Physical Characterization Methods

microscopy X rays Vis Infrared UV Neutrons scattering spectroscopy calorimetry chromatography density measurements 2 OUTLINE A host of characterization methods are used to investigate nanoscale structures at the morphological and/or molecular levels. These are listed here into broad categories: Some of these methods are briefly described here. SCATTERING METHODS This author's research interests are in Small-Angle Neutron Scattering (SANS). This characterization method probes from the near atomic (nanometer) to the near optical (micrometer) length scales and is based at a few neutron scattering research labs. It has had major impact on research in the following fields of research: polymers, complex fluids, biology and materials science. Small-Angle X-ray Scattering (SAXS) probes a size scale comparable to that of SANS. X-rays, however, are scattered from the electron cloud around atoms and are therefore characterized by different contrast factors than neutrons. SAXS and SANS complement each other with SAXS characterized by high fluxes and easy access to beamtime and SANS characterized by the advantage of partial deuteration. Dynamic Light Scattering (DLS) is the technique of choice for investigations of diffusive modes in soft materials. It is also used to measure " particle " sizes and size distributions in solutions. Wide-Angle X-ray Scattering (WAXS) monitors the molecular structure at the local " chemical " level. It is effective in detecting and quantifying the amount of crystallinity in semi-crystalline materials. The scattering variable range is higher than small-angle scattering methods. Scattering methods are based in the Fourier transform (so-called reciprocal) space. This is different from microscopy methods which are based in the direct space. The reciprocal space is hindered by the phase problem. Taking the inverse Fourier transform of 2D scattering data does not produce a unique picture in direct space whereas the Fourier transform of a microscopy picture produces a unique data set in reciprocal space. Many forms of radiation can be used for scattering purposes: X-rays, neutrons, electrons, laser light, gamma rays, etc. These have different characteristics and are used for different purposes. A Table summarizes various scattering methods. Sensitive to Inhomogeneities in Electron Density Density of Nuclei Electron Cloud Polarizability (Refractive Index) Scattering Methods SAXS, WAXS SANS, WANS LEED SLS, DLS Sample Thickness < 1 mm 1-2 mm 100 μm 1-5 mm Problems with Absorption Low Fluxes Low Penetration Scattering from Dust The small-angle neutron and X-ray scattering methods (SANS, SAXS) probe size scales from the near atomic to the near micron. …