Adsorption of Nonspherical Particles at Solid/Liquid Interfaces

Localized adsorption of nonspherical particles at solid/liquid interfaces was analyzed theoretically. Aproximate models for calculating interactions between particles and interfaces as well as between particles were discussed. It was demonstrated that for convex particles the Derjaguin model can be used for small separations, whereas for larger separations the equivalent sphere approach proved more appropriate. These analytical energy expressions were used in numerical Monte-Carlo RSA (random sequential adsorption) simulations of particle adsorption. Theoretical results concerning the blocking parameter (available surface function) and adsorption kinetics for short and long times were reported for prolate and oblate spheroids. Similarities and differences between flat (2D) and unoriented (quasi 3D) adsorption of particles were discussed and limiting power-law for the long-time regimes were specified. By extrapolation of the kinetic results the maximum (jamming) coverages for hard and interacting spheroids were determined. It was demonstrated that the jamming coverages under the conditions of unoriented adsorption exceed these of flat adsorption by many times for elongated objects. It was also demonstrated that the repulsive double-layer interactions decrease significantly the monolayer capacity of adsorbed layers of spheroidal particles. Implications of this phenomenon for protein adsorption were discussed

Transdermal buprenorphine ameliorated pruritus complicating advanced hepatocellular cancer

Itch is a difficult to treat symptom that may accompany neoplastic disease. At least some of the itch symptoms are due to abnormal endogenous opioid synthesis in the liver. In the past opioid receptor antagonists were found useful to treat itch in such patients. However, their use is limited by the abstinence symptoms experienced by the patient. Another approach would be to use an opioid with high affinity and slow dissociation from the receptor not to allow endogenous opioids to interact with the opioid receptors. In this paper we describe a patient with severe itch due to hepatocellular cancer who responded to the treatment with buprenorphine.Itch is a difficult to treat symptom that may accompany neoplastic disease. At least some of the itch symptoms are due to abnormal endogenous opioid synthesis in the liver. In the past opioid receptor antagonists were found useful to treat itch in such patients. However, their use is limited by the abstinence symptoms experienced by the patient. Another approach would be to use an opioid with high affinity and slow dissociation from the receptor not to allow endogenous opioids to interact with the opioid receptors. In this paper we describe a patient with severe itch due to hepatocellular cancer who responded to the treatment with buprenorphine

Construction of a numerical groundwater flow model in areas of intense mine drainage, as exemplified by the Olkusz Zinc and Lead Ore Mining Area in southwest Poland

Areas of intense mine drainage that are subjected to numerical modelling require the construction of a complex model structure that will properly reflect actual conditions. This paper presents the process and results of constructing such a structure for the Olkusz Zinc and Lead Ore Mining Area, an area situated in a cone of depression the extent of which reaches 500 km 2 . This size range calls for a selection of appropriate external boundaries, properly separated from these of the mine drainage area. The complex geological structure of the Olkusz area, associated with considerable variation in the thickness of rock formations, discontinuities of rock levels and occurrence of numerous faults, must be schema- tised so that calculation layers can be identified. The faults in the study area have to be reflected in the regional model structure, although only those faults that actually affect groundwater flows should be selected. The model structure needs to include detailed recognition and reflection of hydraulic contacts between aquifer levels, together with a selec- tion of hydrogeological parameters that are different for particular formations. Only a complex structure built in such a manner may be the foundation of further model studies

Electrophysical properties of the multicomponent PbFe1/2Nb1/2O3 ceramics doped by Li

