TY - JOUR A1 - Madeja, B. A1 - Gebauer, D. A1 - Marsiske, M. R. A1 - Ott, A. A1 - Rückel, M. A1 - Rosenberg, R. A1 - Baken, A. A1 - Stawski, Tomasz M. A1 - Fernandez-Martinez, A. A1 - Van Driessche, A.E.S. A1 - Cölfen, H. A1 - Kellermeier, M. T1 - New insights into the nucleation of portlandite and the effects of polymeric additives N2 - The crystallization of calcium hydroxide (Ca(OH)2, CH, portlandite) is a key process during the early stages of cement hydration. In the present work, we have revisited the formation of this mineral through nucleation and growth from supersaturated aqueous solutions, in the light of the currently emerging picture of multistage “non-classical” crystallization. To that end, we developed a titration-based assay, in which stock solutions of both relevant ions are added simultaneously into a reservoir, where supersaturation increases slowly at constant stoichiometry until nucleation occurs. This procedure allows both pre- and early post-nucleation phenomena to be analyzed quantitatively. Complementarily, the early stages of portlandite mineralization were probed by various advanced characterization techniques, including cryo-transmission electron microscopy (cryo-TEM), in-situ small-angle X-ray scattering (SAXS), pair distribution function (PDF) analysis of high-energy X-ray scattering (HEXS) data, and analytical ultracentrifugation (AUC). The experimental data show that the formation of calcium hydroxide starts with the association of ions into complexes and clusters, which subsequently coalesce to form amorphous nanoparticles – much like what has been observed in the case of calcium carbonate and other prominent minerals. Subsequently, these particles aggregate and build networks, which eventually transform into hexagonal Ca(OH)2 crystals. The presence of a soluble polycarboxylate – as a known inhibitor of portlandite crystallization – does not change the main characteristics of this multistep nucleation pathway, but it proved capable of significantly extending the lifetime of the amorphous intermediate phase and thus delaying the transition to the final crystalline phase. Our observations confirm the notion that “non-classical” crystallization is a much more common phenomenon than initially believed – and that, for minerals forming in aqueous environments, it may actually be the rule rather than the exception. KW - General Materials Science KW - Building and Construction PY - 2023 U6 - https://doi.org/10.1016/j.cemconres.2023.107258 SN - 0008-8846 VL - 173 SP - 1 EP - 13 PB - Elsevier B.V. AN - OPUS4-58162 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Opel, J. A1 - Hecht, Mandy A1 - Rurack, Knut A1 - Eiblmeier, J. A1 - Kunz, W. A1 - Cölfen, H. A1 - Kellermeier, M. T1 - Probing local pH-based precipitation processes in self-assembled silica-carbonate hybrid materials N2 - Crystallisation of barium carbonate in the presence of silica can lead to the spontaneous assembly of highly complex superstructures, consisting of uniform and largely co-oriented BaCO3 nanocrystals that are interspersed by a matrix of amorphous silica. The formation of these biomimetic architectures (so-called silica biomorphs) is thought to be driven by a dynamic interplay between the components, in which subtle changes of conditions trigger ordered mineralisation at the nanoscale. In particular, it has been proposed that local pH gradients at growing fronts play a crucial role in the process of morphogenesis. In the present work, we have used a special pH-sensitive fluorescent dye to directly trace these presumed local fluctuations by means of confocal laser scanning microscopy. Our data demonstrate the existence of an active region near the growth front, where the pH is locally decreased with respect to the alkaline bulk solution on a length scale of few microns. This observation provides fundamental and, for the first time, direct experimental support for the current picture of the mechanism underlying the formation of these peculiar materials. On the other hand, the absence of any temporal oscillations in the local pH – another key feature of the envisaged mechanism – challenges the notion of autocatalytic phenomena in such systems and raises new questions about the actual role of silica as an additive in the crystallisation process. KW - Silikat-Karbonat-Biomaterialien KW - Self-Assembly KW - Fluoreszenz KW - PH PY - 2015 U6 - https://doi.org/10.1039/c5nr05399d SN - 2040-3364 SN - 2040-3372 VL - 7 IS - 41 SP - 17434 EP - 17440 PB - RSC Publ. CY - Cambridge AN - OPUS4-35098 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Seto, J. A1 - Ma, Y. A1 - Davis, S.A. A1 - Meldrum, F. A1 - Gourrier, A. A1 - Kim, Y.