Incorporating Diblock Copolymer Nanoparticles into Calcite Crystals: Do Anionic Carboxylate Groups Alone Ensure Efficient Occlusion?

Abstract

New spherical diblock copolymer nanoparticles were synthesized via RAFT aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA) at 70 °C and 20% w/w solids using either poly(carboxybetaine methacrylate) or poly(proline methacrylate) as the steric stabilizer block. Both of these stabilizers contain carboxylic acid groups, but poly(proline methacrylate) is anionic above pH 9.2, whereas poly(carboxybetaine methacrylate) has zwitterionic character at this pH. When calcite crystals are grown at an initial pH of 9.5 in the presence of these two types of nanoparticles, it is found that the anionic poly(proline methacrylate)-stabilized particles are occluded uniformly throughout the crystals (up to 6.8% by mass, 14.0% by volume). In contrast, the zwitterionic poly(carboxybetaine methacrylate)-stabilized particles show no signs of occlusion into calcite crystals grown under identical conditions. The presence of carboxylic acid groups alone therefore does not guarantee efficient occlusion: overall anionic character is an additional prerequisite.

Model Anionic Block Copolymer Vesicles Provide Important Design Rules for Efficient Nanoparticle Occlusion within Calcite

“…[21][22][23][24] There is no doubt that the nanoparticle surface chemistry dictates their occlusion. [25][26][27] However, the precise design rules required for efficient nanoparticle occlusion within inorganic crystals have not yet been elucidated. Appropriate surface functionality and optimal stabilizer surface density appear to be important parameters for optimizing the extent of nanoparticle occlusion.…”

Stimulus-responsive non-ionic diblock copolymers: protonation of a tertiary amine end-group induces vesicle-to-worm or vesicle-to-sphere transitions

“…25 Over the past decade or so, this living radical polymerisation technique has been utilised by many research groups for the convenient synthesis of a wide range of block copolymer nanoparticles via polymerisation-induced self-assembly (PISA) at relatively high copolymer concentration (10-50% w/w). [26][27][28][29][30][31][32][33][34][35][36][37] In a typical PISA protocol, a macromolecular chain transfer agent (macro-CTA) is chain-extended using either RAFT emulsion polymerisation 33,34,[38][39][40][41] or RAFT dispersion polymerisation. 26,35,[42][43][44][45] Self-assembly occurs in situ as the growing second block becomes insoluble in the reaction medium.…”

Efficient occlusion of oil droplets within calcite crystals

“…49 However, overall anionic character is retained, which is essential for nanoparticle occlusion. 50 It is important to establish that the nanoemulsion droplets remain stable on the time scale of this reaction (24 h). The z-average diameter of the nanoemulsion droplets is relatively constant at pH 9 in the presence of Ca 2+ ions as determined by dynamic light scattering (DLS) ( Fig.…”