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.

The present work demonstrates the first application of Brillouin light scattering (BLS) to probe film-guided elastic waves in transparent-substrate supported polymer thin films. In comparison with earlier BLS studies that were restricted to films either free-standing or supported on opaque substrates, the progress made in this work substantially extends the applicability of BLS and permits direct access to the elastic properties of thin films lying on transparent substrates, which is of important practical relevance. A series of thin supported polystyrene and poly(methyl methacrylate) films with thickness in the range of 40-500 nm were explored, and no noticeable trend in elastic properties with thickness has been found, in conformity with earlier BLS results. The first measurement of glass transition temperature, T g , of supported polymer thin films by BLS is also reported. We observed that the ultrathin (40 nm) films for both polymers exhibit a clear reduction in T g .