ISSN:0258-0322    

DOI:10.1002/masy.19920610103

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractAmongst other techniques, dynamic light scattering may be used to obtain molar mass distributions. The first step in this process consists in the Laplace inversion of the time correlation function that was measured by dynamic light scattering. This inversion gives a distribution of diffusion coefficients. In order to convert this distribution into the corresponding molar mass distribution, a relationship between diffusion coefficient and molar mass of monodisperse fractions has to be known. Such a relationship can be derived for linear and star‐branched macromolecules from measurements of polydisperse systems, since the polydispersity of the distributions does not change with the molar mass. The problem is more involved with randomly branched materials, since in these cases the polydispersity increases strongly as the point of gelation is approached. A procedure is suggested for deriving the diffusion‐molar mass dependence of monodisperse samples from polydisperse systems.After an outline of this background the method is applied to the three selected systems (i) radically polymerized linear PMMA, (ii) a star‐branched microgel where monodisperse arms are attached to a microgel center and (iii) a randomly branched poly(dicyanate) sample based on bisphenol A. The results are compared with the combined column chromatography SEC/LALLS/VISC. Good agreement was found up to molar masses of about 10 millions g/mol, but systematic deviations occured in the high molar mass region. These differences result from the limitations of size permeation chromatography. Finally it is shown that the size distribution can be determind by this method, even for assoc

ISSN:0258-0322    

DOI:10.1002/masy.19920610104

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractWith photon correlation spectrometry the diffusion coefficients of colloid particles in highly diluted aqueous suspensions can be measured and average diameters and polydispersities of the samples can be determined. Electrokinetic and electroviscous effects caused by polarization of the electrostatic double layer influence the diffusion of the particles. The adsorption of macromolecules at the interfaces of the particles results in an increase of the hydrodynamic diameter and a decrease of the diffusion and sedimentation coefficients. The hydrodynamic thicknesses of the polymer layers can be evaluated. The thickness values and their dependences on adsorbed amount and molar mass can only be interpreted by the existence of long tails of the adsorbed macromolecules dangling from the interface into the solution. The resulting conformation model is supported by the new theory of Scheutjens‐Fleer. Special importance have those tails for the interaction of particles and their stability and flocculation in disperse system

ISSN:0258-0322    

DOI:10.1002/masy.19920610105

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractFour different cationic polyelectrolytes were investigated, which are used as flocculating agents in the dewatering of sediments from Hamburg harbour. The chemical structures of these polyelectrolytes were characterized by means of IR and13C NMR spectroscopy. The substances concerned are the two copolymers of acrylamide formed with acrylate and methacrylate esters, and the homopolymers of these esters. The charge density was determined with the aid of titrimetric methods and quantitative evaluation of IGATED13C NMR spectra. Determination of the molar mass and steric characterization were carried out by multi‐angle laser light scattering. In order to resolve the experimental problems which arise especially during light scattering in water‐soluble cationic systems, a special method of sample preparation has been devised to remove impurities, which will be described in detail. This method involves the combination of filtration and ultracentrifugation. Evaluation of the light scattering data provided the values for the molar mass Mw′the second virial coefficient A2and the radius of gyration0,5Z, which also gives information about the solution structure. By comparing the curve of the scattering function extrapolated to zero concentration with model curves and with the aid of theaexponent of the [η]‐M‐relationship, it can be seen that the polyelectrolyte has a highly expanded coil structure in salt solution. This can be primarily attributed to the steric influence of the s

ISSN:0258-0322    

DOI:10.1002/masy.19920610106

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractAlthough xanthan has long been the subject of wide‐ranging investigations, it has not yet been possible to establish any clear link between the solution properties and the chemical and steric microstructure. This is due to the fact that large variations in the properties may occur between samples of different manufacturers. Hence more than fifty different samples in liquid and powder form were investigated. This involved the determination of pyruvate and acetate content for all the samples by means of enzymatic analysis and Comparison with results from1H NMR spectroscopy. In addition, the contents of the side groups are for the first time given in mass and molar percentages.Low angle and multi‐angle laser light scattering as well as viscometry were employed for the determination of the steric microstructure. Here it was ascertained that preliminary treatment of the sample has a crucial influence on the results of light scattering. A method of sample preparation was therefore devised which is aimed at avoiding the formation of microgels and preserving the structure of the native. xanthan. In addition, xanthan is used to illustrate a novel procedure which enables very readily interpretable Zimm plots to be obtained from one individual reading over a few minutes. In a comparison of the scattering curve extrapolated to c=0 with calculated model curves for semiflexible rods, the structure of native xanthan was determined to be more rigid than corresponds with the exponents of previously published [η]‐Mwrelatio

