Confinement suppresses instabilities in particle-laden droplets

Abstract

Tiny concentrations of suspended particles may alter the behavior of an evaporating droplet remarkably, leading to partially viscous and partially elastic dynamical characteristics. This, in turn, may lead to some striking mechanical instabilities, such as buckling and rupture. Here, we report certain non-trivial implications of the consequent morpho-dynamics (macro to nano scales), when such an evaporating droplet is encapsulated in a confined environment. Compared to unconfined scenario, we report non-intuitive suppression of rupturing beyond a critical confinement. We attribute this to confinement-induced dramatic alteration in the evaporating flux, leading to distinctive spatio-temporal characteristics of the internal flow leading to preferential particle transport and subsequent morphological transitions. We present a regime map quantifying buckling-non buckling pathways. These results may turn out to be of profound importance towards achieving desired morphological features of a colloidal droplet, by aptly tuning the confinement space, initial particle concentration, as well as the initial droplet volume.

Engineering Interfacial Processes at Mini-Micro-Nano Scales Using Sessile Droplet Architecture

“…Growth of the daughter cavity inside the droplet is found to be controlled by solvent evaporation from the droplet periphery . To confirm this, temporal variation in the cavity growth is compared to the evaporation flux, i.e., d V DC /d t ≈ JA ε. Here, V DC is the volume of the daughter cavity at any time instant t , A is the droplet surface area, and ε is the shell porosity obtained from Voronoi reconstruction of SEM images . The value of ε is computed to be 0.36, which corresponds to random close packing.…”

“…Yunker et al and Clement et al studied the evaporation and agglomeration dynamics of colloidal droplets sandwiched between two glass plates. On the other hand, Bansal et al , studied the evaporation dynamics of pure and colloidal droplets dispensed inside rectangular channels of various dimensions (Figure a). Similar to interacting droplets, they also observed an increase in the total evaporation time as compared to an unconfined scenario.…”

“…(h) Universal representation of the confined droplet lifetime (normalized by the lifetime of an unconfined droplet) with the extent of channel confinement for V 1 (= 1.5 μL) and V 2 (= 1 μL). Reproduced from ref with permission from Springer Nature and ref with permission from the American Institute of Physics.…”

“…These stimuli thus aid in rapid particle transport which in turn affects the precipitate morphodynamics and subsequent buckling characteristic. On the other hand, multiple droplet interaction and droplet confinement restrict the natural axisymmetric vapor diffusion guiding particle transport to preferential locations. Finally, on heterogeneously wettable substrates, it is possible to re-engineer the interface shape to exhibit multiple curvatures, thereby introducing asymmetry into evaporation and flow and contact line dynamics.…”

Impact of polydispersity and confinement on diffusion in hydrodynamically interacting colloidal suspensions

“…Confined dynamics plays an important role in the functionality of many industrial suspensions as well, for example the application and curing of particle-laden droplets such as pesticides, coatings and paints, which is a complex function of particle concentration, size polydispersity and confinement (Galliker et al. 2012; Gilet & Bourouiba 2014; Bansal, Basu & Chakraborty 2017). In the pharmaceutical industry and research, some drug delivery mechanisms rely on enclosing a therapeutic suspension within vesicles, where stability inside the vesicle can be affected by polydispersity (Grenha et al.…”