Tingting Ren

Superhydrophobic self-cleaning antireflective coatings on Fresnel lenses by integrating hydrophilic solid and hydrophobic hollow silica nanoparticles

Superhydrophobic self-cleaning antireflective coatings were fabricated on Fresnel lenses by integrating solid silica nanoparticles (SSNs) and stearic acid (STA) and 1H,1H,2H,2H-perflurooctyltriethoxysilane (POTS) co-modified hollow silica nanoparticles (SPHSNs) via spin- and spray-assembly without any high temperature pre- or post-treatment. Transmission electron microscopy (TEM) was used to observe the morphology and structure of nanoparticles. Transmission spectra were recorded using a UV-Vis-NIR spectrophotometer. Surface wettability was studied by an automatic contact angle/interface system. Condensation performance of the Fresnel lenses was studied by measuring the focal length and the powers before and after being focused. The (SSNs)1/(SPHSNs)2 coating turned out to simultaneously demonstrate excellent superhydrophobic self-cleaning and antireflective properties, which has a maximum transmittance of 99.0% and average transmittance of 98.5% in the wavelength range of 400–800 nm, and the condensing efficiency of the coated Fresnel lens has also been significantly improved. The surface morphology and structure of coatings were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The effects of surface morphology and structure on the optical and wetting properties of coatings were also discussed. The density of SPHSNs on the coating surface was considered to significantly influence both the light transmission and hydrophobicity of coated Fresnel lenses.

A versatile route to polymer-reinforced, broadband antireflective and superhydrophobic thin films without high-temperature treatment.

Broadband high transmittance, good mechanical robustness as well as simple and low temperature fabrication are three important aspects that dictate the practical applications of superhydrophobic thin films, especially on organic substrates. However, it has proved difficult to meet these challenges. In the present work, superhydrophobic thin films were prepared by first dip-coating solid silica nanoparticles, then spray-coating hollow silica nanoparticles, followed by spray-coating mesoporous silica nanosheets & poly(vinyl alcohol) (PVA), and eventually chemical vapor deposition of 1H,1H,2H,2H-perflurooctyltriethoxysilane (POTS) at 90°C. The optimized thin film has a maximum transmittance of 96.0% in the wavelength range of 300-2500nm and a WCA of 164° and a RA of 1°. The thin film also shows good mechanical robustness toward water droplet impact test, sand impact abrasion test and tape adhesion tests, which results from PVA as a binder, the formation of covalent bond between the hydroxyl group of PVA and the ethoxy group of POTS and the chemical inertness of CC, CF bonds of POTS molecules. To our best knowledge, it is the first example where antireflective and superhydrophobic thin films of excellent mechanical robustness were realized at low temperature on organic substrates (PMMA, PC). The current work would provide a promising route to meet the challenges in practical applications simultaneously posed by the requirements of broadband antireflection, good mechanical robustness as well as simple and low temperature fabrication of superhydrophobic thin films.

Novel SiO2/H2Ti2O5·H2O-Nanochain Composite with High UV-Visible Photocatalytic Activity for Supertransparent Multifunctional Thin Films.

In the current work, a peroxo titanium complex (PTC) solution was used as a novel water-soluble precursor to fabricate H2Ti2O5·H2O and the SiO2/H2Ti2O5·H2O-nanochain composite at low temperature (90-100 °C). The average width of H2Ti2O5·H2O nanochains is 4.5 ± 1.5 nm. Under full-spectrum irradiation, the Si/Ti-nanochain composite showed good UV-visible light absorption and excellent photocatalytic activity, which is 2.8 times that of P25. In the composite, SiO2 not only contributes to the formation of nanochains and improves the catalytic performance of H2Ti2O5·H2O but also reduces the refractive index of the complex. When coated on transparent organic substrates, the composite thin film exhibited excellent antireflective (as high as 99.3% on PC and 98.9% on PMMA) and self-cleaning properties. Pencil hardness, washing, and tape adhesion tests showed favorable adhesion-to-substrate and mechanical robustness of thin films, which make them extremely attractive for applications as highly transparent and self-cleaning thin films on lenses, photovoltaic cells, and windows of high-rise buildings.

