Zhanhua Wang

Bioinspired Silica Surfaces with Near-Infrared Improved Transmittance and Superhydrophobicity by Colloidal Lithography

In this paper, we report a kind of bioinspired high performance near-infrared improved transmittance silica surfaces with superhydrophobic properties by colloidal lithography, with transmittance about 99% from 1300 to 2000 nm. Meanwhile, the optical properties of such surfaces can be controlled by the antireflective structure morphologies resulting from the different reactive ion etching conditions. Using proper microspheres as mask, the high-performance near-infrared telecommunication optics can be achieved. Besides, the antireflective surfaces possess superhydrophobic properties after modified by fluorosilane. Such antireflective surfaces are promising for fabrication of highly light transmissive, antireflective, and superhydrophobic near-infrared optical materials to be used in many important fields.

Bioinspired silicon hollow-tip arrays for high performance broadband anti-reflective and water-repellent coatings

High performance anti-reflective coatings were fabricated using high aspect ratio silicon hollow-tip arrays. They can suppress surface reflection from ultraviolet, visible light, to the mid-infrared region, with specular reflectance lower than 1% in the 250–1600 nm range. In addition, the tip arrays possess perfect water-repellent properties due to their high aspect ratio.

Suppression of the coffee ring effect by hydrosoluble polymer additives.

A simple and novel method has been demonstrated for avoiding coffee ring structure based on hydrosoluble polymer additives during droplet evaporation. The polymer additives lead to the motion of the contact line (CL) resulted from the viscosity and Marangoni effect. The viscosity provides a large resistance to the radially outward flow. It results in a small amount of spheres deposited at droplet edge, which do not facilitate the pinning of the CL. The Marangoni effect resulted from the variation of polymer concentration at droplet edge during droplet evaporation contributes to the motion of the CL. Thus, uniform and ordered macroscale SiO(2) microspheres deposition is achieved. Whats more, the coffee ring effect can be eliminated by different hydrosoluble polymer. This method will be applicable to a wide of aqueous system and will be of great significance for extensive applications of droplet deposition in biochemical assays and material deposition.

Colorful detection of organic solvents based on responsive organic/inorganic hybrid one-dimensional photonic crystals

Solvent sensitive organic/inorganic hybrid one-dimensional photonic crystals (1DPCs) were prepared through alternating thin films of poly methyl methacrylate-co-hydroxyethyl methacrylate-co-ethylene glycol dimethacrylate (PMMA-co-PHEMA-co-PEGDMA) and titania nanoparticle sol by spin-coating. Since the titania layer has a higher refractive index compared with the polymer layer, an obvious photonic stop band (PSB) can be easily obtained in several layers. Meanwhile, the materials take on evident color as the PSB falls into the visible region. The PSB can be reversibly tuned by introducing or removing organic solvents. Due to different interactions between the polymer and solvent molecules, the PSB can be shifted to different positions when introducing different solvents. At the same time, the 1DPCs present different colors, and the solvents used can be differentiated by the naked eye through color change. The solvent responsive process is very quick and the solvent sensitivity is very high. Almost all common solvents can be distinguished in this way. As well as pure solvents, mixtures can also be detected through the changes of optical properties. The shift of the PSB and the response speed can be modulated by changing the thickness of the polymer layer, while the thickness of the titania layer has little influence on them.

Facile UV-healable polyethylenimine–copper (C2H5N–Cu) supramolecular polymer networks

This study focuses on the development of facile polyethylenimine–copper (C2H5N–Cu) supramolecular polymer networks which upon mechanical damage are capable of reversible UV-induced self-repairs by the reformation of Cu–N coordination bonds. The chemical changes responsible for self-healing that leads to network remodeling include the formation of C2H5N–Cu complexes which, upon UV absorption, induce charge transfer between σ(N) bonding and dx2–y2(Cu) antibonding orbitals. The primary structural component responsible for network remodeling is the C2H5N–Cu coordination complex center that, upon UV exposure, undergoes square-planar-to-tetrahedral (D4h → Td) transition. The energy difference between dx2–y2 and dxz/yz orbitals during process change decreases significantly, enabling the σ(N) → dx2–y2(Cu) charge transfer and leading to energetically favorable Cu–N geometries. Manifested by virtually no temperature changes during UV-initiated self-healing, a unique feature of this network is the high efficiency of the damage–repair cycle resulting from the reversible conversion of electromagnetic radiation to chemical energy.

