Search Results (75)

It is widely recognized that fine surface structures found in nature contribute to surface functionality, and studies on the design of functional materials based on biomimetics have been actively conducted. In this study, polymer thin films with hierarchically ordered surface structure were prepared by combining both nanoimprinting using anodically oxidized porous alumina (AAO) as a template and surface-initiated atom transfer radical polymerization (SI-ATRP). To prepare such polymer films, we designed a new copolymer (poly{[2-(4-methyl-2-oxo-2H-chromen-7-yloxy)ethyl methacrylate]-co-[2-(2-bromo-2-methylpropionyloxy)ethyl methacrylate]}; poly(MCMA-co-HEMABr)) with coumarin moieties and α-haloester moieties in the pendants. The MCMA repeating units function to fix the pillar structure by photodimerization, and the HEMABr ones act as the polymerization initiation sites for SI-ATRP on the pillar surfaces. Surface structures consisting of vertically oriented multiple pillars were fabricated on the spin-coated poly(MCMA-co-HEMABr) thin films by nanoimprinting using an AAO template. Then, the coumarin moieties inside each pillar were crosslinked by UV light irradiation to fix the pillar structure. SEM observation confirmed that the internally crosslinked pillar structures were maintained even when immersed in organic solvents such as 1,2-dichloroethane and anisole, which are employed as solvents under SI-ATRP conditions. Finally, poly(2,2,2-trifluoroethyl methacrylate) and poly(N-isopropylacrylamide) chains were grafted onto the thin film by SI-ATRP, respectively, to prepare the hierarchically ordered surface structure. Furthermore, in this study, the surface properties as well as the thermoresponsive hydrophilic/hydrophobic switching of the obtained polymer films were investigated. The surface morphology and chemistry of the films with and without pillar structures were compared, especially the interfacial properties expressed as wettability. Grafting poly(TFEMA) increased the static contact angle for both flat and pillar films, and the con-tact angle of the pillar film surface increased from 104° for the flat film sample to 112°, suggesting the contribution of the pillar structure. Meanwhile, the pillar film surface grafted with poly(NIPAM) brought about a significant change in wettability when changing the temperature between 22 °C and 38 °C. Full article

This study explores the development and optical characterization of a hybrid material combining nanoporous anodic alumina with J-aggregates of pseudoisocyanine dyes, highlighting its potential for photonic applications in bright broadband sources. The hybrid material was synthesized by impregnating an alumina matrix with a dye solution, which facilitated a thermally stimulated self-assembly process for the formation of J-aggregates. The incorporation of J-aggregates within the matrix was confirmed through several independent optical measurement techniques. A distinct absorption peak and corresponding luminescence signal were attributed to J-aggregate formation, while energy transfer from the alumina’s intrinsic oxygen vacancy centers to the dye aggregates was observed under specific excitation conditions. Amplified spontaneous emission was achieved under pulsed laser excitation, characterized by spectral narrowing and a nonlinear increase in emission intensity beyond a critical pump threshold, indicative of a similarity with random lasing facilitated by scattering within the porous structure. Full article

Anodizing can generate porous wear-resistant layers, which can act as reservoirs for gradually releasing lubricants. Studies on the formation of zinc dialkyl dithiophosphate (ZDDP) tribofilms in non-ferrous metals are relatively rare. Furthermore, adding nanoparticles can improve wear resistance in various applications. This investigation aims to correlate several anodized surfaces using H₂SO₄ (5 or 10%wt. concentration and 45 or 60 min exposition) to tribological outputs, contributing to understanding the friction behavior of non-metallic layers. Three steps were applied on anodized Alumold 500 alloy. Firstly, the scratching test, to select the layers with higher critical loads. The greatest scratch resistance was obtained with the highest H³/E² value and thickest layer. Secondly, lubricated tests with only poly-alpha-olefin oils (PAO6) were performed in a reciprocating test rig using an alumina ball as the counterpart. From that, only the best AAO condition was selected. Finally, three more lubricant compositions were tested, as follows: adding ZDDP to PAO6, alumina nanoparticles (~100 nm) to PAO6, and ZDDP + nanoparticles. The addition of nano-alumina to the PAO6 resulted in the maintenance of COF values with only PAO6 (~0.1), when the most significant drop in the surface roughness was observed along with the tests. Full article

