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Abstract
The seminar related to dilute solution rheology and microfluidics will be composed of two parts.
The first part is the observation of sodium hyaluronate (Hyaluronic Acid Sodium salt, Na-HA) solution in planar abrupt contraction-expansion microchannels to discuss the effects of polymer flexibility and entanglement on elastic instability. As the rigidity of Na-HA depends on the ionic strength of a solvent, Na-HA was dissolved in water and phosphate buffered saline. The flow regimes of the Na-HA solutions in several planar abrupt contraction-expansion channels were characterized by rheological properties of the solution. It was found that the entanglement of Na-HA in the solution is a more dominant factor affecting the flow regimes than the solution relaxation time and polymer rigidity [1].
The second part of the seminar is measurements of drag force due to synthetic polymers in flowing fluids by using a scanning probe microscope (SPM). Methoxy polyethyleneglycol thiol (mPEG-SH) was attached to the cantilever probe of the SPM, which was further immersed in flows of glycerol and polyethyleneglycol (PEG) solutions. The mPEG-SH-bonded cantilever detects the extra force due to polymer-polymer and polymer-fluids interaction in flowing fluids. The conformation of the mPEG-SH polymer bonded to the probe of the cantilever was predicted, and the drag force due to the deformed mPEG-SH was calculated. The forces detected by experiments using the SPM and the forces obtained by model calculations were compared, and found to be reasonably close [2].
Fig.1. Entry flow of Na-HA PBS solution in in the upper stream region of a planar abrupt contraction-expansion microchannel.
Fig.2. Schematic of mPEG-SH-bonded cantilevers in flows of glycerol or PEG solution.
References
[1] Ruri Hidema et al., Physics of Fluids, 31, 072005 (2019)
[2] Ruri Hidema et al., Physical Review Fluids, 4, 074201 (2019)