@article{oai:oist.repo.nii.ac.jp:00000983,
 author = {Haward, Simon J. and Kitajima, Naoyuki and Toda-Peters, Kazumi and Takahashi, Tsutomu and Shen, Amy Q.},
 issue = {9},
 journal = {Soft Matter},
 month = {Jan},
 note = {We employ time-resolved flow velocimetry and birefringence imaging methods to study the flow of a well-characterized shear-banding wormlike micellar solution around a novel glass-fabricated microfluidic circular cylinder. In contrast with typical microfluidic cylinders, our geometry is characterized by a high aspect ratio alpha = H/W = 5 and a low blockage ratio beta = 2r/W = 0.1, where H and W are the channel height and width, and the cylinder radius r = 20 mum. The small cylinder radius allows access up to very high Weissenberg numbers 1.9 </= Wi = lambdaMU/r </= 3750 (where lambdaM is the Maxwell relaxation time) while inertial effects remain entirely negligible (Reynolds number, Re < 10-4). At low Wi values, the flow remains steady and symmetric and a birefringent region (indicating micellar alignment and tensile stress) develops downstream of the cylinder. Above a critical value Wic approximately 60 the flow transitions to a steady asymmetric state, characterized as a supercritical pitchfork bifurcation, in which the fluid takes a preferential path around one side of the cylinder. At a second critical value Wic2 approximately 130, the flow becomes time-dependent, with a characteristic frequency f0 approximately 1/lambdaM. This initial transition to time dependence has characteristics of a subcritical Hopf bifurcation. Power spectra of the measured fluctuations become complex as Wi is increased further, showing a gradual slowing down of the dynamics and emergence of harmonics. A final transition at very high Wic3 corresponds to the re-emergence of a single peak in the power spectrum but at much higher frequency. We discuss this in terms of possible flow-induced breakage of micelles into shorter species with a faster relaxation time.},
 pages = {1927--1941},
 title = {Flow of wormlike micellar solutions around microfluidic cylinders with high aspect ratio and low blockage ratio},
 volume = {15},
 year = {2019}
}