Using electromagnetic and electrochemical theories as a framework, this study examines the influence of carbon sphere electrodes on the distribution patterns of anodic oxidation and deposition current densities in metallic aluminium and porous anodic alumina. Theoretical calculations show that the current density symmetrically decreases from the centre outward under the effect of carbon sphere electrodes. Increasing the electrode distance improves the uniformity of the current distribution across the film, while decreasing the distance increases the rate of gradient change in current density. Simulation results reveal that at electrode spacings of 15 cm and 1 cm, the oxidation current density at the film centre is 1333 A/m² and 2.9 × 10⁵ A/m², respectively. The current density gradually decreases outward along the radius, reaching 1330 A/m² and 1.8 × 10⁵ A/m² at the edges, with observed current density gradient change rates of 500 A/m³ and 1.83 × 10⁷ A/m³, respectively. Experimental results confirm that carbon sphere counter electrodes can create non-uniform oxidation and deposition electric fields. Microstructures with gradually varying symmetry can be generated by adjusting the electrode spacing, resulting in porous anodic alumina and composite films exhibiting iridescent, ring-like structural colours. The experimental findings align well with theoretical calculations and simulation results. Full article

This study reports the production of mid-infrared (MIR) porous anodic alumina (PAA)-based microcavities with tunable optical quality. The spectral position of the cavity resonance peak (λ_C), along with its intensity (I_R) and Q-factor, varies depending on the geometric positioning of the cavity layer within the multilayer stack of alternating low- and high-porosity layers, as well as the type of cavity produced—either by high voltage (Cv_H-type) or low voltage (Cv_L-type) pulses. In most cases, PAA microcavities with Cv_H-type cavity layers exhibited superior light confinement properties compared to those with Cv_L-type cavities. Additionally, shifting the cavity layer from the center toward the edges of the multilayer stack enhanced the intensity of the resonance peak. For PAA microcavities with Cv_H-type cavity layers, the highest intensity (I_R = 53%) and the largest Q-factor (Q = 31) were recorded at λ_C of around 5.1 µm. The anodization approach used in this study demonstrates significant potential for designing PAA-based microcavities with high optical performance in the MIR spectral region, especially with further refinement of electrochemical parameters. These findings pave the way for the development of new photonic materials specifically tailored for the MIR spectral range, broadening their applications in various optoelectronic and sensing technologies. Full article

Pyocyanin is considered a maker of Pseudomonas aeruginosa (P. aeruginosa) infection. Pyocyanin is among the toxins released by the P. aeruginosa bacteria. Therefore, the development of a direct detection of PYO is crucial due to its importance. Among the different optical techniques, the Raman technique showed unique advantages because of its fingerprint data, no sample preparation, and high sensitivity besides its ease of use. Noble metal nanostructures were used to improve the Raman response based on the surface-enhanced Raman scattering (SERS) technique. Anodic metal oxide attracts much interest due to its unique morphology and applications. The porous metal structure provides a large surface area that could be used as a hard template for periodic nanostructure array fabrication. Porous shapes and sizes could be controlled by controlling the anodization parameters, including the anodization voltage, current, temperature, and time, besides the metal purity and the electrolyte type/concentration. The anodization of aluminum foil results in anodic aluminum oxide (AAO) formation with different roughness. Here, we will use the roughness as hotspot centers to enhance the Raman signals. Firstly, a thin film of gold was deposited to develop gold/alumina (Au/AAO) platforms and then applied as SERS-active surfaces. The morphology and roughness of the developed substrates were investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The Au/AAO substrates were used for monitoring pyocyanin secreted from Pseudomonas aeruginosa microorganisms based on the SERS technique. The results showed that the roughness degree affects the enhancement efficiency of this sensor. The high enhancement was obtained in the case of depositing a 30 nm layer of gold onto the second anodized substrates. The developed sensor showed high sensitivity toward pyocyanin with a limit of detection of 96 nM with a linear response over a dynamic range from 1 µM to 9 µM. Full article

In this work, two types of nanoporous alumina membranes were prepared and tested. Structural features of the samples obtained by using different acids were investigated by scanning electron microscopy (SEM). And further SEM-images were analyzed by different types of fractal dimension estimation methods. The transmission and scattering of accelerated He⁺ ions were studied in experiments on the ion irradiation of dielectric channels based on porous alumina. An ion accelerator was used as a source of the He⁺ beam with an energy of 1.7 MeV. Ion scattering was studied by Rutherford backscattering spectrometry. Helium transition through nanoporous alumina at various angles between the normal to the sample and the beam direction were observed. It is shown that the porous structure of anodic aluminum oxide is excellent as a dielectric matrix of nanocapillaries. Owing to the small angle scattering, it allows for the transportation of the accelerated charged particles through the dielectric capillaries, and, as a result, the localization of high energy ion irradiation effects. Additionally, according to the transmission of UV–V is spectra, the energy gaps of samples obtained were calculated. Full article