Improved light extraction efficiency of white organic light-emitting devices by biomimetic antireflective surfaces

One simple method to increase the light extraction from white organic light-emitting devices by using biomimetic silica antireflective surfaces is demonstrated. A silica cone array was directly etched on the opposite side of the indium–tin–oxide coated fused silica substrate. The antireflective surfaces can dramatically suppress the reflection loss and increase the transmission of light over a large range of wavelength and a large field of view. Using such surfaces, the luminance efficiency of the device in the normal direction is increased by a factor of 1.4 compared to that of the device using flat silica substrate.

UV-induced self-repairing polydimethylsiloxane–polyurethane (PDMS–PUR) and polyethylene glycol–polyurethane (PEG–PUR) Cu-catalyzed networks

UV-induced self-repairing polydimethylsiloxane–polyurethane (PDMS–PUR) crosslinked networks capable of repairing mechanical damage upon UV exposure were developed. Induced by the presence of the copper chloride (CuCl2) catalyst, the network remodeling and bond reformation are achieved by the formation of Cu–O coordination complexes, covalent Si–O–Si hydrolysis with subsequent bond reformation. Upon UV exposure, Cu–O complexes undergo tetrahedral-to-distorted tetrahedral rearrangements which parallel the Si–O bond reformation. When PDMS was substituted with OH-terminated polyethylene glycol (PEG) to form PEG–PUR crosslinked networks, square planar-to-tetrahedral rearrangements occur during the damage–repair cycle. Alkyl backbone distortions and segmental motions induced by the local Cu–O symmetry changes result in volume changes of the metal–ligand complex center. These studies show that a combination of supramolecular and covalent bonds facilitates self-repairing.

Polymer Bragg stack as color tunable photonic paper

Polymer 1D photonic crystals with perfect optical tuning and distinctive brilliant colors are successfully fabricated through alternating thin films of PMMA and PNIPAM-co-PGMA, which can be easily processed as photonic paper by combining with top-down assisted photolithograph. The photonic paper is prewritten by ultraviolet light cross-linking with a photo mask and read with water as ink. The writing and erasing process is smoothly reversible by repeatedly exposing the material to water and air. The color of letters written on the paper can be modulated by tuning the cross-linking density and ink temperature. Moreover, multicolors can be integrated onto the photonic paper simultaneously by making the degree of cross-linking of different regions of the photonic paper different. The fabrication method is simple and low-cost, and the photonic paper can be easily manufactured in large areas. The integrated multicolor and its diverse change with external stimuli promises the photonic paper lots of potential applications, such as colorful sensors, security labels, full-color printing, displays and so on.

Self-Healing Superhydrophobic Fluoropolymer Brushes as Highly Protein-Repellent Coatings

Superhydrophobic surfaces with micro/nanostructures are widely used to prevent nonspecific adsorption of commercial polymeric and/or biological materials. Herein, a self-healing superhydrophobic and highly protein-repellent fluoropolymer brush was grafted onto nanostructured silicon by surface-initiated atom transfer radical polymerization (ATRP). Both the superhydrophobicity and antifouling properties (as indicated for isolated protein solutions and for 10% blood plasma) are well repaired upon serious chemical degradation (by e.g. air plasma). This brush still maintains excellent superhydrophobicity and good antifouling properties even after 5 damage-repair cycles, which opens a new door to fabricate long-term antifouling coatings on various substrates that can be used in harsh environments.

Patterning organic/inorganic hybrid Bragg stacks by integrating one-dimensional photonic crystals and macrocavities through photolithography: toward tunable colorful patterns as highly selective sensors.

Herein, we report a simple method to fabricate patterned organic/inorganic hybrid 1DPCs by top-down assisted photolithography. Versatile colorful pattern with different size and shape can be produced by selectively exposing the 1DPCs under UV light with predesigned photomask directly. The period change, especially the thickness variation of the top polymer layer, is the main reason for the colorful pattern generation. Because of the swelling property of the polymer layers, the pattern color can be modulated by introducing or taking off organic solvents, leading the as-prepared patterned 1DPCs to be effective sensors with high selectivity.