Although organic–inorganic hybrid materials have played indispensable roles as mechanical1,2,3,4, optical5,6, electronic7,8 and biomedical materials9,10,11, isolated organic–inorganic hybrid molecules (at present limited to covalent compounds12,13) are seldom used to prepare hybrid materials, owing to the distinct behaviours of organic covalent bonds14 and inorganic ionic bonds15 in molecular construction. Here we integrate typical covalent and ionic bonds within one molecule to create an organic–inorganic hybrid molecule, which can be used for bottom-up syntheses of hybrid materials. A combination of the organic covalent thioctic acid (TA) and the inorganic ionic calcium carbonate oligomer (CCO) through an acid–base reaction provides a TA–CCO hybrid molecule with the representative molecular formula TA2Ca(CaCO3)2. Its dual reactivity involving copolymerization of the organic TA segment and inorganic CCO segment generates the respective covalent and ionic networks. The two networks are interconnected through TA–CCO complexes to form a covalent–ionic bicontinuous structure within the resulting hybrid material, poly(TA–CCO), which unifies paradoxical mechanical properties. The reversible binding of Ca2+–CO32− bonds in the ionic network and S–S bonds in the covalent network ensures material reprocessability with plastic-like mouldability while preserving thermal stability. The coexistence of ceramic-like, rubber-like and plastic-like behaviours within poly(TA–CCO) goes beyond current classifications of materials to generate an ‘elastic ceramic plastic’. The bottom-up creation of organic–inorganic hybrid molecules provides a feasible pathway for the molecular engineering of hybrid materials, thereby supplementing the classical methodology used for the manufacture of organic–inorganic hybrid materials.
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We thank S. Chang and J. Guo for assistance with 3D cryo-TEM tomography reconstruction and FIB-SEM in the Center of Cryo-Electron Microscopy (CCEM), Zhejiang University. We thank the Chemistry Instrumentation Center, Zhejiang University for characterization support, including Y. Qiu for help with SAXS and GPC data analysis; F. Chen for assistance with electron microscopy; Y. Liu for assistance with NMR; Q. He for help with MS; G. Lan for GC-MS analysis; and D. Shi and X. Hu for in situ heating XRD analysis. We thank L. Xu for assistance with DSC and DMA at the State Key Laboratory of Chemical Engineering, Zhejiang University. We thank Y. Li at the University of California, Santa Barbara, for discussions. We thank Ansys for providing software support and Shanghai AIYU Information Technology Co., Ltd for the service support. We acknowledge funding support from the National Natural Science Foundation of China (22022511, 22275161), the National Key Research and Development Program of China (2020YFA0710400) and the Fundamental Research Funds for the Central Universities (226-2022-00022, 2021FZZX001-04).
The authors declare no competing interests.
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Extended data figures and tables
a, Snapshot of the CCO ethanol solution. b, Size distribution of CCO analysed by dynamic light scattering. The mean size of the CCO was 1.25 nm, which corresponded to a typical molecular formula (CaCO3)3 for CCO (ref. 23). c, Snapshot of the TA ethanol solution. d, Mass spectrum of the TA ethanol solution. The main peaks were at m/z = 171 and 205, which were for the characteristic fragment ions of TA.
a, Mass fraction of S and Ca elements in a TA-CCO hybrid molecule, which were measured by ICP-OES, giving an approximate Ca:TA molar ratio of 1.5. Error bars represent standard deviation, n = 8. b,c, Liquid-state 13C NMR spectra of CCO and TA in ethanol. The peaks at 160 ppm and 176 ppm contributed to the carbonate (in CCO) and carboxyl (in TA) groups, respectively. d, The peaks for carbonate and the carboxyl group in TA-CCO have almost similar symmetry to those of pure TA and CCO. The small shoulder (at 181.15 ppm) on the carboxyl group peak was attributed to by-products generated during the reaction. e, TEM image of amorphous CaCO3 nanoparticles (NP) with an average diameter of 41.3 nm. f, Snapshot of a TA-NP mixed ethanol solution. g,h, Liquid-state 13C NMR and mass spectra of the TA-NP mixed solution. The absence of a chemical shift for carbonate indicated the unsuccessful construction of hybrid molecules from CaCO3 nanoparticles.
