Estimation of thermodynamic interactions between polyethylene and n-alkanes by means of melting point measurements

Summary The thermodynamic interaction parameters for linear polyethylene-n-alkanes were investigated with n-C₆H₁₄, n-C₇H₁₆, n-C₈H₁₈, n-C₁₈H₃₈, and n-C₃₂H₆₆ as diluents, by determining the melting temperatures of polyethylene in its mixtures with n-alkanes. It follows that, with increasing the number of carbon atom in n-alkanes, the entropy parameter ₁ increases, the enthalpy parameter ₁ remains approximately equal to zero, and the free energy parameter ₁ decreases and approaches to zero. The change of the interaction parameters with the number of carbon atom in n-alkanes were discussed byPrigogine's theory.

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Zusammenfassung Die thermodynamischen Wechselwirkungsparameter für das System lineares PolyÄthylen/n-Alkane wurden durch die Schmelzpunktsmessungen von PolyÄthylen in den Mischungen mit n-Alkanen bestimmt. Die als Verdünnungsmittel verwandten n-Alkane waren n-C₆H₁₄, n-C₇H₁₆, n-C₈H₁₈, n-C₁₈H₃₈ und n-C₃₂H₆₆. Es wurde gefunden, da\ mit steigender Zahl der Kohlenstoffatome in den n-Alkanen der Entropieparameter ₁ zunimmt, wÄhrend der Enthalpieparameter ₁ annÄhernd Null bleibt. Der Parameter der freien Energie ₁ nimmt ab und nÄhert sich Null. Die VerÄnderung der Wechselwirkungsparameter von der Zahl des Kohlenstoffatome in den n-Alkanen wurden nach der Prigogineschen Theorie diskutiert.

     

Long-wavelength near-infrared spectroscopic imaging for in-vivo skin hydration measurements

A digital imaging system has been developed to collect skin hydration data. The system combines a near-infrared camera with a liquid-crystal tunable filter (LCTF) to acquire spectral images at multiple narrow wavelength bands between 960 and 1700 nm. Software has been developed to control the instrument and to process the data. Reflectance images were collected of subjects whose forearms had been treated to increase and decrease skin moisture. The infrared absorption band between 1400 and 1500 nm was used to calculate relative skin moisture, and the intensity of this band was plotted as a function of position in the form of a grayscale image. This is a rapid, non-contact and non-invasive technique to provide information on skin hydration of use to medical and cosmetic research and clinical practice.     

Estimation of exposure levels by measurements and models

Summary Results from environmental and biological monitoring programs are abundant, but it is a question to what extent such data can be used for exposure assessments. The quality of such data depends not only on sampling and analytical errors, but also, and probably more, on the sampling strategy used. Therefore, uncritically use of such results can be biased and associated with large variations. The size of bias between two studies carried out in the same industry was found to be a factor of 5–7. Samples that are not representative of the exposed population studied are misleading. An estimation of exposure to cobalt in the porcelain industry illustrates the distinction between biological measurement data and air cobalt measurement data done on selected individuals. Following improvement of the working environment during the period 1983–1990, the change of cobalt concentration in urine indicates a reduction of cobalt exposure with a factor of 10, but air monitoring data do not verify that figure. Furthermore, results must always be interpreted with caution, when used beyond the purpose for what they were originally made. Great care should be taken to secure that data are representative and a quality assurance-quality control program should be used to ensure data quality.     

Study of chromate coatings by means of electrode impedance measurements

The corrosion resistance of chromate layers on zinc sheet was studied by electrode impedance measurements in 0.1 mol/1 NaClO₄ solutions. A correlation was found to exist between the inhomogeneity and corrosion protection of the chromate layers and impedance data measured at different spots of the specimen. The results of impedance measurements and humidity tests agreed within the experimental error.     

Characterization of aluminium surface treatments by means of gas adsorption measurements

Adsorption measurements were used to determine the specific surface area of a.c. electrolytically grained aluminium and the porosity distribution diagram of porous anodized aluminium. Alternating current electrolytic graining of aluminium is used to increase the specific surface area for the preparation of litho sheets or capacitor foil. The specific surface area S (calculated by the BET procedure from the nitrogen adsorption isotherm) was studied as a function of the graining frequency between 0.1 and 1000 Hz. The results were related to the graining morphology by comparing them with scanning electron microscopy micrographs. It is concluded that in contrast to the more common surface investigation techniques the method can be used to measure quantitatively the gain in surface area after such a treatment as a.c. electrolytic graining. In the second part of the paper the pore size distribution diagrams are calculated from the adsorption isotherm for porous sulphuric acid films. It is shown that the dominant pore diameter corresponds rather well to the pore diameter observed in transmission electron microscopy sectional views. This means that the adsorption method can be applied to study the porosity of the aluminum oxide films. The method was then used to study the influence of the pretreatment on the porous oxide film morphology.     

