Abstract
The poly(acryloyloxyethyl trimethyl ammonium chloride–co–acrylamide), P(DAC-AM), is a kind of cationic polyelectrolyte usually applied in a solution form, and its performance is affected by its structure and the environment where it is used. In particular, its viscosity properties in salt solutions are directly related to its efficacy in various applications, and the performance is one of the most important solution properties. Therefore, in this paper, the effects of the salt concentration and valence of seven kinds of inorganic salts, NaCl, LiCl, KCl, MgCl2, AlCl3, Na2SO4, and Na3PO4, on the values of apparent viscosity (ηa) of P(DAC-AM) samples with cationicity of 10%, 50%, and 90%, and intrinsic viscosity ([η]) of 5, 10, and 15 dL/g were investigated. The ηa was determined using a rotational viscometer. The interaction mechanism between the polymers and salt ions was also investigated. The results showed that depending on the salt concentration, the ηa firstly decreased sharply to the inflection point which indicated the minimum volume of the molecule shrinking, and then either maintained the value unchanged or increased. The salt concentration corresponding to the inflection point decreased with the increase of the salt ion valence but with the reduction of the cationicity of the polymer. The ηa at the inflection point increased as the [η] of the polymer grew. This indicated that the salt concentration and the salt ion valence had a notable impact on the stretch of the cationic polymer molecule in the salt solutions. It was discovered that the phenomenon of the increase of the ηa of P(DAC-AM) samples in the multivalent salt solutions after the inflection point was caused by not only the increase of the ηa of the complexes formed from the pure salts, but also the viscosity resistance of the charge and volume between the polymer molecules and salt ions, as well as the complexes themselves. The linear relationship between the increased ηa and the salt concentration, representing the interaction both among the complexes themselves and between the polymer and complexes, was obtained. Furthermore, the interaction model between the salt ions and P(DAC-AM) molecules in a wide range of salt concentrations was illustrated.
Highlights
Polyelectrolyte is a kind of water-soluble polymer, dissolved in the form of macromolecular solution and releasing a large amount of counter ions which makes it become the charged colloidal particle
On the basis of the hypothesis, it could be speculated further that if the change of residual values of ηa of the P(DAC-AM) samples in the multivalent salt solutions, after deducting the ηa of the corresponding pure salt solutions, remained unchanged, it would verify that these increases of ηa after the inflection point were completely caused by the formation of salt complexes [38,39] and the increase of their concentration
The ηa of monovalent salt solutions were unchanged or increased a little, but the ηa of multivalent salt solutions increased linearly with salt concentration. These might verify the formation of complexes in the multivalent salts themselves resulting in the increase of the ηa of salt solutions [38,39]
Summary
Polyelectrolyte is a kind of water-soluble polymer, dissolved in the form of macromolecular solution and releasing a large amount of counter ions which makes it become the charged colloidal particle. The effect of the trivalent salt ion (Al3+ ) on the viscosity property of polymers in salt solutions was mentioned in reports [13], only the model of the interaction between the polymer and monovalent or bivalent salt ions was established [20,21,22]. This study described the viscosity properties of the polyelectrolyte solutions with different cationicity and molecular weights, but their interaction with salt was not mentioned. For the P(DAC-AM) samples with serial cationicity and molecular weights (i.e., [η]), there had been rare studies systematically reporting their viscosity properties in different kinds of salt solutions. The results could provide the theoretical and experimental basement for the research on other properties, theoretical computation of their salt solutions, and the practical application of P(DAC-AM) samples with serial cationicity and [η]
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