Layer-by-Layer Assembled Films of Cellulose Nanowires with Antireflective Properties

Abstract

Natural nanowires (NWs) of cellulose obtained from a marine animal tunicate display surprisingly high uniformity and aspect ratio comparable with synthetic NWs. Their layer-by-layer assembled (LBL) films show strong antireflection (AR) properties having an origin in a novel highly porous architecture reminiscent of a "flattened matchsticks pile", with film-thickness-dependent porosity and optical properties created by randomly oriented and overlapping NWs. At an optimum number of LBL deposition cycles, light transmittance reaches nearly 100% (lambda approximately 400 nm) when deposited on a microscope glass slide and the refractive index is approximately 1.28 at lambda = 532 nm. In accordance with AR theory, the transmittance maximum red-shifts and begins to decrease after reaching the maximum with increasing film thickness as a result of increased light scattering. This first example of LBL layers of cellulose NWs can be seen as an exemplary structure for any rigid axial nanocolloids, for which, given the refractive index match, AR properties are expected to be a common property. Unique mechanical properties of the tunicate NWs are also a great asset for optical coatings.

Template free preparation of nanoporous organically modified silica thin films on flexible substrates

“…Antireflective coatings are routinely designed to enhance the light transmission through these surfaces. 15,[32][33][34][35][36][37][38][39][40][41][42] However, antireflective coatings on flexible substrates are still rare. 32 An antireflective coating is based on destructive interference between the reflected light from the air/ film and the substrate/film interfaces.…”

“…32 An antireflective coating is based on destructive interference between the reflected light from the air/ film and the substrate/film interfaces. 34 To achieve destructive interference between these interfaces, two conditions must be met. First, the refractive index (n) of the film must be selected as n c ¼ ffiffiffiffiffiffiffiffi ffi n a n s p , where n c , n o and n s are refractive indices of coating, air and substrate respectively, according to Fresnel equations to achieve minimum reflection.…”

Bio-inspired iridescent layer-by-layer assembled cellulose nanocrystal Bragg stacks

“…These features produce highly porous assemblies with colloidal silica to create a low refractive index. While CNCs have been successfully used in LbL assembly to produce anti-reflective films, 43 this study demonstrates their first use with LbL assembly to produce iridescent, biomimetic, Bragg reflectors. …”

Cellulose Nanocrystals as Advanced "Green" Materials for Biological and Biomedical Engineering

“…The optical properties of CNC film dispersions can be modulated by controlling the cholesteric pitch, which in turn can be influenced by dispersion composition, polyelectrolyte, temperature, and shear. It has been found that incorporation of polyelectrolyte layers can change the colour and reflectiveness of CNC-based materials (Cranston and Gray, 2006;Podsiadlo et al, 2007). Moreover, manipulating the packing density results in regulation of the interstices between the fibers and avoids light scattering, which leads to regulated transparency, while maintaining the original high performance qualities ).…”