Universally Applicable Fabrication Technique for Biomimetic Nanocone Arrays on Flexible Polymer Substrates for Anti-Reflection Functionality

Abstract

Inspired by the anti-reflection functionality of cicada wings decorated with nanocone arrays, a facile technique to endow flexible polymer substrates of diverse chemical compositions with the same functionalities has been devised. In this universally applicable two-step technique based on a capacitatively coupled radiofrequency plasma (CCRP), first oxygen-plasma treatment (OPT) is implemented to grow arrays of vertical elongated nanostructures with almost uniform cross-sectional diameter of the polymer substrate, and then fluorocarbon polymer deposition (FPD) is carried out so that the nanostructures evolve into nanocones with small apex angle. The dependence of ion-bombardment-induced sputtering on the local impingement angle of ions taper the vertical nanostructures into the nanocones during the FPD under CCRP. The nanocone arrays exhibit low specular reflectance in a broad wavelength range and a wide incidence angle range that is quite insensitive to the polarization state of the incident light. The effective refractive index gradient of irregularly arranged nanocone arrays is characterized from the refractive index of the fluorocarbon polymer and the volume fraction considering the nanocone probability with the Gaussian distribution. The excellent broadband and omnidirectional anti-reflection properties are in consequence of a graded refractive index.

Biomimetic Random Arrays of Nanopillars and Nanocones with Robust Antiwetting Characteristics

“…Biomimetic Nanopillar and Nanocone Arrays. To investigate the antiwetting characteristics of irregular arrays of nanopillars and nanocones, a maskless nanotexturing technique combining OPT and FPD in a CCRP reactor 28 was utilized to fabricate the nanopillars and nanocones on PP substrates. OPT for 10 min was used to create nanopillars arrays on the substrates.…”

“…35 If FPD is allowed to occur only for 1 min, the hydrophobic chemistry of the nanopillar surfaces is modified without influencing the shapes of the nanopillars; however, FPD for 20 min transforms the nanopillars into nanocones. 28 These nanocones inherit the dimensional variability and irregularity of placement of the nanopillars created by OPT.…”

“…PP sheets (20 × 20 mm 2 , 1 mm thick) were first cleaned with ethanol in an ultrasonic bath for 15 min, washed repeatedly with deionized water, dried in an oven at 70 °C for 12 h, and then stored in a desiccator. A CCRP reactor 28 was used to fabricate nanostructures arrays by a twostep nanotexturing technique. Two planar stainless-steel electrodes of 200 mm diameter and separated by 110 mm were placed inside the CCRP reactor.…”

“…In the work reported here, biomimetic random arrays of dissimilar nanopillars/nanocones were fabricated on polypropylene (PP) substrates by a maskless nanotexturing technique comprising oxygen−plasma treatment (OPT) followed by fluorocarbon polymer deposition (FPD) in a capacitively coupled radio frequency plasma (CCRP) reactor. 28 The nanopillars and the nanocones with the fluorocarbon polymer film on nanotextured PP substrates preserve the similar tip diameter, placement irregularity, and chemical composition, which is well utilized to study the effects of dimensional variability and irregularity of placement on the antiwettability characteristics. The Cassie-to-Wenzel and the Wenzel-to-Cassie transitions were investigated while the nanotextured substrates were being impacted by waterdrops.…”

Antireflection and antiwetting functionalities of plasma‐nanotextured polymer surfaces with biomimetic nanopillars

“…Plasma nanotexturing is a templateless technique to fabricate nanostructures on various polymer substrates. [17][18][19][20] During the plasma treatment processes, the metal nanoparticles sputtered from the reactor wall and the electrodes were deposited on the polymer substrates as random masks to induce the formation of the polymer nanopillars. [21,22] The natural microstructure of polymer materials is also another factor to influence the distribution of random nanopillars on the treated surfaces, because the degradation of polymer chains at the amorphous domains is commonly easier than that at the hard crystalline domains.…”