Occlusion of Sulfate-Based Diblock Copolymer Nanoparticles within Calcite: Effect of Varying the Surface Density of Anionic Stabilizer Chains.

Yin Ning,Yun-Wei Wang,Lee A Fielding,Fiona C Meldrum,Liam P D Ratcliffe,Steven P Armes

doi:10.1021/jacs.6b05563

Abstract

Polymerization-induced self-assembly (PISA) offers a highly versatile and efficient route to a wide range of organic nanoparticles. In this article, we demonstrate for the first time that poly(ammonium 2-sulfatoethyl methacrylate)-poly(benzyl methacrylate) [PSEM–PBzMA] diblock copolymer nanoparticles can be prepared with either a high or low PSEM stabilizer surface density using either RAFT dispersion polymerization in a 2:1 v/v ethanol/water mixture or RAFT aqueous emulsion polymerization, respectively. We then use these model nanoparticles to gain new insight into a key topic in materials chemistry: the occlusion of organic additives into inorganic crystals. Substantial differences are observed for the extent of occlusion of these two types of anionic nanoparticles into calcite (CaCO3), which serves as a suitable model host crystal. A low PSEM stabilizer surface density leads to uniform nanoparticle occlusion within calcite at up to 7.5% w/w (16% v/v), while minimal occlusion occurs when using nanoparticles with a high PSEM stabilizer surface density. This counter-intuitive observation suggests that an optimum anionic surface density is required for efficient occlusion, which provides a hitherto unexpected design rule for the incorporation of nanoparticles within crystals.

Highlights

Biominerals such as bones, teeth and seashells provide a wonderful demonstration of the remarkable control that organic molecules can achieve over inorganic crystal growth.[1−4] biomineralization is of considerable academic interest since it provides inspiration for the design of new synthetic organic/inorganic nanocomposite materials with superior toughness and hardness.[5−12] In this context, exploring the molecular interaction between additives and inorganic hosts to gain a better understanding of the precise biomineralization mechanism is extremely important.[13,14] this remains a formidable technical challenge
Gel permeation chromatography (GPC) studies confirmed that each macro-CTA had a relatively narrow molecular weight distribution (Mw/Mn < 1.15, see Figure S1, Supporting Information), which in principle enables the preparation of sterically stabilized nanoparticles with uniform corona thicknesses
Chain extension experiments conducted using these PSEM macroCTAs indicated high blocking efficiencies on addition of a further charge of sulfatoethyl methacrylate (SEM) monomer, which suggests a high degree of reversible addition− fragmentation chain transfer (RAFT) end-group functionalization

Summary

■ INTRODUCTION

Biominerals such as bones, teeth and seashells provide a wonderful demonstration of the remarkable control that organic molecules can achieve over inorganic crystal growth.[1−4] biomineralization is of considerable academic interest since it provides inspiration for the design of new synthetic organic/inorganic nanocomposite materials with superior toughness and hardness.[5−12] In this context, exploring the molecular interaction between additives and inorganic hosts to gain a better understanding of the precise biomineralization mechanism is extremely important.[13,14] this remains a formidable technical challenge. The PBzMA chains are likely to be slightly more solvated (and more stretched, leading to more closely packed copolymer chains in the nanoparticle cores) when grown in the 2:1 v/v ethanol/water mixture, compared to PISA syntheses conducted in pure water.[57] One reviewer of this manuscript suggested that the higher stabilizer surface density observed for PSEM73−PBzMA300 (dispersion) might be the result of a significant change in core solvation during dialysis againt water Both literature data[57] and DLS studies conducted before and after dialysis do not support this hypothesis, because only a rather small change in the intensity-average particle diameter is observed (see Figure S12). This is in good agreement with the calcite system and further suggests that an optimum stabilizer surface density is required to maximize the extent of occlusion

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES