Water structure change-induced expansion and collapse of zwitterionic polymers surface-grafted onto carbon black

We demonstrate the expansion and collapse of surface-grafted zwitterionic polymer brushes in water caused by the addition of urea. We hypothesize that at low urea concentrations, this is an effect of an ion-dipole interaction between urea and the polymer, and at high urea concentrations, an effect of a change in water structure causing change in solvation of the brushes and hence a change in the dipole-dipole interaction, and that it is analogous to the effects of urea on protein stability.