Colloids and DLVO Flashcards
1
Q
Colloids in water
A
2
Q
Gel formation (coherent)
A
- Floccules of small particles bound by strong
van der Waals forces. - Macromolecules bound by strong van der Waals forces or cross-linked by chemical
bonds.
3
Q
Colloidal Properties
A
- absorption: as the finely divided colloidal particles have a large exposed surface area.
- generally aggregates of numerous atoms or molecules.
- can be detected by light-scattering, sedimentation and osmosis
- chemical and physical properties of inorganic colloids can be significantly changed when their size is reduced
4
Q
Faraday-Tyndall effect: Brownian motion
A
- Colloidal particles are kept dispersed throughout a medium by random collisions with other particles or another stuff
- Light may be adsorbed, scattered, polarized, refracted, or reflected by the dispersed phase of a colloid
-
observed light scattering and cone formation with turbid appearance of the colloid
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5
Q
DLVO Theory
A
Vt = Va + Vr
The resultant (total) potential is the sum of attraction and repulsion potentials
6
Q
DLVO Equation
A
7
Q
VDW Attractive
A
- Large: gravity, small: surface energy
- dipole-dipole interaction W(r) = C/r6
8
Q
Hamaker constant
A
- attraction parameter that is a measure of strength,
- neglected the interaction between atoms within the same solid
- Greater constant means more area under graph for attractive and starts at a larger distance
9
Q
Electric double layer (EDL)
A
- Surface potential: dense layers of uniform charge
- Middle: more disperse but layered
- Bulk: pairing of charges equal
10
Q
Molar salt concentration
A
- Increase salt in solution will decrease EDL thickness, Debye length, the ζ potential value, and eventually the EDL will collapse
- Increasing salt concentration will affect the EDL through salt screening effect.
- As a result, the overall potential function is lower and deteriorated the colloid stability.
11
Q
Zeta potential
A
- Surface potential at the shear plane
- At low zeta potential, there is not enough electrostatic repulsion and the total potential function shows little-to-no energy barrier—causing the particle aggregation. As the zeta potential increases, the energy barrier increases and the particles are stable.
- At the isoelectric point (specific pH) the zeta potential becomes zero
- A charged particle will move with a fixed velocity in a voltage field. Zeta potential can be quantified by tracking the colloidal particles through a microscope as they migrate in a voltage field
- Increasing electrolyte (monovalent) decreases zeta
- For divalent electrolytes, however, and for high concentrations, the sign of the ζ potential can be reversed and the IEP is shifted
- a gold surface, which is positively charged, is submerged in a Na2SO4 solution, the SO42- ions will adsorb on the surface, and if the concentration is enough, all the surface sites are covered. In this case there will be an excess of negative charge that will inverse the sign of ζ-potential.
12
Q
Stability factors
A
13
Q
Colloidal stability process
A
14
Q
Aerosol particle deposition graph
A
- Diffusion: worse collection with size
- Interception and impaction: better collection with size
- Settling: only large sizes