Critical temperature measurements of liquids by means of differential thermal analysis

When studying crytalline substances and liquids in sealed off glass ampoules by differential thermal analysis the melting ranges but not the heat of evaporation of the liquids and fused substances are found, because inside the glass ampoule, there will always be the vapour pressure equillibrium which corresponds to the temperature. With liquids undergoing decomposition, it is possible to measure the range and heat of decomposition. Given a suitable quantity inside the ampoule the critical temperature, e.g., of water of ethanol can be measured for non-decomposing liquids. The measuring effect is based on the pronounced change of the liquid's specific heat at the critical temperature.Fundamental studies of the measurement of critical temperatures of liquids were carried out by the turn of the century. One the methods reported is the meniscus method, optimal measurement of the critical temperature, which comprises a liquid being filled into a glass tube which is then sealed by melting. The glass tube is heated while observing the meniscus. Its rise means that the critical volume has been exceeded, while a drop means that it has not yet been reached. The conditions are only met when that volume of liquid has been filled into the tube at which the meniscus neither rises nor falls on heating but rather remains, e.g. at mid level of the tube until it disappears. The tube contains the critical volume at the critical density when the critical temperature is reached. The critical pressure is then present. These conditions are obtained when the meniscus disappears and the liquid completely goes over into the vapour phase.The melting range (and the latent heat of fusion) are found when investigating a crystalline material under normal pressure by differential thermal analysis. Given a suitable arrangement the boiling temperature and, in rough approximation, the heat of evaporation are also found (Fig.1). The latent heat of fusion is found again when carrying out the same measurement in a closed system (glass tube sealed by melting). The heat of evaporation can no longer be measured since the vapour pressure equilibrium coresponding to the given temperature is present in the glass tube.     

Estimation in multiple measurements

A recent paper by Nam et al. (Accred Qual Assur 14:43–47, 2009) considers the issue of repeated measurements of a same measurand. The paper is a follow-up of two previous papers (Choi et al. in Accred Qual Assur 8:13–15, 2003, 8:205–207, 2003) on the same topic. The first two papers show a well-known fact, i.e., that systematic effects are not reduced by repeating measurements, and give formulae for the uncertainty of the estimate of the average from repeated measurements in the case that the differences between individual results are not (Choi et al. in Accred Qual Assur 8:13–15, 2003) or are (Choi et al. in Accred Qual Assur 8:205–207, 2003) statistically significant, respectively. The last paper addresses a more interesting issue, that is, a difference in the estimate average for non-linear models depending on how raw data is processed in the model. In the present paper, I re-discuss the whole issue of multiple measurements, trying to clarify the various aspects of the topic. Papers Published in this section do not necessarily reflect the opinion of the Editors, the Editorial Board, and the Publisher.     

Estimation of chloride in oxidizing media by means of ion-selective electrodes

Chloride concentrations down to the ppm level in a large excess of chlorate or perchlorate can be quantitatively estimated by use of chloride ion-selective electrodes (ISEs). Similarly traces of chloride in chromic acid solutions can be estimated with a heterogeneous silicone-rubber based chloride ISE. However, homogeneous chloride ISEs pose a problem for practical applications, because their response in chromic acid solutions changes with time owing to chemical attack on the membrane surface. In permanganate solutions, both homogeneous and heterogeneous type electrodes can be used for monitoring chloride ions. The Orion electrode, however, was found to show a slightly super-Nernstian response in such solutions. The presence of 10(-3)M iron(III) had no adverse effect on the performance of these electrodes in permanganate solutions.     

The tautomerization phenomenon of glibenclamide drug monitored by means of volumetric measurements

In this paper, we investigate the tautomerization process of glibenclamide drug by monitoring the changes in the specific volume. The density changes observed during the chemical equilibration process, carried out at a pressure of p = 10 MPa and at three different temperatures, enable us to study the kinetics of tautomerization reaction, i.e., to determine the activation energy and to recognize the real time scale of this process at various temperature conditions. The results obtained from analysis of V(sp)(t) dependencies were next compared with the kinetic data previously obtained from dielectric spectroscopy studies.     

Following protein kinase acivity by electrochemical means and contact angle measurements

The electrochemical analysis of the protein kinase, casein kinase, is accomplished by the voltammetric response of Ag(+) ions associated with the phosphorylated product; the sensing surface is regenerated by the cleavage of the phosphorylated product with alkaline phosphatase, and the phosphorylation/de-phosphorylation processes are monitored by XPS and contact angle measurements.     

