Use of the optical admittance function and its WKB approximation to simulate and evaluate transmittance spectra of graded-index colloidal films

Effect of Silver Modification on the Photoactivity of Titania Coatings with Different Pore Structures

Nanostructured photoactive systems are promising for applications such as air and water purification, including self-cleaning coatings. In this study, mesoporous TiO₂ sol-gel coatings with different pore structures were prepared and modified with silver by two methods: the "mixing" method by adding AgNO₃ to the precursor sol, and the "impregnation" method by immersing the samples in AgNO₃ solution (0.03 and 1 M) followed by heat treatment. Our aim was to investigate the effects that silver modification has on the functional properties (e.g., those that are important for self-cleaning coatings). Transmittance, band gap energy, refractive index, porosity and thickness values were determined from UV-Vis spectroscopy measurements. Silver content and structure of the silver modified samples were characterized by X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, High-resolution transmission electron microscopy and Energy Dispersive X-ray Spectrometry elemental mapping measurements. Wettability properties, including photoinduced wettability conversion behavior were investigated by water contact angle measurements. Photoactivity was studied under both UV and visible light with rhodamine 6G and methylene blue dye molecules, at the liquid-solid and air-solid interfaces modeling the operating conditions of self-cleaning coatings. Samples made with "impregnation" method showed better functional properties, in spite of their significantly lower silver content. The pore structure influenced the Ag content achieved by the "impregnation" method, and consequently affected their photoactivity.

Accumulation of 2-Acetylamino-5-mercapto-1,3,4-thiadiazole in chitosan coatings for improved anticorrosive effect on zinc

Chitosan (Chit) coatings were applied on zinc substrates by the dip-coating method. Subsequently, the coatings were impregnated with a corrosion inhibitor, 2-Acetylamino-5-mercapto-1,3,4-thiadiazole (AcAMT) to obtain an increased anticorrosive effect. The coating thickness and the AcAMT accumulation were determined using UV-Vis spectroscopy on glass and quartz substrates, respectively. The surface morphology and coverage were investigated with atomic force microscopy. Electrochemical impedance spectroscopy and potentiodynamic polarization techniques were used to investigate the protective properties of the impregnated coatings. The chitosan coatings facilitated the accumulation of the corrosion inhibitor inside the polymeric matrix (a multiplication of 380 times compared to the impregnating solution concentration was calculated), channeling high amounts of AcAMT to the Zn surface, which resulted in an inhibition efficiency of >90%. This effect demonstrates the applicability of chitosan coatings as carriers for corrosion inhibitors, significantly reducing the amount of inhibitor needed to achieve good anticorrosive effects.

Nanoporous block copolymer films using highly selective solvents and non-solvent extraction

Nanoporous block copolymer thin films are fabricated by selective solvent swelling of the majority phase and subsequent rapid extraction with a miscible non-solvent (water). Selection of the initial solvent provides a facile route to tune the porosity of the films. Poly(butylnorbornene)-block-poly(hydroxyhexafluoroisopropyl norbornene) (BuHFA) is used to generate these porous thin films due to its high Tg (>300 °C) and the selectivity of primary alcohols towards poly(hydroxyhexafluoroisopropyl norbornene) (pHFANB) to enable a relatively environmentally benign process. As the solvent quality for the HFA increases from ethanol to isopropanol to n-butanol, the porosity of the film developed by water extraction increases up to 69%. Aqueous mixtures of ethanol provide an addition handle to tune the porosity between 10 and 54%. These nanoporous films are robust with the porosity nearly unchanged after extended heating at 160 °C. Their elastic moduli are investigated using surface wrinkling and the modulus, E, scales with the film density, ρ, as E ∼ ρ(2.2), which is similar to cellular solids. The nanopores are templated by the self-assembled structure of the block copolymer, so these coatings are transparent despite the high porosity. These thin films act as anti-reflective coatings for glass slides. Spin coating provides a coating on both sides and processing to generate 55% porosity leads to an increase in transmittance from approximately 92% to 99.1% (average for the full range of visible light). A maximum transmittance of 99.8% is found at 523 nm. This methodology is simple and highly tunable; extension to other block copolymer systems is likely possible if sufficient solubility contrast between segments exists.

Introducing nanoscaled surface morphology and percolation barrier network into mesoporous silica coatings

The advantages of surface pattern and mesoporous character of silica thin films were combined, while preserving the interconnected pore system or creating laterally separated porous volumes surrounded by nonpermeable compact zones.

Langmuir and Langmuir-Blodgett films of bidisperse silica nanoparticles

We present the studies on the structure and optical properties of bidisperse Stöber silica nanoparticulate Langmuir films prepared at the air/water interface in a Wilhelmy film balance and transferred onto glass slides using the Langmuir-Blodgett technique. Three different compositions (covered area ratios: 4:1; 1:1, and 1:4) of two bidisperse systems were used in the experiments. Bidisperse samples (B1 and B2) were prepared by mixing the appropriate amount of monodisperse sols of particles with 61 and 100 nm diameters (B1) and those with 37 and 100 nm diameters (B2). By surface pressure-area isotherms and (transmission and scanning) electron microscopy images we provide information about the structure of the films. Optical properties of the supported films were measured with UV-vis spectroscopy and the transmittance spectra were evaluated in terms of an optical model which allows monotonous in-depth variation of the refractive index across the film. (1) We have found that the refractive index decreased from the substrate-layer interface toward the air-layer interface when the smaller particles were in majority, and increased otherwise. That would suggest that the smaller particles of each bidisperse system can be positioned at the air side of the film if they are in minority in the sample and they can be situated on the substrate if they are in majority. The scanning electron microscope images of bidisperse films supported the in-depth film structure suggested by optical studies.

Complex Langmuir-Blodgett films of SiO2 and ZnO nanoparticles with advantageous optical and photocatalytical properties

Multifunctional Langmuir-Blodgett (LB) films were fabricated on the surface of glass substrates using sol-gel derived ZnO and SiO2 particles. ZnO particles of 6 and 110 nm diameter were synthesized according to the methods of Meulenkamp and Seelig et al. (Meulenkamp, E. A. J. Phys. Chem. B 1998, 102, 5566; Seelig, E. W.; Tang, B.; Yamilov, A.; Cao, H.; Chang, R. P. H. Mater. Chem. Phys. 2003, 80, 257). Silica particles of 37 and 96 nm were prepared by the Stober method (Stober, W.; Fink, A.; Bohn, E. J. Colloid Interface Sci. 1968, 26, 62). Alternate deposition of monoparticulate Langmuir films of SiO2 and ZnO nanoparticles provided complex (six- and nine-layered) LB films with both antireflective and photocatalytic properties. The LB films were investigated with scanning electron microscopy (morphology and structure) and UV-vis spectroscopy (optical properties and stability). The photocatalytic activity was measured by immersing the UV-irradiated films into an aqueous solution of Methyl Orange and following the photodegradation of the dye by optical spectroscopy. Adding ZnO particles to the silica films slightly lowered the antireflection property but ensured strong photocatalytic activity. Both the photocatalytic activity and antireflection properties were proved to be sensitive to the sequence of the silica and ZnO layers, with optimum properties in the case of nine-layered films with a repeated (SiO2-ZnO-ZnO) structure.