Polyelectrolyte Behavior Of Diblock Copolymer Micelles Having Phosphonic Diacid Groups At The Corona

The polyelectrolyte behavior of block copolymer micelles originated from the self-assembly of poly(n-butyl acrylate)-block-poly((1-ethoxycarbonyl)vinylphosphonic diacid) (PBuA-b-PECVPD) chains was studied in detail by a combination of potentiometry, static and dynamic light scattering (SLS and DLS), small-angle X-ray scattering (SAXS), and cryo-transmission electron microscopy (cryo-TEM). In aqueous media, the hydrophilic PECVPD micelle corona bearing negatively charged phosphonic diacid groups [-P(O)(OH)2] With two distinct acid dissociation constants conferred interesting pH-, salt-, and concentration-dependent polyelectrolyte features to the system. Light scattering measurements showed the existence of three different regimes in the total scattered intensity (I-sc) and apparent hydrodynamic radius (RHapp) vs pH plots, reflecting the influence of the increase in the negative charge density at the micellar corona due to deprotonation. The conformation and interactions of polyelectrolyte chains were more strongly affected by salt addition for solutions with pH similar to 4.0. In such a case, the slope of KCp/I(q) vs q curves in SLS experiments changed from negative to positive values as the salt concentration (C-s) increased. During this transition, the variation of RHapp measured using DLS put forward the osmotic brush and salted brush regimes, the latter being characterized by a typical RHapp proportional to C-s(-0.21) scaling law. SAXS measurements revealed the core-shell structure and the electrostatic interactions between the micelles which decreased as expected upon the addition of salt. The analysis of the intensity profiles over a wide, range of concentrations showed an inhomogeneous core-shell structure with the micelle shell thickness shrinking in presence of added salt. Cryo-TEM images confirmed the spherical shape and narrow size distribution of the micellar nanoparticles.