Nanoporous membranes (NPMBs) have been the focus of interest of many scientists in the last decade. However, the fouling phenomenon that takes place during the implantation period blocks pores and causes failure in the local implant. In this study, alumina NPMBs were developed using electrochemical anodization through two steps. Furthermore, graphene oxide (GO), free and impregnated with ZIF-8 MOF, was synthesized and loaded in a mixture of PVDF/PVP polymer matrix at different ratios, and was applied to the produced NPMBs using spin-coater. The NPMBs were characterized before and after coating by SEM/EDX, TEM, FTIR, XRD, contact angle and AFM. The antifouling features of the NPMBs were analyzed against two different bacterial species. The prepared alumina NPMBs demonstrated homogeneous porous structures with pore sizes ranging from 36 to 39 nm. The coated layers were proven to possess microporous coatings on the surfaces of the NPMBs. The numbers of released ions (Al and Zn) from the coated NPMBs were below the allowed limits. Bovine serum albumin (BSA) uptake in artificial cerebrospinal fluid (ACSF) was impressively reduced with the presence of coating materials. In addition, the antifouling behavior of the coated NPMBs against the selected strains of bacteria was greatly enhanced compared with the pure alumina NPMBs. Finally, NPMBs’ uncoated and polymer-coated membranes were tested for their ability to deliver donepezil HCl. The results reveal the downregulation of donepezil release, especially from NPMBs coated with PVDF/PVP 0.5GO. It is advised to use the current antifouling materials and techniques to overcome the limitations of the inorganic NPMBs implants. Full article

In this paper, we focused on the initiation of porosity in the anodic alumina under galvanostatic conditions in chromic acid, using an ¹⁸O isotope tracer. The general concept of the initiation and growth of porous anodic oxide films on metals has undergone constant development over many years. A mechanism of viscous flow of the oxide from the barrier layer to the pore walls has recently been proposed. In this work, two types of pre-formed oxide films were analysed: pure Al₂O₃ formed in chromic acid, and a film containing As ions formed in a sodium arsenate solution. Both were anodized in chromic acid for several different time durations. Both pre-formed films contained the oxygen isotope ¹⁸O. The locations and quantities of ¹⁸O and As were analysed by means of ion accelerator-based methods supported by transmission electron microscopy. The significant difference observed between the two oxide films is in the ¹⁸O distribution following the second step of anodization, when compared with galvanostatic anodization in phosphoric or sulfuric acid reported in previous works. From the current experiment, it is evident that a small amount of As in the pre-formed barrier layer appears to alter the ionic conductivity of the film; thus, somehow, it inhibits the movement of oxygen ions ahead of advancing pores during anodization in chromic acid. However, anodising pure alumina film under these conditions does not enhance oxygen movement within the oxide layer. In addition, the tracer stays in the outer part of the growing porous oxide film. A lower-than-expected value for pure alumina enrichment in ¹⁸O in the pre-formed films suggests, indirectly, that the pre-formed film may contain hydrogen species, as well as trapped electrons, since no Cr is detected. This may lead to the presence of space charge distribution, which has a dual effect: it both retards the ejection of Al³⁺ ions and prevents O²⁻ ions from migrating inward. Thus, the negative- and positive-charge distributions might play a role in the initiation of pores via a flow mechanism. Full article

Recently, the icing disaster of transmission lines has been a serious threat to the safe operation of the power system. A superhydrophobic (SHP) anti-icing surface with a honeycomb nanopore structure was constructed using anodic oxidation technology combined with a vacuum infusion process. When the current density was 87.5 mA/cm², the honeycomb porous surface had the best superhydrophobic performance (excellent water mobility), lowest ice-adhesion strength (0.7 kPa) and best anti-frosting performance. Compared with other types of alumina surfaces, the ice-adhesion strength of the SHP surface (87.5 mA/cm²) was only 0.2% of that of the bare surface. The frosting time of the SHP surface (87.5 mA/cm²) was 150 min, which was much slower. The former is attributed to the air cushion within the porous structure and the stress concentration, and the latter is attributed to the self-transition of the droplets and low solid–liquid heat transfer area. After 100 icing or frosting cycles, the SHP surface (87.5 mA/cm²) maintained a low ice-adhesion strength and superhydrophobic performance. This is because the anodic oxidation process forms a hard porous film, and the nano porous structure with a high aspect ratio can store modifiers to realize self-healing. The results indicate that the SHP surface with a honeycomb nanopore structure presents excellent anti-icing performance and durability. Full article

A porous anodic alumina film is proposed to construct an optical fiber temperature and humidity sensor. In the sensor structure, a fiber Bragg grating is used to detect the environment temperature, and the porous film is used to detect the environment humidity. The proposed porous anodic alumina film was fabricated by anodic oxidation reaction, and it is suitable for the use of humidity detection due to its porous structure. Experimental results show the temperature sensitivity of the proposed sensor was 10.4 pm/°C and the humidity sensitivity of the proposed sensor was 185 pm/%RH. Full article

