Real-space observation of salt-dependent aging in Laponite gels

Colloidal gels gradually evolve as their structures reorganize, a process known as aging. Understanding this behavior is essential for fundamental science and practical applications such as drug delivery and tissue engineering. This study examines the aging of low-concentration Laponite suspensions with varying salt concentrations using fluorescence microscopy, scattering imaging, and particle tracking microrheology. Structural heterogeneity appeared earlier at higher salt concentrations, and the average size of aggregates decreased as the salt concentration increased further. Fourier transform analysis corroborated these trends, and scattering images showed similar results. Microrheology revealed distinct dynamics in Laponite-rich and Laponite-poor regions: the poor phase exhibited liquid-like behavior, while the rich phase exhibited gel-like properties. Further analysis suggested the presence of submicron or nanoscale structural heterogeneities within the rich phase. These findings provide insight into how aging and salt concentration shape the structure and dynamics of colloidal gels.