Identifizierung von radionukliden durch halb quantitative autoradiographische bestimmung ihrer halbwertszeit mit hilfe der ringofenmethode

In the proposed method, a series of 9 rings is prepared from different μl-volumes of a solution of the radionuclide under test (specific activity 1.5–2.5 /μC/μl). At a starting time t = o and at 3 later times, each series of rings is placed on X-ray. film strips for a period of i h. After the usual development of the 4 strips, 4 density scales are obtained corresponding to 4 different times, and these can be compared by the method of weighted means. From the decrease in density of the rings, the half-life of the radionuclide cari be estimated. The method is explained for the examples ¹⁹⁸Au,⁹⁹Mo/^99mTc, ¹⁵³Sm und ¹³¹I.     

Sizes and interfacial free energies of crystallites formed from fractionated linear polyethylene

Replicas of fracture surfaces of fractions of linear polyethylene, which were crystallized at elevated temperatures for extended time periods, were examined by electron microscopy. Striated. lamella-type crystallites were observed for all molecular weights over the range 3.2 × 10³?5.7 × 10⁵. In agreement with Anderson's previous report, for molecular weights of 12,000 or less, the crystallite thicknesses were comparable to the extended chain length. As the molecular weight increased above this level, however, the crystallite sizes increased only slightly and hence at high molecular weights were very much smaller than the extended chain length. From the measured melting temperatures, crystallite interfacial free energies were calculated from the theory for the melting of finite size crystals comprised of chains of finite length. The crystallite interfacial free energy was found to increase with molecular weight. Based on these results, a crystallization process is outlined which allows for the formation of either extended chain crystallites, or crystallites whose size is much smaller than the extended chain length without any change in nucleation mechanism or arbitrary adjustment in growth mechanism with molecular weight.     

Electrokinetic properties of mixed solutions of dodecyldimethylamine oxide and sodium dodecyl sulfate: specific adsorption effects of small ions

Electrophoretic light-scattering measurements and potentiometric titrations were carried out on aqueous mixtures of dodecyldimethylamine oxide and sodium dodecyl sulfate. The electrophoretic mobility and the surface charge density of the micelles were always negative, ranging from –2.5 to –3.1×10^–4 cm²V^–1s^–1, and –0.033 to –0.045 cm^–2, respectively, for all surfactant mixing ratios, indicating the specific adsorption of Cl^–, in addition to Na⁺, on micelles. The solution pH, as well as the aggregation number previously reported, displayed maxima at intermediate surfactant mole fractions, that is, the non-ideal behavior. The fractional adsorption of Na⁺ per surfactant molecule in the micelles increased gradually with mixing fraction up to 0.82 atX=[SDS]/([SDS]+[C₁₂DAO])=1, while that of Cl^– decreased from 0.25 atX=0 to zero atX>0.4.     

Adsorption characteristics of traces of radium on membrane filters,glass and polyethylene

Adsorption of radium was studied on glass and polyethylene from aqueous solutions containing 8–40 pg·dm^{–3 224}Ra and on membrane filters, glass and polyethylene bottles from waste and river waters containing 2–170 pg·dm^{–3 226}Ra. The adsorption from aqueous solutions was determined as a function of pH and composition of the solutions and interpreted as due to ion exchange of Ra²⁺ ions for counter ions in the electric double layer on glass and polyethylene or due to chemisorption of RaSO₄ (RaCO₃) ion pairs on glass. Borosilicate glass adsorbed radium substantially more than polyethylene. The adsorption of dissolved forms of radium from the waste and river waters during storage and membrane filtration of the waters was negligible, but a significant loss of particulate forms of radium was sometimes observed during the storage. It has been recommended to separate dissolved and particulate forms of radium soon after the sampling and to prefer polyethylene to glass as container material for storage of dissolved forms of radium.     

