Formation and Stability of Soluble Stochiometric Polyelectrolyte Complexes: Effects of Charge Density and Polyelectrolyte Concentration

Abstract

Sterically stabilized polyelectrolyte complexes with stoichiometric composition between oppositely charged synthetic polyelectrolytes carrying strong ionic groups and significantly different molecular weights have been prepared. Poly(sodium styrenesulfonate) (NaPSS) was used as polyanion and a range of brush copolymers with various molar ratio (X = 1, 0.75, 0.5, 0.25) of the poly-methacryloxyethyl trimethylammonium chloride poly(METAC) and the nonionic poly(ethylene oxide) methyl ether methacrylate poly(PEO₄₅MEMA) were used as polycations. Formation and stability of PECs have been investigated by dynamic and static light scattering (LS), turbidity and electrophoretic mobility measurements as a function of polyelectrolyte solution concentration and charge density of the cationic polyelectrolyte. The data obtained suggest that the PEO₄₅- rich systems, NaPSS/PEO₄₅MEMA:METAC-25 and NaPSS/PEO₄₅MEMA:METAC-50, form small, water-soluble, molecular complexes having nonspherical shape. The PEO₄₅–poor NaPSS/PEG₄₅MEMA:METAC-75 form turbid colloidal dispersions, whereas insoluble PECs were revealed for the PEO₄₅-free NaPSS/METAC system. The aggregation level of the PEO₄₅-poor systems is mainly controlled by the concentration of the component solutions used for the preparation of PECs, whereas the aggregation of PEO₄₅-rich nanoparticles is prevented by means of steric stabilization. Electrophoretic mobility data indicate a close to charge neutral state of the generated polyelectrolyte complexes.

Keywords:

• Bottle-brush polyelectrolyte
• dynamic light scattering
• electrophoretic mobility
• Polyelectrolyte complex
• self-assembled nanoparticles
• static light scattering
• steric stabilization
• turbidity

The authors gratefully acknowledge financial support from the Swedish Research Council (VR). The work has also been supported by the European Commission in the sixth Framework Programme under The Marie Curie Intra-European Fellowships, Contract No. MEIF-CT-2006–024997, Project PE-NANOSTRUCTURES. Joseph Iruthayaraj is thanked for fruitful discussions.

Notes

^a Data extracted from SLS measurements:^{[ 34 ]} M _w – weight averaged molecular weight, R _g – radius of gyration, B–second virial coefficient (×10⁴ cm³ mol g⁻²).

^b R _h – hydrodynamic radius, evaluated from DLS measurements, SD = ±1 nm.

^c m – electrophoretic mobility (µm cm/V s).

^#Data extracted from SLS measurements: R _g – radius of gyration, ∗– data evaluated from DLS measurements: R _h -hydrodynamic radius, SD =± 1 nm.

∗∗m – electrophoretic mobility (µm cm/V s).

Part of the special issue, Surface and Colloid Chemistry Without Borders: An International Festschrift for Professor Per Stenius on the Occasion of His 70th Birthday.