Colloidal suspension, turbidity

In the absence of multiple scattering, the turbidity of a colloidal suspension is given as... 

It is possible to relate observed scattered intensity to turbidity through knowledge of the geometry of the photometer but calibration with substance of known turbidity is common by practice. These substances include reflecting standards, colloidal suspensions, and simple liquids. Tungstosilicic acid, H4SiW12O40,... 

Since the scattering due to dust is negligible relative to the very large scattering from colloidal suspensions, procedure (b) is inherently attractive. Using the definition of turbidity t and the interrelation between r and R90, the calibration constant of the instrument is given by... 

Hence c(g/ml) is the concentration of colloidal suspension G90 is the reading on the LS photometer at 6 = 90°, 2 is the path length, which equals the cell diameter when using a cylindrical cell t is the turbidity obtained from measurements of optical density. Table 4 gives the results of calibrating a Sofica instrument with colloidal... 

G. Mie, Contributions to the optics of turbid media, especially colloidal suspensions of... 

Urban, C., and Schurtenberger, P. (1998). Characterization of turbid colloidal suspensions using light scattering techniques combined with cross-correlation methods. J. Colloid Interf. Sci. 207, 150-158. 

Electrophoresis. Electrophoresis, or cataphoresis as it is sometimes called, is concerned with the movement of colloidal particles in an electric field. A simple apparatus, due to Burton, by which the phenomenon of electrophoresis may be demonstrated, is shown in Fig. 3. The solvent is first poured into the tube, T, followed by the colloidal suspension. If precautions are taken to avoid mixing of the solutions, boundaries between the colloidal suspension and solvent will be present at equal heights, such as a-a, and these will be visible if the suspension is colored or turbid. If now a potential is applied at the electrodes E-Er the boundaries will, in general, move. Rough estimates of the mobilities of the colloidal particles may be obtained by measuring the distances passed through by the boundaries. However, there is little or... 

In addition to the iodometiic determination, direct precipitation as barium sulfate before and after treatment with bromine was suggested for both quantitative and qualitative test for sulfur dioxide in wine (see Monier-Williams, 1927). Precipitation of SO2 after oxidation with H2O1 as the benzidine sulfate was proposed by Rothen-fusser (1929) reduction of the molybdenum in phosphomolybdic acid by the sulfite ion present in an aqueous solution of the food was proposed by Sasaki (1928) as a colorimetric method formation of a blue color from a solution of 1% methylene blue and 5% iodine in potassium iodide was proposed by Svershkov (1939). Mathers (1949) proposed a turbidimetric method based on the distillation of wine into a dilute solution of lead acetate to form a colloidal suspension of lead sulfite whose spectral transmittance in the range of 400 to 700 mn could be used as a measure of sulfur dioxide. This is similar to turbidimetric methods based on turbidity produced by adding BaCfii to a... 

When colloidal suspensions are probed by SAXS, the X-ray absorption in the solvent has to be considered because it attenuates the scattered intensities. Maximum scattering intensities are achieved for a sample transmission of 37 %, which is approximately the transmission through a 1 mm sheet of water when a typical copper anode (wavelength 1.54 nm) is used. Because of this intrinsic background turbidity, SAXS characterisation of colloidal suspensions has to be conducted in relatively small measurement volumes. 

The optical spectroscopy is commonly applied to such colloidal suspensions that obey the Rayleigh limit or the Rayleigh-Debye-Gans limit of scattering (cf. Appendix B.2). In this case the spectra usually have a smooth and monotone shape, from which only a few details of the size distribution can be deduced. Yet, for metals with a surface plasmon resonance in the optical domain (e.g. Ag or An), one observes a distinct, size dependent maximum in the turbidity spectra of nanoparticles (Fig. 2.17 cf. Njoki et al. 2007). The presence of such a maximum can clearly enhance the information content of the spectrum. 

We then study, in sections 15.4 and 15.5, how the stirring of a fluid can maintain a dispersed set of particles in suspension. Practitioners of underwater diving have remarked that water becomes turbid in the event of a storm sediments are kept in suspension within the water layer by turbulence. In a fluid at rest, Browruan motion can also maintain a colloidal suspension (e g. paint), which is composed of very fine particles. Both physical awareness and observation show that the denser and the larger the particles are, the greater is the energy of turbulence or the molecular stirring energy required to keep the particles in suspension. 

Fig. 9.4.23 Dispersibility of colloidal systems of a kind of metals in various organic liquids. er. Relative dielectric constant of liquids A, electron affinity disp, dispersion (O) floe, flocculation ( ) upon stirring, the suspension becomes turbid then particles slowly sediment) coag, coagulation ( immediately after stirring of the suspension, particles aggregate again to sediment). ( ) Boundary between disp and floe ( ) boundary between Hoc and coag. Broken lines divide each region, (a) Hexane, (b) benzene, (c) diethyl ether, (d) ethyl acetate, (e) letrahydrofuran. (0 dichloroethane. (g) benzyl alcohol, (h) 2-butanol, (i) butanol, (j) acetone, (k) ethanol. (From Ref, 23.)...

If the dispersed phase concentration is not too high, and the species are very small, light-scattering can yield size information. The theory underlying the determination of size distribution for a colloidal dispersion is quite involved [13,75,76], When a beam of light enters a suspension some light is absorbed, some is scattered, and some is transmitted. Many dilute, fine emulsions and suspensions show a noticeable turbidity given by,... 

Particles can be broadly classified as either colloids or as macroparticulate powders. Colloids typically have dimensions smaller than 1000 A and are optically transparent, while dispersed powders are generally larger and form turbid suspensions. Neither colloidal dispersions nor powder suspensions are usually monodisperse, and to the extent that particle size can influence attainable surface charge and area, many such systems will typically reflect a distribution of properties as a function of preparation method. Recent advances in synthetic techniques for providing materials with reduced polydispersity are likely to allow for better characterization of these effects in the near future. 

---