Biominerals exhibit morphologies, hierarchical ordering and properties that invariably surpass those of their synthetic counterparts. A key feature of these materials, which sets them apart from synthetic crystals, is their nanocomposite structure, which derives from intimate association of organic molecules with the mineral host. We here demonstrate the production of artificial biominerals where single crystals of calcite occlude a remarkable 13 wt% of 20 nm anionic diblock copolymer micelles, which act as 'pseudo-proteins'. The synthetic crystals exhibit analogous texture and defect structures to biogenic calcite crystals and are harder than pure calcite. Further, the micelles are specifically adsorbed on {104} faces and undergo a change in shape on incorporation within the crystal lattice. This system provides a unique model for understanding biomineral formation, giving insight into both the mechanism of occlusion of biomacromolecules within single crystals, and the relationship between the macroscopic mechanical properties of a crystal and its microscopic structure.

Physical gelation by block copolymer worms can be explained in terms of multiple inter-worm contacts using percolation theory, suggesting that worm entanglements are irrelevant in this context.

RAFT dispersion polymerization is used to prepare diblock copolymer nano-objects using a poly(methacrylic acid) macromolecular chain transfer agent (PMAA macro-CTA) as the steric stabilizer and AIBN initiator at 70 °C. The core-forming block is a 1:1 alternating copolymer comprising styrene (St) and N-phenylmaleimide (NMI), and the continuous phase is an ethanol/1,4-dioxane mixture. The 1,4-dioxane cosolvent is essential for this formulation because it aids solubilization of the NMI comonomer within the growing diblock copolymer micelles. Even so, kinetic studies reveal a significant retardation effect once micellar nucleation has occurred. More importantly, the relatively high glass transition temperature of the P(St-alt-NMI) core-forming block (T g = 219 °C) has an interesting influence on the evolution of the copolymer morphology with conversion. At the polymerization temperature of 70 °C, this alternating copolymer is so stiff that 2D lamellae are formed, rather than the vesicular phase that is commonly observed for other RAFT dispersion polymerization formulations. A detailed phase diagram is reported for a series of PMAA79–P(St-alt-NMI) x diblock copolymers, which enables the reproducible synthesis of pure spheres, worms, and the lamellar phase. It is also noteworthy that the worm phase region is unusually broad compared to previous polymerization-induced self-assembly (PISA) formulations. The worms are relatively short and stiff but form free-standing gels above 9% w/w. Increasing the mean degree of polymerization of the core-forming block leads to stronger, more brittle gels. On transferring the diblock copolymer nano-objects into water via dialysis, highly negative zeta potentials are observed above the pK a of the PMAA stabilizer chains, regardless of the copolymer morphology. Thermogravimetric analyses indicate that these diblock copolymer nano-objects have relatively high thermal stabilities, with little or no mass loss being observed on heating in air up to 347 °C.

Manipulation of inorganic materials with organic macromolecules enables organisms to create biominerals such as bones and seashells, where occlusion of biomacromolecules within individual crystals generates superior mechanical properties. Current understanding of this process largely comes from studying the entrapment of micron-size particles in cooling melts. Here, by investigating micelle incorporation in calcite with atomic force microscopy and micromechanical simulations, we show that different mechanisms govern nanoscale occlusion. By simultaneously visualizing the micelles and propagating step edges, we demonstrate that the micelles experience significant compression during occlusion, which is accompanied by cavity formation. This generates local lattice strain, leading to enhanced mechanical properties. These results give new insight into the formation of occlusions in natural and synthetic crystals, and will facilitate the synthesis of multifunctional nanocomposite crystals.

A simple, one-pot method is presented whereby gold nanoparticles coated with a zwitterionic diblock copolymer are incorporated within single crystals of calcite. This may provide a versatile alternative to dyeing crystal with organic molecules and could be extended to create a series of new nanocomposite crystals with novel properties.

Dialkylphosphonate-functionalized and phosphonic acid-functionalized macromolecular chain transfer agents (macro-CTAs) are utilized for the reversible addition−fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate (BzMA) at 20% w/w solids in methanol at 64 °C. Spherical, worm-like, and vesicular nano-objects could each be generated through systematic variation of the mean degree of polymerization of the coreforming PBzMA block when using relatively short macro-CTAs. Construction of detailed phase diagrams is essential for the reproducible targeting of pure copolymer morphologies, which were characterized using transmission electron microscopy (TEM) and dynamic light scattering (DLS). For nano-objects prepared using the phosphonic acid-based macro-CTA, transfer from methanol to water leads to the development of anionic surface charge as a result of ionization of the stabilizer chains, but this does not adversely affect the copolymer morphology. Given the well-known strong affinity of phosphonic acid for calcium ions, selected nano-objects were evaluated for their in situ occlusion within growing CaCO 3 crystals. Scanning electron microscopy (SEM) studies provide compelling evidence for the occlusion of both worm-like and vesicular phosphonic acid-based nano-objects and hence the production of a series of interesting new organic−inorganic nanocomposites.

Scalable preparation of micrometer-sized diblock copolymer particles exhibiting complex internal structure is achieved by RAFT-mediated polymerization-induced self-assembly (PISA).

We report a new nonaqueous polymerization-induced self-assembly (PISA) formulation based on the reversible addition–fragmentation chain transfer (RAFT) dispersion alternating copolymerization of styrene with N-phenylmaleimide using a nonionic poly(N,N-dimethylacrylamide) stabilizer in a 50/50 w/w ethanol/methyl ethyl ketone (MEK) mixture. The MEK cosolvent is significantly less toxic than the 1,4-dioxane cosolvent reported previously [YangP.YangP.Macromolecules20134685458556]. The core-forming alternating copolymer block has a relatively high glass transition temperature (Tg), which leads to vesicular morphologies being observed during PISA, as well as the more typical sphere and worm phases. Each of these copolymer morphologies has been characterized by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) studies. TEM studies reveal micrometer-sized elliptical particles with internal structure, with SAXS analysis suggesting an oligolamellar vesicle morphology. This structure differs from that previously reported for a closely related PISA formulation utilizing a poly(methacrylic acid) stabilizer block for which unilamellar platelet-like particles are observed by TEM and SAXS. This suggests that interlamellar interactions are governed by the nature of the steric stabilizer layer. Moreover, using the MEK cosolvent also enables access to a unilamellar vesicular morphology, despite the high Tg of the alternating copolymer core-forming block. This was achieved by simply conducting the PISA synthesis at a higher temperature for a longer reaction time (80 °C for 24 h). Presumably, MEK solvates the core-forming block more than the previously utilized 1,4-dioxane cosolvent, which leads to greater chain mobility. Finally, preliminary experiments indicate that the worms are much more efficient stabilizers for aqueous foams than either the spheres or the oligolamellar elliptical vesicles.