The paper presents the results of research on the influence of sintering temperature on microstructure, DC electrical conductivity, dielectric, ferroelectric and magnetic properties of PbFe1/2Nb1/2O3 ceramics doped by Li in the amount of 5.0% wt., in the abbreviation PLiFN. The ceramic samples of the PLiFN material were obtained by the two-stage synthesis – columbite method and sintered by free sintering methods. Introduction to the basic PbFe1/2Nb1/2O3 composition of the lithium admixture to decrease the electrical conductivity and reduction of dielectric loss. The tests have shown that the increase in sintering temperature orders the PLiFN ceramic microstructure, which has a positive effect on its electrophysical properties. At room temperature, the PLiFN ceramic samples show both ferroelectric and ferromagnetic properties. Considering the functional parameters of the obtained ceramic samples, the optimal technological conditions are 1100°C/2 h.[1] H. Schmid, Ferroelectrics 162, 317 (1994). [2] W. Cheong, M. Mostovoy, Nat. Mater. 6, 13 (2007). [3] K.F. Wang, J.-M. Liu, Z.F. Ren, Adv. Phys. 58, 4, 321-448 (2009). [4] D. Bochenek, J. Alloy. Compd. 504, 508-513 (2010). [5] D. Bochenek, J. Dudek, Eur. Phys. J.– Spec. Top. 154, 19-22 (2008). [6] G.A. Smolenskii, A.I. Agranovskaia, S.N. Popov, V.A. Isupov, Sov. Phys.-Tech. Phys. 3 1981 (1958). [7] G.A. Smoleński, W.M. Judin., Fiz. Twierdogo Tela 6, 3668 (1964). [8] Y.E. Roginskaya, Y.N. Venevcev, S.A. Fedulov, Sov. Phys. Crystallogr. 8, 490 (1964). [9] S. Picozzi et al., J. Phys. – Condens. Matt. 20, 43, 434208 (2008). [10] H. Schmid, J. Phys. – Condens. Matt20, 43, 434201 (2008). [11] W. Eerenstein, N. D. Mathur, J. F. Scott, Nature 442, 759 (2006). [12] K. Wójcik, K. Zieleniec, M. Mulata, Ferroelectrics 289, 107 (2003). [13] D. Bochenek, P. Kruk, R. Skulski, P. Wawrzała, J. Electroceram. 26, 8-13 (2011). [14] D. Bochenek, Z. Surowiak, J. Krok-Kowalski, J. Poltierova-Vejpravova, J. Electroceram. 25, 122-129 (2010). [15] D. Bochenek, G. Dercz, D. Oleszak, Arch. Metall. Mater. 56, 4, 1015-1020 (2011). [16] D. Bochenek, Z. Surowiak, J. Alloy. Compd. 480, 732-736 (2009). [17] Y. Xu, Ferroelectric materials and their applications, Elsevier, North – Holland, Amsterdam 1991. [18] R.D. Shannon, Acta Cryst. A 32, 751-767 (1976). [19] O. Raymond, R. Font, N. Juarez-Almodovar, J. Portelies, J.M. Siqueiros, J. Appl. Phys. 97, 084107, 1-8 (2005). [20] M. Kuwabara, J. Am. Ceram. Soc. 73, 5, 1438-1439 (1990). [21] L.B. Kong, J. Ma, Mater. Lett. 51, 95-100 (2001)

Mechanisms of Fibrinogen Adsorption on Silica Sensors at Various pHs: Experiments and Theoretical Modeling

International audienceThe adsorption kinetics of human serum fibrinogen at silica substrates was studied using optical waveguide lightmode spectroscopy (OWLS) and quartz crystal microbalance (QCM) techniques. Measurements were performed at pH 3.5, 4, and 7.4 for various ionic strengths. The experimental data were interpreted in terms of a hybrid random sequential adsorption model. This allowed the mass transfer rate coefficient for the OWLS cell and maximum coverages to be determined at various pHs. The appearance of different, pH-dependent mechanisms of fibrinogen adsorption on silica substrates was confirmed. At pH 3.5 the molecules mostly adsorb in the side-on orientation that produces a low maximum coverage of ca. 1 mg m-2. At this pH, the kinetics derived from the OWLS measurements agree with those theoretically predicted using the convective-diffusion theory. In consequence, a comparison of the OWLS and QCM results allows the water factor and the dynamic hydration of fibrinogen molecules to be determined. At pH 7.4, the OWLS method gives inaccurate kinetic data for the low coverage range. However, the maximum coverage that was equal to ca. 4 mg m-2 agrees with the QCM results and with previous literature results. It is postulated that the limited accuracy of the OWLS method for lower coverage stems from a heterogeneous structure of fibrinogen monolayers, which consist of side-on and end-on adsorbed molecules. One can expect that the results acquired in this work allow development of a robust procedure for preparing fibrinogen monolayers of well-controlled coverage and molecule orientation, which can be exploited for efficient immunosensing purposes

Formation of poly-L-lysine monolayers on silica : modeling and experimental studies

