Core shell particles

The formal study of core-shell particles may be traced back to the late sixties in the development of a novel sorbent of HPLC comprising porous spherical soft shells supported by fluid-impermeable glass microspheres [1]. Such ‘pellicular’ structures were found to be more stable at increasing pressures, changing column temperatures, and eluent compositions than conventional monolithic soft sorbents. Since then, many core-shell-type particles have been designed for various purposes because such composite particles exhibit the combined properties of the core and shell materials. The study of core-shell particles has expanded exponentially in the past few decades, given the variety of structures possible and the vast gamut of applications they can support (Figure 1). The composites that have been studied have been of various constituents, gross sizes, relative sizes, and morphologies (Figure 2). While the shell is almost always solid, the cores contain solids, liquids (capsules), or gases (hollow particles). These composite nanoparticle cores and shells have been in various combinations of inorganic, organic, polymeric, and crystalline materials. The entire ensembles have been nanometric or micrometric in size. The core has comprised single particles or multiple ones, and shells that have been studied have been continuous, multi-layered, or discontinuous domains. These particles themselves have been of various shapes as well.