bluuebunny/crossref_metadata_2025_split huggingface dataset:
Etude de la polydispersité au moyen de la diffusion brownienne
Authors: Daune M. , Freund L. 
Published: April 2003

AbstractOn rappelle d'abord les résultats déja obtenus lorsqu'on utilise la méthode interférométrique de Scheibling dans l'étude de la diffusion brownienne de corps polydispersés. On développe ensuite le calcul de trois coefficients de diffusion moyens, qu'on peut relier à des moyens en masses particulières, et qui dans le cas d'une fonction de distribution de forme connue permettent de la déterminer complètement. De plus on peut faire l'analyse complète, a partir de ces trois moyennes d'un mélange de deux espèces différents en proportions quelconques. Quelques exemples expérimentaux montrent les possibilités et la précision de cette méthode. On montre enfin qu'on peut mettre la fonction représentant la courbe expérimentale sous la forme d'un produit de composition, ce qui permet d'obtenir la fonction de distribution par deux transformations de Fourier successives. L'application de ce procédé à une répartition théorique donne un résultat satisfaisant qui justifie une étude expérimentale plus poussée.
Dynamic flow birefringence, optical anisotropy, and shape of macromolecules in solutions
Authors: Tsvetkov Victor N. 
Published: April 2003

AbstractThe experimental study of the dynamic double refraction in polymer solutions in different solvents shows a parabolic dependence of the dynamooptical constant from the refractive index of the solvent. This character of the said dependence can be explained qualitatively in terms of the molecular coil asymmetry; it can be interpreted quantitatively on the basis of the equivalent molecular ellipsoids model. The investigation of the Maxwell effect in a series of polymer fractions with different MW gives the following law: If the refractive indexes, ns and nk of the solvent and polymer are equal, the ratio [n]/[η] is independent of the MW. Here [η] is the dynamooptical constant and [η] is the intrinsic viscosity. If the value of nk − ns is high enough, the ratio [n]/[η] increases as the MW becomes higher and sometimes changes the sign. This law is determined also by the form anisotropy of macromolecules. It agrees well with the theory of equivalent ellipsoids. This theory can be used for the quantitative interpretation of the experimental results. It gives the estimation of the value of the molecular coil asymmetry in agreement with Kuhn's theory. In some cases (e.g., polystyrene in dioxane) the experiment shows change of sign of double refraction as the flow velocity gradient increases. This effect can be explained also by the equivalent molecular ellipsoids theory. As the molecular chains are uncoiling in the field of flow velocity gradient, their intrinsic optical anisotropy increases more than the form anisotropy. The comparative study of photoelasticity in the films of some polymers and of dynamic double refraction in their solutions shows the direct dependence of both effects to be in accordance with Kuhn's statistical theory.
Etude expérimentale de l'effet maxwell présenté par les solutions de macromolécules en chaîne
Authors: Leray Joseph 
Published: April 2003

AbstractOn effectue sur deux types de polymères des expériences de biréfringence d'écoulement analogues à celles de Cerf, c'est‐à‐dire que l'on mesure la pente tg α de la tangente à l'origine de la courbe d'extinction dans des solvants de viscosité η0 variable. (a) Polystyrènes. Les mesures portent sur quatre échantillons de masses 520.000, 1.240.000, 3.530.000 et 10.000.000. Pour chacun d'eux, à une concentration c donnée, tg α est une fonction linéaire de η0. Les droites relatives à diverses concentrations ont měme ordonnée à l'origine B. La quantité B est proportionelle à la masse moléculaire. Ces résultats faciliteront les extrapolations à c = 0 et à η0 = 0 des mesures d'angle d'extinction. (b) Acides désoxyribonucléïques. Les valeurs de tg α obtenues sur un échantillon de masse 6 × 106 se placent au voisinage de deux droites d'ordonnées à l'origine respectivement nulle et positive et dont les pentes sont dans un rapport de l'ordre de 4,5. Des observations analogues sont faites sur les résultats obtenus par d'autres auteurs, à l'aide d'un échantillon de měme masse, préparé par une méthode différente. On effectue une premiére confrontation entre les résultats expérimentaux et une théorie récente, fondée sur le modèle à N sous‐chaǐnes de Gauss et qui tient compte de la viscosité interne de la particule. Une interprétation plus complète nécessitera la connaissance des valeurs de la viscosité intrinsèque des polymères étudiés dans les différents solvants utilisés. D'ores et déjà on peut dire que la plupart des données expérimentales sont en accord avec les conclusions théoriques. En particulier, on confirme la possibilité de déterminer le terme de viscosité interne comme ordonnée à l'roigine de l'asymptote à la courbe tg α en fonction de η0. On corrobore les conclusions de Sadron quant à l'existence de deux catégories d'acides désoxyribonucléïques, les deux échantillons examinés ici présentant une rigidité différente. Toutefois, les variations du terme de viscosité interne avec la masse moléculaire paraissent difficilement compatibles avec la théorie.
Comparaison entre les résultats fournis par la détermination des dimensions et du moment électrique moyen des chaînes macromoléculaires
Authors: Marchal J. , Benoit H. 
Published: April 2003

