Quantification of microstructures in stable and gelated suspensions from Cryo-SEM

It is shown that the microstructures of concentrated suspensionscan be analyzed in a quantitative way from cryo-SEM images ofhigh-pressure frozen samples, both in the electrostatically stabilizedand in the flocculated state. Suspensions of spherical silica particles(40 vol%) in an aqueous solution were used. The average particle radiuswas 525nmwith a polydispersity of below 7%. The suspensionswere high-pressure frozen, which resulted in a quenching of the configurationwithout apparent change in volume or crack formation.After fracturing the samples at liquid nitrogen temperature, thefracture surface was etched by controlled sublimation of the frozenaqueous phase, coated with 8 nm of platinum, and examined bystereo-cryo-SEM. The 3-dimensional positions of all the visible particles were determined from theSEMimages. Assuming an isotropicparticle configuration in the sample before cracking, it is possible toextract the 3-dimensional pair correlation function from the particlepositions on the fracture surface. A comparison to recent resultsfrom Brownian Dynamics simulations shows good agreement betweenour experiments and the simulations.