Biomedical Engineering Reference
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Figure 11. Spreading of droplets of 0.1% SDS solution over Nitrocellulose membrane, average pore
size is 3.0 µm. L/L max , dimensionless radius of the drop base; l/l max , radius of the wetted area;
θ/θ m , dynamic contact angle; t/t max , dimensionless time [96].
Starov et al. [96] incorporated the previous theoretical model to simulate spread-
ing of surfactant solutions over porous layers. They produced experimental data for
the spreading of different concentrations of aqueous SDS solution over different
pore sizes of nitrocellulose membranes whilst varying drop volume and properties
of porous layers. The dynamic contact angle, radius of the spreading droplet, and
the wetted perimeter were monitored for the spreading/penetrating process. The en-
tire process can be divided into three stages (Fig. 11). During the first stage, the
drop base spreads until it reaches the maximum position whilst contact angle de-
creases rapidly. The drop base then remains constant during the second stage, as
the contact angle decreases linearly with time. Finally comes the third stage, when
the drop base shrinks while the contact angle remains constant until the drop com-
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