ISSN:0258-0322    

DOI:10.1002/masy.19920610107

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe characterization of supermolecular structures in polymer solutions by static light scattering requires an improved analysis of the scattering curves. A comparison of the experimental curves with model calculations for various basic structure types in a scaled plot offers the possibility to extend the range of a reliable determination of the structural parameters to particle sizes up to 500 nm. The influence of the polydispersity and problems of an unambiguous interpretation are discussed. Especially, a closed analytical expression for the scattering function of polydisperse systems of spheres with a Schulz‐Zimm distribution of radii was derive

ISSN:0258-0322    

DOI:10.1002/masy.19920610108

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractBinding isotherms of poly(styrenesulfonate) with hydrogen and selected alkali ions have been determined by dialysis equilibrium and dye spectroscopy, employing Pb2+, Mg2+, and Ca2+as the competing divalent ions. The observed degrees of counterion binding, Θz, defined as the number of bound counterfoils of valencezper poly ion site‐group, agree quite well with those predicted by Manning's two variable theory. The binding preference follows the order Cs+>Rb+>K+>Na+>H+>Li+, indicating that the binding process is of a territorial nature. Independently performed light scattering measurements show that a plot of the radius of gyration,>Sz>, against the actual polyion charge gives a sigmoidal curve. This result is taken to indicate that (1) a polyion is, in general, not completely neutralized in the Θ‐state and that (2) a polyion may be not fully stretched when the polyion charge density is la

ISSN:0258-0322    

DOI:10.1002/masy.19920610109

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractIn this paper we present the small angle neutron scattering characterization of two polyisoprene and one poly(ethylenepropylene) star polymers in solution. In the limit of low scattering vector,Q, and low concentration, φ, the molecular characteristics were determined. The molecular weights obtained are in good agreement with light scattering data. Deviations in second virial coefficients are due to a difference in solvent quality. Radii of gyration of the stars are well determined by the use of Kratky plots as is shown by the good agreement with average values of Zimm and Guinier analysis. Additionally, some thermodynamic properties were investigated in dilute and semidilute solutions. We have found that the concentration dependence of the osmotic compressibility is influenced by an expected step at the overlap concentration in both concentration regions

ISSN:0258-0322    

DOI:10.1002/masy.19920610110

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractTwo methods, the H2O/D2O‐analysis and the Coupling‐Particle‐Size‐Distribution(PSD)‐Technique, to determine the distribution of the density and the sire of sub‐micron particles by means of an ultracentrifuge, are outlined. Either of them base only on Stokes' equations and on Mie's light scattering theory. Because of the possibility to measure seven samples simultaneously and to raise the rotor speed exponentially from 0 to 40,000 rpm, particle diameters from 10 to 3000 nm can be measured at high resolution. The H2O/D2O‐analysis supplies a density distribution and also a size distribution, provided the sample is chemically homogeneous. The Coupling‐PSD‐Technique allows to determine highly resolved size distributions of extremely broad distributed dispersions by only one single run. Several examples applying either

ISSN:0258-0322    

DOI:10.1002/masy.19920610111

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper describes the deformation of gels in a centrifugal field leading to a continuous equilibrium. A gel is considered to be a binary mixture of cross‐linked polymer and solvent and is assumed to remain isotropic during the deformation. From the equation for the osmotically effective pressure, called swelling pressure, the thermodynamic properties of a gel can be calculated. For highly swollen gels the expression of Svedberg and Pedersen is obtained. It is shown that the complete concentration dependence of the swelling pressure in the concentration range of the maximally swollen gel up to that at the cell bottom can be measured in a single equilibrium experiment. The homogeneity of weakly cross‐linked gels can be examined by means of the method described. Soluble parts which are not incorporated into the polymer network can also be detected if they are present. From the swelling pressure‐concentration curves it is possible to derive the thermodynamic properties of the physically crosslinked gelatin/water gels that were investigated. These gels can be described by means of a slightly modified Flory‐Huggins equation with an interaction parameter χw in the weight fraction scale, which depends linearly on concentration. The interaction parameters show a dependence on concentration which is explained by an increased branching and crosslinking of the polymer with increasing initial polymer concentration of the gels. At low initial polymer concentration, the primary chains have to aggregate to build up relatively long chains between the network junctions. The static shear modulus G which can be calculated from the network term has the same order of magnitude as the real part of the complex shear modulus which is measured at low f

ISSN:0258-0322    

DOI:10.1002/masy.19920610112

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY