Evaporation of an axisymmetric-polymer liquid bridge

Experiments were performed to understand which conditions lead to a stable polymer gel structure after complete solvent evaporation, a structure resembling a micro-pillar. An axisymmetric-unbounded aqueous polymer liquid bridge was formed between two horizontal substrates at various Bond numbers ($0.2 \leq Bo = \Delta \rho g a^2/\gamma \leq 0.8$). Images of the liquid bridge were captured as it evaporated using a CCD camera. Polymer concentration (pre-evaporation) were initially low $0.5 \% <c_0<0.75 \%$ with initial drop volumes $1 \mu$l $<V_0<$250 $\mu$l. Due to evaporation of the solvent phase (water), the polymer concentration increased, and the liquid bridge became a gel. We measured the liquid bridge profile to estimate transient quantities such as volume, top and bottom contact angles, and minimum bridge diameter. For a given $Bo$ and $c_0$, we found a critical initial volume above which we observe stable gel structures. We discuss on how substrate properties, gap spacing and initial polymer concentration contributed to these observations.