Colloid, associated

Colloidal associations are particularly important in soil because they allow for movement of otherwise immobile or slowly mobile species. They can also lead to confusing analytical results in that atoms, ions, or molecules may appear to be soluble above their solubility limit when in reality the analytical results represent a very different species. 

Meier, H., Zimmerhackl, E. Zeitler, G. 2003. Modeling of colloid-associated radionuclide transport in porous groundwater aquifers at the Gorleben site, Germany. Geochemical Journal, 37, 325-350. 

Liquid Third Phase. A third liquid with colloidal structure has been a known component in emulsions since the 1970s (22) for nonionic surfactants of the poly(ethylene glycol) alkylaryl ether type. It allows low energy emulsification (23) using the strong temperature dependence of the colloidal association structures in the water—surfactant—hydrocarbon systems. 

Profound controversial disputes on the nature of polymers colloidal associates ("micelles") or giant molecules Hofmann starts his work on synthetic rubber Baekeland makes the first synthetic industrial plastic (Bakelite)... 

Backhus, D.A. et al., Sampling colloids and colloid-associated contaminants in ground water, Ground Water, 31, 466, 1993. 

Figure 7. At low water content (< 35% by weight) the water is not involved in colloidal association structures in a pentanol/potassium oleate (weight ratio 3.0)...

Advances in the fields of polymers and amphiphilic colloidal association structures have progressed in a most pronounced manner in the past decade. However, the interaction between these two disciplines and the beneOts of cross-fertilization have been limited. 

Pollutant-Colloid Association by Field-Flow Fractionation... 

Here, the amount of water added will not be sufficient to act as a diluting factor. Since the UF polymer becomes more hydrophobic with increasing molecular weight, the presence of additional water tends to drive the UF colloid more to intramolecular bonds and fewer UF-water bonds. Thus, the formation of colloidal associations. When taken to its logical extreme, the addition of an excess amount of water will cause the UF resin to precipitate, which has been noted (3, 8). 

PCBs in water are transported by diffusion and currents. PCBs in surface water essentially exist in three phases dissolved, particulate, and colloid associated (Baker and Eisenreich 1990). The heavier and less soluble congeners in the water column are more likely to be associated with particulates and colloids, and do not freely exchange into the vapor phase. However, the more water soluble, lower chlorinated (and ori/io-rich) congeners are predominantly in the dissolved state in the water column and can readily partition into the vapor phase. In New Bedford Harbor, Massachusetts, Burgess et al. (1996) reported that the ratio of colloid associated PCBs to freely dissolved PCBs increased from 1.2 to 8.0 (di-CBs to octa-CBs, respectively) as the degree of chlorination increased. However, at this site, the majority of the PCBs were associated with the particulate phase regardless of solubility or chlorination. 

It is of interest to note that the focus of research on the self-association of hydrotrope molecules was due, in part, to the early discussions about the fundamental nature of the solubility-enhancing capacity of hydrotrope molecules in aqueous solutions. These early attempts at clarification argued for the phenomena of colloidal solubilization versus molecular dispersion [6-8], This dispute was resolved by the results from traditional surface chemistry analysis of interfacial tension, etc., which favored a colloidal association of molecules at high concentrations [48,49], and from vapor pressure measurements [42],... 

The function of hydrotropes in detergency has been discussed as regards their interaction with surfactant colloidal association structures, especially lyotropic liquid crystals. The main activity of the hydrotrope as a part of a liquid detergent is to avoid gelation in both the concentrated package system and under the dilute conditions in the actual laundry process. 

Brown, J. N. and Peake, B. M., Determination of colloidally-associated polycyclic aromatic hydrocarbons (PAHs) in fresh water using solid phase extraction disks. Anal. Chim. Acta, 486, 159-169, 2003. 

A second class of colloids of particular importance in the general context of surface chemistry, but less familiar to most people, is that of the so-called association colloids. Association colloids consist of aggregates or units of a number (sometimes hundreds or thousands) of molecules that associate in a dynamic and thermodynamically driven process leading to a system that may be simultaneously a molecular solution and a true colloidal system. As we shall see, the formation of association colloids involving specific substances will often depend on various factors such as concentration, temperature, solvent... 

A number of other NMR-probed w/o microemulsions have appeared in recent literature. The diffusion coefficients in water/SDS/pentanol and ammonium hydro-xide/SDS/pentanol microemulsions investigated by Olsson et al. [35] estabhshed that replacement of water by ammonium hydroxide destabilizes the liquid crystalline phase and reduces the size of the colloidal association structure in the isotropic liquid region, Olsson and Schurtenberger [36] worked on nonionic microemulsions prepared from D2O, pentaethylene glycol dodecyl ether and decarie. Discrete oil-swollen micelles have been evidenced by NMR self-diffusion measurements the preparations are in conformity with the hard-sphere model. The NMR self-diffusion measurements on a water/octyl glucoside/pentanol/decane microemulsion system advocated a progressive decrease in the mean curvature of the surfactant film with water addition at a constant level of the oil [37]. It was concluded that the... 

A microemulsion is water/hydrocarbon dispersion stabilized by an ionic surfactant such as a soap, alkyl sulphate or sul-phonate and most often also contains a cosurfactant in the form of a medium chain length alcohol (pentanol). Of these four components water, surfactant and cosurfactant are called the structure forming elements since they form colloidal association structures similar to the microemulsions with no hydrocarbon present. The formulation and preparation of microemulsions is greatly enhanced by a knowledge of these composition dependent structures, hence an introductory description of them will be given. 

Isolation of fine colloids associated to larger entities,... 

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