Nanoporosity-Driven Superhydrophilicity:  A Means to Create Multifunctional Antifogging Coatings

Abstract

Multifunctional nanoporous thin films have been fabricated from layer-by-layer assembled silica nanoparticles and a polycation. The resultant multilayer films were found to exhibit both antifogging and antireflection properties. The antifogging properties are a direct result of the development of superhydrophilic wetting characteristics (water droplet contact angle <5 degrees within 0.5 s or less). The nearly instantaneous sheetlike wetting promoted by the superhydrophilic multilayer prevents light scattering water droplets from forming on a surface. The low refractive index of the multilayer film (as low as 1.22) resulting from the presence of nanopores was found to impart excellent antireflection properties. Glass slides coated on both sides with a nanoporous multilayer film exhibited transmission levels as high as 99.8%. Stable superhydrophilic wetting characteristics were obtained only after a critical number of bilayers were deposited onto a surface. The assembly conditions (solution pH and nanoparticle concentration), as well as the choice of nanoparticle size, were found to strongly influence film properties. It is suggested that the superhydrophilic behavior is driven by the rapid infiltration of water into a 3D nanoporous network created under specific assembly conditions.

A colloidoscope of colloid-based porous materials and their uses

“…Polydisperse particles, which are unable to crystallize in an ordered matrix, can be used to prepare amorphous assemblies without long-range order ( Figure 3B). 4,82 Simplistic and scalable approaches such as spray coating 83,84 or layer-by-layer assembly 85,86 of particles that are not suitable for crystallization due to high attractive forces or insufficient crystallization time can still be used to prepare disordered assembly structures in an experimentally straightforward way. Indeed, as we discuss in detail in several of the following sections, order is not necessary for every application of CBPM, and controlled disorder may even create desired properties.…”

“…CBPM have also been used in other transport applications such as for cell culture, 210,211 for drug delivery, 212,213 and as membranes and filters, 214 applications we do not cover in this review. 86 Reproduced with permission from the American Chemical Society. (B) Cassie-Baxter state for superhydrophobic self-cleaning surfaces.…”

“…For example, water condensate spreads on a hydrophilic antifogging coating on glass containing roughness features instead of forming droplets as it does on an untreated flat glass substrate, decreasing light scattering and maintaining transparency ( Figure 12A). 86 However, such behavior is not suited for applications where repellency is desired, since it would result in liquid pinning, high contact angle hysteresis, and failure of the coating.…”

“…When the sizes of these metal oxide particles are below the wavelength of visible light, they form transparent coatings. 85,86 The particles can also be sintered to improve the mechanical robustness of the coating. 232 However, the sintering process may limit substrates to those that can withstand high temperature treatments.…”

Surfaces Inspired by the Nepenthes Peristome for Unidirectional Liquid Transport

“…[6] Without energy input, these biological surfaces can harness the movement of water through their unique structural features and chemical composition, [11][12][13] which gives inspiration for designing and fabricating functional surfaces and materials with wide applications in fields including antifogging and fog-collection, [14][15][16] microfluidic devices, [17][18][19][20][21] lubrication, [22,23] and liquid transport. [24][25][26][27] One-dimensional materials for unidirectional liquid transport, inspired by spider silk and cactus spines, have attracted major research interest in the last few years.…”