Surface charge density and diffuse layer properties of highly defined 2:1 layered silicate platelets

Abstract

Clays are not only ubiquitous in nature, but they are also used in huge quantities in a broad range of industrial applications, such as thixotropic drilling fluids, ore pelletizers, waste disposal sealants, or fillers in polymer nanocomposites. In order to model environmental processes or to design new materials on a rational base, it is of prime importance to determine and possibly modify the interfacial properties of clay platelets at the solid/electrolyte interface. In this context, the fundamental question rises how far the stoichiometric interlayer charges as determined by the composition of the silicate layer correlates with the diffuse doublelayer properties. Here, this question is addressed by means of a series of purposely synthesized sodium 2:1 layered silicates with defined composition and hence interlayer charge densities, respectively. Platelets of layered silicates of large enough diameter to perform AFM colloidal probe measurements were produced by melt synthesis. For comparison also, a natural muscovite mica has been included in this study. The diffuse layer properties in electrolyte solution have been determined by direct force measurements using the colloidal probe AFM technique and by electrokinetic measurements, respectively. We find that the diffuse layer potential decreases with increasing interlayer charge of the 2:1 layered silicates. This counterintuitive finding is attributed to ion adsorption and was further corroborated by determining the quantitative adsorption of polyelectrolytes, namely poly(amidoamine) dendrimers.

Dendrimer stabilized nanoalloys for inkjet printing of surface-enhanced Raman scattering substrates

“…An interesting follow up of this topic, is the use of AFM colloidal probe measurements to understand the effect of PAMAM deposition on surface charge density and its possible interaction with the surfactant SDS of the PS spheres. [67][68][69][70] Finally, it should be noted that the resulting paper substrates are characterized by its "biofriendliness" and relatively low-cost. In fact, the printing method used in this work, allows the preparation of hundreds of spots in a single paper sheet, where the total amount of PAMAM dendrimer and polystyrene deposited on the paper substrates represents a small fraction of the total components (<0.5% w/v).…”

“…The AFM analysis of the above paper substrates after deposition of thiram (FigureS10-B and -D) retain the topographic profile, further reinforcing the hypothesis that the conformational change of the dendrimer structure after deposition may contribute to improved SERS sensitivity. Furthermore, the deposition of the PAMAM stabilized nanoassemblies may change the surface charge density of the paper substrates previously treated with PS, due to conformational changes on the dendrimer structure after deposition[67][68][69][70].…”