AbstractLes auteurs ont mesuré les moments électriques des polyoxyéthylèneglycols et des polyoxyéthylèneglycols diéthoxylés de degré de polymérisation compris entre 2 et 230. Ils ont calculé, en tenant compte des interactions, les valeurs théoriques correspondantes qui sont en accord avec les résultats expérimentaux. Ils montrent ensuite que le carré moyen du moment électrique \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\mu ^2 } $\end{document} est, dans les cas usuels, proportionnel au degré de polymérisation, ce qui signifie que l'“effet de volume” n'a pas d'influence sur la grandeur de \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\mu ^2 } $\end{document}. Ils en déduisent une méthode de mesure des interactions à courte distance dans un solvant quelconque. L'étude du polyméthacrylate de méthyle montre que ces interactions sont indépendantes du solvant et de la température, aux erreurs d'expérience près.
Le comportement diélectrique des polymères en solutions diluées
Authors: De Brouckere L. , Buess D. , Van Beek L. K. H. 
Published: April 2003

AbstractLes propriétés diélectriques et les facteurs de perte ont été mesurés pour des solutions diluées de chlorure de polyvinyle dans le tétrahydrofurane et des mélanges de ce solvant avec l'heptane, pour des solutions de polyméthacrylate de méthyle dans le benzène et le toluène, et pour des solutions d'acétate de polyvinyle dans le toluène. Les concentrations variaient de 0.5 à 8 g./100 ml. Les fréquences allaient de 0.01 à 35 mégacycles/sec. et les température de −35° à +25°C. Un seul échantillon de chlorure de polyvinyle a été utilisé (DP = 1750); par contre quatre fractions de polyméthacrylate de méthyle (DP = 240–12.500) et quatre d'acétate de polyvinyle (DP = 2.550–23.250) ont été utilisées. Les valeurs numériques des trois polymères étaient plutǒt similaires. Les moments dipolaires moyens étaient proportionnels à la carrée du DP. Les temps de rélaxation étaient pratiquement indépendants du DP.
Etude de l'interaction solvant‐macromolécule par la constante diélectrique statique des solutions diluées de hauts polymères
Authors: Mandel M. 
Published: April 2003

AbstractIl semble possible d'attribuer partiellement les propriétés diélectriques de solutions de hauts polymères à une interaction entre la macromolécule et les molécules du solvant, si ce dernier est polaire. L'étude de la variation de la constante diélectrique statique avec la température peut alors apporter des renseignements intéressants. Appliquant à la solution diluée d'une macromolécule polaire dans un solvant polaire, un modèle analogue à celui proposé par Fröhlich pour les liquides purs, on peut définir un facteur de corrélation (g) si l'on tient compte de la polarisation de déformation d'une façon macroscopique à travers l'indice de réfraction de la solution. Le raisonnement est valable aussi bien pour le cas où l'on considère la macromolécule comme un tout plus ou moins rigide que pour celui où on la décompose en chaǐnons statistiques. L'exemple d'une solution à 2% de polyméthacrylate de butyle dans le toluène montre que l'effet existe. I'étude de ces propriétés, commencée depuis peu au laboratoire, aura e.a. pour but de voir s'il existe une relation entre le facteur g pour différentes solutions de hauts polymères dans différents solvants, notamment par rapport à une éventuelle température de précipitation.
Temperature‐dependence of light scattering and intrinsic viscosity of hydrogen bonding polymers
Authors: Silberberg A. , Eliassaf J. , Katchalsky A. 
Published: April 2003

