Dynamics of a tethered polymer in shear flow

Area of Science:

• Polymer physics
• Fluid dynamics
• Soft matter science

Background:

• Understanding polymer behavior in flow is crucial for materials science and biophysics.
• Tethered polymers exhibit complex responses to external forces like shear flow.

Purpose of the Study:

• To investigate the dynamics of a single polymer tethered to a surface under shear flow.
• To elucidate the mechanisms behind observed shear-enhanced fluctuations in polymer extension.

Main Methods:

• Utilized fluorescently labeled DNA chains to visualize polymer dynamics.
• Employed shear flow to induce and observe polymer responses.
• Conducted simulations to model and understand the observed anomalous dynamics.

Main Results:

• Observed dramatic, shear-enhanced temporal fluctuations in polymer chain extension.
• Found that the rate of fluctuations initially decreased with increasing shear rate (gamma), then increased above a critical gamma.
• Simulations identified continual recirculating or cyclic motion as the source of anomalous dynamics.

Conclusions:

• Anomalous polymer dynamics in shear flow arise from a coupling between flow-induced velocity and thermally driven fluctuations.
• Cyclic dynamics, involving recirculating motion, explain the observed non-monotonic response of fluctuations to shear rate.