Natural rubber with nanomatrix of non-rubber components observed by focused ion beam-scanning electron microscopy

Naturally occurring nanomatrix structure formed in natural rubber was observed with a field emission scanning electron microscope equipped with a focused ion beam (FIB-SEM), and it was related to viscoelastic properties of the rubber. Film specimen used for the FIB-SEM observation was prepared from serum fraction of natural rubber latex, in which serum rubber contained about 15 w/w% proteins. Morphology of the film specimen was observed by FIB-SEM, after pinning the nanomatrix structure with glutaraldehyde followed by staining the serum rubber with OsO₄. Three-dimensional image of the nanomatrix structure was successfully reconstructed in mesoscale without defects and voids, in which rubber particles of 200 nm in diameter were dispersed in the matrix of non-rubber components such as the proteins and phospholipids of several 10 nm in thickness. Storage modulus at plateau region of the serum rubber was about 500 times as high as that of deproteinized natural rubber, suggesting that the nanomatrix of the non-rubber components was completely continuous.