AbstractA group of chemically related polymers—polymethacrylic acid polymethacrylamide, polyacrylic acid, and polyacrylamide—having a large number of groups capable of forming hydrogen bonds along the chain, was investigated by studying the temperature dependence of the 90° scattering of light and of the viscosity of dilute aqueous solutions, mineral acid being added in the case of the polyacids in order to suppress ionization. The intercepts of the light scattering plot indicated no dependence of molecular weight on temperature, but the slope B of this plot and the intrinsic viscosity [η] were found to change markedly with temperature. The slope parameter B and the intrinsic viscosity decreased with increase in temperature in the case of polymethacrylic acid, but increased with increase in temperature in the other three cases. The exceptional behavior of polymethacrylic acid is correlated with its known tendency to form gels on heating in concentrated aqueous solution. A discussion of the light scattering plot slope parameter B and its temperature‐dependence is given, based on fluctuation theory and the experimental evidence. It is emphasized that B is a measure of the interactions between the kinetic units as they exist in the solution and that its temperature‐dependence gives information about the entropy and energy changes accompanying changes in concentration. These quantities are calculated and briefly discussed. The correlation between B and the intrinsic viscosity [η] is examined in the light of the Flory‐Fox‐Krigbaum treatment. Relationships involving, respectively, the heat and entropy of dilution are derived and used for comparison. Our results are found to conform well with these theoretical predictions. Calculations of the length of the statistical chain element show that these values in the case of polymethacrylic acid and amide are about half the value for polyacrylic acid under corresponding conditions. This is at variance with the fact that the presence of the methyl group should have a marked stiffening effect on the chain. The discrepancy is attributed to intramolecular hydrogen bonding, the polymethacrylic chain being assumed to be the more strongly bonded. The possibility of intramolecular bonding makes the agreement with Flory's treatment of coil expansion particularly interesting. A possible explanation is suggested.
Sorption and diffusion in ethyl cellulose. Part I. History‐dependence of sorption isotherms and permeation rates
Authors: Barrer R. M. , Barrie J. A. , Slater J. 
Published: April 2003

AbstractThe sorption and permeation of benzene, acetone, and methanol in and through ethyl cellulose has been investigated from the point of view of hysteresis and time‐dependence. The three sorbates are imbibed decreasingly in the order given, at any relative pressure, and so swell the polymer to different extents. The medium is one in which anomalous diffusion is to be expected. The study was made in the lower range of concentrations of penetrant. The initial isotherm of acetone at 50°C. lay below subsequent ones at the same temperature. The higher the temperature the smaller this difference tended to be, while the greater the pressure and so the amount imbibed the greater it became. Eventually “settled” reproducible isotherms were found. If the outgassed polymer, following lower temperature isotherms, was “annealed” at a higher temperature and then cooled again, the initial isotherm at 50°C. was more nearly approached. However, subsequent isotherm determinations at the same temperature again established the “settled” isotherm. Permeation rates were determined as a function of pressure under various treatments. Repeated permeation runs caused the permeability of the polymer to decrease to a “settled” value. This behavior may be ascribed to some orientation of polymer, by mass flow, during permeation. After establishing the settled permeability the polymer was outgassed and “annealed” at a higher temperature, and the permeability at the original temperature then lay below the “settled” value. Benzene, which swelled the membrane more than the other sorbates, showed more pronounced effects of the same kind as acetone. On the other hand methanol, which was least sorbed, showed less pronounced time‐ and history‐dependence. Sorption always occurred more slowly than desorption. The various effects have been discussed in terms of a model of the polymer having rather stiff chains with some semipermanent interchain bonds, but other bonds more easily rearranged. The history‐dependent effects can arise at temperatures well above the glass transition usually quoted for ethyl cellulose.
On the additivity of the configurational and electrostatic properties of polyelectrolytes in solution
Authors: Lifson Shneior 
Published: April 2003

