Deformation and shape of flexible, microscale helices in viscous flow

TL;DR

This study experimentally investigates how microscale flexible helical ribbons deform and behave in viscous flow, revealing their shape changes, frictional properties, and reversible transitions under flow conditions.

Contribution

It provides new experimental data on microscale helix deformation, friction coefficients, and non-linear elastic behavior in viscous flow, expanding understanding of flexible microstructures.

Findings

Frictional coefficients match resistive force theory calculations.

Helix deformation follows non-linear finite extensibility models.

Reversible global to local helical transitions occur at high flow rates.

Abstract

We examine experimentally the deformation of flexible, microscale helical ribbons with nanoscale thickness subject to viscous flow in a microfluidic channel. Two aspects of flexible microhelices are quantified: the overall shape of the helix and the viscous frictional properties. The frictional coefficients determined by our experiments are consistent with calculated values in the context of resistive force theory. Deformation of helices by viscous flow is well-described by non-linear finite extensibility. Under distributed loading, the pitch distribution is non-uniform and from this, we identify both linear and non-linear behavior along the contour length of a single helix. Moreover, flexible helices are found to display reversible global to local helical transitions at high flow rate.