Interaction of pNIPAM chains with Hydrophobic ions

Fecha: 23 de Noviembre de 2023.
Hora: 12:30h a 13:30h.
Lugar: Aula A22 de la Facultad de Ciencias.

Ponente: Delfi Bastos González (Universidad de Granada).

Organiza: Grupo de Física de Fluidos y Biocoloides de la UGR.

Resumen: Poly (N-isopropylacrilamide) (pNIPAM), one of the most studied thermoresponsive polymers, undergoes a liquid-liquid phase separation in aqueous solutions above its lower critical solution temperature (LCST) around 33˚C. In this talk we will present results concerning to the formation of stable clusters of pNIPAM chains in water at temperatures above the LCST, induced by the presence of sodium tetraphenylborate, NaPh4B. The hydrophobic Ph4B− ions interact strongly with the pNIPAM chains, providing them with a net effective negative charge, which leads to the stabilization of pNIPAM clusters for temperatures above the LCST, with a mean cluster size that depends non-monotonically on salt concentration. Combining experiments with physical modeling at the mesoscopic level and atomistic molecular dynamic simulations, we show that this effect is caused by the interplay between the hydrophobic attraction between pNIPAM chains and the electrostatic repulsion induced by the associated Ph4B− ions. These results provide insight on the significance of weak associative anion−polymer interaction driven by hydrophobic interaction and how this anionic binding can prevent macroscopic phase separation. Harvesting the competition between attractive hydrophobic and repulsive electrostatic interaction opens avenues for the dynamic control of the formation of well-calibrated polymer microparticles.