Programmable Transition between Adhesive/Anti-Adhesive Performances on Porous PVDF Spheres Supported by Shape Memory PLLA.

Jiaqin Zhao,Xiong Cheng,Jiayao Wang,Liang Zhang,Jichun You,Yongjin Li

doi:10.3390/polym14030374

Abstract

Superhydrophobic surfaces with switchable adhesive/anti-adhesive performances are highly desired but still challenging. Herein, by loading porous poly (vinylidene fluoride) (PVDF) spheres on a shape memory polylactic acid (PLLA) film, a quasi-superhydrophobic surface of composite film (PVDF@PLLA) with the ability to tailor its surface structures/composition and related adhesive behaviors was fabricated. The as-prepared surface is covered by porous PVDF spheres. The combination of hydrophobicity of PVDF and hierarchical roughness resulted from porous spheres contributing to the high contact angle and low sliding angle, corresponding to Cassie state and lotus leaves effect. Upon uniaxial or biaxial tension, the distance among hydrophobic spheres is so high that more and more hydrophilic defects (PLLA film) have been exposed to water droplets, accounting for the quasi-superhydrophobic surface with a higher sliding angle. This is the reason for the Wenzel state and rose petals effect. After heating, PLLA film recovers to its original state. The porous PVDF spheres cover the whole film again, leading to the enhanced mobility of water droplets on the surface. The transition between the rose petals effect and the lotus leaves effect is programmable and reversible. Our result provides a novel strategy to tailor adhesive behaviors by combining (quasi-)superhydrophobic surface with shape memory effect.

Highlights

In nature, many plants and insects, including plant leaves, the wing of the butterfly and the leg of the water strider, exhibit excellent superhydrophobicity [1,2,3,4]
In a ternary blend of PVDF/PMMA/polylactic acid (PLLA) with compatibilizers (SZ-01, 0.5 wt%), phase separation produced PVDF/PMMA mixed phase and PLLA phase. The latter acted as a matrix due to the higher volume fraction. Both PLLA matrix and PMMA in mixed phase were removed, yielding porous PVDF spheres with a diameter of several microns (Figure 1B)
Water droplets come in contact with only PVDF spheres, which is an efficient way to avoid the influence of the supporting layer on the contact angle

Summary

Introduction

Many plants and insects, including plant leaves, the wing of the butterfly and the leg of the water strider, exhibit excellent superhydrophobicity [1,2,3,4]. It is possible to achieve this transition by varying chemical composition [18,19] Su and his co-workers introduced hydrophilic defects on polyelectrolyte multilayer (PEM) surfaces supported by rough silica nanoparticles. The surface of PVDF@PLLA composite film exhibits the lotus leaves effect because of the hydrophobic performance and roughness resulting from neighboring spheres, corresponding to a high contact angle and low sliding angle. Upon uniaxial or biaxial tension, there is obvious deformation on PLLA films, leading to the exposed area which has not been covered by porous PVDF spheres This is the reason for the occurrence of hydrophilic defects (PLLA) on hydrophobic PVDF surfaces, accounting for the enhanced contact angle hysteresis, i.e., rose petals effect. Scocmhepmosiete1s.uSrfcahcee. matic diagram of droplet anti-adhesion/adhesion mechanism on the PVDF@PLLA composite surface

Materials

Microstructure Characterization

Results and Discussion