a, Scattering plots of different concentrations of (CaCO 3 ) n measured by synchrotron SAXS. The red curve is the fitting result from DAMMIF. At a concentration of 57.0 mg l−1 an increase in the scattered intensity was detected, and this broad shoulder peak indicated the aggregation of (CaCO 3 ) n with a large distribution of sizes. A pronounced maxima of the scattered intensity could be observed at a concentration of 285 mg l−1, demonstrating inter-oligomer correlations induced by the formation of larger (CaCO 3 ) n aggregates. b, Size distribution function of oligomer aggregates at 57.0 mg l−1. The inset shows the simulated shape of aggregates, indicating the existence of chain-like structures, including branches at high concentrations. c, Liquid-cell TEM of the aggregates of the (CaCO 3 ) n oligomers showing a chain-like contrast; the boundary between the background (blue) and sample (yellow) is enhanced in the false colour image on the right, and the chain-like aggregates are marked with arrows. d, Viscosity of (CaCO 3 ) n oligomers measured at 5 °C (n ≥ 3). The change in the viscosity with concentration is better fitted with the Huggins equation (R2 = 0.98) than with the Einstein equation (R2 = 0.94), indicating that the shape of the aggregates in solution was more chain-like than spherical. e, The hydrodynamic diameter of (CaCO 3 ) n oligomers or their aggregates at different oligomer concentrations measured by dynamic light scattering with a Ca:TEA ratio of 1:20. The increase (decrease) of the hydrodynamic diameter is reversible by condensing (diluting) the (CaCO 3 ) n oligomer solution. f, Reversible aggregations and disaggregations of the (CaCO 3 ) n oligomers revealed by synchrotron SAXS. g, Scheme of the reversible aggregations and disaggregations of the oligomer unit are controllable by the concentration changes. h, In situ liquid-cell TEM observation of (CaCO 3 ) n oligomers. The chain aggregates remain in dynamical change (aggregation–disaggregation) states.