Fabrication of slender elastic shells by the coating of curved surfaces.

A Lee,J Marthelot,P M Reis,G Balestra,F Gallaire,P -T Brun

doi:10.1038/ncomms11155

Abstract

Various manufacturing techniques exist to produce double-curvature shells, including injection, rotational and blow molding, as well as dip coating. However, these industrial processes are typically geared for mass production and are not directly applicable to laboratory research settings, where adaptable, inexpensive and predictable prototyping tools are desirable. Here, we study the rapid fabrication of hemispherical elastic shells by coating a curved surface with a polymer solution that yields a nearly uniform shell, upon polymerization of the resulting thin film. We experimentally characterize how the curing of the polymer affects its drainage dynamics and eventually selects the shell thickness. The coating process is then rationalized through a theoretical analysis that predicts the final thickness, in quantitative agreement with experiments and numerical simulations of the lubrication flow field. This robust fabrication framework should be invaluable for future studies on the mechanics of thin elastic shells and their intrinsic geometric nonlinearities.

Highlights

Various manufacturing techniques exist to produce double-curvature shells, including injection, rotational and blow molding, as well as dip coating
A theoretical analysis of the underlying lubrication flow during drainage, which includes the evolution of the rheological properties of the polymer as it cures, is able to accurately predict the final thickness of the shell as a function of the material properties of the polymer and the geometry of the substrate
With time, crosslinking of the polymer film that emerges from the drainage process yields a thin elastic shell that can be readily peeled from the mold

Summary

Introduction

Various manufacturing techniques exist to produce double-curvature shells, including injection, rotational and blow molding, as well as dip coating These industrial processes are typically geared for mass production and are not directly applicable to laboratory research settings, where adaptable, inexpensive and predictable prototyping tools are desirable. A significant advantage for these geometries is that, when compared to their double-curved counterparts, they are more amenable to theoretical modeling to predict how the final film thickness depends on the control parameters[7,8] In these cases, the flow driven by viscous stresses and held by capillary forces is ‘frozen’ as the media cools, cures or dries, yielding a defect-free and uniform finish. Spin-casting exploits centrifugal forces on a rotating cylindrical surface to evenly distribute a polymer solution and fabricate nearly constant thickness shells in a highly controllable manner[11]. Our approach provides a fast, robust and predictable mechanism to fabricate thin shells with flexibility in their material and geometric properties by tuning the control parameters

Methods

Results

Conclusion