Spherical polyelectrolyte block copolymer micelles: Structural change in presence of monovalent salt

Abstract

Spherical polyelectrolyte block copolymer micelles were investigated as a function of added NaCl salt concentration using Small-Angle Neutron Scattering (SANS) and Light Scattering (LS). The micelles are formed by the self-association of charged-neutral copolymers made of a long deuterated polyelectrolyte moiety (NaPSS(d))251 and a short hydrophobic moiety (PEP)52. In presence of salt, the core shape and the aggregation number of the micelles are not affected. The hydrodynamic radius of the micelle is found to be identical to the radius of the whole micelle deduced from neutron scattering and thus the hydrodynamic radius is a valid measure of the corona thickness. At the lowest salt concentrations investigated the thickness of the corona, R(s), remains essentially constant and a contraction is observed above an added-salt concentration c(s) of 2 x 10(-2) M where this crossover concentration corresponds to the average ionic strength of the free counterions in the corona. The contraction takes place while maintaining a rod-like behavior of the chains at short scale and obeys to: R(s) approximately c(s)(-0.18). The exponent 0.18 suggests an electrostatic persistence length proportional to the Debye screening length.

Ionic strength dependence of polyelectrolyte brush thickness

“…Although the predicted values of exponents are asymptotic (expected for very long chains N → ∞), the assumption l p ≃ r D and the corresponding value of exponent −3/7 seem to be more consistent with existing experimental data[13, 12, 14, 15, 16, 17] on PE brushes.…”

“…The theoretical value of exponent −1/3 was found to be in reasonable agreement with experiments [11, 12, 13, 14, 15, 16, 17] and computer simulations[18, 19]. …”

“…The crossover salt concentration $c_s^{\mathit{III}}$ (end of plateau) does not correspond to the boundary between counterion and salt dominated regimes of osmotic pressure (see Eq 10). Unfortunately, the accuracy of the available data[13, 12, 14, 15, 16, 17] does not allow one to discriminate between exponents −1/3 and −3/7 of the salt dependence of brush thickness H ( c s ).…”

Nanoscopic Polymer Particles with a Well‐Defined Surface: Synthesis, Characterization, and Properties

“…[3,4] Colloidal particles of type ii) have also been prepared by dissolution of block copolymers in suitable solvents. [61][62][63][64][65][66][67][68][69][70] This leads to the formation of micelles with a hydrophobic core and a hydrophilic shell. If the hydrophilic block consists of polyelectrolyte chains the resulting structure may be described by Figure 2 in good approximation.…”

Polyelectrolyte Block Copolymers

“…4 It was reported that at low added salt concentration, the PSSA polyelectrolyte shell in the PEE-b-PSSA diblock examined has typical features of a polymer brush. 79,81,82 The scaling of corona chain dimensions has been compared with previous results and the predictions of scaling theories. Guenoun and coworkers suggest that changes in aggregation number depend on copolymer asymmetry 79 -an increase in association number p has been observed for the symmetric diblock studied by Forster et al, whereas p decreases for a highly asymmetric diblock.…”