AbstractThe theories of Hermans and Overbeek, of Kimball, Cutler, and Samelson and of Katchalsky and Lifson concerning the dimensions of polyelectrolyte molecules in solution are discussed. The assumption that the configurational forces acting in a polyelectrolyte molecule may be adequately represented by the theory of nonelectrolytic polymers is applied in different ways by each theory, and leads to widely different results. It is found that, when additivity of the configurational and electrostatic contributions to the free energy is assumed, the configurational contribution is underestimated. The contribution is overestimated, on the other hand, when the potentials of the forces acting on each segment are assumed to be additive.
SECTION II: Polybase properties of polyvinylamine
Authors: Katchalsky A. , Mazur J. , Spitnik P. 
Published: April 2003

AbstractThe polybase properties of polyvinylamine hydrobromide were studied by pH‐metric titration at concentrations ranging from 10−4 to 10−1 M, in the presence, as well as in the absence, of neutral monomonovalent salt at high concentrations. The dependence of pH on degree of ionization, in all the range of concentrations studied, diverges from the known behavior of polyacids and polybases. The titration curve could not be characterized by a single dissociation constant, even when the electrostatic potential, determined electrophoretically, was taken into account, or when this potential was suppressed by high concentrations of neutral salt. An attempt is made to explain the unusual behavior of polyvinylamine by taking into account the nearest neighbor interaction. A statistical treatment, based on the unidimensional Ising model, leads to potentiometric equations involving two constants‐the intrinsic dissociation constant pK, and a nearest neighbor interaction constant ΔpK. The experimental titration curve could be satisfactorily described by these theoretical potentiometric equations. The titration constants for polyvinylamine derived by this procedure are pK = 9.4 and ΔpK = 1.20. These values compare favorably with the constants obtained from the microscopic dissociation constants of diethylenetriamine and of triethylenetetramine.
Preparation and titration of amphoteric polyelectrolytes
Authors: Alfrey Turner , Pinner S. H. 
Published: April 2003

AbstractA series of amphoteric polyelectrolytes have been made by copolymerizingN‐dialkylaminoethyl acrylates and methacrylates with acrylic, methacrylic, or itaconic acids in unbuffered aqueous solutions or in nonaqueous solutions at 70°C. using potassium persulfate or azobisisobutyronitrile as the catalyst. The purified copolymers were titrated electrometrically on a semimicro scale. The composition of the copolymers as obtained by titration agreed with calculations based on the analysis of nitrogen content. Except for itaconic acid copolymers, the titration curves exhibited separate and nonoverlapping ionization regions for the acid and basic components and allowed the assessment of the pKvalues of the acid and amine groups and also the pIvalues of the copolymers. The pKand pIvalues varied with the composition of the copolymers in the expected manner. As the frequency of a given group along the main chain increased, its apparent strength decreased. The pIvalues also shifted to lower pH values as the number fraction of acid groups increased. All these effects could be explained on the basis of the theory of the electrical free energy of ionization. The pIvalues computed graphically agreed within experimental error with those calculated from the equation:where α is the degree of ionization of the group present in excess in the polyelectrolyte. The implication is that the electrical free energy of ionization does not appear to vanish at the iso‐electric point.
L'Influence de l'acide polyméthacrylique sur la réfraction moléculaire des électrolytes forts et concentrés
Authors: Kryszewski M. 
Published: April 2003

AbstractOn a mesuré l'influence de l'acide polyméthacrylique ajouté aux solutions concentrées de NaCl, NaBr, NaI sur la réfraction moléculaire de ces sels. On trouve que la présence d'acide polyméthacrylique cause une diminution de réfraction moléculaire des sels qu'on ne peut pas expliquer seulement par la concentration du polymère.
Influence of pH and ionic strength on size, shape, and electric charge of the deoxyribonucleic acid molecule
Authors: Mathieson A. R. , Matty Sheila 
Published: April 2003

