1 research outputs found
Correcting for a Density Distribution: Particle Size Analysis of Core–Shell Nanocomposite Particles Using Disk Centrifuge Photosedimentometry
Many types of colloidal particles possess a core–shell
morphology.
In this Article, 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 X-ray 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