Dear all,
In an aqueous dispersion of a hydrophobic material like CNT/graphite obtained by surfactants, how can we determine the amount of contribution of "free micelles" on zeta potential?
Of note, consider the concentration of the surfactant to be much higher than its CMC.
I am
Do you have measured data value of that dispersion for "Zeta potential"?
Do you mean how much the micelles contribute to the overall zeta potential distribution as measured by light scattering? That will depend on a number of things including the relative sizes of the micelles and your particles, the refractive index difference for both compared to water, the mass of surfactant vs. mass of particles.
If you mean how do free micelles affect the particle zeta potential of the particles - they don't (unless the concentration of the particles is so high that the micelles are forced to be near the particles). Zeta potential is an interfacial property. By definition, "free" micelles aren't at the interface.
Dear John Francis Miller
Yes, I mean how much contribution do free micelles have on the overall zeta potential?
or in other words, could we split the overall measured zeta potential into two parts, one due to surfactant-wrapped particles and the other by free micelles? If yes, how could we determine each part?
Dear Nadeesha Maduwanthi Hettiarachchi
Yes I measured the zeta potential of the dispersion. But I want to measure the contribution of each part mentioned in my question.
Using light scattering? In principle, yes. But the intensity of the light scattered depends upon the materials present. The most strongly scattering particles will dominate the zeta potential distribution. The factors determining the intensity from a given particle are:
1. The particle size. The intensity scales with the fourth power of the radius.
2. The refractive index difference between the particle and the liquid. For a conducting material, this can get quite complicated.
3. The concentration of particles present (by number).
If your micelles are ~2nm (typical) and your particles are 10nm then, even at the same concentration and with the same refractive index, your particles will scatter 10,000 more than the micelles.
If both species do contribute equally, you should see two peaks if the zeta potentials are different.
If the surfactant adsorbs then the zeta potentials are likely to be the same (or close) for the micelles and the particles.
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