AbstractThe methods of electrometric titration, electrophoresis, streaming birefringence, and viscosity have been used to study the deoxyribonucleic acid (DNA) molecule in solutions of different pH. The dissociation constants of the nitrogen bases have been found at various DNA concentrations and ionic strengths, and the difference between the forward and backward titration curves further studied. The electrophoretic mobility has been measured at various pH values and ionic strengths. Calculations of the electrostatic potential indicate why there is little spreading of the titration curves. Comparison of the titration and electrophoretic data has been made to calculate the charge carried by the DNA ion alone and by the DNA ion together with its associated gegenions, and an estimate of the proportion of bound gegenions has been obtained. Measurements of (tan α)0 and [η] from streaming birefringence and viscosity have been made at various pH's on forward and backward titration, and the molecular length, axial ratio, and molecular weight calculated from these. Between pH 4.5 and 10 the length is unchanged but decreases to half its neutral value between pN 2.5–4.5 and 10–12, due to the breakage of the rigid hydrogen‐bonded structure by titration. On backward titration the length remains below half its undenatured value. The molecular weight is unchanged by treatment with acid or alkali between pH 2.5 and 12.
The structure and properties of levan, a polymer of D‐fructose produced by cultures and cell‐free extracts of aerobacter levanicum
Authors: Feingold D. S. , Gehatia M. 
Published: April 2003

AbstractLiving cultures of Aerobacter levanicum, or cell‐free extracts on sucrose, elaborate levan, a polymer of D‐fructose. Exhaustive methylation of the fructosan‐culture levan, and the levan produced in vitro with dimethyl sulfate and sodium hydroxide yielded fully methylated trimethyllevan, which afforded on hydrolyses 1,3,4,6‐tetra‐,1,3,4‐tri‐, and 3,4‐di‐O‐methyl‐D‐fructose in the molar ratio 1 : 7 : 1, respectively. These results indicate that the levan polymers are branched: main linkage C‐2,6; branch linkage C‐2,1; average basal chain length 9. The structural similarity of culture and “enzyme” levan was confirmed by infrared analysis. Partial hydrolyzates of levan examined chromatographically were found to contain more than one oligosaccharide at each level of DP above three. This observation is further evidence for branching in the native molecule. Oligosaccharides of DP 2–10 prepared by mild (2.5%) and extensive (66%) hydrolyses of the native polymer were all totally hydrolyzed to fructose by yeast invertase. This suggests that all the linkages in the levan molecule‐both those at the chain terminals and those within the chains‐are of the β‐fructofuranosyl type. Diffusion and sedimentation measurements on levan provided values from which average molecular weights were calculated. Studies of the use of degraded levan preparations as plasma volume expanders are in progress.
Physical chemistry of native cellulose
Authors: Usmanov H. U. 
Published: April 2003

AbstractThe knowledge of the physical chemical properties of cellulose and the laws of their alteration during the growth of natural filaments is very important for scientifically increasing the production of natural cellulose filaments. While dealing with cotton growing we have been continuously performing the physical chemical investigation of natural cellulose. The results obtained may be summarized as follows. Cellulose appears in the cotton tissue together with the flower and pod and not several days after blossoming, as is the general opinion to be encountered in the literature. The synthesis of cellulose in cotton is at first very slow, showing an acceleration by the 15th day after bloom with a subsequent slow‐down again and complete cessation approximately on the 40th day after bloom. Thus the characteristic curve of cellulose accumulation in cotton has an S‐shaped form. The natural cellulose of an early age has a very low degree of polymerization which later, by the 25th to 30th day after bloom, shows an abrupt increase and remains almost stable. The filament then almost completely consists of α‐cellulose. The kinetics of the polymerization and accumulation of cellulose is connected with the ripening period of cotton under investigation and makes it possible to predict the time of the ripening of pods. Early cellulose is very porous, it easily hydrolyzes, and has a higher sorption capacity and heat of solution than the cellulose of a mature age. However, the tightness of packing of the natural cellulose evaluated in terms of water sorption and heat of solution in water, reaches its maximum in the vegetation period, i.e., approximately on the 40th day of the maturation of filaments. The gradual increase in tightness of cellulose packing and its drop after 40 days can be accounted for if we consider the possibility of synthesis in all layers of the secondary wall of the filament, i. e., throughout the tissue of cellulose and not only in the channel of the filament. The main physicochemical and technological properties of cellulose bodies are the functions of the tightness of molecular packing of cellulose. The tightness of packing may vaccilate within a very broad range depending on the conditions of biosynthesis or processing.