Light-Scattering Study of Polyelectrolyte Complex Formation between Anionic and Cationic Nanogels in an Aqueous Salt-Free System

Abstract

We studied complex formation in an aqueous salt-free system (pH approximately 3 and at 25 degrees C) between nanogel particles having opposite charges. Anionic gel (AG) and cationic gel (CG) particles consist of lightly cross-linked N-isopropylacrylamide (NIPA) copolymers with 2-acrylamido-2-methylpropane sulfonic acid and with 1-vinylimidazole, respectively. The number of charges per particle was -4490 for AG and +20 300 for CG, as estimated from their molar masses (3.33 MD for AG and 11.7 MD for CG) by static light scattering (SLS) and their charge densities (1.35 mmol/g for AG and 1.74 mmol/g for CG) by potentiometric titration. The complexes were formed through the addition of AG to CG and vice versa using a turbidimetric titration technique. At the endpoint of the titration, the aggregate formed was a complex based upon stoichiometric charge neutralization: CG(n)()(+) + xAG(m)()(-) --> CG(n)()(+) (AG(m)()(-))(x)() where x = (n)()/(m)(). At different stages of the titration before the endpoint, the resulting complexes were examined in detail using dynamic light scattering, SLS, and electrophoretic light scattering (ELS). The main results are summarized as follows: (i) When AG with a hydrodynamic radius (R(h)) of 119 nm is added to CG (R(h) approximately 156 nm), the (R(h)) of the complex size decreases from 156 to 80 nm. (ii) In contrast to this (R(h)) change, the molar mass increases from 11.7 MD to 24 MD with increasing amounts of added AG. (iii) Upon addition of CG to AG, the complex formed has the same size ((R(h)) approximately 80 nm) and the same molar mass (55 +/- 2.5 MD) until 55 +/- 5% of AG has been consumed in the complexation. To understand these results, we used the following two models: the random model (RM), in which the added AG particles uniformly bind to all of the CG particles in the system via a strong electrostatic attraction, and the all-or-none model (AONM), in which part of the AG particles in the system preferably bind to the added CG particles to neutralize their electric charges but the other AG particles are uncomplexed and remain in the system. The complex formations upon addition of AG to CG and CG to AG were elucidated in terms of RM and AONM, respectively.

Non-coalescence of oppositely charged droplets in pH-sensitive emulsions

“…Immediate heterocoagulation occurs when the plain microgel dispersions M1 and M2 are mixed, as it is expected for oppositely charged colloidal particles (41)(42)(43). Similarly, excess free microgels in the continuous phase of the emulsions also flocculate when these two emulsions are mixed; however, the stability of the mixed emulsion droplets is not reduced.…”

Surface-active amphiphilic poly[(2-acrylamido-2-methylpropanesulfonic acid)-co -(N -isopropylacrylamide)] nanoparticles as stabilizer in aqueous emulsion polymerization

“…The work reported in the present article aimed to prepare and copolymerize NIPAm as hydrophobic monomer with AMPS as ionogenic monomer in the presence of MBA as crosslinker. A NIPAm/AMPS microgel was previously prepared in the presence of dodecylbenzene sodium sulfonate as emulsifier at an AMPS/NIPAm molar ratio of 79.2/18.8 . Also, a series of random copolymers of NIPAm and sodium 2‐acrylamido‐2‐methyl‐1‐propanesulfonate were synthesized by free radical copolymerization in dimethylformamide as a solvent .…”

A novel route to prepare highly surface active nanogel particles based on nonaqueous emulsion polymerization

“…The TEM analysis indicates that both NIPAm/AMPS nanoparticles and microparticles occurred during the preparation. Surface activity of the NIPAm/AMPS nanogels Although NIPAm/AMPS microgel was previously prepared in the aqueous emulsion polymerization in the presence of dodecylbenzene sodium sulfonate as emulsifier at NIPAm/AMPS mol ratio (79.2/18.8) [21] , very little is known about their surface activity and interfacial behavior in water or organic solvent. Although knowledge of surface and interfacial properties is important for the application of nanogels and microgels in dispersion and emulsification, not too many publications are dealing with this topic because of the complexity of describing interfacial and surface properties.…”