Effect of coating nanostructure on the electrokinetics of polyelectrolyte-coated particles. Grafted vs adsorbed polymer

In this work, the electrokinetic response of nanoparticles suspensions under action alternating electric fields is analyzed for case that particles are coated with a shell polyelectrolyte. This an important field application colloidal systems, as coating necessary or even unavoidable control stability functionalization specific use. Characterization in situ not easy task, and electrokinetics can help answering question, if one goes beyond simple routine evaluation electrophoretic mobility particles, which will provide information on sign (and perhaps sort effective amount) surface charge potential, but little more. The richness rigour much more significant AC used. techniques evaluated present investigation, namely, electrophoresis dielectric dispersion. They jointly sweep several decades frequency, sensitive different manners to size core shell, thickness rigidity latter, etc. addition, distinction made between coatings soft adsorbed layer structure those grafted, ideally radially arranged (brush-like) A model first described both cases, it demonstrated brush magnifies Maxwell-Wagner (or double layer) polarization, leading elevation frequencies around MHz, very raises amplitude alpha- concentration-polarization relaxation detected distribution thicker region explains these results. Experimental investigations carried out silica spheres by PDADMAC (+) PSS (-) polyelectrolytes soft-layer case, (vinylbenzyl)trimethylammonium chloride sodium 4-vinylbenzenesulfonate monomers were polymerized (grafted) particles. results show produces expected MW mobility, mostly cationic polymer, apparently better attached electrostatic attraction negative contrast, rather monotonous decrease absolute value measured coatings, indicating inertia sets at lower because aggregation. Dielectric spectra confirm presence grafted although low-frequency logarithmic derivative permittivity proof existence aggregates, less abundant any than coatings. data also amounts charge, larger layers anionic ones. Finally, elaborated fit experimental yielding quantitative values main parameters size, overall coating, ionic permeability latter.