Particle electrophoretic mobility, change

Another interesting experimental stndy of concentrated suspensions of hnman erythrocytes was performed by Znkoski and Saville. Although volume fractions as high as 75% were employed, the electrophoretic mobility changed by the factor (1 - ([)) in the whole concentration range, which was simply explained by the backflow of liquid necessary to conserve the snspension volnme. The electrostatic and hydrodynamic particle-particle interactions apparently canceled each other in these experiments. Note that the electrolyte concentration was relatively high and, contrary to the experiments of Deggelmann et al., " the EDL were thin in comparison with the particle size. 

Figure 17. Change in particle electrophoretic mobility with adsorbed anionic, cationic, or amphoteric surfactant. Key SS, Berea sandstone LS, Indiana limestone and Dolo, Baker dolomite. (Reproduced with permission from reference 12. Copyright 1992 Elsevier Science Publishers.)...

A second possibility is that the Au particles scavenge electrons from the reaction electrodes, walls and solvent. This is the explanation we favor at the present time since we have been able to effect changes in electrophoretic mobilities by supplying electrical potential to the colloid solution as the particles form,( l ) and the fact that such charging has been reported before, for example with oil droplets in water.(43)... 

Mechanistic Ideas. The ordinary-extraordinary transition has also been observed in solutions of dinucleosomal DNA fragments (350 bp) by Schmitz and Lu (12.). Fast and slow relaxation times have been observed as functions of polymer concentration in solutions of single-stranded poly(adenylic acid) (13 14), but these experiments were conducted at relatively high salt and are interpreted as a transition between dilute and semidilute regimes. The ordinary-extraordinary transition has also been observed in low-salt solutions of poly(L-lysine) (15). and poly(styrene sulfonate) (16,17). In poly(L-lysine), which is the best-studied case, the transition is detected only by QLS, which measures the mutual diffusion coefficient. The tracer diffusion coefficient (12), electrical conductivity (12.) / electrophoretic mobility (18.20.21) and intrinsic viscosity (22) do not show the same profound change. It appears that the transition is a manifestation of collective particle dynamics mediated by long-range forces but the mechanistic details of the phenomenon are quite obscure. 

Fig. 4. Electrophoretic mobilities (Ug)of natural (untreated) - curve A - and treated particles as a function of salinity (S°/°<>) for two sets of samples from Keithing Burn (KB 1 open symbols - 31 March 1982 KB 2 closed symbols - 30 dune 1982). Shaded area B indicates the spread of results from other estuaries (redrawn from Fig. 3 of Hunter and Liss 1979). Curve D - suspended particles centrifuged and resuspended in UV- oxidized sample supernatant and then UV-oxidized. Curve C - natural samples (particles plus supernatant) UV-oxidized. Curve E - sample supernatant UV-oxidized to form new particles (UV-PPT). Several UV-PPT samples from KB2 were centrifuged and the particles resuspended in their original untreated sample supernatant. The resulting changes in Ug are indicated by the dashed lines (asterisks - final values). Keithing Burn suspended matter is mostly composed of iron oxides (after Loder and Liss, 1985).

Temperature has dramatic effect on the electrokinetic properties of thenno-sensitive polymers. A pH independent electrophoretic mobility of about -0.5x10 m" V s" (pH 3-11) in the presence of 0.1 mol dm NaCl was reported for synthetic poly (A-isopropylacrylamide) latex (persulfate initiator) at 20°C [17]. The same material has a mobility of about -5x10 m V s" (ten times greater ) at 50 C. This dramatic change occurs when the lowest critical solubility temperature is exceeded, and it is accompanied by substantial decrease in particle size (factor about two,... 

US with changing salt concentration, indicating the presence of relatively thick adsorbed layers on the sulfur particles (see Fig. 4). This, as well as surface charge density measurements showing values comparable to surface charge densities of bacterial cell walls and humic acids, support the suggestion of proteins adsorbed on the particles. In addition, electrophoretic mobility experiments showed an iso-electric point comparable to the pKa-value of carboxylic acid groups in proteins (pKa=2.3) [45]. 

The bottom chamber contains two types of particles having electrophoretic mobilities p E and p2E- The change in the number of type-1 particles in a stage n during step r will be equal to the number of bioparticles that migrated to the top chamber during step r. So the general equation can be written for this situation by material balance as... 

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