Nonlinear dynamics on the path to clogging in gelling polymer microflows

While clogging represents failure in many contexts, both natural and industrial, we rarely discuss it in the scientific literature. Instead, in practical situations we aim to avoid it, and present methods which 'succeed' rather than investigating the boundaries of failure. In this study we investigate transitions between flow and clogging in microchannels, in flows of dilute polymers allowed to gel while flowing. Gelation leads to deposition and occlusion, which cause driving pressure to increase if the flow rate is fixed. Gel ablation returns the system to baseline, and the process repeats. A wide range of compositions and flow parameters can lead to this intermittency that resembles neither flow nor clogging. This system exhibits regular, highly reproducible way for some range of control parameters. However, as control parameters are pushed toward the clogging regime, the intermittent dynamics become increasingly irregular. The pressure trace exhibits features like moving baselines and perioud doubling. Interestingly, the Reynolds number remains in the laminar regime, and the system does not exhibit the normal stresses required for turbulence induced by elastic instabilities. We quantify this transition through parameters like the fractal dimension of the pressure trace, the Holder exponent, and the power law decay of the frequency spectra, all inspired by theories of non-linear dynamics and chaos.