Protocol more accurately analyzes thermo-rheological behavior of associative polymers

The complex temperature dependences of associative polymers make it difficult to study their dissociation kinetics and chain dynamics.

Li et al. developed a new protocol to analyze the thermo-rheological behavior of poly(vinyl alcohol) (PVA) and borax aqueous solution, an associative polymer, where the hydrolysis of borax yields borate ions that crosslink the PVA chains.

The authors examined the linear viscoelastic relaxation of the PVA and borax solution above the entanglement concentration. Analyzing the sticker dissociation and chain relaxation processes independently allowed them to better understand the relaxation mechanism of the reversible gels. They found they could consistently determine the activation energy for sticker dissociation by analyzing data from the ion dissociation process.

The protocol often used in previous studies of associative polymers entailed determining the activation energy of sticker dissociation using data from the terminal relaxation process. However, these findings suggest focusing on the terminal relaxation process can be misleading for associative polymers that have an association energy on the same order of their thermal energy.

For these associative polymers, the terminal relaxation process depends on the chain relaxation mechanism, which changes with temperature. The authors believe focusing on the ion dissociation process instead provides a more accurate activation energy for sticker dissociation.

“This study paves a pathway toward reliable analysis of the thermo-rheological complexity of associative polymers,” said author Quan Chen.

The authors will attempt to extend this analyzing protocol to other associative polymers.

Source: “Thermo-rheological complexity of poly(vinyl alcohol)/borax aqueous solutions,” by Jingjing Li, Xiao Cao, Yonggang Liu, and Quan Chen, Journal of Rheology (2020). The article can be accessed at https://doi.org/10.1122/8.0000043 .