Disentangling kinetics from thermodynamics in heterogeneous colloidal systems

Abstract

In Nucleation and Growth, the process by which most heterogeneous systems form, thermodynamics sets the asymptotic boundaries toward which the system must evolve, while kinetics tries to cope with it by imposing the transport rates. In all heterogeneous colloidal systems observed in nature, composition, shape, structure and physical properties result from the trade-off between thermodynamics and kinetics. Here we show, by carefully selecting colloidal systems and controlling phase separation in microfluidic devices, that it becomes possible to disentangle kinetics effects from thermodynamics. Using amyloids and nanocellulose filamentous colloids, we demonstrate that decoupling kinetics from thermodynamics in the phase separation process unveils new physical phenomena, such as orders of magnitude shorter timescales, a wider phase diagram, and structures that are not observable via conventional liquid-liquid phase separation. Our approach enables on-demand fabrication of multicomponent heterogeneous liquid crystals, enhancing their potential, and introducing original fundamental and technological directions in multicomponent structured fluids.

Evaporation-Driven Liquid–Liquid Crystalline Phase Separation in Droplets of Anisotropic Colloids

“…This indicates that the time-scale of the self-assembly of the amyloid fibrils from disorder to fully relaxed cholesteric structures inside of the droplet is on the order of +10 d. Once the cholesteric structures are formed, we expose the droplet to ambient conditions, observing that the drying dynamics of the droplet do not disturb the already formed cholesteric structures inside of the droplet (Supplementary Movie S6). Our results on controlling the kinetics of the liquid crystal evaporation to form uniform deposits may provide insights into the formation of composite deposits, where amyloid fibrils can be used to align guest particles, e.g., gold nanrorods − or other functional colloids.…”

Nematic to Cholesteric Transformation in the Cellulose Nanocrystal Droplet Phase

“…However, spontaneous self-assembly of the mesogens in the co-existing phase driven by the surface and elastic properties produces LC droplets and domains that may go through various phase transitions before producing a bulk structure. As discussed before, a recent experiment shows, by decoupling the kinetics of the nucleation and growth process from its thermodynamics, that the induction time of tactoid formation can be significantly reduced, opening up a room to control the phase separation, composition, morphology, and equilibrium structures. During the phase transition process, various defects get trapped in the bulk structure (a kinetically arrested gel-like state forms at higher concentrations), resulting in a non-homogeneous director field.…”

“…As such, the pitch will vary depending on the size of the tactoids, as different sizes will accumulate different concentrations of rods during the nucleation and growth process. This has been experimentally observed in the amyloid system. , Recently, this relationship has been explored more comprehensively by decoupling the kinetic effects occurring during the conventional nucleation and growth process from the thermodynamics with the help of microfluidic manipulation . Here, the kinetic pathway is bypassed to fast-track the tactoid formation, where the timescale of tactoid formation is reduced from few days to few minutes.…”

“…18,24 Recently, this relationship has been explored more comprehensively by decoupling the kinetic effects occurring during the conventional nucleation and growth process from the thermodynamics with the help of microfluidic manipulation. 31 Here, the kinetic pathway is bypassed to fast-track the tactoid formation, where the timescale of tactoid formation is reduced from few days to few minutes. It was observed that the pitch remains constant over a wide range of tactoid volume, indicating its easy-toexploit nature by controlling the naturally occurring size fractionation during the nucleation and growth process.…”

Evaporation-induced self-assembly of liquid crystal biopolymers

“…26,101–103 In particular, Mezzenga et al discovered the formation of tactoids along a concentration gradient, such as homogeneous, bipolar, and cholesteric ones, and analyzed the order and orientation transition in a confinement effect and hydrodynamic system with a support of theoretical estimation. 104–107…”