Improvement of Mechanical Properties and Solvent Resistance of Polyurethane Coating by Chemical Grafting of Graphene Oxide.

Waterborne polyurethane coatings (WPU) are widely used in various types of coatings due to their environmental friendliness, rich gloss, and strong adhesion. However, their inferior mechanical properties and solvent resistance limit their application on the surface of wood products. In this study, graphene oxide (GO) with nanoscale size, large surface area, and abundant functional groups was incorporated into WPU by chemical grafting to improve the dispersion of GO in WPU, resulting in excellent mechanical properties and solvent resistance of WPU coatings. GO with abundant oxygen-containing functional groups and nanoscale size was prepared, and maintained good compatibility with WPU. When the GO concentration was 0.7 wt%, the tensile strength of GO-modified WPU coating film increased by 64.89%, and the abrasion resistance and pendulum hardness increased by 28.19% and 15.87%, respectively. In addition, GO also improved the solvent resistance of WPU coatings. The chemical grafting strategy employed in this study provides a feasible way to improve the dispersion of GO in WPU and provides a useful reference for the modification of waterborne wood coatings.

Enhancing the Mechanical Properties of Waterborne Polyurethane Paint by Graphene Oxide for Wood Products.

Water-based polyurethane paint is widely used for wood furniture by virtue of the eco-friendliness, rich gloss, and flexible tailorability of its mechanical properties. However, its low solution (water or alcohol) resistance and poor hardness and wear resistance limit its application. The emerging graphene oxide has a high specific surface area and abundant functional groups with excellent mechanical properties, endowing it with great potential to modify waterborne polyurethane as a nanofiller. In this study, graphene oxide prepared by Hummers' method is introduced in the chemosynthetic waterborne polyurethane through physical blending. The testing results demonstrate that the appropriate usage of graphene oxide at 0.1 wt% could obviously improve water absorption resistance and alcohol resistance, significantly enhancing the mechanical properties of waterborne polyurethane paint. The corresponding tensile strength, abrasion resistance, and pendulum hardness of the graphene oxide-modified paint film increase by 62.23%, 14.76%, and 12.7%, respectively, compared with the pristine paint film. Meanwhile, the composite paint film containing graphene oxide possesses superiority, including gloss, abrasion resistance, pendulum hardness, and tensile strength in contrast with the commercial paint. The use of graphene oxide to enhance the waterborne polyurethane possesses strong operability and practical value, and could provide useful reference for the modification of waterborne wood paint.

Tetrad phase vortex structure in scattered SPP field produced by silver nano-ring-slit under linearly polarized illumination.

We report the tetrad phase vortex structure in the scattered surface plasmon polariton (SPP) field produced by a silver nano-ring-slit with linearly polarized illumination. In the experiment, Mach-Zehnder type interferometer is constructed in which a microscopic objective (MO) is used to collect and image the scattered SPP field, and the phase map is extracted by Fourier transform of the interference intensity. To explain the formation of the tetrad phase vortices in the central area of the ring, we propose an empirical model for the ring-slit-excited SPP source field by trial calculations with the Huygens-Fresnel principle for SPP propagations. It is shown that the azimuthal variation of the amplitude of the source SPP is roughly a half of a constant base, and the variation of the phase is a little greater than π/2. The intensity and the phase distributions of the SSP field calculated with the formulations of this model phenomenologically conform the experimental results.

Generation of high-order optical vortices with asymmetrical pinhole plates under plane wave illumination.

We propose a novel and simple method for generating optical vortex with high topological charge (TC), merely using an asymmetrical pinhole plate illuminated by plane wave. N pinholes are arranged along a particular spiral line around the plate origin, with constant azimuth angle increment and varied radial distances. The radial differences introduce a constant variation of m/N wavelength to the optical paths from the N pinholes to the observation plane origin, and this increases the phases of the transmitting waves by progressively 2mπ/Nand totally 2mπ. We numerically calculate the transmitted light field according to the Fresnel diffraction theory, and find the vortex with TC m around the observation plane origin. The experimental verifications are performed using some self-made asymmetrical pinhole plates fabricated by a femtosecond laser, with the high TC vortices both generated and detected in a Mach-Zehnder type interferometer. The experimental results coincide with the theoretical simulations well.

Evolutions of speckles on rough glass/silver surfaces with film thickness.

This paper reports experimental studies on speckles produced by the rough silver films. The speckles on the rough glass/silver surfaces are measured with a microscopic imaging system. The structures of speckle patterns have the characteristics of fractals and multi-scaled sizes. We find that with the increase of the silver film thickness, the contrast of the speckles increases, and the intensity probability density functions gradually transit to exponential decay. We calculate the global and the local correlation functions of the speckle patterns, and find that both the fractal exponent and correlation length of the small-sized speckles decrease with the thickness of the silver films. We use the mechanisms of rough dielectric interface scattering and random surface plasmon waves to give the preliminary explanations for the evolutions of the speckles.