Dr. Peter William de Oliveira

A new water-based silica sol was developed to provide single-layer anti-reflective (AR) coatings. The combination of nanoparticle-based aqueous coating and wiping-coating method facilitated to reduce the solvent waste. The wiping-coating process requires only 35 ml sol to cover a large glass substrate (80 × 160 cm). Samples coated on one side show an improvement in light transmission in the visible range: the maximum transmission is 95.12 ± 0.33% on float glass and 92.48 ± 0.25% on display glass. This is an excellent performance compared to the extra 99.04% maximum transmission of samples coated on both sides. The layer thickness distribution defined by the ellipsometry of 98 samples (10 × 10 cm) shows homogeneity (77.4 ± 2.2 nm) over the total area. Homogeneous films with good surface wetting were applied on glass, polycarbonate (PC), and acrylic glass (PMMA). The cured layers were successfully tested against dry heat, damp heat (40 °C/98% RH), and climatic change (−40 °C–40 °C/98% RH) on all three substrate materials. No delamination from the substrate was observed. The changes in the minimum reflection after exposure to damp heat and climatic change were minimal (ΔR = ±0.6%) in the wavelength range of 400–1000 nm. The addition of Levasil nanoparticles into the water-based silica sol improved coating hardness on glass sheets up to 3H pencil hardness without significant loss in transmission.

The application of optical technologies in treating pathologies and monitoring disease states requires the development of soft, minimal invasive and implantable devices to deliver light to tissues inside the body. Here, we present soft and degradable optical waveguides from poly(d,l-lactide) and derived copolymers fabricated by extrusion printing in the desired dimensions and shapes. The obtained optical waveguides propagate VIS to NIR light in air and in tissue at penetration depths of tens of centimeters. Besides, the printed waveguides have elastomeric properties at body temperature and show softness and flexibility in the range relevant for implantable devices in soft organs. Printed waveguides were able to guide light across 8 cm tissue and activate photocleavage chemical reactions in a photoresponsive hydrogel (in vitro). The simplicity and flexibility of the fiber processing method and the optical and mechanical performance of the obtained waveguides exemplify how rational study of medically approved biomaterials can lead to useful inks for printing cost-effective and flexible optical components for potential use in medical contexts.

Sustainable production of anti-reflective coatings demands environmentally friendly approaches. This paper introduces a novel method of preparing thin films from an aqueous medium using a sol-gel technique. Single-layer anti-reflective coatings, from water-based silica sols, were prepared and characterized. The thicknesses of thin films were found to be between 75 and 135 nm with refractive indexes between 1.23 and 1.41 and porosities between 7 and 53%. The maximum transmissions of manufactured coatings reached from 99.85% to 99.03% in the visible region. The ageing of silica particles in the aqueous medium was studied using TEM. The transparent water-based sol consisted of individual silicon-dioxide nanoparticles with narrow size distribution (15–20 nm). The TEM images showed, that the silica nanoparticles become uniform and distinguishable within two weeks and no aggregation occurs within 46 days. It was found, that the aqueous silica sol is stable and clear for more than 6 months. The aqueous silica films deposited onto large glass surfaces were found to be homogeneous, with excellent adhesion (Cross Hatch Test is 0; ISO 2409 test standard) and hardness equal to 2H. We present a schematic illustration of the adsorption mechanism of non-ionic silicone surfactant and Pluronic surfactant on the silica surface.

Optical polymers cover only a rather narrow range of optical properties. This is a limiting factor for the design of polymer-based optical systems such as smartphone cameras. Moreover, it also poses a problem for femtosecond two-photon lithography, which is a state-of-the-art technology to 3D print high-quality optics from photopolymers. To overcome the limitations of conventional polymers, we introduce nano-inks based on the commonly used photopolymers IP-DIP and IP-S as polymer matrix and zirconium dioxide (ZrO2) nanoparticles. We show that the refractive index and dispersion of these nano-inks can be purposefully tailored by varying the constituent materials and the volume fraction of the nanoparticles. Furthermore, we demonstrate the suitability of our nano-inks for optical applications by 3D printing single micro-lenses and a multi-material achromatic Fraunhofer doublet. Our findings confirm that nanocomposites expand the range of optical properties that are accessible for polymer-based systems and allow for the design of tailored optical materials.

Abstract Transition metal dichalcogenides are attractive two-dimensional electrode materials for electrochemical energy storage devices due to their high reversible charge storage capacity. Hybridization of these materials with carbon promises enhanced performance by facilitating the access to reactive sites and extended mechanical stabilization. Herein, we introduce a NbS2/C hybrid material exhibiting a gyroidal microstructure synthesized through macromolecular co-assembly of a tailored block copolymer and an organometallic niobium precursor and subsequent sulfidation. Our synthesis allows the preparation of mechanically stable monoliths with NbS2 nanocrystals engulfed in a highly porous carbon shell. Due to the curvature of the gyroidal structure, abundant reactive sites are exposed that lead to an attractive performance in a lithium-containing electrolyte with a capacity of up to 400 mAh/g.