-Y. A1 - Schilde, U. A1 - Sztucki, M. A1 - Burghammer, M. A1 - Maltsev, Sergey A1 - Jäger, Christian A1 - Cölfen, H. T1 - Structure-property relationships of a biological mesocrystal in the adult sea urchin spine N2 - Structuring over many length scales is a design strategy widely used in Nature to create materials with unique functional properties. We here present a comprehensive analysis of an adult sea urchin spine, and in revealing a complex, hierarchical structure, show how Nature fabricates a material which diffracts as a single crystal of calcite and yet fractures as a glassy material. Each spine comprises a highly oriented array of Mg-calcite nanocrystals in which amorphous regions and macromolecules are embedded. It is postulated that this mesocrystalline structure forms via the crystallization of a dense array of amorphous calcium carbonate (ACC) precursor particles. A residual surface layer of ACC and/or macromolecules remains around the nanoparticle units which creates the mesocrystal structure and contributes to the conchoidal fracture behavior. Nature’s demonstration of how crystallization of an amorphous precursor phase can create a crystalline material with remarkable properties therefore provides inspiration for a novel approach to the design and synthesis of synthetic composite materials. KW - Calcium carbonate biomineralization KW - Echinoderm skeleton KW - Hierarchical structuring KW - Mesocrystal KW - Skeletal elements PY - 2012 U6 - https://doi.org/10.1073/pnas.1109243109 SN - 0027-8424 SN - 1091-6490 VL - 109 IS - 10 SP - 3699 EP - 3704 PB - National Academy of Sciences CY - Washington, DC AN - OPUS4-27726 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Casse, O. A1 - Shkilnyy, A. A1 - Linders, J. A1 - Mayer, C. A1 - Häussinger, D. A1 - Völkel, A. A1 - Thünemann, Andreas A1 - Dimova, R. A1 - Cölfen, H. A1 - Meier, W. A1 - Schlaad, H. A1 - Taubert, A. T1 - Solution behavior of double-hydrophilic block copolymers in dilute aqueous solution N2 - The self-assembly of double-hydrophilic poly(ethylene oxide)–poly(2-methyl-2-oxazoline) diblock copolymers in water has been studied. Isothermal titration calorimetry, small-angle X-ray scattering, and analytical ultracentrifugation suggest that only single polymer chains are present in solution. In contrast, light scattering and transmission electron microscopy detect aggregates with radii of ca. 100 nm. Pulsed field gradient NMR spectroscopy confirms the presence of aggregates, although only 2% of the polymer chains undergo aggregation. Water uptake experiments indicate differences in the hydrophilicity of the two blocks, which is believed to be the origin of the unexpected aggregation behavior (in accordance with an earlier study by Ke et al. [Macromolecules2009, 42, 5339–5344]). The data therefore suggest that even in double-hydrophilic block copolymers, differences in hydrophilicity are sufficient to drive polymer aggregation, a phenomenon that has largely been overlooked or ignored so far. KW - Nanotechnology KW - Small-angle X-ray scatering KW - SAXS PY - 2012 U6 - https://doi.org/10.1021/ma300621g SN - 0024-9297 SN - 1520-5835 VL - 45 IS - 11 SP - 4772 EP - 4777 PB - American Chemical Society CY - Washington, DC AN - OPUS4-26072 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Jäger, Christian A1 - Cölfen, H. T1 - Fine structure of nacre revealed by solid state 13C and 1H NMR N2 - Solid-state NMR investigations of nacre reveal the presence of an amorphous surface layer around the aragonite platelets. This surface layer contains hydrogen carbonate groups, presumably at its outer surface and water molecules slightly hindered in their mobility in a proton ratio of 1:33, i.e. about 16 water molecules per HCO3– unit. The 1H spin–lattice relaxation T1 times of protons in the protein/polysaccharide matrix (about 300 ms), of the mobile water molecules (2 s) and of the hydrogen carbonate units (12 s) differ significantly, thus revealing no spatial proximity between the protein/polysaccharide matrix with the hydrogen carbonate units of the amorphous carbonate surface layer suggesting no significant interaction between protein matrix and the amorphous calcium carbonate (ACC) layer. These results are discussed in the context of recent publications on novel structural aspects of nacre. KW - NMR KW - Nacre KW - Amorphous carbonate layer KW - Protein interaction PY - 2007 U6 - https://doi.org/10.1039/b708600h SN - 1466-8033 VL - 9 SP - 1237 EP - 1244 CY - London, UK AN - OPUS4-17582 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Nassif, N. A1 - Pinna, N. A1 - Gehrke, N. A1 - Antonietti, M. A1 - Jäger, Christian A1 - Cölfen, H. T1 - Amorphous layer around aragonite platelets in nacre KW - Nacre KW - NMR KW - Aragonite KW - Amorphous Surface KW - Protein binding PY - 2005 SN - 0027-8424 SN - 1091-6490 VL - 102 IS - 36 SP - 12653 EP - 12655 PB - National Academy of Sciences CY - Washington, DC AN - OPUS4-11009 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -