  When a soft glassy colloidal suspension is displaced by a Newtonian fluid in
a radial Hele-Shaw geometry, the pattern morphology that develops at the
interface is determined by the complex rheology of the former. We had reported
in an earlier work [Palak, V. R. S. Parmar, D. Saha and R. Bandyopadhyay, JCIS
Open, 6 (2022) 100047] that a range of interfacial patterns can be formed by
controlling the elasticity of the displaced suspension, the flow rate of the
displacing fluid and the interfacial tension of the fluid pair. Interestingly,
all the different morphological features can be distinguished in terms of their
areal ratios, defined as the ratio of the areas occupied by the fully-developed
pattern and the smallest circle enclosing it. In a significant advance to this
earlier work, we show here that a systematic study of spatio-temporal pattern
growth can reveal important information about pattern selection mechanisms. We
analyse the time-evolution of the patterns to reveal interesting correlations
between their growth mechanisms and fully-developed morphologies. We believe
that such systematic identification of the unique temporal features
characterising pattern growth at the interface between an aging viscoelastic
clay suspension and a Newtonian fluid can be useful in predicting and
suppressing the onset and evolution of interfacial instabilities in the
displacement of mud and cement slurries.
