Cristina Ruiz-Agudo

Light‐induced direct patterning allows intricate spatiotemporal control over microscopic structures and has even been extended to functional inorganic materials. However, while sol–gel‐based materials such as silica maintain structural continuity, photoinduced precipitation of salts such as carbonates and phosphates typically suffers from a granular nature and produces loose particle assemblies. In this study, UV‐induced release of phosphoric acid from an organic precursor is exploited for locally modulating supersaturation levels. This allows for controlled interplay between photogeneration and precursor supply, for the precipitation of structurally continuous, non‐granular barium phosphate from solution. Based on these insights, nanoscopic thin films with controllable thickness are deposited in an illuminated spot. By moving the light beam, this approach is extended to direct writing based on user‐defined patterns. Moreover, by triggering photoinduced mineralization within organic templates, complex morphologies can be replicated with high fidelity. This versatility and precision will open new opportunities for the design of functional, biologically relevant inorganic materials.

Phosphate-based additives are commonly used in concrete technology as hydration retarders and dispersion enhancers, playing a critical role in controlling cement hydration kinetics.

Magnesium silicate (MS) cement, which uses magnesium silicate hydrate (M-S-H) as its primary binding phase, is a promising low-carbon alternative to Portland cement. However, the slow dissolution of MgO limits the release of Mg ions, which is critical for the formation of M-S-H. To address this issue, solubilizers that complex Mg2+ and promote MgO dissolution have been proposed, provided that they do not significantly hinder M-S-H formation. This study systematically examined the effects of four anionic additives—acetate, citrate, orthophosphate, and carbonate—on M-S-H nucleation and early growth, developing a highly reproducible crystallization scenario. The observed reduction in supersaturation at the nucleation point for specific additive concentrations suggests that Mg-anion complexes may play an active role in M-S-H nucleation, potentially allowing M-S-H to form at lower supersaturation levels, which could be beneficial for MS cement applications. However, as shown here, additives such as citrate, while not inhibiting nucleation, can significantly slow the growth of M-S-H, potentially compromising the strength development of MS cement. Among the additives studied, moderate concentrations of phosphate and carbonate show the most promise, as they have minimal effects on the formation process while potentially reducing the supersaturation for M-S-H nucleation. Although further research is necessary to fully understand the effects of these anions, this study provides valuable insights into their impact on M-S-H nucleation and early growth.

Hydrogels represent multifarious functional materials due to their diverse ranges of applicability and physicochemical properties. The complex coacervation of polyacrylate and calcium ions or polyamines with phosphates has been uncovered to be a fascinating approach to synthesizing of multifunctional physically crosslinked hydrogels. To obtain this wide range of properties, the synthesis pathway is of great importance. For this purpose, we investigated the entire mechanism of calcium/polyacrylate, as well as phosphate/polyamine coacervation, starting from early dynamic ion complexation by the polymers, through the determination of the phase boundary and droplet formation, up to the growth and formation of thermodynamically stable macroscopic coacervate hydrogels. By varying the synthesis procedure, injectable hydrogels, as well as plastic coacervates, are presented, which cover a viscosity range of three orders of magnitude. Furthermore, the high calcium content of the calcium/polyacrylate coacervate (~19 wt.%) enables the usage of those coacervates as an ions reservoir for the formation of amorphous and crystalline calcium-containing salts like calcium carbonates and calcium phosphates. The exceptional properties of the coacervates obtained here, such as thermodynamic stability, viscosity/plasticity, resistance to acids, and adhesive strength, combined with the straightforward synthesis and the character of an ions reservoir, open a promising field of bioinspired composite materials for osteology and dentistry.

Understanding the crystallization of cement-binding phases, from basic units to macroscopic structures, can enhance cement performance, reduce clinker use, and lower CO₂ emissions in the construction sector. This review examines the crystallization pathways of C-S-H (the main phase in PC cement) and other alternative binding phases, particularly as cement formulations evolve toward increasing SCMs and alternative binders as clinker replacements. We adopt a nonclassical crystallization perspective, which recognizes the existence of critical intermediate steps between ions in solution and the final crystalline phases, such as solute ion associates, dense liquid phases, amorphous intermediates, and nanoparticles. These multistep pathways uncover innovative strategies for controlling the crystallization of binding phases through additive use, potentially leading to highly optimized cement matrices. An outstanding example of additive-controlled crystallization in cementitious materials is the synthetically produced mesocrystalline C-S-H, renowned for its remarkable flexural strength. This highly ordered microstructure, which intercalates soft matter between inorganic and brittle C-S-H, was obtained by controlling the assembly of individual C-S-H subunits. While large-scale production of cementitious materials by a bottom-up self-assembly method is not yet feasible, the fundamental insights into the crystallization mechanism of cement binding phases presented here provide a foundation for developing advanced cement-based materials.