Dispersed samples

By using dispersed samples, the surface-to-bulk ratio is increased, and standard methods of studying bulk samples will work (see the article on EXAFS). 

As established in [214], in roller-mixed PVC-based composites one observes a much better uniformity of filler distribution over the matrix volume the relative viscosity is thereby considerably reduced. That is, for a fixed filler content, the viscosity of a system with agglomerates is always higher than that of the well-dispersed sample. 

The selection of an optimum surfactant, or combination of surfactants, was necessary primarily to prevent re-agglomeration of the dispersed sample while settling. In addition, it was demonstrated that the use of a blender (Waring) was an effective aid in dispersing these two components. The violent action of the blender did not cause a change in the concn of coarse particles in the dispersion with increasing blending times up to 17 minutes... 

Tissue extracts from 19 bald eagle Haliaectas leucocephalus) carcasses were examined to determine if biomagnification of TCDD had occurred in a manner similar to DDT. These carcasses came from the states of Alaska, Maine, North Dakota, Wisconsin, Michigan, Minnesota, Arkansas, Illinois, Missouri, Maryland, Virginia, Iowa, New York, New Jersey, and Florida between 1966 and 1971 and were collected and furnished by scientists at the Patuxent Wildlife Center, U.S. Department of the Interior, Laurel, Md. The samples were selected from these states to provide a widely dispersed sampling population. 

By using the valne Q = 220 J,C/cm, one can readily determine the true surface area of any compact or disperse sample of platinnm without adducing any other methods, simply by measuring the total amount of charge required to accomplish the potential shift. 

Fig. 2 Optical microscopy image of a small section of a poly(ethylene oxide) (PEO) droplet dispersion sample, see text (1000-mm wide) obtained at Tc = - 2.6 °C. Amorphous droplets appear dark and semicrystalline droplets appear white under nearly crossed polarizers. The plot shows the fraction of crystallized droplets as a function of temperature upon cooling (0.4 °C min-1) for homogeneous nucleation. (Reprinted with permission from [84], Copyright 2004 by the American Physical Society)...

When the dispersed sample zone reaches the detector, neither the chemical reaction nor the dispersion process has reached a steady state. However, experimental conditions are held identical for both samples and standards in terms of constant residence time, constant temperature and constant dispersion. The sample concentration can thus be evaluated against appropriate standards injected in the same manner as samples (Fig. 1.1 (c)). 

The photocatalytic decomposition products of methyl orange were separated by RP-HPLC and identified by MS, MS/MS techniques. Methyl orange was irradiated in the presence of Ti02 dispersions. Samples were taken after various incubation times, filtered... 

Sandwich between NaCI discs KBr disc containing dispersed sample... 

For the assessment of dispersibility, samples of about 0.1 gram of Graphon were accurately weighed into standard tubes approximately 1.5 cm. wide and 13 cm. long fitted with B14 Quickfit joints. A known amount of solution (—10 ml.) was added and the tubes were rotated end-over-end in the thermostat at 25° at approximately 20 r.p.m. for... 

Similar results on the kinetics and temperature dependence of the recombination of electron and hole centres have been obtained [68-71] in studying highly dispersed samples of magnesium oxide MgO. As distinct from CaO, however, in MgO the hole centres are mainly stabilized on the surface (so-called Vs -centres) while the electron centres are stabilized both on the surface (Fs+ -centres) and in the volume (F1 -centres). After irradiation is over a slow recombination of radiation defects is observed... 

Infant formula Disperse sample in nonaqueous solvent mixture (DMSO/DMF/ CHC13, 2 + 2+1) containing 0.1% (w/v) ascorbic acid. Partition total lipid fraction into hexane, centrifuge. Radial-PAK cartridge containing Resolve silica 5 /xm... 

This method of extraction is different from SPE in that for the latter the samples put in the column must be in the form of a liquid solution. The interactions between the various components of the dispersed sample are stronger and to some extent different from those occurring in SPE. Specific interactions among all elements of the system, that is, analytes, interferants, the sample matrix, the solid sorbent added to the sample, and the solvent used for extraction, have been observed. The obtained extracts were purified using SPE or were subjected to final analysis using chromatographic techniques without purification. 

Fig. 23. Radial distribution around Ni. (a) Crystalline NiO. Two monolayer-dispersed samples (b) 0.10 g NiO/g -y-A Oj (c) 0.20 g NiO/g y-Al20,. Monolayer dispersion capacity is 0.26 g NiO/g y-Al203. See text for discussion of peaks.

With practice much may be learned from the shape of the sedimentation curves shown in Figure 17. Thus, a curve with a rapidly changing slope indicates a poly-dispersed sample, while a curve approaching a straight line indicates mono-dispersion. Two samples have approximately the same particle-size distribution when their slopes at corresponding times are the same. The curves are also valuable since they give a graphical comparison of the density. The relative densities of various materials sized in this manner are in accordance with the point of ordinate interception. 

A dispersed sample may also be obtained by means of an aerosol sampling device. A suitable technique is to form a sandwich of plastic film particles and 20 nm thick carbon. The underlying plastic may then be washed away with solvent and the specimen examined after shadowing 159,160,162]. 

Drop stabilization methods rely on the immediate stabilization of drops by encapsulation with thin polymer films or surfactants [219-221] a photomicrographic method has been employed usually after encapsulation of drops. However this method cannot always be used due to incompatibility of the encapsulating materials with some systems. The method also has the disadvantage of the influence of the chemical treatment on drop size. A special sampling apparatus has been developed to withdraw a sample of dispersed phase from the mixing vessel to stabilize drops with a surfactant and to force the dispersed sample through a capillary with a photometer assembly to measure both droplet size and concentration [222]. 

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