Mechanical properties and enzymatic degradation of poly[(R)-3-hydroxybutyrate] fibers stretched after isothermal crystallization near Tg

Poly[(R)-3-hydroxybutyrate] (P(3HB)) fibers with high tensile strength were prepared by stretching the fibers after isothermal crystallization near the glass transition temperature. Two samples with different molecular weights (M_w = 0.7 × 10⁶ and 4.3 × 10⁶) were used to investigate the effect on tensile strength. Increasing the time for isothermal crystallization of P(3HB) fibers resulted in a decrease in the maximum draw ratio. But, the tensile strength of P(3HB) fibers increased remarkably when the isothermal crystallization time was prolonged to more than 24 h. The tensile strength of low-molecular-weight drawn fibers was higher than that of high-molecular-weight fibers. Therefore, it can be concluded that this procedure does not increase the tensile strength of the high-molecular-weight drawn fibers. This is because, in this drawing method, small crystal nuclei grow initially during the isothermal crystallization process. Then, the molecular chains between the small crystal nuclei that acted as the entanglement points are oriented by stretching. In the case of the high-molecular-weight fibers, because the molecular length between the entanglement points of the small crystal nuclei is too long, the molecular chains are not sufficiently oriented by the stretching process. However, in the case of the low-molecular-weight fibers, the molecular length is suitable for generating the extended chains. Based on the result of X-ray analysis of P(3HB) fibers stretched after isothermal crystallization, fibers have the oriented α-form crystal with 2₁ helix conformation and β-form with planar zigzag conformation. The enzymatic degradation of the stretched P(3HB) fibers was performed by using an extracellular PHB depolymerase purified from Ralstonia pickettii T1. The enzymatic erosion rate of β-form was faster than that of α-form in the P(3HB) fibers stretched after isothermal crystallization.     

Electronic states of 1,4-bis(phenylethynyl)benzene: A synchrotron radiation linear dichroism investigation

The electronic transitions of 1,4-bis(phenylethynyl)benzene (BPEB) were investigated by UV synchrotron radiation linear dichroism (SRLD) spectroscopy in the range 25,000-58,000 cm⁻¹ (400-170 nm) on molecular samples aligned in stretched polyethylene. The investigation was supported by variable temperature spectroscopy and by quantum chemical calculations in the LCOAO and TD-DFT models. The molecular alignment of BPEB in stretched polyethylene was found to be remarkably efficient, leading to an orientation factor equal to 0.95 for the long molecular axis. The observed band shape depended strongly on the degree of stretching and on temperature. The combined experimental and theoretical evidence leads to the characterization of several previously unobserved transitions and supports the assumption that BPEB adopts a nearly planar conformation in stretched polyethylene.     

Role of solvation energy in starch adsorption on oxide surfaces

The effect of potassium and sodium cations on the adsorption of starch onto hematite and quartz was investigated. The role of these ions was analyzed in terms of their water structure-making or -breaking capabilities. In the presence of Na⁺, a structure maker, the polymer adsorption density did not change compared to the adsorption levels observed in distilled water. However, in the solutions of K⁺, a structure-breaking cation, the adsorption density of starch significantly increased. Assuming hydrogen bonding and chemical interaction to be the driving adsorption mechanism, it was proposed that the starch–oxide interactions can be envisioned as the competition between chemical interaction/hydrogen bonding and solvation energy:

K⁺ reduces solvation energy by disturbing interfacial water structure and thus increases the free energy of adsorption, allowing the polymer to more closely approach the oxide surfaces. In contrast, Na⁺ which is indifferent to solvation energy does not interfere with the free energy of adsorption.     

Modification and characterization of polystyrene surfaces used for cell culture

Surfaces of polystyrene Petri dishes used for cell culture were chemically modified by 5% fuming sulfuric acid. The sulfonation was performed at room temperature for various times. Formation of polar groups takes place essentially on the surface of the polymer. Wettability and ionic character of the modified surfaces were determined by contact angle measurements and surface conductivity measurements, respectively. Radioactive calcium (⁴⁵Ca) adsorption at these surfaces was investigated by means of radiotracer techniques. The chemical composition (concentration of polar sites produced) of these modified polystyrene surfaces was thus determined. It was found that the wettability of these surfaces is directly related to the concentration of sulfonate groups. The cation-exchange capacity of treated surfaces with inorganic cations (Na⁺, Mg²⁺, Ca²⁺, and Al³⁺) were determined by the radiotracer technique.     

Studies of temperature influence on adsorption behaviour of nonionic polymers at the zirconia–solution interface

The temperature influence (15–35 °C) on the adsorption mechanism and conformation of nonionic polymers (polyethylene glycol (PEG), polyethylene oxide (PEO) and polyvinyl alcohol (PVA)) on the zirconium dioxide surface was examined. The applied techniques (spectrophotometry, viscosimetry, potentiometric titration and microelectrophoresis) allowed characterization of the changes in structure and thickness of polymer adsorption layers with the increasing temperature. The rise of temperature favours more stretched conformation of polymer chains on the ZrO₂ surface, which results in higher adsorption and thicker adsorption layer. Moreover, these conformational changes of adsorbed macromolecules affect the electric (solid surface charge density) and electrokinetic (zeta potential) properties of the zirconia–polymer interface. The obtained data indicate that the polyvinyl alcohol adsorption has a greater influence on zirconia properties in comparison to that of PEG and PEO. It is due to the presence of acetate groups in the PVA macromolecules (degree of hydrolysis 97.5%), which undergo dissociation.     