In situ formation of artificial moth-eye structure by spontaneous nano-phase separation

Unprecedented in situ formation of artificial moth-eye structure is demonstrated by spontaneous nano-phase separation of a silica-based system on substrate. The moth-eye thin film with a homogenously distributed nipples array shows broadband antireflection functionalities. The mechanism of nano-phase separation is unveiled as spinodal decomposition by chemical freezing method and thermodynamic analysis. The current method may provide a new avenue to ready fabrication of patterned nanostructures toward a variety of applications.

CuO Nanoparticles-Containing Highly Transparent and Superhydrophobic Coatings with Extremely Low Bacterial Adhesion and Excellent Bactericidal Property

Human health and industrial instruments have been suffering from bacterial colonization on the surface of materials for a long time. Recently, antibacterial coatings are regarded as the new strategy to resist bacterial pathogens. In this work, novel highly transparent and superhydrophobic coatings with extremely low bacterial adhesion and bactericidal performance were prepared by spray-coating hydrophobic silica sol and CuO nanoparticles. The coated glass showed high transmittance in 300-2500 nm with a maximum value of 96.6%. Compared with bare glass, its superhydrophobic characteristics resulted in a reduction in adhesion of bacteria ( Escherichia coli, E. coli) by up to 3.2 log cells/cm2. Additionally, the live/dead staining test indicated that the as-prepared coating exhibited excellent bactericidal performance against E. coli. Moreover, the as-prepared coating could maintain their superhydrophobicity after the sand impact test. The proposed method to fabricate such coatings could be applied on various substrates. Therefore, this novel hybrid surface with the abilities to reduce bacterial adhesion and kill attached bacteria make it a promising candidate for biosensors, microfluidics, bio-optical devices, household facilities, lab-on-chips, and touchscreen devices.

Hydrogel-Encapsulated Enzyme Facilitates Colorimetric Acute Toxicity Assessment of Heavy Metal Ions

Conventional analysis of heavy metal ions in water requires highly skilled staff and sophisticated equipment. These limitations make conventional approaches difficult to perform analysis on-site without delay. Herein, we report a facile colorimetric sensing system developed for acute toxicity assessment of heavy metal ions. A bioactive enzyme, β-galactosidase, was used as sensing agent rather than bacteria or other higher organisms to improve selectivity and response time. The developed bioassay is capable of assessing the toxicity of heavy metal ions such as Hg(II), Cd(II), Pb(II), and Cu(II). The effects of enzyme concentration on the assessing performances (i.e., sensitivity and response time) of bioassay were explored and illustrated. Generally, low enzyme concentration facilitates sensitivity enhancement, achieving a 50% inhibiting concentration (IC50) of 0.76 μM (=152 ppb) Hg(II), and high enzyme concentration ensures quick response, enabling a response time down to 9 min. Moreover, the enzyme and substrate were respectively encapsulated by hydrogel to further simplify the assay procedure and enhance the stability of the enzyme. The hydrogel-encapsulated enzyme worked well even when heated up to 60 °C and retained ca. 90% activity after storage for 5 months. Moreover, the developed toxicity-assessing system is feasible for assessing toxicity of actual water samples. This assay approach is low cost and time effective and has no potential ethic issues. In addition, this work paves the way for the development of toxicity assessment kits for on-site analysis based on functional bioactive molecules.

Chapter 1:The Inspiration of Nature: Natural Counterparts with Self-cleaning Functions

A self-cleaning function is the capability of a material to maintain its contamination-free surface, avoiding the deposition of dirt. Quite a few self-cleaning surfaces have been found in nature that provide inspiration for fabricating various biomimicking artificial surfaces. In this chapter, we review the structure, performance and principle of those natural self-cleaning surfaces. Based on the self-cleaning mechanisms, the natural self-cleaning surfaces are divided into the following categories: (a) hydrophobic self-cleaning surfaces, (b) elastic effect of tomentum-induced self-cleaning surfaces, (c) micro/nanostructured slippery surfaces, (d) hydrophilic and oleophobic (in water) self-cleaning surfaces, and (e) disequilibrium of interfacial force induced self-cleaning surfaces. The self-cleaning functions of natural surfaces are generally induced either from interfacial wettability or interfacial force disequilibrium. The knowledge learned from Mother Nature would guide the development of artificial self-cleaning materials, which may have great potential in many fields, such as self-cleaning, antifouling, corrosion-resistance, anti-icing, anti-fingerprint and water–oil separation, etc.