Electroacoustic Spectroscopy of Nanoparticle-DopedHydrogels.

This paper probes the nanoparticle(NP) interaction with hydrogelsusing electroacoustic spectroscopy at MHz frequencies. We measureddynamic electrophoretic mobility spectra of silica NPs in polyacrylamidegels for a variety of NP sizes and gel concentrations. The spectraare exquisitely sensitive to NP entrapment, size, and charge as wellas to gel rheology and gelation kinetics. For NPs that are large comparedto the gel mesh size, many of these influences can be quantified usingelectrokinetic theory, which furnishes the apparent NP ζ-potentialand a complex gel shear modulus at MHz frequencies. The methodologyprovides new insights into the NP–hydrogel interaction, sinceit noninvasively probes the nanostructure and the combined influencesof particle and gel properties. Electroacoustic spectroscopy may thereforebe a valuable new tool for characterizing soft nanocompositesonethat complements other noninvasive methods, such as bulk rheometryand microrheology. [ABSTRACT FROM AUTHOR]