A periodically
precipitating system wherein interband distance
successively decreases is known as revert Liesegang banding. The phenomenon
is rare, and the underlying mechanism is implicit. In the present
paper, the Liesegang system comprising of AgNO
3
and KBr
as the outer and inner electrolyte pair showing revert banding in
agar gel by employing a 1D experimental setup is studied under varying
concentrations of participating species. Revert banding was observed
under all the experimental conditions. The concentrations of inner
and outer electrolytes were found to play a major role in reverting
since they build the ionic strength inside Liesegang tubes. We hypothesize
that the band reverting is the interplay of van der Waals and electrical
double-layer interactions, and hence classical DLVO (Derjaguin–Landau–Verwey–Overbeek)
theory can be applied to interpret reverting. We propose that revert
deposition of precipitates is the outcome of flocculation and peptization
of sols, which is the manifestation of balancing attractive and repulsive
interactions acting on colloidal particles responsible for band formation.
In
the present study, a method is described for precise determination
of spatial characteristics of Liesegang bands formed by employing
a classical 1D setup using a web-based free resource (). The method involves the compartmentalization of the information
on each pixel into R (red), G (green), or B (blue) values from the
pattern images obtained using a simple digital camera. The values
can further be converted to absorbance values by using the system
blank. Each trough (or peak) in the graph of RGB values (or absorbance
values) corresponds to a band in the pattern. The method is employed
to determine the spacing and width of the periodically precipitating
AgCl, AgBr, and Co(OH)2 in an agar gel. It is observed
that AgCl shows revert banding, and AgBr shows revert banding at the
top of the tube and then diverges to regular banding at the bottom
of the tube, whereas the Co(OH)2 patterns explicitly show
regular banding under given experimental conditions. It is also observed
that minute instabilities, such as the formation of secondary bands,
can also be visualized by the present method.
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