Nanofibrillar Patterns by Plasma Etching: The Influence of Polymer Crystallinity and Orientation in Surface Morphology

Abstract

This manuscript explores the possibility of exploiting polymer morphology (thermal or flow-induced) as materials inherent template, and domain-selective plasma etching as pattern developer, to obtain nanopatterned surfaces with different and controlled geometries, with a particular focus on nanofibrillar patterns. Oxidative plasma treatment of PET films has rendered patterned surfaces with different geometries depending on the crystallinity and orientation of the PET sample and plasma treatment time (or etching ratio). Homogeneous patterns with either randomly distributed or aligned nanofibrils with diameters between 20 and 40 nm and lengths up to 1 μm (after extensive etching) were observed depending on the sample pretreatment. Our results demonstrate the potential of oxidative plasmas as templateless nanopatterning technique and reveal a complex interplay between plasma etching parameters and polymer microstructure driving the pattern formation mechanism. These results open the possibility of fabricating gecko-inspired surfaces in a cost-effective manner.

Superhydrophilic and superhydrophobic nanostructured surfaces via plasma treatment

“…PET samples were plasma treated using previously reported conditions [17]. Nanofibrils with 30-40 nm diameter and an estimated height from tilted SEM images of 70 nm were observed at the surface after 2-5 min plasma treatment ( Fig.…”

“…1). This was attributed to a collapse of the fibrils when the aspect ratio (or etching rate) increases since they become mechanically unstable [17]. The number of fibrils in the bundles increased with etching time.…”

“…The length scale and complexity of the surface features fabricated on individual materials upon plasma treatment can be controlled by tuning the plasma processing parameters [5,6,[16][17][18][19]. This is an important advantage of plasma-based processes that can be exploited for obtaining hierarchical organisation of the nanostructures in a single-step structuring process.…”

Interaction between model poly(ethylene terephthalate) thin films and weakly ionised oxygen plasma

“…The observed cone formation may be also due to preferential etching of amorphous parts in comparison to crystalline parts. [31] The spin-coated PET films are known to be semi-crystalline, with 18-40% of crystallised PET. [31,32] Here we should also mention that polymer films can orientate along the crystallographic axes of the support quartz crystal material, but this can be usually expected only in the case when the polymer film is deposited relatively slowly or when the film can re-organise itself very quickly.…”

“…[31] The spin-coated PET films are known to be semi-crystalline, with 18-40% of crystallised PET. [31,32] Here we should also mention that polymer films can orientate along the crystallographic axes of the support quartz crystal material, but this can be usually expected only in the case when the polymer film is deposited relatively slowly or when the film can re-organise itself very quickly. Spin-coated films are usually formed very fast and it is common that they have an orientation governed by the centrifugal forces rather than by the substrate crystal axis.…”