Correcting for a Density Distribution: Particle Size Analysis of Core–Shell Nanocomposite Particles Using Disk Centrifuge Photosedimentometry

Abstract

Abstract. Many types of colloidal particles possess a core-shell morphology. In this paper we show that, if the core and shell densities differ, this morphology leads to an inherent density distribution for particles of finite polydispersity. If the shell is denser than the core, this density distribution implies an artificial narrowing of the particle size distribution as determined by disk centrifuge photosedimentometry (DCP). In the specific case of polystyrene/silica nanocomposite particles, which consist of a polystyrene core coated with a monolayer shell of silica nanoparticles, we demonstrate that the particle density distribution can be determined by analytical ultracentrifugation and introduce a mathematical method to account for this density distribution by reanalyzing the raw DCP data. Using the mean silica packing density calculated from small-angle xray scattering, the real particle density can be calculated for each data point. The corrected DCP particle size distribution is both broader and more consistent with particle size distributions reported for the same polystyrene/silica nanocomposite sample using other sizing techniques, such as electron microscopy, laser light diffraction and dynamic light scattering. Artifactual narrowing of the size distribution is also likely to occur for many other polymer/inorganic nanocomposite particles comprising a low-density core of variable dimensions coated with a high-density shell of constant thickness, or for core-shell latexes where the shell is continuous rather than particulate in nature.

DLS and zeta potential – What they are and what they are not?

“…A detailed discussion and in-depth analysis of these techniques fall out of the scope for this review although excellent literature material and technical notes are available [97][98][99]. In short, these techniques utilize high centrifugal force to deposit NPs in fractions based on density.…”

Comparison of the effects of different protocols on the particle size distribution of TiO2 dispersions

“…Due to this separation capability, DCS is able to better distinguish the signals arising from different particle sizes, whereas in a DLS system, the signal from larger particles often masks that of their smaller counterparts . One of the limitations associated with DCS is the need to have accurate density information (Bell, Minelli, Tompkins, Stevens, & Shard, 2012), which becomes increasingly challenging if particles are not pristine, e.g., due to the presence of adsorbed species on the surface of the particles (Fielding et al, 2012;Neumann et al, 2013). Recently, methods have been developed to correct density information in such cases, but this correction is only possible if certain assumptions are made, such as the amount of adsorbed species.…”

Preparation of Pickering emulsions and colloidosomes using either a glycerol-functionalised silica sol or core–shell polymer/silica nanocomposite particles

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