Electron tomography on latex particles suspended in water using environmental scanning electron microscopy.

Tilted image series are acquired on liquid suspensions of latex particles supported by a carbon membrane. To do this, a home-made stage fitting in an Environmental Scanning Electron Microscope (ESEM) is optimized to minimize cold losses and thus improve both sample stability and spatial resolution in the images. As latex particles are electron-sensitive materials, sample degradation and stability are taken into account in the choice of the parameters for tilted image series acquisition. Despite the limited number of images, conventional algorithms are used to reconstruct the volume and study the three-dimensional arrangement of latex particles. The packing modes are in good agreement with what can be observed on frozen suspensions, although the domain sizes are smaller. Several quantitative parameters such as latex particle size and distance to first neighbors are extracted from the 3D model. Finally, the spatial resolution in the tomograms is estimated using Crowther criterion and by Fourier Shell Correlation analysis. It is also measured directly by analyzing a suspension containing latex particles and a surfactant of interest for composite formulation.