Modification of solid substrates by poly-l-lysine (PLL) layers has been widely employed in order to improve their biocompatibility, for promoting protein and cell immobilization for fabrication of biosensor arrays and antibacterial coatings. However, despite many studies conducted in the literature, there is a deficiency in a quantitative description of PLL adsorption processes. It is postulated that this becomes feasible by applying direct experimental techniques combined with thorough theoretical modeling. In this work, the kinetics of PLL adsorption on silica for various ionic strengths was determined in situ under controlled flow conditions using the optical reflectometry and the streaming potential methods. Both the initial adsorption rates and longer time kinetic runs were acquired and quantitatively interpreted in terms of the convective diffusion and the random sequential adsorption theoretical modeling based on the coarse-grained Monte Carlo approach. This unique combination of experimental and theoretical approaches enabled us to gain new insight into the mechanism of macroion adsorption controlled by the electrostatic interactions, which affect both the molecule conformations and the blocking effects. Besides significance for basic science, the results obtained in this work can be exploited for developing reliable procedures for preparing stable PLL monolayers of well-controlled coverage and electrokinetic properties

Titanium dioxide/silver nanoparticle bilayers prepared in self-assembly processes

A new method for the preparation of TiO2/Ag bilayers via colloid self-assembly process using well-characterized titanium dioxide and silver suspensions was developed. The titanium dioxide nanoparticles, forming a supporting layer, were 46 nm in diameter, exhibiting an isoelectric point at pH 6.4. The silver nanoparticles, forming an external layer of the diameter of 50 nm were prepared via a chemical reduction method with the presence inorganic phosphate salts. The electrophoretic mobility measurements revealed that the zeta potential of silver nanoparticles was highly negative for a broad range of pH and ionic strengths. By explaining this information, the optimum condition for the silver nanoparticle immobilization on TiO2 supporting layers were selected. The coverage of the first layer was adjusted by ionic strength of the suspensions and by the deposition time. Afterward, the silver nanoparticle monolayers of controlled coverage were deposited under the diffusion-controlled transport. Their coverage was determined by a direct enumeration of deposited nanoparticles from AFM images and SEM micrographs. The experimental results showed that for extended deposition times, the coverage of silver nanoparticle layers significantly increases with ionic strength. Therefore, it was proven that the formation of bilayers is mainly controlled by electrostatic interactions and that it is feasible to produce uniform TiO2/Ag materials of desired coverage and structure

Ammonia CI engine aftertreatment systems design and flow simulation

Investigation of exhaust emissions and ammonia flow behavior in the exhaust system incorporating with Selective Catalytic Reduction (SCR) unit is discussed. An aftertreatment system is designed to work without additional urea injection to improve feasible temperature of operating and reduce size. This study is focused on obtaining optimal parameters for catalysis using gaseus ammonia as reducing agent. Its effectiveness is considered as a function of basic parameters of exhaust gases mixture and SCR material characteristics. A 3D geometry of SCR with porous volume has been simulated using Ansys Fluent. Moreover, a 1D model of ammonia dual-fuel CI engine has been obtained. Results were focused on obtaining local temperature, velocity, and exhaust gases composition to predict optimal probes placement, pipes insulation parameters, and characteristic dimensions

Ammonia CI engine aftertreatment systems design and flow simulation

Investigation of exhaust emissions and ammonia flow behavior in the exhaust system incorporating with Selective Catalytic Reduction (SCR) unit is discussed. An aftertreatment system is designed to work without additional urea injection to improve feasible temperature of operating and reduce size. This study is focused on obtaining optimal parameters for catalysis using gaseus ammonia as reducing agent. Its effectiveness is considered as a function of basic parameters of exhaust gases mixture and SCR material characteristics. A 3D geometry of SCR with porous volume has been simulated using Ansys Fluent. Moreover, a 1D model of ammonia dual-fuel CI engine has been obtained. Results were focused on obtaining local temperature, velocity, and exhaust gases composition to predict optimal probes placement, pipes insulation parameters, and characteristic dimensions

Fabrication and dielectric properties of modified calcium (Pb0.75Ba0.25)(Zr0.7Ti0.3)O3 ceramics

The aim of the present work is to report investigations concerning the influence of homovalent modificators on relaxor properties of PBZT 25/70/30 ceramics. The selection of the proper homovalent additive was very important. Literature reports as well as data taken from the periodic table indicated, that calcium ions substitute themselves for lead ions with high likelihood of occurrence. The investigations showed that the substitution significantly changed the microstructure of ceramics – with grains of calcium modified ceramics decreasing and density increasing. The XRD measurements indicate that the pure PBZT ceramics as well as calcium dopant were characterised by tetragonal structure with space group I4/mmm. Addition of calcium leads to a slight decrease in the lattice constant and crystal structure. The calcium modification also changes the dielectric properties. The temperature characteristic of the dielectric constant achieved a broadened maximum at temperature Tm, which decreases with increasing Ca content. The properties typical for ferroelectric relaxors weaken with increasing calcium dopant