From dynamic self-organization to avalanching instabilities in soft-granular threads

• Published in: Soft matter 2022-03, Vol.18 (9), p.1801-1818
• Main Authors: Guzowski, J, Buda, R J, Costantini, M, Ćwiklińska, M, Garstecki, P, Stone, H A
• Format: Article
• Language: English
• Subjects: Chains; Chemistry; Compressive properties; Deformability; Droplets; Fluid films; Fluidization; Fluidizing; Foams; Formability; Grains; Granular materials; Hydrogels; Landslides; Liquid phases; Materials science; Metastable state; Microgels; Self-assembly; Thin films; Three dimensional printing; Tissue engineering
• ISSN: 1744-683X; 1744-6848; 1744-6848
• DOI: 10.1039/d1sm01350e

We study the dynamics of threads of monodisperse droplets, including droplet chains and multi-chains, in which the droplets are interconnected by capillary bridges of another immiscible liquid phase. This system represents wet soft-granular matter - a class of granular materials in which the grains are soft and wetted by thin fluid films-with other examples including wet granular hydrogels or foams. In contrast to wet granular matter with rigid grains ( , wet sand), studied previously, the deformability of the grains raises the number of available metastable states and facilitates rearrangements which allow for reorganization and self-assembly of the system under external drive, , applied viscous forces. We use a co-flow configuration to generate a variety of unique low-dimensional regular granular patterns, intermediate between 1D and 2D, ranging from linear chains and chains with periodically occurring folds to multi-chains and segmented structures including chains of finite length. In particular, we observe that the partially folded chains self-organize limit cycle of displacements and rearrangements occurring at a frequency self-adapted to the rate of build-up of compressive strain in the chain induced by the viscous forces. Upon weakening of the capillary arrest of the droplets, we observe spontaneous fluidization of the quasi-solid structures and avalanches of rearrangements. We identify two types of fluidization-induced instabilities and rationalize them in terms of a competition between advection and propagation. While we use aqueous droplets as the grains we demonstrate that the reported mechanisms of adaptive self-assembly apply to other types of soft granular systems including foams and microgels. We discuss possible application of the reported quasi-1D compartmentalized structures in tissue engineering, bioprinting and materials science.