6: Interparticle Interactions & Col Stab

the ability of a colloidal suspension to remain as such, even when the spontaneous tendency should be to aggregate; that is, the kinetics of the aggregation process is slow enough

an important parameter characterizing VW interactions, in simplified form: $A_{12}=\pi^2 u'_{12} \rho_1 \rho_2$ where $u'_{12}$ is a constant collecting all quantities independent of distance in the van der Waals interaction potential energy expression for an ion attracted to a surface

$\tilde{F}(d)=-\frac{\partial{U(d)}}{\partial{d}}$

able to react chemically as either an acid or a base

constant potential
constant charge
charge regulation

the potentials of both surfaces are assumed to remain constant as d decreases

the surface charge densities of both surfaces are assumed to remain constant as d decreases

neither the potential nor the charge is assumed constant but adjust along with the surface reaction equilibria as the particles approach each other

d1: both surfaces have positive values of potential and charge
d2: slope of the potential profile at surface 2 vanishes (surface charge is null)
d3: the potential profile matches the case of an isolated surface so that the force vanishes
d4: overall force is attractive

the stability of colloidal suspensions is a result of the balance between VW and electrostatic double layer interactions: the dispersion interactions, being always attractive between similar particles, favors flocculation, whereas the repulsive electrostatic interactions prevents or, more precisely, delays this process

the concentration value at which a suspension transitions from “stable” to “unstable”

the CCC decreases with the counterion charge approximately as $z^6$

a clay whose structure collapses completely at remolding and whose shear strength is thereby reduced almost to zero

the change that occurs in clay that has been disturbed and lost shearing strength but gained compressibility

-usually leads to compaction of clay sediment
-in quick clays, may result in collapse

-quick clay is deposit of clay minerals of marine origin, thus with high saline contents
-water in turn has high ionic concentrations
-attractive forces dominate; large aggregates of particles sediment without any preferred orientation => high void ratio
-when wetted/flooded, salt is slowly leached out
-clay particles need expanded double layers to neutralize particle charge => reflocculation is not possible
-if e high, w may be higher than LL => landslide

-$I \le 0.01 \text{M}$
-interparticle distances not less than a few nanometers
-for soil-related problems, most of the time correct predictions
-in some cases, e.g., highly saline soils, it can fail severely