Temperature effect on adsorption properties of silica-polyacrylic acid interface

The temperature influence (15–35 °C) on the adsorption mechanism and conformation of nonionic polymers (polyethylene glycol (PEG), polyethylene oxide (PEO) and polyvinyl alcohol (PVA)) on the zirconium dioxide surface was examined. The applied techniques (spectrophotometry, viscosimetry, potentiometric titration and microelectrophoresis) allowed characterization of the changes in structure and thickness of polymer adsorption layers with the increasing temperature. The rise of temperature favours more stretched conformation of polymer chains on the ZrO₂ surface, which results in higher adsorption and thicker adsorption layer. Moreover, these conformational changes of adsorbed macromolecules affect the electric (solid surface charge density) and electrokinetic (zeta potential) properties of the zirconia–polymer interface. The obtained data indicate that the polyvinyl alcohol adsorption has a greater influence on zirconia properties in comparison to that of PEG and PEO. It is due to the presence of acetate groups in the PVA macromolecules (degree of hydrolysis 97.5%), which undergo dissociation.     

Kinetics of adsorption and desorption of sodium alkyl sulfates to and from nylon particles

The desorption rate of surfactant ions from nylon particles was investigated at the concentrations below the critical micelle concentration by applying the stopped-flow method. A mixing cell of stopped-flow spectrophotometer was modified with platinum electrodes for electric conductivity detection. The change in electric conductivity with time in the desorption process was monitored by a memory-recorder system. The surfactants used were sodium decyl, sodium dodecyl, sodium tetradecyl, and sodium hexadecyl sulfates. The desorption rate was independent of the surfactant concentration and the rate constants were obtained by applying the first-order reaction scheme. The adsorption rate constants were estimated from the experimental desorption rate constants and equilibrium constants assuming the second-order kinetics. The desorption rate constants were determined to be 1–6 sec^–1 and the adsorption rate constants to be 2–8×10⁴ mol^–1 dm³ sec^–1; the former decreased and the latter increased with increasing number of carbon atoms in alkyl chain of the surfactants.     

Interactions between Adsorbed Layers of a Low Charge Density Cationic Polyelectrolyte on Mica in the Absence and Presence of Anionic Surfactant

Interactions between two negatively charged mica surfaces across aqueous solutions containing various amounts of a 10% charged cationic polyelectrolyte have been studied. It is found that the mica surface charge is neutralized when the polyelectrolyte is adsorbed from a 10–50 ppm aqueous solution. Consequently no electrostatic double-layer force is observed. Instead an attractive force acts between the surfaces in the distance regime 250–100 Å. We suggest that this attraction is caused by bridging. Additional adsorption takes place when the polyelectrolyte concentration is increased to 100 and 300 ppm, and a long-range repulsion develops. This repulsive force is both of electrostatic and steric origin. The polyelectrolyte layer adsorbed from a 50 ppm solution does not desorb when the polyelectrolyte solution is replaced with an aqueous polyelectrolyte-free solution. Injection of sodium dodecyl sulfate (SDS) into the measuring chamber to a concentration of about 0.01 CMC (8.3 × 10⁻⁵M) does not affect the adsorbed layers or the interaction forces. However, when the SDS concentration is increased to 0.02 CMC (0.166 mM) the adsorbed layer expands dramatically due to adsorption of SDS to the polyelectrolyte chains. The sudden swelling suggests a cooperative adsorption of SDS to the preadsorbed polyelectrolyte layer and that the critical aggregation concentration between the polyelectrolyte and SDS at the surface is about 0.02 CMC. The flocculation behavior of the polyelectrolyte in solution upon addition of SDS was also examined. It was found that 0.16–0.32 mol SDS/mol charged segments on the polyelectrolyte is enough to make the solution slightly turbid.     

