Diffuse Scattering Apparatus

Fig. 18. Schematic diagram of the long-wavelength elastic diffuse scattering apparatus used to study the paramagnetic scattering from ruby [Ref. (20)]...

The static laser light scattering apparatus used as an on-line GPC detector has been popular for a while. Here, we illustrate another but less known method of combining the results from (gel permeation chromatography) and DLS. The basic principle is as follows There is a similarity between these two tools in that the translational diffusion coefficient D obtained by DLS and the elution volume V in GPC are related to the hydrodynamic size of a given macromolecule. In a first approximation, if the hydrodynamic size is proportional to the molar mass, we have... 

Fig. 18. Diagram of reactive scattering apparatus for the study of non-metal reactions A, scattering chamber B, source chambers C, liquid nitrogen cooled cold shield D, detector E, source bulkheads G, liquid nitrogen trap H, oil diffusion pumps N, free radical source P, nozzle source Q, skimmer E, ion source H, liquid He trap I, ion lenses P, photomultiplier Q, quadrupole rods R, light baffle S, slide valve T, radial electric field pumps (from C. F. Carter et al. 02 by permission of the Chemical...

Arachin, 93.7% iS2o 13.3 and 6.3% <820" 21.1, was examined in phosphate buffer, n = 0.5, pH 7.4, protein concentration 0.38 g./lOO ml., by means of light scattering apparatus. In a filtered solution arachin had an apparent molecular weight of 17,000,000 with ho/1120 of 1.8. On further clarification by ultrafiltration, the molecular weight was 333,000 with ho/1 no of 1.074. This value is in agreement with the accepted value for the molecular weight of arachin of 330,000 calculated from sedimentation and diffusion constants (89). 

The ultimate resolution available today with a state-of-the-art He-atom scattering apparatus is better than 100 peV and allows to study diffusion of adsorbates on surfaces by analyzing the energetic width of the quasi-elastic scattering peak [88FRE]. The method has been applied to quite different systems, e.g. H/Pt(lll) [99GRA] andXe/Pt(lll)[99EEE]. 

An alternative to the common device of determining relative intensities is a study of the fine structure of the scattered beam. This entails resolving the spectrum of scattered light into its three peaks, viz. a central peak and two side ones. The need is thus obviated to refer to I0 or, according to the apparatus, the scattering power of a standard calibration material. The method is used mainly for determining diffusion constants and thermodynamic properties of liquids. 

From QELS the diffusion coefficient, and hence the particle radius, can be found, provided the particles are spherical and homodlsperse and the sol is dilute. Deconvolution is difficult when one of these premises does not apply. Dilution of the sol is a prerequisite to avoid multiple scattering and any hydrodynamic interaction between the particles. A variety of apparatus is nowadays commercially available, based on one of the above-mentioned techniques, or a combination of them, so that velocity and size are both obtained. With some of these instruments size and/or velocity distributions can be derived, but the caveat must be made that these tend to be based on software progreims in which a certain type of distribution is presupposed. 

As implied above, the complete setup for measuring diffuse elastic x-ray scattering from supercritical solutions has been assembled. The cells and their seals have been successfully tested up to the maximum pressure. What remains for the sample containing portion of the apparatus is to test it under supercritical conditions by adding the elevated temperature. 

The size distribution of the liposomes is determined by dynamic light scattering (DLS) with a Dynapro apparatus (http //www.wyatt.com). DLS is a hydrodynamic method by which one determines the rate of diffusion of particles through the solvent. The hydrodynamic radius is defined as the radius of a theoretical hard sphere that diffuses with the same speed as the particle under examination. The measurement is performed at 25° and requires about 2 /ul of the extruded liposome suspension diluted in 18 /ul of liposome buffer (final lipid concentration in the range of 0.1 roM). Ten autocorrelation functions are sequentially measured, from which the size distribution of the liposome is determined using the Dynamics v5 software from Dynapro. A complete measurement takes a few minutes. Figure lA shows typical size distributions of extruded liposomes as determined by DLS. Figure IB shows how the actual hydrodynamic radius of the liposomes varies with the pore size of the polycarbonate filter. 

Scanning tunneling microscopy Light-scattering Ion beam analysis (forward recoil spectrometry) Chaudhury-Whitesides apparatus Atomic resolution, relatively inexpensive Determines interior surface areas Surface composition and diffusion coefficients can be determined Measures adhesion forces nondestructively Resolution limited with insulating materials Secondary scattering must be eliminated Length scale resolution 150 A at best Polymer must be in the rubber-elastic state... 

FIGURE 37.14 Schematic of apparatus to study light scattering in diffuse transmitting material. 

Second, the diffuse X-ray background caused by air, apparatus, Compton scattering, thermal agitation of atoms and molecules, as well as structural distortions and defects (e.g., vacancies) should be subtracted. 

The specific surface Ssp of silver blacks was determined by the BET method through the adsorption of N2. The specific surface of supported Ag catalysts was calculated from the data on chemisorption of O2. Size distribution of Ag particles was obtained by transmission electron microscope JEM-100 CX and the SAXS method (KRM-1 apparatus). An average value of the regions of coherent X-ray scattering was determined through the widening of X-ray lines registered with a DRON type apparatus. Spectra of diffused reflection were recorded by the Shimadzu UV-300 spectrometer. 

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