Characterisation of hollow Russian doll microspheres

Poly(1-methylpyrrol-2-yl)squaraine (PMPS) particles have been characterised using SEM. The PMPS particles were used as templates to prepare bare silica and iron-silica hollow spheres, which were characterised using TEM and SEM. The PMPS particles and the hollow spheres are not uniformly sized and are agglomerated. The hollow spheres with larger diameters (>900 nm) contain an internal 'Russian doll' structure. The iron-silica hollow spheres are fused to one another, and the hollow spheres have a heterogeneous wall thickness. The silica and iron silica hollow spheres both aggregate by size. There are two different size populations (for the diameter) of the bare silica and iron-silica hollow spheres. The smaller silica spheres have thinner walls compared to the larger silica hollow spheres. The larger silica hollow spheres and the iron-silica hollow spheres have similar wall thicknesses. The iron compound in the iron-silica hollow spheres has an oxidation state of 3+ and is crystalline.