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The thermodynamic behavior of chitosan in acidic aqueous solutions with ionic strengths between 0.04 × 10 −2 and 24.30 × 10 −2 M was investigated at 25°C. The intrinsic viscosity and other thermodynamic parameters of chitosan with the molecular weight and the degree of acetylation of 7.14 × 10 5 g mol −1 and 26%, respectively, were determined and discussed by using both classical equations (Huggins and Fedors) and a new model (Wolf). At low ionic strengths of the solvent, the highest values of the intrinsic viscosity were obtained due to the expansion of the chitosan chains. Two critical concentrations, c* (which separates the dilute-semidilute regimes) and c + (at which the dimensions of the polymer coils are considered to have shrunk to their unperturbed dimensions), were estimated, and the effect of the solvent ionic strength on their values was discussed. By increasing of the solvent ionic strength from 0.04 × 10 −2 to 24.30 × 10 −2 M, the persistence length decreased from 17.14 to 4.60 nm, suggesting an increase of the chitosan flexibility due to the decrease of repulsive potential between the polymer chains. The radius of gyration and the persistence length in the unperturbed state were determined as being 52.50 and 3.90 nm, respectively. The viscometric data were corroborated with those obtained by the zeta potential, conductivity, and turbidity measurements for the ionic strength of the solvent between 0.04 × 10 −2 and 42.25 × 10 −2 M.

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In this article, thermal-induced gelation of polyacrylonitrile (PAN) solutions in dimethylformamide was studied through rheological measurements. The entangled and non-entangled states were delimited for an overlap parameter of macromolecular coils of 2.7. In temperature sweep experiments, two types of gelation processes were identified for PAN entangled solutions at: (1) a reversible gelation in the region of low temperatures (below 15 • C) due to the formation of a crosslinked structure with a small region of order that dissolves completely in an excess of solvent, and (2) an irreversible gelation at high temperatures (above 60 • C) and this gel is insoluble in an excess of solvent, due to the formation of a chemical three-dimensional network. Physical PAN gels with good elastic properties were also obtained by the freezing and thawing method. The gel properties depend on the thermal history of the solution (freezing time, aging time, and aging temperature), its composition (concentration and molar mass of the polymer), and gelation conditions (freezing rate). The gelation was attributed to the formation of junction zones via an aggregation process between a certain number of chain segments due to attractive dipole-dipole interactions.

The viscometric behaviour of polyacrylonitrile solutions in dimethylformamide has been examined in dilute and extremely dilute regimes of concentration. For semidilute and concentrated solutions, viscoelastic properties were determined and discussed. The overlap concentration was evidenced as being the crossover of two scaling laws characterizing the entangled and nonentangled solution regimes.

In this work, we investigated the behavior of poly(dimethylsiloxane-co-diphenylsiloxane)s under good and theta solvent conditions by using turbidimetry and viscosimetry. The evolution of the optical properties as a function of the solvent quality allowed the composition of the methylbenzene/methanol mixtures at the theta point to be determined. The intrinsic viscosity was determined in good (methylbenzene) and theta (methylbenzene/methanol) solvents at T = 298 K using different approaches. The unperturbed dimension parameters were calculated and are discussed as a function of copolymer composition. The introduction of the diphenylsiloxane units into a poly(dimethylsiloxane) chain results in an increase in the unperturbed dimensions as a consequence of the decrease in chain flexibility.

The paper investigates the hydrodynamic properties of polyacrylonitrile (PAN) and poly(N-(4-carboxyphenyl)maleimide) (PMI) solutions in dimethylformamide (DMF) in comparison with PMI/PAN/DMF ternary mixtures. The experimental data obtained by viscometry have been discussed by means of two methods: first, the plots obtained with the classical Huggins equation are analyzed, and in parallel, an evaluation of the parameters given by the new Wolf model is presented. The experimental data obtained for binary polymer/solvent and ternary polymer/polymer/solvent mixtures fit well with this last method and allow the calculation of intrinsic viscosities and other hydrodynamic parameters, which provide new information about the competition between different types of interactions for polymer mixtures in solution. The compatibility of the two polymers dissolved in a common solvent is also discussed on the basis of two parameters: Δb and α, reflecting the interactions between the polymer segments and polymer/polymer miscibility, respectively. The sign of these parameters shows that the PMI/PAN blends in DMF are miscible in the range of PAN mass fraction between 0.36 and 0.75.

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