a, HRTEM images of partial single TA-CCO hybrid molecules with lengths of approximately 3.2 nm. The variation in image contrast implied the coexistence of CaCO3 (higher electron density) and TA (lower electron density) in the TA-CCO hybrid molecule. b, Size of a TA-CCO hybrid molecule calculated with the Multiwfn program62, which was consistent with the HRTEM results. c, Typical chemical shift of tertiary carbon on the carbon ring before and after polymerization indicates ring-opening polymerization of disulfide bonds63,64.
a, UV–Vis spectra of poly(TA-CCO) and pTA-NP bulk with the same thicknesses of 2 mm. The poly(TA-CCO) bulk exhibited an average transmittance of 85% at 420–800 nm, whereas it was nontransparent at 200–420 nm. This was because the homogeneous structure of poly(TA-CCO) did not reflect or scatter light. Moreover, the TA absorbed light between wavelengths of 200 and 420 nm. By contrast, the pTA-NP bulk was completely opaque. The heterogeneous structure of pTA-NP caused by the aggregation of nanoparticles scattered all the light, leading to nontransparency. This further confirmed the homogeneity of the poly(TA-CCO) bulk from the microscale to the macroscale, which differs from that of traditional nanocomposites. The inset shows snapshots of poly(TA-CCO) bulk with different shapes, demonstrating the mouldable construction of poly(TA-CCO). b, The enlarged spectra of a over the range 200–400 nm, exhibiting full absorption (over 99.9%) by the poly(TA-CCO) bulk in the ultraviolet region owing to the characteristic ultraviolet absorptions of the organic segments in the TA-CCO hybrid molecule. The inset images demonstrate that fluorescence of the letters under ultraviolet irradiation was prohibited by covering the transparent poly(TA-CCO) bulk over the letters. This suggested that the optical features of the organic segments were preserved in the organic–inorganic hybrid molecule. c, Snapshots of pTA showing the high viscosity, which was commonly used as an adhesive material65. d, SEM image of pTA with a homogeneous structure. e, Snapshots of pTA-NP. f, SEM image of pTA-NP with apparent phase separation of the inorganic and organic phases. The yellow circles represent aggregated CaCO3 nanoparticles.
a, TG-DSC curve of poly(TA-CCO) from room temperature to 1,400 °C. b More detail in a temperature range from 160 to 400 °C. c, In situ XRD patterns of poly(TA-CCO) during the heating and cooling process. The temperature of the heating and cooling cycle began at 25 °C, increased gradually to 70, 100, 130, 160 and 190 °C and finally decreased to 25 °C by the same temperature steps. The results indicated an amorphous feature of poly(TA-CCO) throughout the thermal treatment. d, XRD spectra of the residual composition at different temperatures in the TG-DSC curve. The green circles, pink triangles and red diamonds represent CaSO4, CaCO3 and CaO, respectively. The exact composition of poly(TA-CCO) could be calculated from the TG-DSC and XRD analysis, which indicated a 1.5:1 molar ratio of Ca to TA, which is consistent with the TA-CCO hybrid molecule. e, TG-DSC curve of pTA-NP. The inorganic content was 42 wt%, corresponding to a 1.5:1 molar ratio of Ca to TA that is similar to that of poly(TA-CCO).
