Celebrating Soft Matter's 10th Anniversary: monitoring colloidal growth with holographic microscopy.

Holographic video microscopy offers valuable and previously unavailable insights into the progress of colloidal synthesis by providing measurements of the size and refractive index of individual colloidal particles in the dispersion. These measurements are precise enough to track subtle changes in particles' properties and rapid enough for real-time process control. We demonstrate this technique by applying it to the synthesis of monodisperse samples of crosslinked polydimethysiloxane (PDMS) spheres. The measured time dependence of these spheres' most probable radius is consistent with the LaMer model for colloidal growth. The joint distribution of size and refractive index, however, also reveals a small proportion of undersize, lower-density spheres. Trends in the distribution's time evolution offer insights into their origin. Applied over longer time periods, holographic characterization also tracks how the newly-synthesized spheres age, and illuminates the aging mechanism.