Dynamic Reversible Evolution of Wrinkles on Floating Polymer Films under Magnetic Control

Chenchen Jiang,Conghua Lu,Lele Li,Juanjuan Wang,Xue Han,Enping Liu

doi:10.3390/coatings11050494

Abstract

In this paper, we present a simple and versatile method to dynamically and reversibly tailor surface wrinkles on a floating polymer film by combining a magnetic droplet and neodymium magnet. The magnetic force from the attraction of the neodymium magnet to the magnetic droplet is the main reason for surface instabilities of floating polymer films, which can induce radial stress in the radial direction, and further, compressive stress in the circumferential direction. This compressive stress can trigger not only floating film wrinkling but also a wrinkle-fold transition. Surface morphologies on the floating polymer film have been systematically studied, by varying the distance between the magnetic droplet and neodymium magnet, polymer film thickness, and magnetic droplet volume. With the decrease in the distance between a magnetic droplet and a neodymium magnet, the decrease in polymer film thickness, and the increase in the magnetic droplet volume, the wrinkle numbers increase and even a wrinkle-fold transition happens. Additionally, the coupling effect of multiple magnetic droplets on the floating film has also been used to achieve novel surface wrinkle patterns, which greatly widens the applications of surface wrinkling.

Highlights

Surface wrinkling, as a very common phenomenon in nature [1], e.g., wrinkles on the human face and the surface of dried fruits, has attracted wide attention due to its diverse applications, including thin film metrology [2], stretchable electronics [3], anticounterfeiting [4], structured templates [5] and so on [6,7]
This was achieved by magnetic control have been controllably fabricated for the first time. This was achieved dripping a magnetic droplet on the floating film and placing a neodymium magnet by dripping a magnetic droplet on the floating PS film and placing magnet directlybelow belowthe themagnetic magneticdroplet
Surfacemorphologies morphologies floating film, includdirectly ofof thethe floating film, including ing wrinkle the wrinkle number the mutual transition between wrinkles folds, the number and and the mutual transition between wrinkles andand folds, cancan thusthus be be modulated a predictable way, using experimentalparameters parameterssuch suchas asthe the distance distance modulated in ainpredictable way, using experimental betweenthe themagnetic magneticdroplet dropletand and neodymium magnet, PS film thickness, magbetween thethe neodymium magnet, and and magnetic netic droplet volume

Summary

Introduction

As a very common phenomenon in nature [1], e.g., wrinkles on the human face and the surface of dried fruits, has attracted wide attention due to its diverse applications, including thin film metrology [2], stretchable electronics [3], anticounterfeiting [4], structured templates [5] and so on [6,7]. The surface wrinkling system is usually a bilayer system, with a stiff film attached to a compliant substrate. Due to the modulus mismatch of the film and substrate, once the applied in-plane compressive stress (σ) in the film exceeds the bilayer-determined critical wrinkling stress (σc ), the balance of the system is broken, resulting in surface wrinkles [8].

Methods

Results

Conclusion