Multifunctional Inverted Nanocone Arrays for Non-Wetting, Self-Cleaning Transparent Surface with High Mechanical Robustness

• Published in: Small (Weinheim an der Bergstrasse, Germany) Germany), 2014-06, Vol.10 (12), p.2487-2494
• Main Authors: Kim, Jeong-Gil, Choi, Hyungryul J., Park, Kyoo-Chul, Cohen, Robert E., McKinley, Gareth H., Barbastathis, George
• Format: Article
• Language: English
• Subjects: Acrylates; anti-fogging; anti-reflectivity; Arrays; mechanical properties; Nanostructure; Nanostructures; Nanotechnology; Polyurethane resins; Robustness; self-cleaning; Specific surface; Topography; Wetting
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.201303051

A multifunctional surface that enables control of wetting, optical reflectivity and mechanical damage of nanostructured interfaces is presented. Our approach is based on imprinting a periodic array of nanosized cones into a UV‐curable polyurethane acrylate (PUA), resulting in a self‐reinforcing egg‐crate topography evenly distributed over large areas up to several cm2 in size. The resulting surfaces can be either superhydrophilic or superhydrophobic (through subsequent application of an appropriate chemical coating), they minimize optical reflection losses over a broad range of wavelengths and a wide range of angles of incidence, and they also have enhanced mechanical resilience due to greatly improved redistribution of the normal and shearing mechanical loads. The transmissivity and wetting characteristics of the nanoscale egg‐crate structure, as well as its resistance to mechanical deformation are analyzed theoretically. Experiments show that the optical performance together with self‐cleaning or anti‐fogging behavior of the inverted nanocone topography is comparable to earlier designs that have used periodic arrays of nanocones to control reflection and wetting. However the egg‐crate structures are far superior in terms of mechanical robustness, and the ability to replicate this topography through several generations is promising for large‐scale commercial applications where multifunctionality is important. Inverted nanocone arrays arranged in an egg‐crate structure are fabricated using UV‐curable polyurethane acrylate to create a multifunctional transparent surface. The periodic nanotexture provides enhanced anti‐reflectivity to broadband illumination together with self‐cleaning or anti‐fogging characteristics (depending on the specific surface chemistry). The egg‐crate structure also confers greatly enhanced mechanical robustness due to redistribution of local stresses amongst the interconnected features.