Hierarchical Microtextures Embossed on PET from Laser-Patterned Stamps.

Felix Bouchard,Robert Baumann,Marcos Soldera,Andrés Fabián Lasagni

doi:10.3390/ma14071756

Abstract

Nowadays, the demand for surface functionalized plastics is constantly rising. To address this demand with an industry compatible solution, here a strategy is developed for producing hierarchical microstructures on polyethylene terephthalate (PET) by hot embossing using a stainless steel stamp. The master was structured using three laser-based processing steps. First, a nanosecond-Direct Laser Writing (DLW) system was used to pattern dimples with a depth of up to 8 µm. Next, the surface was smoothed by a remelting process with a high-speed laser scanning at low laser fluence. In the third step, Direct Laser Interference Patterning (DLIP) was utilized using four interfering sub-beams to texture a hole-like substructure with a spatial period of 3.1 µm and a depth up to 2 µm. The produced stamp was used to imprint PET foils under controlled temperature and pressure. Optical confocal microscopy and scanning electron microscopy imaging showed that the hierarchical textures could be accurately transferred to the polymer. Finally, the wettability of the single- and multi-scaled textured PET surfaces was characterized with a drop shape analyzer, revealing that the highest water contact angles were reached for the hierarchical patterns. Particularly, this angle was increased from 77° on the untreated PET up to 105° for a hierarchical structure processed with a DLW spot distance of 60 µm and with 10 pulses for the DLIP treatment.

Highlights

Nature provides countless surface structures that influence the macroscopic physical properties
Likewise, increasing the number of direct laser interference patterning (DLIP) pulses led to an increase in the water contact angle (WCA) for all the studied samples. These results show that the hierarchical patterns presented higher WCA than the corresponding single-scale textures based on either direct laser writing (DLW) or DLIP processes (WCA corresponding to the DLIP structures are shown in Figure 10 with dashed lines, red: 1 pulse, green: 5 pulses, blue: 10 pulses)
We presented a strategy to produce hierarchical surface structures on polyethylene terephthalate (PET) foils

Summary

Introduction

Nature provides countless surface structures that influence the macroscopic physical properties. Famous examples are the self-cleaning effect on the lotus leaf, the anti-bacterial behavior of spring-tail skin, and the high adhesion skin on gecko feet [1,2,3] All these structures have in common that surface features with different size scales are combined, normally in the micrometer range with nanometer substructures. There are several innovative strategies to manipulate the wetting behavior of polymer surfaces, for instance plasma activation, thermal drawing, nanoparticles deposition, or applying functional coatings [8,9,10,11,12] These methods are mainly devised for small areas and are not directly scalable to industrial throughputs

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Conclusion