Grafting characterization of natural rubber latex particles: wet-STEM imaging contributions

Natural rubber latexes investigated in this study have been chemically modified by seeded emulsion polymerization. Depending on the water affinity of the monomer involved (MMA or DMAEMA), the expected result was the grafting of the corresponding polymer inside or on the surface of the latex particles. The present article focuses on the grafting characterization of these modified natural rubber latexes. In this purpose, non-imaging classical experimental methods such as dynamic light scattering and nuclear magnetic resonance have been completed by microscopy techniques, including transmission imaging in scanning electron microscopy (SEM) and a recent imaging mode called wet-STEM. It consists in transmission imaging in an Environmental SEM operating in the wet-mode, allowing transmission observations of particles suspended in a liquid layer with good resolution and contrast. In the present study, we have adopted a comparative characterization approach between a nongrafted natural rubber latex and two grafted ones. Such an approach indeed contributes to highlight the particles morphology resulting from chemical modification using either MMA or DMAEMA. Transmission images in SEM of thin foils are relatively well interpreted and are completed with wet-STEM images of latexes in their native state, bringing important contributions for grafting characterization.