Bioinspired mechanical mineralization of organogels

Abstract

Mineralization is a long-lasting method commonly used by biological materials to selectively strengthen in response to site specific mechanical stress. Achieving a similar form of toughening in synthetic polymer composites remains challenging. In previous work, we developed methods to promote chemical reactions via the piezoelectrochemical effect with mechanical responses of inorganic, ZnO nanoparticles. Herein, we report a distinct example of a mechanically-mediated reaction in which the spherical ZnO nanoparticles react themselves leading to the formation of microrods composed of a Zn/S mineral inside an organogel. The microrods can be used to selectively create mineral deposits within the material resulting in the strengthening of the overall resulting composite.

Fig. 1. Synthesis and chemical characterization of the microrods.

a Plausible reaction scheme showing the formation of the coordination compound Zn(McMT)_n and picture of white slurry consisting of a microrod suspension in DMF; b SEM image of the microrods (scale bar 1 μm); c XPS and d XRD spectra of ZnO nanoparticles, microrods, and Zn(McMT)_n complex; and e FTIR spectra of McMT, Zn(McMT)_n complex, and microrods.

Fig. 2. Study of the growth of the microrods under sonication (US 40 kHz).

a Photos of control reactions: (i) all components, (ii) no ZnO, (iii) no US (vortex 400 rpm), (iv) w/ ZnBr₂, and (v) w/ McMT disulfide dimer. b SEM images comparing the products of the reaction with (left) and without (right) ultrasound. c Shear viscosity measurements of the formation of the microrods at different reaction timepoints. d SEM images of the products isolated at different reaction timepoints.

Fig. 3. Modifying the rheology of a polymer solution by growing microrods in situ.

a Photos of representative samples (left to right): All components, No McMT control, and No ZnO control. After the formation of the microrods, the viscosity of the solution changes, thus preventing flow when the vial is turned upside down. This phenomenon does not occur in the control samples. b Shear viscosity measurements of the samples. The shear viscosity measurement of the polyurethane alone is included for reference. All reactions and rheological measurements were done in triplicate (Supplementary Figs. 23 and 24).

Fig. 4. In situ growth of the microrods within a crosslinked polymer organogel.

a Photos of the resulting polymer composites after sonication and drying: (i) All components, (ii) No McMT control, and (iii) No ZnO control. b Representative DMA oscillatory amplitude measurements for the polymer composite samples. c Light microscopy with cross-polarizer (left) and TEM (right) images of the All components sample showing the presence of the crystalline microrods in bundles.