Application of ion mobility spectrometry in study of surfactants adsorbed on different dish surfaces

Sodium lauryl sulfate (SLS) and sodium lauryl ether sulfate (SLES) are commonly used in many dishwashing liquids. These chemicals are adsorbed on the dish surface during the washing process and then transferred to food or drink in the cooking process. In this work, the adsorption of SLS and SLES on different dish surfaces in aqueous solution was studied. Stainless steel, copper, aluminum, Pyrex, Teflon and arcopal china ware were used in this study. The adsorbed chemical remained on the surface after rinsing was measured by thermal desorption using an ion mobility spectrometer as the detector. Although arcopal china ware showed the maximum amount of adsorption, and Pyrex and stainless steel dishes showed the minimum amount of residual chemical, the results showed that the amount of adsorbed chemicals on dish surfaces is less than 428 ng.cm^?2, which is well below the health risk dosage. The released SLS and SLES from dish surfaces into cold or hot water were also measured and compared for different dishes.     

Polyethylene compounds with antimicrobial surface properties

The present study aims at antimicrobial polyethylene surfaces. To achieve this, LLDPE was compounded with the polymeric biocide poly(2-tert-butylaminoethyl) methacrylate TBAM (bulk modification with 1.5-5.0 wt.% of TBAM). Surfaces of these polymer compounds were then subjected to microbial assays. Using standard methods the colony forming units (CFU) for Escherichia coli and Staphylococcus aureus were determined on these surfaces. In all cases, polyethylene surfaces with highly antimicrobial properties were achieved. An average reduction of 10⁴ CFU ml⁻¹ compared to neat LLDPE was achieved. The surfaces of these LLDPE/TBAM compounds were assessed by electrokinetic (zeta potential) measurements. The results indicate a relation between the antimicrobial activity and the zeta-potential of the polymer compounds. Moreover, the antimicrobial compounds were investigated towards biofilm formation. Compared to pristine LLDPE, the surfaces of the polymer compounds showed less adhering biofilm after a testing period of 16 weeks.     

AFM study on the wettability of mica and graphite modified with surfactant DTAB

In this work atomic force microscopy (AFM) was applied to study the wettability of mica and graphite modified with surfactant dodecyltrimethylammonium bromide (DTAB) at varying DTAB concentrations (below the cmc) and adsorption time. The coverage states of DTAB on surfaces were analyzed from the AFM images, while the contact angle measurement was made for the wettability of DTAB-modified surfaces. The experimental results have shown that the adsorption aggregates formed as needle-like dots covering on the mica surface with the surfactant concentration of 10^?6–10^?4?mol/L. The coverage of DTAB aggregates increased with the increasing concentration, leading to a strong hydrophobicity on the surfaces. However, the large aggregates which might be caused by bilayer adsorption of surfactant occurred on mica surface at surfactant concentration of 10^?3?mol/L, resulting in the reverse of the wettability as the adsorption time extended. In the case of hydrophobic graphite, DTAB aggregates mainly formed as stripe covering on the surfaces, leading to the reduction of hydrophobicity. This reduction became stronger as more DTAB aggregates covered on graphite surfaces.     

Simultaneous quantitative trace analysis of anionic and nonionic surfactant mixtures by reversed-phase liquid chromatography

The aim of this work was to simultaneously analyse mixtures of a polydisperse polyethylene oxide (PEO) nonionic surfactant and an anionic surfactant (sodium dodecylsulphate, SDS) in water containing sodium chloride in order to quantify trace amounts of these mixtures after their adsorption at water-solid interfaces. A fractional factorial design was then used to optimise the separation by ion-pair reversed-phase liquid chromatography as a function of six factors: the chain length of the tetraalkylammonium salt used as ion-pairing reagent which varied from methyl (C1) to n-propyl (C3); the concentration of this ion-pairing salt; the acetonitrile percentage in water used as organic modifier; the flow-rate; the temperature of analysis and also the sodium chloride concentration. The factorial design enabled in a limited number of analyses, not only to determine which factors had significant effects on retention times or on resolution between a pair of nonionic oligomers, but also to modelize and then find the interesting and rugged area where this resolution was optimal as well as the conditions where time of analysis was not prohibitive. After optimisation of HPLC analysis, we used a trace enrichment procedure to quantify very low concentrations of SDS and C12E9 polydisperse PEO in water. A C18 cartridge and a strong anionic exchange cartridge were coupled and the conditions of elution were optimised in order to obtain concentrated samples which were injected in the same eluent than the HPLC mobile phase. Under such conditions, we were able to quantify, in a single run, mixtures of anionic and nonionic surfactants at concentrations as low as 3.6 microg l(-1) for SDS and 2.5 microg l(-1) for each PEO oligomer in water.     