Bendamustine (BENDA) is a bifunctional alkylating agent with alkylating and purinergic antitumor activity, which exerts its anticancer effects by direct binding to DNA, but the detailed mechanism of BENDA–DNA interaction is poorly understood. In this paper, the interaction properties of the anticancer drug BENDA with calf thymus DNA (ctDNA) were systematically investigated based on surface-enhanced Raman spectroscopy (SERS) technique mainly using a novel homemade AuNPs/ZnCl₂/NpAA (NpAA: nano porous anodic alumina) solid-state substrate and combined with ultraviolet–visible spectroscopy and molecular docking simulation to reveal the mechanism of their interactions. We experimentally compared and studied the SERS spectra of ctDNA, BENDA, and BENDA–ctDNA complexes with different molar concentrations (1:1, 2:1, 3:1), and summarized their important characteristic peak positions, their peak position differences, and hyperchromic/hypochromic effects. The results showed that the binding modes include covalent binding and hydrogen bonding, and the binding site of BENDA to DNA molecules is mainly the N7 atom of G base. The results of this study help to understand and elucidate the mechanism of BENDA at the single-molecule level, and provide guidance for the further development of effective new drugs with low toxicity and side effects. Full article

The possibility of improving dental restorative materials is investigated through the addition of two different types of fillers to a polymeric resin. These fillers, consisting of porous alumina and TiO₂ nanotubes, are compared based on their common physicochemical properties on the nanometric scale. The aim was to characterize and compare the surface morphological properties of composite resins with different types of fillers using analytical techniques. Moreover, ways to optimize the mechanical, surface, and aesthetic properties of reinforced polymer composites are discussed for applications in dental treatments. Filler-reinforced polymer composites are the most widely used materials in curing dental pathologies, although it remains necessary to optimize properties such as mechanical resistance, surface characteristics, and biocompatibility. Anodized porous alumina nanoparticles prepared by electrochemical anodization offer a route to improve mechanical properties and biocompatibility as well as to allow for the controlled release of bioactive molecules that can promote tissue integration and regeneration. The inclusion of TiO₂ nanotubes prepared by hydrothermal treatment in the resin matrix promotes the improvement of mechanical and physical properties such as strength, stiffness, and hardness, as well as aesthetic properties such as color stability and translucency. The surface morphological properties of composite resins with anodized porous alumina and TiO₂ nanotube fillers were characterized by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), and X-ray chemical analysis. In addition, the stress–strain behavior of the two composite resins is examined in comparison with enamel and dentin. Full article

Nanoporous alumina sheets can inhibit the growth of the frost layer in a low-temperature environment, which has been widely used in air-conditioning heat exchangers. In this study, nanoporous alumina sheets with pore diameters of 30 nm, 100 nm, 200 nm, 300 nm, and 400 nm were prepared by using the anodic oxidation method with the conventional polished aluminum sheet as the reference. A comprehensive and in-depth analysis of the frosting mechanism has been proposed based on the contact angle, specific surface area, and fractal dimension. It was found that compared with the polished aluminum sheet, the nanoporous alumina sheets had good anti-frost properties. Due to its special interface effects, the porous alumina sheet with a 100 nm pore diameter had strong anti-frost performance under low temperatures and high humidity. In an environment with low surface temperature and high relative humidity, it is recommended to use hydrophilic aluminum fins with large specific areas and small fractal dimensions for the heat exchange fins of air source heat pump air conditioning systems. Full article

The entrance of even a small amount of phosphorus compounds into natural waters leads to global problems that require the use of modern purification technologies. This paper presents the results of testing a hybrid electrobaromembrane (EBM) method for the selective separation of Cl⁻ (always present in phosphorus-containing waters) and H₂PO₄⁻ anions. Separated ions of the same charge sign move in an electric field through the pores of a nanoporous membrane to the corresponding electrode, while a commensurate counter-convective flow in the pores is created by a pressure drop across the membrane. It has been shown that EBM technology provides high fluxes of ions being separated across the membrane as well as a high selectivity coefficient compared to other membrane methods. During the processing of solution containing 0.05 M NaCl and 0.05 M NaH₂PO₄, the flux of phosphates through a track-etched membrane can reach 0.29 mol/(m²×h). Another possibility for separation is the EBM extraction of chlorides from the solution. Its flux can reach 0.40 mol/(m²×h) through the track-etched membrane and 0.33 mol/(m²×h) through a porous aluminum membrane. The separation efficiency can be very high by using both the porous anodic alumina membrane with positive fixed charges and the track-etched membrane with negative fixed charges due to the possibility of directing the fluxes of separated ions in opposite sides. Full article