What Dictates the Spatial Distribution of Nanoparticles within Calcite?

Abstract

Crystallization is widely used by synthetic chemists as a purification technique because it usually involves the expulsion of impurities. In this context, the efficient occlusion of guest nanoparticles within growing host crystals can be regarded as an interesting technical challenge. Indeed, although there are various reports of successful nanoparticle occlusion within inorganic crystals in the literature, robust design rules remain elusive. Herein, we report the synthesis of two pairs of sterically-stabilized diblock copolymer nanoparticles with identical compositions but varying particle size, morphology, stabilizer chain length and stabilizer chain surface density via polymerization-induced self-assembly (PISA). The mean degree of polymerization of the stabilizer chains dictates the spatial distribution of these model anionic nanoparticles within calcite (CaCO3): relatively short stabilizer chains merely result in near-surface occlusion, whereas sufficiently long stabilizer chains are essential to achieve uniform occlusion. This study reconciles the various conflicting literature reports of occluded nanoparticles being either confined to surface layers or uniformly occluded and hence provides important new insights regarding the criteria required for efficient nanoparticle occlusion within inorganic crystals.

How Many Phosphoric Acid Units Are Required to Ensure Uniform Occlusion of Sterically Stabilized Nanoparticles within Calcite?

“…Under these conditions,b oth step lengths and kink sites are more prevalent, which facilitates nanoparticle occlusion. [18] More uniform, dense nanoparticle occlusion can be achieved at higher anionic phosphate contents (see Figure 2d-f). This is because there are now sufficient anionic groups to ensure strong binding to the crystal surface,w hich leads to nanoparticle engulfment by the advancing steps.C aCO 3 crystals precipitated in the presence of an equivalent molar concentration of each of the water-soluble macro-CTAs used in this study (e.g.…”

“…Zuschriften statistical copolymerization of the non-ionic Gmonomer with the anionic Pmonomer while targeting aconstant intermediate DP of around 50 can avoid such problems.P rior studies showed that P 32 -B 300 nanoparticles are surface-confined [18] while (P 32 -stat-G 13 )-B 300 are uniformly occluded. This is most probably because the latter stabilizer chains can adopt more conformations.…”

“…[12d] More importantly, arelatively short stabilizer chain DP is expected to restrict the conformational entropy of the stabilizer chains, [17] hence leading to weaker nanoparticle binding to the growing crystal surface and reducing nanoparticle occlusion. [18] Conveniently,…”

How Many Phosphoric Acid Units Are Required to Ensure Uniform Occlusion of Sterically Stabilized Nanoparticles within Calcite?

“…DP=100) should result in smaller nanoparticles with relatively low stabilizer surface densities . More importantly, a relatively short stabilizer chain DP is expected to restrict the conformational entropy of the stabilizer chains, hence leading to weaker nanoparticle binding to the growing crystal surface and reducing nanoparticle occlusion . Conveniently, statistical copolymerization of the non‐ionic G monomer with the anionic P monomer while targeting a constant intermediate DP of around 50 can avoid such problems.…”

“…Conveniently, statistical copolymerization of the non‐ionic G monomer with the anionic P monomer while targeting a constant intermediate DP of around 50 can avoid such problems. Prior studies showed that P 32 ‐B 300 nanoparticles are surface‐confined while (P 32 ‐ stat ‐G 13 )‐B 300 are uniformly occluded. This is most probably because the latter stabilizer chains can adopt more conformations.…”