Morphological Sensitivity to pH of Silica and Chalk Nanocrystalline Self-Organized Biomorphs.

Inorganic-inorganic self-organized composite architectures resulting from the chemical coupling of alkaline-earth carbonate and polymeric silica are a promising alternative to organic-based hybrid bio-mimetic systems for developing innovative multi-functional materials. Although the importance of pH in the generation of these structures reminiscent of primitive living organisms (and for this called biomorphs) is widely acknowledged, the effect of pH is generally investigated on the basis of starting pH value. This approach inadvertently neglects the important spatial and temporal pH gradients associated with biomorph nucleation and growth. A deep understanding of the role of pH on morphogenesis requires the ability to detect locally the pH in real-time with a non-invasive technique and correlate pH to the different stages of biomorphic growth. This aim is achieved by combining optical and fluorescence imaging. An accurately selected pH probe suitable for ratiometric pH measurement in the silica gel is exploited during a typical counter-diffusion experiment. The results are compared with computer simulation of the synthesis of biomorphs by counter-diffusion experiments. The results demonstrate the existence of two main morphogenetic regimes. Interestingly, the morphogenetic process controlling the complex shaping of biomorphs results to be independent of the silica speciation.