Low-viscosity oil thickened by r-GO microcapsules. (a) SEM and (b) TEM images of the r-GO capsules. (c) Effect of particle loading on the viscosity of a low-viscosity silicone oil (red, dashed line). (d) An optical microscopy image taken near the edge of a thickened oil film on glass slide, confirming a network structure of r-GO capsules. Thicker parts of the film are hard to image due to overlapping particles.