Phosphonic Acid-Functionalized Diblock Copolymer Nano-Objects via Polymerization-Induced Self-Assembly: Synthesis, Characterization, and Occlusion into Calcite Crystals

Dialkylphosphonate-functionalized and phosphonic acid-functionalized macromolecular chain transfer agents (macro-CTAs) were 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 all be generated through systematic variation of the mean degree of polymerization of the core-forming PBzMA block when using relatively short macro-CTAs. Construction of detailed phase diagrams is essential for the reproducible targeting of pure copolymer morphologies, where these 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 dispersion 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 CaCO3 crystals. Scanning electron microscopy (SEM) studies provide convincing 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

Droplet Microfluidics XRD Identifies Effective Nucleating Agents for Calcium Carbonate

The ability to control crystallization reactions is required in a vast range of processes including the production of functional inorganic materials and pharmaceuticals and the prevention of scale. However, it is currently limited by a lack of understanding of the mechanisms underlying crystal nucleation and growth. To address this challenge, it is necessary to carry out crystallization reactions in well‐defined environments, and ideally to perform in situ measurements. Here, a versatile microfluidic synchrotron‐based technique is presented to meet these demands. Droplet microfluidic‐coupled X‐ray diffraction (DMC‐XRD) enables the collection of time‐resolved, serial diffraction patterns from a stream of flowing droplets containing growing crystals. The droplets offer reproducible reaction environments, and radiation damage is effectively eliminated by the short residence time of each droplet in the beam. DMC‐XRD is then used to identify effective particulate nucleating agents for calcium carbonate and to study their influence on the crystallization pathway. Bioactive glasses and a model material for mineral dust are shown to significantly lower the induction time, highlighting the importance of both surface chemistry and topography on the nucleating efficiency of a surface. This technology is also extremely versatile, and could be used to study dynamic reactions with a wide range of synchrotron‐based techniques

Skin-Deep Surface Patterning of Calcite

The influence of soluble additives on the growth of calcite (CaCO3) is usually rationalized based on changes in crystal morphologies, where preferential association of the additives with either the acute or obtuse steps on the crystal surface gives rise to specific growth forms. In this work we investigate the influence of a highly acidic organic additive with calcite, cp20k from the barnacle Megabalanus rosa, and demonstrate that in addition to modifying the crystal morphology, additives can be used to generate calcite crystals with different surface architectures. These can potentially rise to interesting optical effects that may be important in applications such as in coatings and paints. These surface features form during dissolution/reprecipitation at the crystal surface during the incubation of crystals in solution, and confocal fluorescence microscopy confirmed they are limited to the surface of the crystal only. The surface patterning can also be tuned using alternative additives, mixtures of additives and by varying the solution conditions. Notably, we also show that surface structures can be used to determine the mode of interaction of additives with the microscopic surface steps under conditions where only minor changes in morphology have occurred

The role of phase separation and related topography in the exceptional ice-nucleating ability of alkali feldspars

Our understanding of crystal nucleation is a limiting factor in many fields, not least in the atmospheric sciences. It was recently found that feldspar, a component of airborne desert dust, plays a dominant role in triggering ice formation in clouds, but the origin of this effect was unclear. By investigating the structure/property relationships of a wide range of feldspars, we demonstrate that alkali feldspars with certain microtextures, related to phase separation into Na and K-rich regions, show exceptional ice-nucleating abilities in supercooled water. We found no correlation between ice-nucleating efficiency and the crystal structures or the chemical compositions of these active feldspars, which suggests that specific topographical features associated with these microtextures are key in the activity of these feldspars. That topography likely acts to promote ice nucleation, improves our understanding of ice formation in clouds, and may also enable the design and manufacture of bespoke nucleating materials for uses such as cloud seeding and cryopreservation

Hydroxyl-rich macromolecules enable the bio-inspired synthesis of single crystal nanocomposites

Acidic macromolecules are traditionally considered key to calcium carbonate biomineralisation and have long been first choice in the bio-inspired synthesis of crystalline materials. Here, we challenge this view and demonstrate that low-charge macromolecules can vastly outperform their acidic counterparts in the synthesis of nanocomposites. Using gold nanoparticles functionalised with low charge, hydroxyl-rich proteins and homopolymers as growth additives, we show that extremely high concentrations of nanoparticles can be incorporated within calcite single crystals, while maintaining the continuity of the lattice and the original rhombohedral morphologies of the crystals. The nanoparticles are perfectly dispersed within the host crystal and at high concentrations are so closely apposed that they exhibit plasmon coupling and induce an unexpected contraction of the crystal lattice. The versatility of this strategy is then demonstrated by extension to alternative host crystals. This simple and scalable occlusion approach opens the door to a novel class of single crystal nanocomposites

Colouring crystals with inorganic nanoparticles

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

Control over the hierarchical structure of titanate nanotube agglomerates

An alkaline hydrothermal treatment of several types of ordered macroporous TiO2 structures, namely microtubes, sea urchin shapes and anodic nanotubes array has been investigated under stationary conditions. The effect of the size and geometry of these structures on the morphology of forming hierarchical agglomerates of titanate nanotubes have been systematically studied. It has been revealed that at sizes larger than the critical value (ca. 1 ?m), the whole geometry of the initial ordered TiO2 structure is maintained under reaction conditions leading to formation of hierarchical structures, in which bulk TiO2 is replaced with titanate nanotube agglomerates. This principle provides a convenient route for the preparation of multi-scale micro- and nanostructures of TiO2 based materials. The analysis of critical size suggests that under reaction conditions, due to the limited transport of dissolved Ti(IV) species, the growth of nanotubes occurs locally

Metastable nature of titanate nanotubes in an alkaline environment

A systematic analysis of the effect of composition and temperature of a NaOH/KOH binary aqueous mixture on the morphological properties of titanate nanostructures formed under alkaline hydrothermal transformation of TiO2 at atmospheric conditions has been performed using HRTEM techniques. All observed nanostructures, including nanosheets, nanotubes, nanofibres and nanoparticles, have been mapped over a wide range of composition (from pure NaOH to pure KOH) and temperature (from 50 ºC to 110 ºC). Attempts to intensify the TiO2 transformation by addition of titanate nanotubes seeds or agitation of the reaction mixture have resulted in formation of thermodynamically stable nanofibres rather than nanotubes. The effects of kinetic and thermodynamic control of the reaction are discussed regarding the transformation of TiO2 to nanosheets, nanotubes and nanofibres