For the next generation of handling systems, reversible adhesion enabled by micropatterned dry adhesives exhibits high potential. The versatility of polymeric micropatterns in handling objects made from various materials has been demonstrated by several groups. However, specimens reported in most studies have been restricted to the laboratory scale. Upscaling the size and quantity of micropatterned adhesives is the next step to enable successful technology transfer. Towards this aim, we introduce a continuous roll-to-roll replication process for fabrication of high-performance, mushroom-shaped micropatterned dry adhesives. The micropatterns were made from UV-curable polyurethane acrylates. To ensure the integrity of the complex structure during the fabrication process, flexible templates were used. The compression between the template and the wet prepolymer coating was investigated to optimize replication results without structural failures, and hence, to improve adhesion. As a result, we obtained micropatterned adhesive tapes, 10 cm in width and several meters in length, with adhesion strength about 250 kPa to glass, suitable for a wide range of applications

Continuous roll-to-roll fabrication is essential for transferring the idea of bio-inspired, fibrillar dry adhesives into large-scale, synthetic, high-performance adhesive tapes. Toward this aim, we investigated process parameters that allow us to control the morphology and the resulting adhesion of mushroom-shaped micropatterned surfaces. Flexible silicone templates enabled the replication process of the polyurethane acrylate pre-polymer involving UV-light-induced cross-linking. For this paper, we particularly tailored the polyurethane acrylate pre-polymer by adding chemical components to tune UV curing kinetics and to reduce oxygen inhibition of radicals. We found that higher intensities of the UV light and faster reaction kinetics improved the quality of the microstructures, i.e., a larger cap diameter of the mushroom tips was achieved. The polymer blend U6E4 exhibited the fastest curing kinetics, which resulted in a micromorphology similar to that of the Ni-shim master structures. Best adhesion results were obtained for adhesive tapes made from U6E4 with 116 kPa pull-off stress, 1.4 N cm−1 peel strength and 71 kPa shear strength. In addition, repeated attachment–detachment tests over 100,000 cycles demonstrated strong robustness and reusability.

Block copolymers are promising materials for electrolytes in lithium metal batteries that can be tuned by changing the individual blocks to independently optimize ion transport as well as electrochemical and mechanical stability. We explored the performance of electrolytes based on modified triblock copolymers poly(isoprene)-block-poly(styrene)-block-poly(ethylene oxide). Large polyethylene oxide (PEO) blocks with a molecular mass of 53 kg mol-1 allowed only for low lithium salt loadings and led to poor ionic conductivity below 60 °C. However, we found that unusually small molecular weight of the ion solvating PEO blocks down to 2 kg mol-1 enabled polymer-in-salt loadings of up to 5:1 Li:EO. A superior total ionic conductivity greater than 1 mS cm-1 was found for optimized compositions above 0 °C with remarkably low temperature dependence in a wide range from -20 °C to 90 °C. We believe that highly ordered 2D lamellae from controlled self-assembly established a beneficial environment for ionic transport with ionic mobility decoupled from segmental polymer motion. This also explains lithium ion transference numbers as high as 0.7 were obtained for the high conductivity samples.

Thin films of Transparent Conducting Oxide (TCO) using Aluminum and Galium doped Zinc Oxide (AZO and GZO) nanoparticulate suspension were doposited via simple wet chemichal deposition technique on borosilicate glass substrate. The electrical properties of the obtained films are competitive with similar layers made of tin doped indium oxide (ITO) suspension. GZO nanoparticles have smaller grain size and higher BET surface area than the AZO one. The GZO layers show better electrical conductivity than the AZO one, where a denser layer was obtained with higher charge carrier concentration and mobility. The obtained results are competitive to the reported result of tin doped indium oxide based on the similar method. Although the number of charge carriers of the metal doped zinc oxide layers are still not in a level to be replaced by ITO coatings, however it has larger charge carrier mobility, which is an emerging step to be developed to enhance the electrical conductivity of such cost effective materials. Both GZO and AZO layers exhibit a high transparency in the visible region for greater than 87%.

We propose a novel optical effect that involves switching the nonlinear refractive index of colloids and solutions by applying an external field. The third-order nonlinear optical properties of the colloidal aluminum-doped zinc oxide nanoparticles were studied using the z-scan technique by employing a polarized continuous-wave laser beam. To produce the anisotropic effect in the nanocolloids, an external electric field was applied. The nonlinear refraction index switches from minus values to positive ones as the magnitude of the electric field increases. Enhancement of linear and nonlinear absorption coefficients due to the amplitude of the electric field confirms potential application of the colloidal nanoparticles for optical switches. This phenomenon was described theoretically using the re-orientation effect and birefringence of the media. This effect could be interesting for application in nonlinear optical devices and sensors.