Extended Data Fig. 6 Size statistics for the inorganic and organic bicontinuous networks in poly(TA-CCO).
a, Statistical widths of the inorganic and organic networks. The inset illustration represents a specific 2D projection acquired from the 3D bulk. Owing to tortuous linear-like distributions of inorganic and organic networks, the widths of the networks changed with the position of the slice and direction of the measurement. In a 2D image acquired with FIB and HAADF-STEM, we statistically measured the widths of inorganic and organic networks in a specific direction. The measured widths of the TA and CaCO3 networks varied from 2.2 nm to 3.9 nm and from 1.1 nm to 1.8 nm, respectively. However, the minimum width was fixed, which corresponded to the periodic width of the TA and CaCO3 networks in the 3D structure. b, Molecular weight distribution curve and characteristic molecular weights of residual organic poly(TA) network after dissolving the inorganic network. The molecular weight of the residual poly(TA) was 5.26 × 105 g mol−1 (Mw). Mn is the number average molecular weight, Mw is the weight average molecular weight, Mz is the Z-average molecular weight, Mz+1 is the Z+1 average molecular weight and PDI is the polydispersity index.
a, Hardness and modulus of pTA, pTA-NP and poly(TA-CCO) bulk. Error bars represent standard deviation, n ≥ 5. b, Snapshots captured from a video of in situ nanoindentation corresponding to the maximum depth and residual impression remaining after unloading the flat indenter. The silicone rubber and poly(TA-CCO) exhibited similar deformation behaviour during loading and unloading. c, AFM height topology of residual Berkovich indentation for a maximum load of 50 mN on poly(TA-CCO). The cross-sectional profiles correspond to the two designated directions indicated by the red and blue lines. The maximum residual depth was 138 nm after 1,813-nm deformation, indicating elastic recovery of the indented surface. d, Variation in the damping factor with increasing temperature for poly(TA-CCO), widely used commodity plastics (PP, PP+CF, ABS, ABS+CF) and engineering plastics (POM and POM+CF). The damping factor for poly(TA-CCO) remained constant before 80 °C and after 160 °C and then slightly increased between 80 and 160 °C, which was close to the temperature of the endothermic peak in DSC. This was because of the breaking of S–S bonds in the organic TA network, which slightly increased the viscosity of poly(TA-CCO). By contrast, the damping factor increased sharply for plastics after the temperature reached their softening temperatures, suggesting a vigorous movement of polymer chains and an increase in viscosity.
Extended Data Fig. 9 Finite element simulation of the mechanical response under uniaxial compression.
a–c, Finite element model of the covalent–ionic bicontinuous network in poly(TA-CCO). The orange part represents the covalent (TA) network and the blue part represents the ionic (CaCO3) network. b,c, Calculated von Mises stress distributions of the covalent network (b) and the ionic network (c) at strains of 2%, 5% and 10%. This demonstrated the flexibility of the inorganic ionic network without accumulation of stresses. The average stress was 196 MPa for poly(TA-CCO) at a strain of 10%. d–f, Finite element model of the nanocomposite structure in pTA-NP. The orange part represents the TA matrix and the blue part represents CaCO3 nanoparticles. e,f, Calculated von Mises stress distributions of the TA matrix (e) and CaCO3 nanoparticles (f) at strains of 2%, 5% and 10%. This showed accumulated stress at the organic–inorganic interface, at which the failure of organic–inorganic nanocomposites commonly occurs. The average value of the stress was 22 MPa for pTA-NP.
a, HAADF-STEM image of the reprocessed poly(TA-CCO) bulk showing preservation of the covalent–ionic bicontinuous network. b, Pair distribution functions (denoted by G(r)) of the original poly(TA-CCO) bulk and reprocessed poly(TA-CCO) bulk. No obvious change was observed after reprocessing, which indicated the dynamic structural reversibility of the covalent–ionic bicontinuous network in poly(TA-CCO).
This file contains Supplementary Notes 1–5, Supplementary Figs. 1–4 and Supplementary Tables 1–3.
In situ deformation and recovery process of silicone rubber and poly(TA–CCO). Both silicone rubber and poly(TA–CCO) exhibit a high degree of elastic recovery after unloading. But at the same load, the silicone rubber was deformed nearly 40 times more than poly(TA–CCO), demonstrating the hard but elastic properties of poly(TA–CCO).
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Fang, W., Mu, Z., He, Y. et al. Organic–inorganic covalent–ionic molecules for elastic ceramic plastic. Nature 619, 293–299 (2023). https://doi.org/10.1038/s41586-023-06117-1
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