Rheological properties of concentrated aqueous solutions of anionic and cationic polyelectrolyte mixtures

Rheological Properties of Aqueous Acid Solutions of Chitosan: Experiment and Calculations of the Viscometric Functions on the Basis of a Mesoscopic Model

“…Sections I and III are approximated by two straight lines (regression lines were drawn by the least square technique) representing tangents to the initial and fi nal sections of the dependence log η max = f (log C ). Both straight lines are described satisfactorily by the power function η max ~ C k , i.e., they obey the classical rheological laws of solutions of high-molecularweight compounds [28], in particular, solutions of chitosan [11][12][13]17] and other polyelectrolytes [14][15][16]. The rate of growth of viscosity with increasing C of chitosan in the solution depends thereby on the concentration range of the polymer system.…”

“…2 and 3 shows that model (2) describes fairly adequately the viscosity rheograms of acetic acid solutions of chitosan and permits determining with good accuracy the value of the highest Newtonian viscosity. (3,7,11,16,19), 10 (12, 17, 20, 23), 40 (8,13,21), and 70 mass% (4,9,14,22,25). The viscosity values are given in 10 -3 Pa·s, and the shear stresses and given in 10 -3 Pa. Figs.…”

“…are obtained mainly from concentrated solutions. For inorganic polymers, chitosan among them, the diagnostic variable of going from the mode of diluted solutions to the mode of concentrated solutions is the formation concentration of a network C e which in absolute value can exceed several times the crossover concentration C * -overlap of coiled molecules [9][10][11][12][13]. The parameter C e in combination with the concentration and gradient dependences of viscosity η permits not only estimating the features of the structure formation of solutions of polyelectrolytes, but also predicting the conditions for the formation of a polymer material, as well as its structure and properties [14][15][16].…”

“…For example, for moderately concentrated solutions (C = 3 and 4 mass%) the Newtonian fl ow remains only in the range of low log τ. When some critical values of the shear stress are reached, the solutions go over to the regime of abnormally viscous fl ow (the region of structural viscosity), i.e., their η decreases with increasing τ (curves [5][6][7][8][9][10][11][12][13][14]. For concentrated solutions of chitosan (C = 5 and 6 mass%) log η decreases throughout the range of shear stresses (curves [15][16][17][18][19][20][21][22].…”

“…In this case, the mass transfer is realized by means of translational movement of coiled macromolecules independent of one another. Section III (C > C e ) is associated with the polymer solution fl ow by the reptation mechanism, according to which the possibility of independent movement of macromolecules disappears [11,13,25].…”