Continuous Optical Measurement of Internal Dynamics in Drying Colloidal Droplets

Abstract

Accessing the colloidal dynamics non-invasively and continuously during the phase transition of a colloidal system is challenging but critical. Here, we demonstrate the use of spatiotemporal coherence-gated light scattering for studying the internal dynamics of drying colloidal droplets. The continuously acquired signal originates from a picoliter-sized volume located at the droplet−substrate interface. The measurement is non-contact, non-invasive, and label free and permits real-time observations of both optical and mechanical changes in the measurement volume. Additionally, some macroscopic descriptors of the drying process can be constructed from the microscopic measurement, providing ample information of the process. Implemented with an endoscopic-like probe, this system can be easily incorporated into the existing drop profiling instruments, which is potential for the full characterization of dynamic colloidal droplets.

Simultaneous Spatiotemporal Measurement of Structural Evolution in Dynamic Complex Media

“…At this stage of the drying process, the magnitude of dynamics is given as β 0 ∝ ρ D 0 , where ρ is the scatter number concentration and D 0 is the diffusivity of a single scatter. 17 As β 0 would have a higher value if the samples have more scatters, it is also critical to compare the normalized total dynamics, β 0,norm = β 0 /ρ ∝ D 0 , as shown on the right axis. It is easy to understand the decreasing trend of β 0,norm since D 0 would decrease with high concentration as the hydrodynamic interaction among the scatters at this condition would decrease the diffusivity of one scatter.…”

“…On the left axis, we showed β 0 , which is the total dynamics averaged over the first 5 min. At this stage of the drying process, the magnitude of dynamics is given as β 0 ∝ ρ D 0 , where ρ is the scatter number concentration and D 0 is the diffusivity of a single scatter . As β 0 would have a higher value if the samples have more scatters, it is also critical to compare the normalized total dynamics, β 0,norm = β 0 /ρ ∝ D 0 , as shown on the right axis.…”

Drying of bio-colloidal sessile droplets: Advances, applications, and perspectives

“…For example, an aging process is exhibited by laponite clay, and its properties change from liquid to gel-like networks [177]. the internal dynamics of colloidal droplets, adopted from [178]. (II) The schematic of the experimental setup and principle of SPR, adopted from [179].…”

“…The acquired signal originates from a sessile droplet, and the measurement of such a signal is non-contact, non-invasive, and label-free. It also allows capturing the optical and mechanical changes in the droplet during the drying process at the microscopic scale [178].…”