Grzegorz D. Sulka

Synthesis of well-ordered nanopores by anodizing aluminum foils in sulfuric acid

Well-ordered nanostructures were produced on industrial aluminum foils by one-, two-, and three-step anodizing processes performed in sulfuric acid at cell potentials between 15 and 25 V. Almost perfect triangular lattices of nanopores were obtained by the two- and three-step anodizing processes. It was found that the third step in the anodizing process neither significantly improves the ordering of the pores nor enlarges the size of the well-ordered domains. The effective growth rate of the oxide layer was calculated for various cell potentials and compared with literature data. The effect of the anodizing time on the ordering of pores and the size of the domains was established. The pore diameters and the interpore distances were evaluated for various cell potentials, too. Anodizing in sulfuric acid results in small pore sizes and interpore distances compared to the ones obtained by anodizing in phosphoric and oxalic acids.

Distributed Bragg reflector based on porous anodic alumina fabricated by pulse anodization

In this paper, we demonstrate a distributed Bragg reflector (DBR) based on nanoporous anodic aluminum oxide (AAO) formed by pulse anodization. The AAO structure with alternating mild anodized (MA) and hard anodized (HA) layers having different porosities and thereby different refractive indices was fabricated in 0.3 M H₂SO₄ using potential pulses of 25 and 35 V. The effective refractive index of the HA layers can be tailored by changing the porosity of the HA layers. The porosity of the HA layers can be significantly increased by selective chemical etching of HA segments in 0.52 M H₃PO₄. Before etching, the porous AAO structure was supported by a polymer nanorod frame. On the selected surface area pores were infiltrated with polymers (polystyrene and PMMA). The designed AAO structure consists of alternating high and low refractive index layers and behaves as a distributed Bragg mirror reflecting light in two different ranges of wavelength. This behavior is extremely important in optical communication lines where two separate spectral bands of high reflectivity in the infrared region are desired.

Effect of Tensile Stress on Growth of Self-Organized Nanostructures on Anodized Aluminum

The effect of an applied tensile stress on the pore ordering during anodization of aluminum was studied. A regular arrangement of nanopores was observed at a relatively low external tensile stress. On the contrary, a high tensile stress completely destroys the pore arrangement on anodized surfaces. Under such conditions, huge holes and pits are formed on the surface. The arrangement of nanopores on samples anodized under applied stresses was examined by Fourier transform analysis and Delaunay triangulation and compared with nonstressed samples. The ordering of pores was found to be dependent on the applied tensile stress. The percent of defects in the triangular lattice increases with increasing applied tensile stress. This result suggests that the surface stress has to be taken into account in a future modeling of the growth of porous oxide layer on anodized aluminum.

Study of the kinetics of the cementation of silver ions onto copper in a rotating cylinder system from acidic sulphate solutions

Abstract The kinetics of the cementation of silver ions onto copper from acidic sulphate solutions were investigated in a rotating cylinder system. The influence of several parameters on the course of the reaction, such as cylinder rotation speed, initial concentration of silver ions, temperature, concentration of sulphuric acid and the presence or absence of oxygen in the system, was investigated, and the reaction was found to follow first-order kinetics. The initial rate of the reaction is limited by diffusion through the mass transfer boundary layer. The experimental values of the initial rate constant calculated from both methods used for recording the changes of the silver ions concentration in the solutions corresponded ideally to the values predicted by semi-theoretical equations describing the turbulent flow in the rotating cylinder system. After the initial period of cementation, an enhancement of the rate was observed. In oxygenated solutions, rate enhancement is associated mainly with changes in the structure of the deposit involving an increase in the effective surface area during the process. However, the rate enhancement phenomenon in the absence of oxygen is attributed not only to an increase in the effective surface area but also to the chemical reaction between the Cu + and Ag + ions.

Study of the mechanism of silver ions cementation onto copper from acidic sulphate solutions and the morphology of the silver deposit

Abstract The mechanism of silver ion cementation with copper in acidic sulphate solutions has been investigated. It was found that oxygen present in solutions can strongly modify the mechanism of the process. In the first stage of the reaction, the Cu + ions appear in the solution independently of the presence or absence of oxygen. In deoxygenated solutions Cu + ions generated in the first stage can be transferred partially into the bulk of the solution. The migration of the reaction front results in a loosely adhering silver deposit. The reaction between Ag + and Cu + ions occurring in the bulk of the solution can be initiated in the deoxygenated solutions after reaching a certain value of the Cu + /Ag + concentration ratio. This reaction occurring in the bulk of the solution, parallel to the cementation reaction, consumes an additional amount of silver ions and produces a silver colloid in the deoxygenated solution. In oxygenated solutions saturated with oxygen the front of the reaction is located on the copper surface. As a result, tight and well-adherent silver deposit is formed. The morphology of the silver deposit is independent of the presence of oxygen in the solution. The tendency of silver deposition on already deposited silver cement was observed in the oxygenated solutions. This phenomenon is attributed to the fact that the surface area of anodic sites is more developed in the presence than in the absence of oxygen in the system due to the corrosion of copper. The anodic sites develop their surface into the bulk of the copper substrate and create cavities under the reaction surface.