Interaction of NO molecules with Pd clusters: Ab initio density–functional study

The adsorption of NO molecules on small Pd_n (n = 1?6) clusters has been studied using first‐principles density‐functional theory. Three adsorption sites were considered: vertex (on–top), bridge, and hollow. Adsorption is strong, ranging from 2 to 3 eV. In all cases NO adsorbs in a bent configuration. Calculated shifts in N–O bond vibration frequencies (with anharmonic corrections) agree very well with available experimental data. In contrast to metallic Pd surfaces, adsorption of NO on palladium clusters causes considerable changes in geometry around adsorption site because palladium d‐orbitals rehybridize to maximize the overlap with NO orbitals (mainly the antibonding π*). Thus, the overall energetic effect of NO adsorption is the result of two competing processes: lowering of the total energy through tighter bonding with NO and rising the energy due to cluster deformation. The Pd_n–NO bond creation is governed by electron transfer from Pd–d orbitals into the NO π*. As a result, the Pd cluster becomes locally demagnetized (with total magnetic moment of 1 μ_B located at Pd atoms not connected to NO) and the NO molecule is activated: the N–O bond length is increased and the vibration frequency is redshifted. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Water adsorption and desorption pretreatment of surfaces increases the maximum amount of adsorbed water molecules by a multiple

The amount of adsorbed water on surfaces in an atmosphere with 100 % relative humidity can be increased by a multiple, if the surfaces are pretreated by cycles of adsorption and desorption of water. This was observed on surfaces of diamond, titanium dioxide and silicon dioxide at temperatures around 22 °C. With a sufficient number of such cycles a faster and stronger adsorption of water molecules was obtained, if compared with untreated surfaces. This also means an increased energy transfer from the atmosphere to the surface. Due to the pretreatment the amount of adsorbed water was more than three times increased. The observed effect is explained by small amounts of specially arranged water molecules, which remain on the surface after the desorption process and which support the adsorption of water. The observed effect can be used to moisten surfaces of small particles very efficiently from the gas phase.     

Characterization by Raman microspectrometry of residual compressive stresses induced by resin curing in single filament composite samples

The present work concerns monofilament composite samples used in the pull-out test to quantify the effect of different fibre surface treatments on the adhesion of a high modulus polyethylene in a polyester resin. Optical observations revealed local deformations induced by a compressive stress generated in the fibre by the resin shrinkage during the curing. The sensitivity of the polyethylene Raman peak at 1130 cm⁻¹ to elastic strain has been used to characterize the local compression state still present in the fibre after the curing. The results show residual stresses varying along the fibre embedded length up to a level depending on the applied surface treatment i.e. on the degree of adhesion between the fibre and the resin. This is consistent with the localization and the morphologies of shear bands observed in the samples. More the Raman microspectrometry has been used to determine the tensile stress profile along the embedded part of the fibre when its free part is stretched. Corrected of the initial compression state this profile represents the stress transfer effectively realized from the fibre to the resin for different adhesion conditions. Its knowledge is very useful to clarify the interface damage and pull-out mechanisms.     

Molecular motion and anisotropy in polymers investigated by fluorescence techniques

Fluorescence polarization has been used to investigate the correlation between the orientation distribution function odf^G of quasi rigid rod fluorescent guest molecules and the odf^H of anisotropic host polymer in which the guests are imbedded, e.g. fluorescent molecules incorporated in the non-crystalline regions of uniaxially stretched polyethylene (LDPE). The orientation correlation between odf^G and odf^H is discussed with respect to the thickness to length ratio t/1 and the length of the probe molecules. For a rigid rod length around 2 nm there is a linear dependence between the factorizable orientation parameter P₂^G of odf^G and the length of rigid rods at given orientation of LDPE. This behaviour is obtained after correcting the different ratios t/1 of the probes. The variation of probe geometry, i.e. reference length and ratio t/1, gives information not only about the mechanism of orientation but also about the change of rotational mobility depending on size and fluorescence lifetime of the probes. Selecting probes of various length in the lifetime region of 1–6 ns, it results that microregions with reference length larger then 2 nm are rotationally immobile in the non-crystalline regions of LDPE at ambient temperature.