CD molecules are located within the PS fiber matrix. Finally, preliminary investigations using x-ray photoelectron spectroscopy (XPS) and time-of-flight static secondary ion mass spectrometry (ToF-static-SIMS) show the presence of the cyclodextrin molecules in the outer molecular layers of the fiber surfaces. The XPS and ToF-SIMS findings indicate that cyclodextrin functionalized PS webs would have the potential to be used as molecular filters and/or nanofilters for the purposes of filtration/purification/separation owing to surface associated β-CD molecules which have inclusion complexation capability. © 2009 IOP Publishing Ltd.
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    ItemOpen Access
    A highly sensitive atomic force microscope for linear measurements of molecular forces in liquids
    (American Institute of Physics, 2005) Patil, S.; Matei, G.; Dong, H.; Hoffmann, P. M.; Karaköse, M.; Oral, A.
    We describe a highly improved atomic force microscope for quantitative nanomechanical measurements in liquids. The main feature of this microscope is a modified fiber interferometer mounted on a five axis inertial slider which provides a deflection sensitivity that is significantly better than conventional laser deflection based systems. The measured low noise floor of 572.0 fmHz provides excellent cantilever amplitude resolution. This allows us to operate the instrument far below resonance at extremely small cantilever amplitudes of less than 1 Å. Thus linear measurements of nanomechanical properties of liquid systems can be performed. In particular, we present measurements of solvation forces in confined octamethylcyclotetrasiloxane and water with amplitudes smaller than the size of the respective molecules. In general, the development of the instrument is important in the context of quantitative nanomechanical measurements in liquid environments.
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    Increasing the sensitivity of the scanning acoustic microscope to anisotropy
    (IEEE, 1987) Atalar, Abdullah
    The response of the scanning acoustic microscope to anisotropic materials is theoretically investigated. For this purpose, the reflection coefficient of plane acoustic waves incident on a liquid-anisotropic-solid interface is calculated. The reflection coefficient depends, in general, on polar and azimuthal angles of incidence. For the acoustic microscope case, a mean reflectance function can be defined which depends only on the polar angle, because there is a circular symmetry. With this mean reflectance function it is possible to explore the effects of changing the lens parameters such as the acoustic field at the back side of the lens. It is found that the response of the scanning acoustic microscope can depend heavily on the orientation of the solid material under investigation, provided that a suitable lens insonification is utilized. The amplitude of the acoustic microscope signal is influenced by the orientation of the material, because there is an interference between the acoustic waves reflected from the material surface at different azimuthal angles. This interference is revealed as a minimum in the mean reflectance function. It is shown by computer simulation that sensitivity to orientation can be increased by use of a ring-shaped transducer in the near field of the acoustic lens. With such lenses, it may be possible to determine the orientation of crystallites in a material.