Characterisation of hollow Russian doll microspheres

Abstract

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 ironsilica 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.

An investigation into the preparation of poly(1‐methylpyrol‐2‐ylsquaraine) particles

“…Multiple reactions run at this reactant concentration routinely returned PMPS yields of 50 g per reaction, equivalent to the initial weight of squaric acid used. The difference between PMPS particles produced from a 35‐mmol/L reaction and those produced from a 175‐mmol/L reaction can be, respectively, observed in comparison of images in the 2005 Lynch et al paper, which were uniformly 1.3 μm in diameter, and those reported in the 2010 Begum et al paper, which were 1.9 μm (diameter) with a distribution of ±0.45 μm, as indicated in Table . These particle size analyses were undertaken using multiple electron microscopy images of the PMPS particles.…”

The uptake of metal elements into poly(1-methylpyrrol-2-ylsquaraine) particles and a study of their porosity

“…Previous SEM images (Begum et al, 2010;Lynch et al, 2005), plus the image in Figure 1, indicate that the surface of PMPS particles is relatively featureless. This is also evident in Figure 4 where little can be gained on the size and shape of the pore openings.…”

“…Ultrathin slices of PMPS particles in resin were prepared according to the literature (Begum et al, 2010). The staining solution used was 30% uranyl acetate in methanol; stained for 7 minutes and then 7 minutes in Reynolds lead citrate.…”

“…Mention of the polysquaraine made from 1 H -pyrrole (or its derivatives substituted in the 3- or 4-position) in the literature (Binda et al., 2009; Chenthamarakshan and Ajayaghosh, 1998a; Chenthamarakshan et al., 1999a; Hasegawa et al., 2009; Ko et al., 2011; Lu et al., 2010a,b, 2013; Triebs and Jacob, 1965, 1966) is about equal (in terms of numbers of articles) to mention of the polysquaraine made from 1-methylpyrrole (Begum et al., 2010; Courgneau et al., 2013; Lynch et al., 2001, 2005, Lynch, 2011; Sant’Ana et al., 2006; Spicer et al., 2006; Triebs and Jacob, 1965, 1966; Yu et al., 1990), with both limited by the fact that (without the aid of 3-position substituted long alkyl chains on the pyrrole groups to aid solubility) they can best be described as ‘black intractable powders’. Irrespective of this, poly(1-methylpyrrol-2-ylsquaraine) (PMPS) particles have been studied for third-order nonlinear optical properties (Yu et al., 1990), both electrical conduction (Sant’Ana et al., 2006) and electrical insulation properties (Lynch et al., 2001); utilized for their size and shape to produce hollow silica particles (Lynch et al., 2005) and core-shell particles (Begum et al., 2010), used as support particles for the addition of ammonium phosphate in polymer fibres (Spicer et al., 2006), and used as an odour adsorbent agent (Courgneau et al., 2013). In the article reporting that PMPS particles could be used to produce core-shell Fe 2 O 3 @SiO 2 particles (Begum et al., 2010), where the Fe 2 O 3 resided inside the silica shells as concentric shells or, as it was referred to in that article as hollow Russian doll microspheres, it was inferred that PMPS particles were porous.…”

Pyrrolyl Squaraines–Fifty Golden Years

“…This is best demonstrated by PMPS whose particles are collected as spheres with diameters of 1.3-4 μm [26,44]. These particles can be used as sacrificial templates to produce hollow silica shells [26,44] and hollow silica shells containing metal oxides [44]. This is possible because PMPS particles not only adsorb the silica precursor, tetraethoxysilane, into their outer layers but they also adsorb metal ions deep inside their internal porous network [92].…”