Benjamin Nachman, Itai Cohen
Droplet breakup is a well studied phenomena in Newtonian fluids. One property of this behavior is that, independent of initial conditions, the minimum radius exhibits power law scaling with the time left to breakup tau. Because they have additional structure and shear dependent viscosity, liquid crystals pose an interesting complication to such studies. Here, we investigate the breakup of a synthetic nematic liquid crystal known as MBBA. We determine the phase of the solution by using a cross polarizer setup in situ with the liquid bridge breakup apparatus. Consistent with previous studies of scaling behavior in viscous-inertial fluid breakup, when MBBA is in the isotropic phase, the minimum radius decreases as tau^{1.03 \pm 0.04}. In the nematic phase however, we observe very different thinning behavior. Our measurements of the thinning profile are consistent with two interpretations. In the first interpretation, the breakup is universal and consists of two different regimes. The first regime is characterized by a symmetric profile with a single minimum whose radius decreases as tau^{1.51 \pm 0.06}. The second and final regime is characterized by two minima whose radii decrease as tau^{0.52 \pm 0.11}. These results are in excellent agreement with previous measurements of breakup in the nematic phase of liquid crystal 8CB and 5CB. Interestingly, we find that the entire thinning behavior can also be fit with an exponential decay such that R_{min} \sim exp((1.2\times 10^2 Hz) tau). This dependence is more reminiscent of breakup in polymers where entropic stretching slows the thinning process. An analogous mechanism for slowing in liquid crystals could arise from the role played by topological constraints governing defect dynamics. Consistent with this interpretation, crossed polarizer images indicate that significant alignment of the liquid crystal domains occurs during breakup.
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http://arxiv.org/abs/1212.5976
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