Sedimentation Equilibrium of Mixtures of Charged Colloids

Z 16=2993a0.6210 3 η iZ 11=2500.40.20150 200 250 300 350Z i1Z 14=27900 5 10 15 2010 3 η iX (cm)Figure 4.7: Example 1: Density profiles of a 21-component colloidal suspensionwith a Gaussian charge distribution as illustrated in the inset anddescribed by (4.15). The components have the same gravitational lengthsL i = 2mm.Example 2, figure 4.8, has the same charge distribution as example 1. Thegravitational length is scaled with the colloidal charge, L i ∝ Z − 3 2i . Thisexample describes a system with different particles, that have a constantmass and charge density, L i /σi 3 = L j /σj 3 resp. Z i /σi 2 = Z j /σj 2 . Except forthe gravitational lengths L i , the system is identical to example 1, to makethem comparable.The results of example 1 show layering of components, with the highestcharge on top. The results of example 2 do not show a layering. This canbe explained from the difference in mass per charge of the components. Inexample 1 the ratio isZ i L i= Z i, (4.16)Z j L j Z jwhereas in example 2√Z i L i Zj= . (4.17)Z j L j Z iTherefore, the variation of the mass per charge in example 2 is much smaller,as we can see in figure 4.8. The total packing fractions are very close to the26