Rheology of polyacrylate systems depends strongly on architecture

Abstract

The relation between polymer architecture of polyacrylic acid (PAA) derivatives and the rheological properties is examined in aqueous systems with and without surfactant. The capability of PAA and its derivates to swell above a critical pH, due to the ionization of the acrylic acid groups, gives completely different properties at low and high pH, both for cross-linked and linear polymers.Four different PAA derivatives of different nature were studied. Two versions are chemically cross-linked and two are linear. In two versions, there exist both long and short hydrophobic groups, while in the other two versions, only short hydrophobic groups are present. The role of chemical cross-linking and of long hydrophobic groups, giving a physical cross-linking, is emphasized. The pH-dependent sol-gel transition observed above a certain polymer concentration, as well as the magnitude of the shear viscosity, is strongly affected by the modification of the polymer architecture. Chemical cross-linking has a very large effect on the sol-gel transition induced by increasing the pH, while physical cross-linking, due to the presence of long hydrophobic groups, plays a more moderate role and is more pronounced in the linear PAA derivatives.It was also found that the onset of polymer swelling occurs at a higher pH for the cross-linked versions of the polymers and for the polymers with long hydrophobic groups. The swelling capacity of the PAA derivatives at low pH, when associated with anionic surfactant, was also explored. The results show a similar rheological behavior of the solutions when pH is increased above 6.5 as when anionic surfactant is added above a certain concentration.

Stabilization of Palygorskite Aqueous Suspensions Using Bio-Based and Synthetic Polyelectrolytes

“…6.5, the polymer is extended, and the solutions containing 1.0 wt % polyacrylate are very viscous, due to the high molecular weight of the polymer and the formation of an entangled polymer network. At low pH values, the polymer collapses, and the solution viscosity is very low, approaching that of water [ 38 ].…”

“…For the HM-PAA, an apparent better performance at pH 12 was observed, where the polymer is extended and can interact with the clay particles; specifically, two homogeneous suspensions using ultrasonication and high-speed homogenization were obtained. This polymer possesses hydrophobic modification, which leads to a shift in the expansion (less expanded) of the polymer chain [ 38 ]; this may explain the poor stabilization effect observed for lower pH values.…”

Improving Colloidal Stability of Sepiolite Suspensions: Effect of the Mechanical Disperser and Chemical Dispersant

“…These results can be explained by two factors: the pKa of the polymer is higher than that of the other three dispersing agents studied, ca. 5.8 [31]; secondly, the polymer possesses hydrophobic modification, which leads to a shift in the expansion of the polymer chain [37]. These two factors can explain the poor stabilization effect observed for low pH values, having been typically observed suspension gelation with time, and a slightly better performance at pH 12, where the polymer is fully ionized and extended, being able to interact and stabilize the clay particles.…”

Viscosity of Polyelectrolyte Surfactant Complexes—The Importance of the Choice of the Polyelectrolyte Seen for the Case of PDADMAC Versus JR 400

“…Some PESCs show a remarkable change in viscosity at relatively low concentrations ,− similar to but usually not quite as strong as in systems with hydrophobically modified polymers. − For example, the addition of a number of different anionic surfactants to 1 wt % semidilute aqueous solutions of cationically modified hydroxyethyl cellulose commercially available as JR 400 leads to an increase in the solution viscosity by up to 3 orders of magnitude compared to the pure PE solution, ,− which is accompanied by a richly changing microstructure . A maximum of viscosity is reached with an excess of PE charges, meaning that the addition of less than 1.5 wt % material to water can increase the viscosity by 4 orders of magnitude.…”