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Interpretation of Coagulation Kinetics Observed by Light Seattering

Mirko Mirnik ; Laboratory of Physical Chemistry, Faculty of Science, University of Zagreb, 41001 Zagreb, P. O. Box 163, Yugoslavia

Sažetak

The coagulation process interpreted as a second order reaction
and it is assumed that the intensity of scattered light on the colloidal
particles follows the Raileygh eq. At each collision of two
aggregates the smaller aggregate loses a given number of primary
particles while the bigger aggregate increases by the same number
of primary particles. The »critical time« (terit) is determined by the
intersection of the tangent through the inflection of the plot "I vs.
19t« with the 19t axis (I = intensity of scattered light, t = time
from the start of coagulation). The coagulation halflife (t1/2) can
be calculated because the following eq. is derived
The intercept of the tangent on the steepest part of the plot »1 vs.
19C« with the 19c axis (c = variable coagulator concentration),
measured at a suitable time t, is the »critical coagulation conceritration «, c.c.c. = Ccoagt., It proves the validity of eq.
Exponent A is explained as the number of coagulator ions which
react with a single primary particle in a fast ionic reaction which
induces coagulation. This means that in the calculated concentration
cl/2,t the suitable time equals the coagulation hilflife, i. e.
t = tl/2. It is also suggested that the theoretical linear plot »1/1 vs.
I/t« could be used for the determination of tJl2.The intersection
of the plot with the III ordinate for I/t = Ois 1/100, The value 2/100
determines the reciprocal of the time which equals the reciprocal
of the halflife, i. e. at 2/100 is Ilt = 1/tl/2. It is also proved that the
linear plots »lg ceoag,t vs. 19C« and the plot »Ig teri! vs. 19c« are
equivalent to the »IgW vs 19C« plot. Bere, W is the »stability factor
« defined as W = kmaJk = tl/itl/2,min' Each coagulator has a concentrationin which the rate constant k = 1/tl/2 has its maximal
value kmax = l/tl/2, min'The same concentration is occasionally called
coagulation concentration, ceoag'Arguments are given suggesting that
terit and ceoag,t can be measured with the highest possible precision.
In short times after the start of coagulation the measured I is the
sum of Is scattered on single primary particles and of la scattered by the aggregates, i. e. I = Is + la' therefore, the tangent on the
plot »1 vs. t« for t -+ Odetermines neither the halflife of the disappearanceof single primary particles nor the halflife of the
increase of the aggregates.

Ključne riječi

Hrčak ID:

175874

URI

https://hrcak.srce.hr/175874

Datum izdavanja:

28.4.1988.

Posjeta: 621 *