Routine drug level measurements by means of a fully mechanized HPLC equipment

Summary Pharmacokinetic studies require a great number of serum drug levels to be determined. It is therefore necessary to rationalize analytical methods. Methods for rational clean-up procedures and the determination by means of mechanized HPLC are shown. The following quality criteria for determination methods are proposed: precision, accuracy, specificity and sensitivity. Quality control in routine analyses is performed by evaluating the criteria of parallel analyses of known admixtures to serum.     

Estimation of thermal stability of phenol stabilizers by means of thermogravimetric analysis

A new method was developed for evaluation of the results of thermal analysis of phenol stabilizers used for the thermal stabilization of light-coloured polymers. The integral observed decomposition temperature obtained by using Doyle's method from the thermogravimetric curves was used as a basis of approach. For this purpose, the computational program TERMOGRAF for PC/AT is suggested. It is considered that the integral observed decomposition temperature is a more reliable and reproducible characteristic of thermal stability than the approach based on the temperature of beginning of decomposition.     

Friction force measurements relevant to de-inking by means of atomic force microscope

In the pulping step of the de-inking process, the ink detaches from the fibers due to shear and physical chemical interaction. In order to get a better understanding of the forces involved between cellulose and ink, the atomic force microscope and the colloidal probe technique have been used in the presence of a model chemical dispersant (hexa-ethyleneglycol mono n-dodecyl ether, C12E6). A cellulose bead was used as the colloidal probe and three different lower surfaces have been used, an alkyd resin, mica and a cellulose sphere. The normal and lateral forces have been measured at a range of nonionic concentrations. It was found that the lateral sliding friction forces deceased with increasing surfactant concentration for both the alkyd resin and mica while no differences were observed for the cellulose surface. In addition, only a very small change in normal force could be detected for the alkyd surface as the concentration changed.     

Determination of degree of crystallinity of drawn polymers by means of density measurements

The well known procedure of determining the degree of crystallinity by means of measuring the density presupposes the knowledge of both the densities ρ_c and ρ_a of the crystalline and of the noncrystalline regions. By combination of small-angle and wide-angle x-ray scattering and of density measurements it can be shown that this method is not justified in the case of drawn polyethylene if the values of ρ_c and ρ_a known from isotropic material are used. Both ρ_c and ρ_a depend considerably on annealing and drawing conditions. In addition the effective density ρ_c^* of the more densely packed phase in a two-phase structure is much lower than the value ρ_c calculated from the positions of the x-ray reflections due to a large number of lattice defects. This conclusion is based on the results of three independent sets of experiments: determination of the mean-square fluctuation of density 〈η²〉 by means of x-ray small-angle scattering; x-ray wide-angle measurements of the positions of the crystal reflections and of the halo arising from the noncrystalline regions; and comparison of densities and long periods of samples treated at various annealing temperatures.     

Estimation of flocculation structure in filled polymer composites by dynamic rheological measurements

 The frequency and concentration dependences of the storage modulus (G ^′) for carbon black and short-carbon-fiber-filled polymer composites were investigated by means of dynamic rheological measurements. It was found that G ^′ at low frequencies and amplitudes could be used as a sensitive experimental parameter for detecting the flocculation structure of the ultra-fine-particle-filled polymer composites. Correlation of electrical resistivity of the composites to the relative storage modulus, G ^′ _r(=G ^′ _c/ G ^′ _p), revealed that the three-dimensional interparticle networks start to construct through the matrix when G ^′ _r increases to 7 regardless of the composite systems. Quantitative calculations in order to determine the flocculation structure were carried out by means of the modified Kerner equation. A plot of the calculated value, defined as the floc index A, dependence of electrical resistivity for various systems was found to be a universal curve. Accordingly, we suggest that A might universally correspond to the flocculation structure of the filler, which is independent of the nature of the filler, the molecular weight, the chemical composition of the polymer and the temperature at which the measurement is made. This method is particularly effective for estimating the flocculation structure of ultra-fine-particle-filled polymer composites no matter whether the filler is conductive or not. Received: 26 May 1999/Accepted in revised form: 28 September 1999     

Evaluation of texture parameters in NdFeB magnets by means of X-Ray and magnetic measurements

NdFeB samples of different texture degree were prepared by uniaxial pressing in a magnetic field of different strength. Afterwards, the texture formation was investigated by means of X-ray diffraction. Usually, a fibre texture with the basal plane (001) perpendicular to the applied magnetic field is expected from the used compaction process. However, by introducing a two-parameter Gauss-function describing the texture, deviations from the rotational symmetry of the texture are found. The texture parameters are compared with those obtained by a fit of demagnetization curves. Knowing the intrinsic magnetic properties of the investigated material, demagnetization curves in the first quadrant of the J-H-plane can be calculated on the basis of the texture parameters.Dedicated to Professor Dr. rer.nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday