# Elastohydrodynamics of a pre-stretched finite elastic sheet lubricated by a thin viscous film with application to microfluidic soft actuators

## TL;DR

This paper develops analytical models for the deformation of a pre-stretched elastic sheet lubricated by a viscous film, providing insights into actuation mechanisms for microfluidic soft devices with finite domains.

## Contribution

It derives closed-form solutions for elastic sheet deformation considering pre-stretching, finite domains, and nonlinear effects, advancing the theoretical understanding of elastohydrodynamic actuation.

## Key findings

- Deformation magnitude depends on spatial wavenumber and pre-stretching.
- Transition between bending- and stretching-dominant regimes identified.
- Spatial discretization affects achievable deformation resolution.

## Abstract

The interaction of a thin viscous film with an elastic sheet results in coupling of pressure and deformation, which can be utilized as an actuation mechanism for surface deformations in a wide range of applications, including microfluidics, optics, and soft robotics. Implementation of such configurations inherently takes place over finite domains and often requires some pre-stretching of the sheet. Under the assumptions of strong pre-stretching and small deformations of the lubricated elastic sheet, we use the linearized Reynolds and Foppl-von Karman equations to derive closed-form analytical solutions describing the deformation in a finite domain due to external forces, accounting for both bending and tension effects. We provide a closed-form solution for the case of a square-shaped actuation region and present the effect of pre-stretching on the dynamics of the deformation. We further present the dependence of the deformation magnitude and timescale on the spatial wavenumber, as well as the transition between stretching- and bending-dominant regimes. We also demonstrate the effect of spatial discretization of the forcing (representing practical actuation elements) on the achievable resolution of the deformation. Extending the problem to an axisymmetric domain, we investigate the effects arising from nonlinearity of the Reynolds and Foppl-von Karman equations and present the deformation behavior as it becomes comparable to the initial film thickness and dependent on the induced tension. These results set the theoretical foundation for implementation of microfluidic soft actuators based on elastohydrodynanmics.