Study of the kinetics of silver ions cementation onto copper from sulphuric acid solution

Abstract The kinetics of silver cementation with copper from sulphuric acid solution has been studied with a rotating cylinder. Two independent methods have been used to monitor the concentration of Ag+ ions in the solution: atomic absorption spectrophotometry (AAS) method and a continuous method with the use of an ion-selective electrode. The reaction has been found to follow first-order kinetics with respect to silver ion concentration. The initial rate of the reaction is limited by diffusion through the mass transfer boundary layer. The rate constant for initial period of cementation is independent of the absence or the presence of oxygen in the solutions and is independent of the presence of Cu2+ ions up to the concentration of 2×10−4 M. After the initial period of cementation a rate enhancement has been observed. In solutions containing 20 mg/L of Ag+ ions, the rate enhancement is associated with changes in the structure of the deposit which involve an increase in the effective surface area during the process. However, the rate enhancement phenomenon in the absence of oxygen at 100 mg/L of Ag+ is attributed not only to an increase in the effective surface area but also to a chemical reaction between Cu+ and Ag+ ions.

GridSpace2 virtual laboratory case study: implementation of algorithms for quantitative analysis of grain morphology in self-assembled hexagonal lattices according to the hillebrand method

This work presents the implementation of a method, originally proposed by Hillebrand et al. [1], of quantitative analysis of the grain morphology in self-assembled hexagonal lattices. This method can be effectively used for investigation of structural features as well as regular hexagonal arrangement of nanoporous alumina layers formed on the metal surface during the self-organized anodization process. The method has been implemented as a virtual experiment in the GridSpace2 Virtual Laboratory [15] which is a scientific computing platform developed in the scope of the PL-Grid [9] project. The experiment is a GridSpace2 pilot and therefore made available to the wider community of PL-Grid users. It is both editable and executable through a web portal offered by the GridSpace2 Experiment Workbench [17], dedicated to PL-Grid users. Moreover, since all GridSpace2 experiments are embeddable on arbitrary web sites owing to the Collage [16] feature, the final version of the experiment has been published as an executable publication [18] with execution rights granted to all PL-Grid users.

Properties of nanostructures obtained by anodization of aluminum in phosphoric acid at moderate potentials

The influence of the process duration, anodizing potential and methanol addition on the structural features of porous anodic alumina formed in a 0.3 M H3PO4 solutions by two# s tep self#organized anodizing was investigated for potentials ranging from 100 to 170 V. The structural features of porous structures including pore diameter and interpore distance were evaluated from FE#SEM top#view images for samples anodized in the presence and absence of methanol. For the highest studied anodizing time and methanol volume fraction, an excellent agreement between experimental values of the interpore distance and theoretical predictions was observed. The pore arrangement regularity was analyzed for various electrolyte compositions and anodizing potentials. It was found that the regularity ratio of porous alumina increases linearly with increasing anodizing potential and time. The addition of methanol improves the quality of nanostructures and especially better uniformity of pore sizes is observed in the presence of the highest studied methanol content.

Nanoporous anodic titanium dioxide layers as potential drug delivery systems: Drug release kinetics and mechanism

Nanoporous anodic titanium dioxide (ATO) layers on Ti foil were prepared via a three step anodization process in an electrolyte based on an ethylene glycol solution with fluoride ions. Some of the ATO samples were heat-treated in order to achieve two different crystallographic structures - anatase (400°C) and a mixture of anatase and rutile (600°C). The structural and morphological characterizations of ATO layers were performed using a field emission scanning electron microscope (SEM). The hydrophilicity of ATO layers was determined with contact angle measurements using distilled water. Ibuprofen and gentamicin were loaded effectively inside the ATO nanopores. Afterwards, an in vitro drug release was conducted for 24h under a static and dynamic flow conditions in a phosphate buffer solution at 37°C. The drug concentrations were determined using UV-Vis spectrophotometry. The absorbance of ibuprofen was measured directly at 222nm, whether gentamicin was determined as a complex with silver nanoparticles (Ag NPs) at 394nm. Both compounds exhibited long term release profiles, despite the ATO structure. A new release model, based on the desorption of the drug from the ATO top surface followed by the desorption and diffusion of the drug from the nanopores, was derived. The proposed release model was fitted to the experimental drug release profiles, and kinetic parameters were calculated.

Primary role of electron work function for evaluation of nanostructured titania implant surface against bacterial infection

The electron work function as an essential descriptor for the evaluation of metal implant surfaces against bacterial infection is identified for the first time. Its validity is demonstrated on Staphylococcus aureus adhesion to nanostructured titania surfaces. The established correlation: work function-bacteria adhesion is of general importance since it can be used for direct evaluation of any electrically conductive implant surfaces.