G. Weill

Polyacrylamide in water: molecular weight dependence of 〈R2〉 and [η] and the problem of the excluded volume exponent

Abstract A commercial sample of polyacrylamide (CALGON) has been carefully purified, analysed and fractionated. With suitable care, the molecular characterization can be carried out by light scattering and viscosity measurements, without disturbances arising from microgels or aggregates. The molecular weight dependence of the radius of gyration and intrinsic viscosity are given by: 〈R 2 〉 1 2 = 7.49 × 10 − M 0.64 ( A ) [η] = 9.33 × 10 −3 M 0.75 (cm 3 /g) The value of the exponent ν = 0.64 in the 〈R 2 〉 1 2 equation has been cross-checked by a study of the asymptotic behaviour of the scattering envelope. Such a value is higher than that expected in a good solvent ( ν = 0.60) and should lead to a higher exponent in the intrinsic viscosity dependence. However, it agrees more closely with the published dependence of sedimentation and diffusion coefficients.

Optical anisotropy of a worm-like chain and its application to the determination of the persistence length in an aromatic polyamide

Abstract The optical anisotropy, as obtained from the depolarization of light scattering, has been evaluated for a worm-like chain as a function of the segment anisotropy δ 0 and of the ratio of the contour length L to the persistence length q . The comparison between the theoretical curves and the experimental data obtained for an aromatic polyamide [poly( para -phenylene terephthalamide)] in a range of DP from 7 to 30 leads to a value of q in good agreement with that calculated from other methods requiring a wider range of molecular weights.

Characterization of polyazomethines in dilute solution. Correlation between the light scattering parameters and the u.v.-visible absorption spectrum

Abstract The high values 1 (up to cm 3 g −1 ) of the refractive index increments d n d c of sulphuric and methane sulphonic acid solutions for a series of polyazomethine compounds at 546 and 628 nm are related quantitatively to the existence of a strong absorption band around 400 nm. The frequency dependence is well explained by the anomalous dispersion calculated from the decomposition of the absorption band into Gaussians. The blue shift and hypochromic effect, and the correlated decrease in d n d c , resulting from an aggregation process in methane sulphonic acid can be interpreted by a side-by-side arrangement of aggregates. This result is substantiated by a calculation of the optical anisotropy from the depolarized part of the scattered light.

Divalent paramagnetic counterions site binding in polyelectrolyte solutions. Analysis of the frequency dependence of the water protons magnetic relaxation and the characteristic parameters of “site binding”

Chemical shift and relaxation time measurements on the water protons in polyelectrolyte solutions containing divalent paramagnetic counterions have shown the existence of three types of counterions: - site bound with loss of water molecules and partial or complete release of the electrostriction in the first hydration sphere, - atmospherically trapped with no change in hydration, - free. The overall stoichiometry of the two former is in agreement with Mannings fraction of condensed counterions. A complete analysis of the frequency dependent contribution of site bound counterions to the water protons relaxation times leads us to interesting conclusions on the modifications of the first hydration shell and on the life time of site binding.

NMR and density study of Co2+ site binding by polyelectrolytes

Abstract The changes of density and chemical shifts of the water proton upon addition of CoCl2 to aqueous solutions of tetramethylammonium salts of seven polyelectrolytes (polyphosphate, maleic acid-methylvinylether alternated copolymer, polyacrylic acid, carboxymethylcellulose of substitution degree 0.98, 1.3, 2.1, 2.65) have been measured. Assuming a negligible contribution of pseudo-contact interaction to the water proton chemical shift and a constant hyperfine constant upon displacement of water molecules by other ligands, has permitted the calculation of (i) the number of water molecules released by Co2+ ions upon binding and the approximate fraction of Co2+ ions bound with loss of water, and (ii) the total volume change upon binding and the individual contributions of counterions and polyelectrolyte charged sites to this volume change. Our results are generally in agreement with those obtained using other methods.

Magnetic birefringence of polystyrene sulphonate: Molecular weight and concentration dependence

Abstract The specific Cotton-Mouton constant of water solutions of PSS-Na+ of different molecular weight have been measured at concentrations below 2% in the absence and presence of added salt. A bare persistence length q=12 A is found from the high ionic-strength molecular weight and concentration independent value. The molecular weight and concentration dependence at low ionic-strength is discussed in terms of the electrostatic contribution to the persistence length and the structure of semidilute polyelectrolyte solutions.

23Na relaxation in polyelectrolyte solutions

Abstract In order to get a better insight into the layer of “condensed” counterions, 23 Na relaxation measurements have been carried out upon progressive addition of ClNa to a solution of the tetramethyl ammonium salt of polyacrylic acid. They show that for r = Na + /TMA + r .

Three-stage melting of an annelide-type copper complex. A new type of organized phase: Tegma crystals

Abstract The solid—solid phase transition of an annlide type copper complex are described. As the temperature is raised, three different constituents of the complex successively melt. In the temperature range 77–95°C, the polyethylene oxide chains and the paraffinic tail are both in a very mobile state while the copper complex sub-units still form a two-dimensional crystalline array.

Relation between the initial slope of some electro-optic decays and the moments of the distribution of size

Abstract Several well defined average values of the rotatory diffusion constant D of a polydisperse system can be obtained using the initial slope of the free decay of different electro-optical phenomena and different degrees of orientation. The type of average depends also on the orientation mechanism. The type of average and its relation to the corresponding moments of the size distribution, which have been previously misused, are derived for rod-like and disc-like particles, different mechanisms of orientation, and two types of electro-optical effect: birefringence (or dichroism) and light scattering in an electric field. Re-examination of the agreement claimed by previous authors between averages of D measured by this technique and calculated from a distribution of size derived from electron micrographs illustrate the difficulties of the measurements at saturation of orientation, and the role of an exact knowledge of the orientation mechanism. Possible experiments are discussed. Two parameters analytical distribution functions, well suited for the expression of the differen moments appearing in the theory, are indicated.

PMR investigation of the structure of native and iodine doped polyacetylene films

Abstract The second moment of the proton magnetic resonance line of native cis - polyacetylene, thermally isomerized trans -polyacetylene, and iodine doped initially cis -polyacetylene has been measured by a pulse technique. The results differ qualitatively and quantitatively from previous reports. They are discussed in terms of the proposed crystalline structures of (CH) x .