Colloidal stability test

Testing of G-l, G-2, and G-3 dendrimers in this application provided insight into the density of surface modification needed to passivate completely the particles and prevent aggregation. The G-l dendron was insufficient in this regard, but both the G-2 and G-3 dendron were big enough to create a surface barrier, which resulted in excellent colloidal stability of the particles in solution. 

Experimental measurements in each lake included particle concentration and size measurements in the water column, sedimentation fluxes in sediment traps, and chemical and size characteristics of materials recovered from sediment traps. The colloidal stability of the particles in the lake waters was determined with laboratory coagulation tests. Colloidal stability was described by the stability ratio (a). For a perfectly stable suspension, a = 0 for a complete unstable one, a = 1.)... 

Devel Section Rept No 8 (1957) (Storage stability tests of colloidal LA for use in low energy electric detonators) 19)Purchase Description X-PA-PD-1217(1957) (Tentative spec for Type I and Type II LA s used in the US for military purposes) 20)K.J.Holloway, G.W.C. Taylor A.T. Thomas, ERDE Rept No 7/R/58(l958) (Prepn and props of RD-1343 lead azide) 21)R.L.Wagner, PicArsn... 

Silver iodide particles in aqueous suspension are in equilibrium with a saturated solution of which the solubility product, aAg+ai, is about 10 16 at room temperature. With excess 1 ions, the silver iodide particles are negatively charged and with sufficient excess Ag+ ions, they are positively charged. The zero point of charge is not at pAg 8 but is displaced to pAg 5.5 (pi 10.5), because the smaller and more mobile Ag+ ions are held less strongly than-the 1 ions in the silver iodide crystal lattice. The silver and iodide ions are referred to as potential-determining ions, since their concentrations determine the electric potential at the particle surface. Silver iodide sols have been used extensively for testing electric double layer and colloid stability theories. 

Latex stability will be determined by the combined effect of two factors the probability of collision between particles and the fraction of the encounters between particles which lead to permanent contact. Tha first factor, the collision frequency, will increase with increasing particle size and particle number. It will also increase with increasing shear rate. The influence of various test conditions on the second factor ought to be discussed on the basis of the DLVO theory of colloid stability. 

X-ray diffraction of sulfur particles excreted by Thiobacillus sp. showed the presence of orthorhombic sulfur crystals. The solubility of crystalline orthorhombic sulfur in water is known to be only 5 /tg 1 [42]. In the solubility test shown in Fig. 7 it was seen that the biologically produced sulfur particles can be dispersed in water but not in hexadecane, whereas crystalline orthorhombic sulfur is soluble in hexadecane but not in water. The reason for the observed hydrophilicity of the biologically produced sulfur particles has to be attributed to the hydrophilic properties of the surface of the sulfur particles. Because of the relatively high stability of the biologically produced sulfur particles at high salt concentrations, it is concluded that the colloidal stability is not merely based on electrostatic repulsion. It is known that hydrophobic sulfur can be wetted by Thiobacillus thiooxidans bacteria due to formation of organic surface-active substances [43, 44]. 

Bitea et al. [2003BIT/MUL] discuss the stability of thorium colloids generated by cou-lometric titration of 10 to 10 M thorium solutions at pH 3 - 5 in 0.5 M NaCl. Using laser-induced breakdown detection (LIBD) and ultrafiltration the colloids formed above the solubility limit of Th(lV) hydroxide were found to be stable within the time period of investigation (up to more than 400 days). Dilution of colloid containing test solutions at constant pH leads to the degradation of colloids into soluble ionic species, whereas dilution with neutral 0.5 M NaCl results in increased over-saturation and colloid formation, as recognised by a pH shift to lower values. This observation was ascribed to the simplified reaction ... 

The sheets, when thoroughly dried, are of a uniform yellowish-grey colour, and of the characteristic colloidal consistency they possess a perfectly smooth surface, and are free from internal blisters or cracks. The temperature of ignition of the finished powder should not be below 172° C., and when subjected to the heat or stability test, it is required to resist exposure to a temperature of 71° C. for thirty minutes without causing discoloration of the test paper. 

For use with high-speed applicators, high shear cone and plate viscometer results may be quoted as secondary information. Many poly(vinyl alcohol)-stabilized products are comparatively insensitive to shear and give broadly similar results with different types of viscometer. This behavior under shear is known as Newtonian and is a feature, inter alia, of large particles with a narrow particle size distribution. High shear viscosity testing also indicates if there is sufficient mechanical stability to allow application by knife or roller, although this is not usually a problem with colloid-stabilized emulsion polymers and adhesives. 

There is a constant challenge for improved techniques in order to make accurate predictions on the colloidal stability of various sytems. In this section we demonstrate how dielectric spectroscopy can be applied as a technique to follow the breakdown of water-in-oil emulsions and to monitor the sedimentation of particle suspensions. Dielectric spectroscopy, combined with statistical test design and evaluation, seems to be an appropriate technique for the study of these problems. However, one should continue to seek satisfactory theoretical models for the dielectric properties of inhomogeneous systems. 

Chaala et al. studied the flocculation and the colloidal stability of crude fraetions (33). Stability was defined as the differential in spectral absorption between the bottom and top of a test vessel. The effects of temperature and of additions of waxes and aro-matics on stability were noted. Increasing both waxes and aromatics generally decreased stability. Temperatme increased stability up to 60°C and then stability decreased. In another study, the resins and asphaltenes were extracted from four crude oils by various means (34). It was found that different extraction methods resulted in different characteristics as measured by FT-IR spectroscopy as well as different stabilities when the asphaltenes and resins were used as stabilizers in model systems. It was concluded that the interfacially active components in crude oil were interacting and were difficult to distinguish. Both the resins and asphaltenes appeared to be involved in interfacial processes. 

Principal component analysis is another statistical technique that has been applied to the results of profile analysis [55]. Ales and lagers were examined and two-dimensional plots of the results using the first two principal components as axes showed resolution of the ales from the lagers and the close proximity of the majority of duplicate samples. Profile analysis has also been used to differentiate various brands of whisky [56]. Throughout the work on profile analysis hedonic expressions have been strictly excluded but other workers [57] have used principal component analysis to classify Continental European beers correctly as good, average or poor on the basis of nine physicochemical parameters colloidal stability (7 days at 40°C/1 day at 0°C), cold sensitivity (24 hours at 0°C), brightness at 12°C, six months test, the content of p-phenylethanol, ethyl caprylate, isoamyl acetate, and isobutanol and foam stability. 

The emulsifier- and electrolyte-free latexes form excellent models to test the theory of colloidal stability (18), e.g., the effect of particle size and surface charge. A number of such studies have been reported by Ottewill and Shaw (14, 19) and by Watillon and Joseph-Petit (20), using systems similar to ours. 

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